Polarography of transition metal complexes

Item Type text; Thesis-Reproduction (electronic)

Authors Harris, Robert A., 1945-

Publisher The University of Arizona.

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polaeograph: of transition metal complexes

by

R obert Adrori H a rr is

■ A .Thesis Subm itted to th e F a c u lty o f th e

DEPARTMENT OF CHEMISTRY

In P a r t i a l F u lf i l lm e n t o f th e Requirem ents For th e Degree o f

MASTER OF SCIENCE

- In th e G raduate College

THE UNIVERSITY'OF ARIZONA '

STATEMHa>TT BY AUTHOR

T his t h e s i s has been su b m itted i n - p a r t i a l f u l f i l lm e n t o f r e qu irem ents f o r an advanced degree a t The U n iv e rs ity o f A rizona and. i s d e p o s ite d in th e U n iv e rs ity L ib ra ry to be made a v a i la b le to borrow ers under r u le s o f th e L ib ra ry .

B r ie f q u o ta tio n s from t h i s t h e s i s a re a llo w ab le w ith o u t s p e c ia l p e rm iss io n , p ro v id e d t h a t a c c u ra te acknowledgment o f source i s made. R equests f o r p e rm iss io n f o r ex tended q u o ta tio n from o r re p ro d u c tio n o f t h i s m an u scrip t in whole o r in p a r t may be g ra n te d by th e head o f th e m ajor departm ent o r th e Dean, o f th e G raduate C ollege when in h is ju d g ment th e p roposed u se o f th e m a te r ia l i s i n th e i n t e r e s t s o f s c h o la r sh ip . In a l l o th e r from th e au th o r.

in s ta n c e s , however, p e rm iss io n must be o b ta in e d

APPROVAL BY THESIS DIRECTOR

ROBERT D. FELTHAM A sso c ia te P ro fe s s o r o f Chem istry

late

ACKROWLEDGMEN-TS

The- a u th o r i s g r e a t ly in d e b te d to Dr. R obert D. Feltham f o r

h i s e x te n s iv e guidance th ro u g h o u t t h i s re s e a rc h . S p e c ia l thanks go

to Dr. Louis Ramaley, Dr. George W ilson, and Dr. E rh ard L e ic h t fo r.

t h e i r many h e lp fu l d is c u s s io n s . .

TABLE OF CONTENTS

Page

LIST OF TA B LES............................................................................................................... v i

ABSTRACT..................................................................................................................................v i i

INTRODUCTION.................................................................................................................... 1

Uncomplexed N itro s y l Groups ...................................................... . . . 1P en tacy an o n itro s y l f e r r a t e ................................................. 4P e n tacy an o n itro s y l c h r o m a t e ................................... 7O ther N itro s y l Complexes ...................................................... 9

EXPERIMENTAL.................................................................................................................... 13

G e n e r a l ............................................................................................................... 13Ditetrapropylam m onium P e n tacy an o n itro s y l f e r r a t e ,

[(C H7 )ltN]2Fe(CH)5I T O ................................................ 3.4

D itetrabutylam m onium P e n tacy an o n itro s y l f e r r a t e ,[ ( C4K9 W e (® 0 5Ho ....................................................................... 15

Tritetrapropylam m onium P en tacy an o n itro sy lch ro m ateD ih y d ra te , [ (C ^)^ N ]^C r(C N ) NO '2HgO . ........................... 15

T etraphenylpho sphonium P e n tacy an o n itro sy lv an ad a teT r ih y d ra te , [ (CgH )^P ]V (m )JK ) ' 3 ^ 0 ........................................ l 6

T r ite tra p h e n y lp h o sphonium P en tacy an o n itro sylm anganateT rihydrate", [ (C g IL )^ P ]^ n (C M )_ N 0 '3 ^ 0 .................................... l 6

T r ite tra p h e n y lp h o sphonium P en tacy an o n itro sy lch ro m ateT e tra h y d ra te , [ (C ^)^P ]^C r(C N )^N 0 4 H g O ............................... 1?

A ttem pted R eduction o f [Fe(CN)j-N0]2“ to [Fe(CN)^M0]^~

and P r e c ip i ta t io n w ith C o ( e n ) ^ ! ^ ............................................. 17

P otassium Amalgam R eduction o f TetrapropylammoniumP e n ta c y a n o n itro s y lf e r r a te .......................................................... 18

RESULTS " , .......................... 21

P re p a ra tio n o f th e N itro s y l C om plexes............................................. 21P o l a r o g r a p h y .................................................................................................. 24

iv

TABLE OF CONTENTS—Continued

3) I SOUS S3! OUT o c & e e o G C o o c o Q o o o o o o o

CONCLUSION e » e & 9 © e e & a . e o e o • « © © c © ©

NHjiFUNNNCES© © © © © © » © © © © © ©.© © © © © © ©

LIST OF TABLES

Table Page

I , P o la rog raphy o f D ith io le n e -N itro s y l .Complexes -o , . « „ „ » 1 1 .

I I , R eductive P o la rog raphy in D ichlorom ethane . . . .. 23 ■

I I I . O x id a tiv e P o la rog raphy in D ichlorom ethane , , « . . . . . . » 2h

ABSTRACT

The compounds [ ( C ^ ^ l I ^ F e ( 0 1 ) ^ 0 , [(C ^ )^ ]gF e(C N )JIO ,

[(C 3H7 )ltM]3Cr(CIl)5H0 -2H20 , [(CgHg)^P]V(CH)gN0 - 3HgO,

[ (C6H5 )]+P ]M n (ar)5N0-3H20 and [ (CgH,)^?] Cr(CM)JlO-Ui^O were prepared.

The preparation o f [Fe(CN)^NO] ™ vras attem pted. The polarography o f

HO, [(C 3H7 ) ltH]2Fe(CN)5HO, [(CgHg)^P]2Fe(CH)gHO,

[(CgH5)[P]3Mn(CM)5NO-3H20, [(CgHj)̂ P]3Cr(ffl)jWO•togO, [Fe(CO)3SCH3]g, and [Fe(NO )^!]^ was s tu d ie d in d ich lo rom ethane. The r e s u l t s o f th e se

s tu d ie s and t h e i r im p lic a tio n s a re d isc u sse d . The p ro to n a tio n re a c t io n s

o f [(C6H5 )j,P]2Fe(CN)5HO, [ (CgH^P^M nCctO^IO-SHgO, and

[ ( CgHy)j+P ] 3Cr ( CH)gNO• UHgO were a lso s tu d ie d in d ich lorom ethane.

raTRODUCTIOH

M etal n i t r o s y l complexes were f i r s t p re p a re d in th e n in e te e n th

c e n tu ry , y e t many a sp e c ts o f th e s e compounds a re s t i l l n o t w e ll u n d er

stood , In p a r t i c u l a r , th e o x id a tio n s t a t e o f th e c e n t r a l atom i s o f te n

i n d is p u te , a s i s th e fo rm al charge on th e (NO) g roup , and th e n a tu re o f

th e o x id a tio n - re d u e tio n re a c t io n s o f th e se complexes i s i l l - d e f in e d .

These p r o p e r t i e s have been in v e s t ig a te d w ith th e a id o f ESR, IE and

v. M ossbauer sp ec tro sco p y as w e ll a s ra d io is o to p e exchange methods. The

r e s u l t s o f th e s e s tu d ie s a re r a th e r ambiguous and a re o f te n in c o n f l i c t

w ith each o th e r . P o la ro g rap h ic s tu d ie s o f th e s e compounds a re n o t a s

numerous a s th e s tu d ie s m entioned above, b u t th e y a re p e rh ap s more

p rom ising and more e x p l i c i t . In t h i s in t r o d u c t io n , th e p o la ro g ra p h ic

. s tu d ie s o f t r a n s i t i o n m eta l n i t r o s y l s w i l l be rev iew ed and an a ttem p t

w i l l be made to keep th e se r e s u l t s in p e rs p e c tiv e b y in tro d u c in g p e r t in e n t

r e s u l t s o b ta in e d by o th e r m ethods.

bhcomplexed N itro s y l Groups

B efore c o n s id e rin g th e p o la ro g rap h y o f th e v a r io u s m e ta l - n i t r o s y l

. com plexes, i t m ight p rove u s e f u l to c o n s id e r th e p o la ro g ra p h ic red u c tio n .

o f v a r io u s u n co o rd in a ted NO groups. The f r e e n itro so n iu m io n can be1produced from th e n i t r i t e io n from th e fo llo w in g s te p s :

1

2

H+HO™ HN02

H+HNOg HgHOg

-Hgb

HgHOg ^ NO+

The o v e r a l l r a t e c o n s ta n t f o r t h i s r e a c t io n ( i . e . , + H+̂ =N O + + H^O)

was de term ined p o la ro g ra p h ic a l ly and found to he 1 .4 x 10^ l /m o le -s e c .

a t i n f i n i t e d i lu t io n and 25°C .^ The re d u c tio n o f a n i t r i t e - 0 .1 M

s u l f u r ic a c id s o lu t io n y ie ld s one wave a t = -1 .0 v . v s . SCE. T his

r e p re s e n ts th e re d u c tio n o f n i t r o u s a c id to hydroxylam ine (HNO ̂ + 4 e

+ 5 H+ = HHgOHg + H^O) . ’3 ̂ As th e pH i s low ered , o th e r vzaves ap p ear,

r e s u l t in g in th re e d i s t i n c t waves in 4 .0 M s u l f u r ic a c id . They o ccu r

a t about -0 .6 v . , -0 .9 v. , and -1 .3 v . v s . SCE. These waves have been

a t t r i b u t e d to th e fo llo w in g r e a c t io n s :^

N0+ + e ” = NO

N0+ + 2 e" = NO™

N0+ + 4 e “ + 4 H+ = NHgOHg

These h a lf-w av e p o te n t i a l s a re a lso dependent on pH. As th e c o n ce n tra

t io n o f th e a c id i s in c re a s e d , th e second and t h i r d waves merge,

r e s u l t in g in o n ly two waves in 12 M s u l f u r ic a c id . ^

+Since th e p o la ro g rap h y o f th e NO group i s com plica ted by pH

v a r ia t io n s , i t would seem prom ising to c o n s id e r th e p o la ro g rap h y o f d i s -6

so lv ed NO gas. T his was f i r s t done by R icco-B oni, Lanza, and Favero who

re p o r te d two waves. The f i r s t wave in v o lv ed a one e le c t r o n re d u c tio n .

3

r e s u l t in g in th e fo rm atio n o f hydroxylainine. Both waves were re p o r te d

to be d i f f u s io n c o n tro l le d , b u t th e r a t i o o f t h e i r h e ig h ts changed w ith

changes in th e NO c o n c e n tra tio n . T his anomolous c o n c e n tra tio n de

pendence in d ic a te s t h a t th e re d u c tio n does n o t p ro ceed by th e two sim ple

s te p s ( i . e . , NO + e = NO ; NO + 3 e + 4h+ = NH^OH*) as would be ex

p e c te d from th e re d u c tio n o f N0+ p o s tu la te d above. R icco-B oni, e t a l .

p roposed th e d im e riz a tio n o f NO b e fo re re d u c tio n as a p o s s ib le ex p lan a

t io n , b u t o f f e re d no p ro o f . ^ Masek has r e c e n t ly re p e a te d t h i s work and

has found t h a t th e sum o f th e two waves i s indeed a d i f f u s io n c o n tro l le d

p ro c e s s , b u t th e f i r s t wave has a p a r t i a l l y k in e t ic c h a ra c te r and i s7

low er th a n would be expec ted f o r a one e le c tro n re d u c tio n . Masek a ls o

re p o r ts t h a t th e h a lf-w ave p o te n t i a l o f th e second wave i s p r a c t i c a l l y

independen t o f NO c o n c e n tra tio n , w h ile t h a t o f th e f i r s t wave becomes

more p o s i t iv e w ith h ig h e r NO c o n c e n tra tio n s . This i s e x p la in ed by a

d im e riz a tio n e q u ilib r iu m b e fo re re d u c tio n :

2 NO === (H0)2 N202"2

As p ro o f , a m od ified I lk o v ic eq u a tio n i s used to m a th em atica lly reproduce

th e observed p o la ro g ra p h ic cu rves. More re c e n t ch ro n o p o ten tio m e tric

work by Ebman and Sawyer^ has in d ic a te d t h a t in aqueous s o lu t io n NO

i s reduced in a s in g le one e le c tro n i r r e v e r s ib l e re d u c tio n which i s

proceeded n o t by a d im e r iz a tio n , b u t by a p ro to n a tio n , v i z . :

NO + H+ NOH+ k = 107

NOH+ + e “ -> NOH

2N 0H -» N^O + HgO

P e n tacy an o n itro s y l f e r r a te

One o f th e most w ide ly s tu d ie d n i t r o s y l complexes i s th e p e n ta -— Pc y a n o n i t ro s y l f e r r a te io n , [Fe(CN)^NO]"~, which i s g e n e ra l ly r e f e r r e d to

a s th e n i t r o p ru s s id e io n . The i ro n i s u s u a l ly co n sid e re d to be F e ( l l ) .

However, i t has been r e f e r r e d to as F e ( l l l ) ^ which has been supported

by ra d io is o to p e exchange and IR s p e c t r a l m ethods. 10 A lso th e Mossbauer2—spectrum o f [Fe(CH)^NO] ~ has a la rg e n e g a tiv e isom er s h i f t which has

been in te r p r e te d as ev idence f o r F e( IV) , 11 as w e ll as F e ( n ) . 11

Both F e ( U l ) and Fe(lV ) have been p roposed on th e b a s i s o f s p e c tr a lllj.

d a ta . Of co u rse , i f th e iro n i s in th e 2+ s t a t e , th e n i t r o s y l must

be N0+ , w hile F e ( l l l ) im p lie s N0°, and Fe(lV ) g iv es NO**.

The f i r s t p o la ro g ra p h ic s tu d y o f [Fe(CN)^NO]^** was re p o r te d by

15Lanza and C o r b e l l in i , ' who found th re e re d u c tio n waves. The number o f

e le c tro n s t r a n s f e r r e d in th e f i r s t re d u c tio n cou ld n o t be determ ined ,

b u t th e second and t h i r d waves were re p o r te d as two and fo u r e le c tro n

re d u c tio n s , r e s p e c t iv e ly . In a d e ta i le d s t u d y , K o l t o f f and Toren a ls o

found th re e waves, b u t th e y a t t r i b u t e th e f i r s t two waves to r e v e r s ib le ,

pH dependent (w ith re g a rd to ha lf-w ave p o t e n t i a l s ) , one e le c tro n r e

d u c tio n s g iv in g [Fe(CN),JtO]^‘* and [Fe(CN)^NO]^~. The t h i r d wave appeared

i r r e v e r s ib l e and pH dependent, and no e x p la n a tio n o f th e e le c tro d e r e

a c t io n was o f fe re d . The approxim ate half-w ave p o te n t i a l s were g iven as

-0 .4 v . , -0 . 6 v. , -1 .2 v . , v s . SCE. As th e pH was in c re a s e d , th e

s o lu tio n changed from re d to yellow and th e wave h e ig h ts d ecreased . T his

17was e x p la in ed by an e q u ilib r iu m proposed e a r l i e r :

[F e (C N )J Io f"" + 2 0 ir= ^ = ^ = [F e ( a j)5N02 ]i+~ + HgO

In th e Lanza p a p e r , i t i s re p o r te d t h a t [Fe(C!M)^NO]^"" does

n o t g iv e an o x id a tio n wave in n e u t r a l o r a c id ic s o lu t io n s , b u t b a s ic

s o lu t io n s a re o x id iz e d a t a r o ta t in g p la tin u m e le c tro d e . The o x id a tio n

appears to in v o lv e one e le c t ro n , and th e half-w ave p o t e n t i a l i s pH de

p en d en t, v a ry in g from 0. 34 v. v s . SCE a t pH 10.15 to 0 .2 9 v. a t pH 11. 5.

S ince th e o x id a tio n o ccu rs o n ly in b a s ic s o lu t io n s , i t i s a t t r ib u te do _

to th e [Fe(CH)^H0g] /[Fe(CTl)^N0g] co u p le , which had been re p o r te d

e a r l i e r . ^ Masek and co-w orkers have in te n s iv e ly s tu d ie d th e aqueous

19p o la ro g rap h y o f sodium n i t r o p r u s s id e . In t h e i r most r e c e n t p a p e r ,

th e pH dependence o f t h i s re d u c tio n p ro c e ss i s d e sc r ib e d and i t i s

re p o r te d t h a t th e f i r s t wave i s a r e v e r s ib le , one e le c t ro n re d u c tio n in

th e pH range from 5 to 10 .5 . Below pH 5 , d e p a r tu re s from r e v e r s i b i l i t y

a re observed . The second wave i s " q u a s i - r e v e r s ib le ” and h ig h ly pH de

penden t as w e ll as dependent on th e c a t io n s in s o lu t io n . This wave may

be view ed as a c tu a l ly b e in g two waves, one r e s u l t in g from th e re d u c tio n

o f a p ro to n a te d s p e c ie s , [Fe(Ctf)^IT0M4 and th e o th e r r e s u l t in g from

th e re d u c tio n o f a sp e c ie s formed by r e a c t io n w ith th e e le c t r o ly te

c a t io n s , i . e . , [Fe(CN)^N0M+ ]2 . I t i s p o s tu la te d t h a t once th e se sp e c ie s

a re reduced , th e y a re in a c t iv e to back o x id a tio n . The t h i r d wave was

found to be t o t a l l y i r r e v e r s ib l e and i t s h e ig h t i s q u ite pH dependent.

At a pH o f 4 , i t co rresponds to a two e le c tro n re d u c tio n w h ile a t a pH

o f 10, i t co rresponds to a fo u r e le c t r o n re d u c tio n . When cyanide io n s

a re added to th e s o lu t io n s , th e second wave d ec rea se s w h ile th e t h i r d

i s u n a ffe c te d . T his i s in te r p r e te d as in d ic a t in g t h a t th e M0 group i s

l a b i l e in [FefCN^ITO]^ and i s s u b s t i tu te d by a CUT" g roup , which e l im i

n a te s th e second re d u c tio n wave. However, t h i s does n o t a f f e c t th e

t h i r d wave so i t cannot in v o lv e th e sim ple one e le c t ro n re d u c tio n o f

[Fe(CH)^NO]^ o r [Fe(CN)j_HOH]^ . I t i s t e n t a t i v e l y p o s tu la te d th a t th e

f i n a l p ro d u c t o f th e t h i r d re d u c tio n i s [Fe(CH)^NHgOH]^'". The fo llo w in g

diagram i l l u s t r a t e s a l l o f th e above p ro c e s s e s , where A and I a re un

s ta b le in te rm e d ia te s .

[Fe(CN)

l e 1 s t wave

[ F e ( a 0 5NOM]2-M

l e 2nd wave a lk a l in e

[Fe(CN)(-NO]

A

3- H [Fe(CN)t-NOH]2 -

l e 2nd wave a c id ic

[Fe(CM) 1K0M]3- [Fe(CH)5HOH]3"

I[Fe(CN) NOH]3-

2e

2HH

3rd wave a c id ic

[Fe(CN )^m 20H] 3-

A1 though compounds c o n ta in in g b o th [Fe(CH)^NO]3*" end

[Fe(CN)c_HO] 1 a re re p o r te d in e a r ly l i t e r a t u r e , t h e i r v a l i d i t y i s

d o u b tfu l and i t i s o n ly re c e n t ly t h a t [Fe(CH)^HO]3*" and [Fe(CN)^NOH],2-

have been i s o la t e d and c h a r a c t e r i z e d . [ F e ( C N ) ^ N O ] 3 (v^q = 1^68 cm "̂)

i s p roduced by a sodium re d u c tio n o f Na2Fe(CN)^I\fO in l i q u i d ammonia. I t

i s p r e c ip i t a t e d by (C2H^)^N+C1** as a y e llo w , a i r - s e n s i t i v e , powder which

r e a d i ly a b s t r a c t s a p ro to n from s o lv e n ts such as a c e to n i t r id e to form

th e deep b lu e sp e c ie s [Fe(a0^N 0H + ]2" (v^Q = 1746 cm**1 ). Both forms

have one u n p a ire d e le c tro n which i s assumed to occupy an o r b i t a l o f•x- p i

p red o m in a te ly c h a r a c te r , as p roposed by Manoharan and Grey. The

bonding in v o lv ed in th e p ro to n a te d sp e c ie s i s n o t u n d ers to o d .

F u r th e r re d u c tio n o f [Fe((3T)^lT0]^“ y ie ld s [Fe(Ol)^NO]^-

(vjj0 = 1605 cm"1 ) and [Fe(CT) HO]4" ( v ^ = 1300 cm"1 ) . 20

P en tacy an o n itro sy lc h r ornate

The p en tacy an o n itro sy lch ro m a te io n , [Cr(CN)^NO]^*", p re s e n ts some

o f th e same problem s as th e i ro n complex. The chromium complex was f i r s t

p re p a re d by G r i f f i t h , who concluded from th e m agnetic moment t h a t i t

has one u n p a ire d e le c t r o n , and fo rm u la ted i t as a C r ( l ) complex. This

i s a lso su p p o rted by ESR d a ta , a lth o u g h C r ( H l) has been p roposed . 10 21

G riffith™ a ls o re p o r te d t h a t in a 1 M KCN s o lu tio n th e complex i s

p o la ro g ra p h ic a l ly reduced in a one e le c t r o n , r e v e r s ib le wave. The r e

duced sp e c ie s was p o s tu la te d as [Cr(CN)^NO]^"", which was l a t e r i s o la te d24as th e p o tass iu m s a l t . The low param agnetism o f t h i s s a l t in d ic a te s

C r(0 ).25

In a r e c e n t s tu d y , B u s tin has shown th a t G r i f f i t h 's ha lf-w ave

p o te n t i a l (-0 .9 3 0 v. v s . SCE) was in e r r o r , and a more v a l id half-w ave

p o te n t i a l f o r th e re d u c tio n o f [ Or((5?)^HO] ^ i s -1 .1 8 v . v s . SCE in

0 .3 M NaCl. T his wave i s r e v e r s ib le , d i f f u s io n c o n tro l le d , and i t s

h e ig h t i s l i n e a r l y dependent on th e c o n c e n tra tio n o f [Cr(CN)^N0]^

above pH 5 and a t h ig h io n ic s t r e n g th s . However, as th e io n ic

s tre n g th i s d ec rea sed , th e r e a c t io n becomes i r r e v e r s ib l e and th e h a l f

wave p o te n t i a l becomes more n e g a tiv e . T his tendency tow ard i r r e v e r s i

b i l i t y i s a t t r i b u t e d to a re p u ls io n o f th e d e p o la r iz e r , [ Cr(CN)^NO]^’’,

a t th e e le c tro d e double la y e r a t low er io n ic s t r e n g th s . The s h i f t in

ha lf-w ave p o te n t i a l s may be e x p la in ed by assuming t h a t io n p a i r in g ta k e s

p la c e w ith th e reduced form b u t n o t w ith th e o x id iz e d form. I t should

be n o ted th a t even a t h ig h io n ic s tr e n g th t h i s e le c tro d e re a c t io n

([Cr(CN)^NO]^ + e [Cr(CN)^NO]* ) appears slow when compared to a

sim ple re d u c tio n such as [Cr(CLT)g]^’' + e~ [Cr(CN )^]^“. This im p lie s

t h a t th e re d u c tio n o f th e n i t r o s y l complex in v o lv e s a rearrangem ent o f26e le c tro n s such t h a t th e bond le n g th s a re changed.

In a c id s o lu t io n , th e re d u c tio n o f [Cr(CN)^NO]^"" i s more com-2 7p l ic a te d . At th e N in th I .C .C .C ., Masek s ta t e d t h a t in a c id s o lu t io n

th e re a re two re d u c tio n w aves, th e f i r s t b e in g a two e le c t ro n re d u c tio n

o f a doubly p ro to n a te d in te rm e d ia te and th e second b e in g a th re e e le c t ro n

re d u c tio n in v o lv in g f u r th e r p ro to n a tio n . The f i r s t doubly p ro to n a te dCj

in te rm e d ia te i s p re s e n te d as an example o f th e extrem e case o f d

chromium and N0° n i t r o s y l . However, th e d a ta su p p o rtin g th e se con

c lu s io n s have n o t been p u b lish e d . W ith re g a rd to th e s e proposed p ro to n a

t io n s , i t i s i n t e r e s t i n g to n o te t h a t when one e q u iv a le n t o f a c id i s

added to [Cr(CN)^NO]^ i t appears to p ro to n a te th e CN t r a n s to th e NO.

F u r th e r a d d i t io n o f a c id g iv e s HCN in s o lu t io n , and f iv e e q u iv a le n ts o f

a c id p roduce [Cr(H20)^N 0]2+ in s o lu tio n .

O ther N itro s y ! Complexes

26Masek b r i e f l y re p o r te d t h a t th e p o la ro g ra p h ic b eh av io r o f

[V(CN)^NO]^ i s s im ila r to t h a t o f th e chromium an a lo g , w h ile he found

no o x id a tio n o r re d u c tio n waves f o r [Mn(CN)^NO]^”. T his i s c o n tra d ic te d28 0by a r e p o r t o f th e o x id a tio n o f th e p u rp le [Mn(CN)^NO]

(v^0 = 1730 cm”1 ) a t + 0 .6 v. to g iv e ye llo w [Mn(CIT)^N0]2 ” ,

(v^ 0 = 1885 cm , m agnetic moment = 1 .7 3 EM).

The p o la ro g rap h y o f n i t r o s y l t r i c a r b o n y lc o b a l t and s e v e ra l o f i t s

d e r iv a t iv e s has r e c e n t ly been in v e s t ig a te d u s in g a c e t o n i t r i l e ( CH^CN),

N,N~dimethylformamide (H iF ), and d im ethy l su lfo x id e (DMSO) as s o lv e n ts . ^

In th e f i r s t two s o lv e n ts , Co(C0)^N0 g iv e s th r e e re d u c tio n waves,

= - 1 .0 , - 1 . 7 , - 2 .3 V. v s . Ag/AgCl, 0 .1 M (CgH^)^NClO^ in CH^CN.

In Hi SO o n ly two waves appear. The f i r s t wave r e p re s e n ts a d if f u s io n

c o n tro l le d , i r r e v e r s i b l e , one e le c t r o n re d u c tio n , w h ile th e second wave

i s a d so rp tio n c o n tro l le d and th e t h i r d wave i s k i n e t i c a l l y c o n tro l le d .

The f i r s t wave i s a t t r i b u t e d to [Co(C0)^N0] + e~ [Co(C0)^N0]” and

th e second wave i s a t t r i b u t e d to Co(C0)^N0 (adsorbed) + e ” -> Co(00)^N0”

w ith th e re d u c tio n ta k in g p la c e o n ly on th e n i t r o s y l group. The t h i r d

wave i s t e n t a t i v e l y e x p la in ed as th e re d u c tio n o f th e p ro to n a te d sp e c ie s

Co(C0)^N0H and i t s f a i l u r e to appear in EMSO i s th u s a t t r i b u t e d to th e

f a c t t h a t DMSO i s n o t as p ro to g e n ic as EMF o r CILCN. The p ro d u c ts o f

t h i s t h i r d re d u c tio n a re p o s tu la te d as Co(CO)^ and NOH , a lthough th e

ev idence i s v e ry ten u o u s. The d e r iv a t iv e s o f Co(C0)^N0 where a t r ip h e n y l

p h o sph ine , a r s in c , o r s t ib in e l ig a n d i s s u b s t i tu te d f o r one carbony l

group g iv e e s s e n t i a l l y th e same r e s u l t s . However, i f two carbony ls a re

10

re p la c e d , th e a d so rp tio n c o n tro l le d wave d isap p e a rs . W ith b o th th e

mono- and d i - s u b s t i tu te d com plexes, in c re a s in g l ig a n d b a s i c i t y

( i . e . , (C^H^)^P>(C^H^)^As>(C^H^)2Sb) s h i f t s th e half-w ave p o te n t ia l o f

th e f i r s t wave to more n e g a tiv e v a lu e s . T his i s ex p la in ed by assuming

t h a t th e re d u c tio n p la c e s an e le c tro n in a jr m o lecu lar o r b i t a l which

i s d e s ta b i l iz e d by in c re a s in g b a s i c i t y o f th e c o o rd in a ted l ig a n d s .30R ecen tly , s e v e ra l n i t r o s y l - d i th io le n e complexes o f c o b a lt and

iro n have been p re p a red and s tu d ie d v o lta m m e tr ic a lly a t a r o ta t in g

p la tin u m e le c tro d e . The fo llo w in g ta b le summarizes th e vo ltam m etric

work and in c lu d e s th e in f r a r e d f re q u e n c ie s fo r th e compounds t h a t have

been i s o la te d .

S ev e ra l o rg a n o m e ta liic n i t r o s y l s have been s tu d ie d p o la ro -

g ra p h ic a l ly in dim ethyoxyethane u s in g a 0 .001 M AgC10,/Ag w ire re fe re n c e

e le c tro d e . ^ The compound ( jt- ) M n (00^)N0+PF^ gave a one e le c tro n

re d u c tio n a t = -0 .8 v . , w h ile [ jt-C^H Î-In ( CO)N0 ]p gave a two e le c tro n

wave a t -2 .0 v . , and (NO) ^ gave two s in g le e le c tro n waves

a t -1 . 5 v . , and -2 . 5 v . A ll o f th e s e waves were i r r e v e r s ib l e . No

in te r p r e t a t i o n o f th e r e s u l t s was a ttem p ted .

The p o la ro g rap h y o f th e complexed and uncomplexed n i t r o sy ls d i s

cussed above i s o b v io u s ly com plicated by p ro to n a tio n r e a c t io n s . Thus,

i t ap pears p rom ising to a ttem p t th e p o la ro g rap h y o f v a r io u s n i t r o s y l

com plexes, as w e ll as n i t r i c o x id e , in a non-aqueous so lv e n t where p ro

to n s may be excluded o r in tro d u c e d a t w i l l .

Table I Polarography o f D ith io le n e -N itro s y l Complexes

Cozplex Couple ^ l/2 V̂* ̂ Slope^ (ny) HO stretching frequencies (crrT̂ )

l ) [Fe(N0 )S4Cu(CH)ur 2 -1 -> -2 +0.03 62 l8 i4 -» 1633-2 -> -3 -1 .34 72 1633 -> ?

2 ) [Fe(NO)S4C4 (CF3)4 r —1 —> —2 -0 .07 58 1829 -» =l6i4-2 -» -3 - 0 . 36 57 =1614 -> ?-1 —> 0 +0 .84 53 1829 -» ?

3) [Fe(N0)(S2C6Cl4)2 ] ’ -1 —» -2 -0 .24 • 64 =1824 -» =1620-1 -> 0 +0.74 58 =1824 -> ?

W [Fe(NO)(S2C6H3CH3)2 ]" —1 —> —2 - 0.64 59 1765 -> =1630-1 -> 0 +0.27 56 1765 -> ?

5) [Fe(H0 )S4C4 (Ĉ H3)4]- -1 -> -2 -0.83 58 1770 -» =1620-1 -> 0 - 0.02 66 1770 -* =18000 —> +1 +0.71 56 1800 -» ?

6 ) [ co(ho) suc4 (ch)4 ] -2 -1 —>-2 +0.16 86 =1700 -> 1617-2 —>-3 -1.32 69 1617 -> ?

a A ll r esu lts obtained in dichloromethane at 25°C, 10*"̂ M in connlex and 1 .0 M in supporting e lec tro ly te [(CgH )̂^HClO ̂ or (C^Hy)^HdO^] vs. a saturated calonel electrode containing 1 M aqueous Li Cl solution.

b Slope o f p lo t o f E . , vs. log i / ( i ^ - i ) . For a reversib le wave, the slope i s th eo retica lly equal to0.059/n v . , where n i s the number of electrons involved in the e le c tr o ly tic process. In th is ta b le , for n = 1 , the slope o f a reversib le wave should be 59 mv.

I t i s postulated that a l l o f the above iron compounds nay be considered as having Fe(H ) and a l l o f the reductions and oxidations as taking place mainly on the d ith io la te and n itro sy l ligands.

12

A d ich lo ro m eth an e , CK^Cl^, system has r e c e n t ly been used f o r 30voltam m etry and was chosen f o r th e s e p o la ro g ra p h ic m easurem ents.

The fo llo w in g re s e a rc h i s d iv id e d in to two p a r t s : l ) sy n th ese s , i n

c lu d in g p re p a ra t io n o f n i t r o s y l complexes which a re s o lu b le in CH^Cl^

and a ttem p ted i s o l a t i o n o f th e p ro d u c ts r e s u l t in g from t h e i r re d u c tio n

o r p ro to n a tio n , and 2) p o la ro g rap h y o f th e CH^Cl^ s o lu b le compounds w ith

and w ith o u t th e in tro d u c t io n o f HC1.

EXPERIMENTAL

G eneral

In f r a r e d s p e c tra were re c o rd ed on P e rk in -E ln e r 137, P e rk in -

Elmer 337, and Beclonan IR-12 sp ec tro p h o to m ete rs . A ll e lem en ta l an a ly se s

were perform ed by Huffman L a b o ra to r ie s , Wheat r id g e , Colorado. The

po larogram s were reco rd ed on a S argen t XV p o la ro g rap h and r e p re s e n ta t iv e

po larogram s were reco rd ed on an id e n t i c a l in s tru m en t to check accuracy .

The r e s is ta n c e o f th e p o la ro g ra p h ic c e l l was m easured w ith an I n d u s t r i a l

In s tru m en ts c o n d u c tiv ity b r id g e model RC l6B2. The p o la ro g ra p h ic c e l l

was a d o u b le - f r i t t e d H -c e ll s u i ta b le f o r use w ith a i r s e n s i t iv e m a te r ia ls .

The r e s i s ta n c e o f th e c e l l was 10,000 ft w ith a 0 .1 0 M (C )^N+Br""/CH^Cl^

s o lu t io n , and 30,000 ft w ith a 0 .05 M (CgH,- ) ^ +C10^/CH^Clg s o lu tio n .

A n a ly tic a l re a g e n t g rade d ich lorom ethane (CHpCl^) was d i s t i l l e d from

phosphorous p en to x id e and s to re d over 4 A m o lecu lar s ie v e s and dry sodium

b ic a rb o n a te in a l i g h t - f r e e c o n ta in e r . The tetrapropylam m onium brom ide,

(C^Hy)j^N+Br , u sed as an e le c t r o ly te was d is so lv e d in d ich lo rom ethane ,

t h i s s o lu t io n was f i l t e r e d , th e so lv e n t removed under vacuum, and th e

r e s u l t in g s o l id was d is so lv e d in e th a n o l and p r e c ip i t a t e d w ith e th y l

a c e ta te . The tetraethylam m onium p e r c h lo r a te , (CoH^)^N+C10^, used as an

e l e c t r o ly te was r e c r y s t a l l i z e d from anhydrous e th an o l. Gaseous hydrogen

c h lo r id e was o b ta in e d d i r e c t l y from a Mat he son le c tu r e b o t t l e , w hile

n i t r i c oxd.de was o b ta in e d from a M atheson cyldlnder and p a sse d th rough

13

14

fo u r d ry - ic e /a c e to n e t r a p s p r io r to u se . The n i tro g e n used to d e a re a te

th e p o la ro g ra p h ic s o lu tio n s was p a sse d th rough BTS c a ta ly s t to remove

t r a c e s o f oxygen. A ll s o l id s were k e p t in a vacuum d e s ic c a to r p r io r

to u se .

A cid c o n c e n tra tio n s in th e d ich lorom ethane-hydrogen c h lo rid e

s o lu t io n s was determ ined by e x tr a c t in g th e s o lu tio n s w ith w a ter and

t i t r a t i n g w ith sodium hydrox ide to a p h en o p h th a lin e end p o in t , which

allow ed th e h e ig h t o f th e p ro to n re d u c tio n wave to be c o r r e la te d w ith

th e c o n c e n tra tio n o f hydrogen c h lo r id e in th e p o la ro g ra p h ic s o lu t io n s .

The p o la ro g ra p h ic re fe re n c e e le c tro d e was s a tu r a te d calom el

u s in g a 1 .0 M aqueous l i th iu m c h lo r id e s o lu t io n . T his a llow s a p o t e n t i a l

ran g e , w ith re s p e c t to t h i s e le c t ro d e , from +0.9 v . (o x id a tio n o f m ercury)

to -1 .5 v. ( re d u c tio n o f CH^Cl^).

D itetranropylam m onium P en tacy an o n itro s y l - f e r r a t e , [ (C.H^HJgFeCCNUTO

T his compound was p re p a re d u s in g a m o d if ic a tio n o f a method r e

p o r te d e a r l i e r . Na^Fe( CN) ^NO (20 g) was d is so lv e d in 60 ml H^O

and e x tra c te d w ith 60 ml d i ch lo r omethane c o n ta in in g 35*7 g (C^H^)^N+Br .

The aqueous la y e r was f u r th e r e x t r a c te d w ith 40 ml and 15 ml p o r t io n s

o f CHgCl^. The CH^Cl^ la y e r was f i l t e r e d and th e s o lv e n t removed under

vacuum a t 35°C. The r e s u l t in g s o l id was d is so lv e d in 450 ml h o t a c e to n e ,

f i l t e r e d and k e p t a t 0°C f o r 24 h o u rs . The la rg e red-brow n c r y s ta l s

were d r ie d under vacuum fo r 24 h o u rs . Y ie ld = 70%. A nal. Calcd f o r

15

[(C 3H7 ))4IT]2Fe(aT )2NO: C, 5 9 . k; H, 9 .4 8 ; N, 19 .15 . Found: C, 59-16;

H, 9 .2 1 ; N, 19 .21 .

Pitetrabutylaniinoniuin P en tacy an o n itro s y l - f e r r a t e , T(C^H9 )^N jgFe(df) NO

Na2F e( CH) ^ 0 •2H20 (30 g) was d is so lv e d in 100 ml w a te r e x tra c te d

w ith 70 g o f (Cj+H9 )I+N+Br d is so lv e d in 100 ml o f d ich lo rom ethane. The

aqueous la y e r was f u r th e r e x tra c te d w ith 60 ml and 30 ml p o r t io n s o f

CHgClg. The Cf^Clp, phase was f i l t e r e d and th e so lv en t removed a t 35°C

under vacuum. The r e s u l t in g s o l id was r e c r y s t a l l i z e d from ace to n e -

e th y l - a c e ta te . The la rg e red-brow n c r y s ta l s were d r ie d under vacuum

f o r 24 hou rs . A nal. Calcd f o r [ ( C ^ H ^ N ^ F e ^ ^ N O : C, 63 . 38 ; H,

1 0 .3 8 ; N, 16 .00 . Found: C, 63 .1 0 ; H, 1 0 .2 4 ; N, l 6 . 31 .

T ritetrapropylam m onium P e n ta c y a n o n itro sy l- chrom ate D ih y d ra te , [ ( ] ^Cr(QT)^N0.2H20

A s o lu tio n o f 1 .2 g K^CrfOTj^IJO2 ^ d is so lv e d in 300 ml w ater was

e x tra c te d w ith 50 ml n itro m eth an e c o n ta in in g 1 .2 g tetrapropylam m onium

brom ide. The e x tr a c t io n was re p e a te d w ith 40 ml and 30 ml p o r tio n s o f

n itro m eth an e . The n itro m eth an e la y e r was f i l t e r e d and th e so lv en t r e

moved under vacuum. The r e s u l t in g s o l id was d is so lv e d in 125 ml h o t

ace to n e . T his s o lu tio n was coo led to 0°C, f i l t e r e d , and 200 ml

d ie th y le th e r was added. A f te r 12 hou rs a t 0°C th e y e llo w p r e c ip i t a t e

was f i l t e r e d , washed w ith 25 ml d ie th y le th e r , and d r ie d under vacuum

f o r 24 hou rs . A nal. Calcd f o r [ (C ^H ^N ^C rtC N ^N O ^I^O : C, 60 .90;

H, 1 1 .0 ; N, 15 .60 . Found: C, 60 .23 ; H, 10 .99 ; N, 15 .77 .

16

T etraphenylpho sphonium P en tacy an o n itro s y l - vanadate T r ih y d ra te , [ ( ] V(CII) NO • 3HgO

S a tu ra te d aqueous s o lu t io n s o f 3 .6 g ( l l raM) K^V(CN)^NO^^ and

3 .7 g (10 mM) te tra p h en y lp h o sphonium c h lo r id e were mixed to g e th e r and

an orange p r e c i p i t a t e form ed im m ediately . This s o l id was d r ie d under

vacuum f o r 2b hou rs and t r e a te d w ith 20 ml d ich lo rom ethane. This p ro

duced a brow n-orange t a r and an orange s o lu t io n . P etro leum e th e r was

added to th e orange s o lu t io n u n t i l i t became cloudy. A f te r two days a t

-1 0 °C an orange s o l id was f i l t e r e d from th e s o lu t io n and d r ie d under

vacuum f o r 2k h o u rs . A nal. Calcd f o r [ (C^H^)^P]V(CN)^N0 ^H^O: C,

57 .62 ; H, 4 .3 4 ; 0 , 10 .59 . Found: C, 56 .7 0 ; H, 4 .1 8 ; 0 , 10 .80 .

T rite trapheny lphosphon ium P e n ta c y a n o n itro sy l- manganate~ T r ih y d ra te , [ ( ) ̂ P J^Mn ( CI'I)

17

T rite tra p h e n y lp h o sphonium P e n ta cya n o n i tro s y l- chrom ate T e tra h y d ra te , [ ( qCr ( aO^lIO*

23S a tu ra te d aqueous s o lu t io n s o f 3» 6 g ( l l mM) K^Cr(a^)^IIO

and 3- 7 g (10 rM) te trapheny lphosphon ium c h lo rid e were mixed w ith

s t i r r i n g . A ye llo w p r e c ip i t a t e formed im m ediately . The p r e c ip i t a t e

was washed w ith ic e w a te r and d r ie d under vacuum f o r 24 ho u rs . A nal.

Calcd f o r [ ( C ^ ) ^ P ] ^ C r ( C N ) ^ 0 '4 ^ 0 : C, 71 .00 ; H, 5 .2 9 ; N, 6 .4 5 ;

0 , 6 . 13 . Found: . C, 69 .7 4 ; H, 4 .9 5 ; N, 6 .8 5 ; 0 , 5 .93 .

" A ttem pted R eduction o f [Fe(Q'T)c:FO]^” to• P

[FefCtOj-NO]^” and P r e c ip i ta t io n vzith C o(en)^!^

A s a tu r a te d aqueous s o lu t io n o f Na^Fe ( (3T) ̂ NO • PH^O was p rep a red

and Na^S^O^ was added u n t i l th e s o lu t io n became dark b lu e . A s a tu r a te d

aqueous s o lu t io n o f C o(en)^!^ was added. The r e s u l t in g g reen p r e c i p i t a t e

was f i l t e r e d , washed w ith w a te r , and d r ie d . The in f r a r e d spectrum o f

th e r e s u l t in g g reen s o l id in d ic a te d i t to be [Co(en)^][Fe((M )^HgO]. The

above experim ent was re p e a te d a t 0°C under an NO atm osphere and y ie ld e d

th e same p ro d u c t.

A s a tu r a te d d im e th y lsu lfo x id e (BMSO) s o lu tio n o f Na^Fe( CN)^NO *2HpO

was su b je c te d to e l e c t r o l y s i s a t -1 .0 v . v s . s a tu ra te d calom el. When

th e s o lu t io n had become dark b lu e , a s a tu r a te d DMSO s o lu t io n o f C o(en)^!^

was added. A b lu e -g re e n p r e c ip i t a t e appeared , b u t i t s in f r a r e d spectrum

d id n o t c o n ta in an NO band.

Potassium Amalgam R eduction o f T e tra p ro p y l- ammonium P en tacy an o n itro s y l f e r r a te

A s o lu t io n o f 2 .95 g (5 mM) [(C H^)^N]gFe(GN)^NO and 1 .13 g

(5 ntii) tetrapropylam m onium brom ide in 4^ ml d ich lorom ethane was p la c e d

in a n itro g e n f i l l e d Schlenk tu b e . A po tass iu m amalgam [2 .2 g K (55 mM),

300 g Hg] was added to t h i s s o lu tio n and a g i ta te d p e r io d ic a l ly f o r 25

hou rs . A serum cap was f i t t e d to th e Schlenk tu b e and th e dark b lu e

s o lu tio n was t r a n s f e r r e d w ith a sy rin g e to an o th e r n i tro g e n f i l l e d

Schlenk tu b e where th e so lv e n t was removed under vacuum a t 25°C. The

in f r a r e d spectrum o f th e r e s u l t in g dark b lu e s o l id in d ic a te d th a t

i t was a m ix tu re o f ap p rox im ate ly 20% s ta r t i n g m a te r ia l ,

[(C H ^ j^ F eC C M ^ N O , 75% [ (C^H^N^FeCCN^NOK, and 5% o f an un

i d e n t i f i e d w h ite compound w ith an in f r a r e d frequency a t i 860 cm .

T a b le I I R e d u c t iv e P o la v o / r r a ^ h y i n D ic h lo r o m c t h a n c ________________ . 1 9

C om pound E l e c t r o l y t eC o n e , o f

D e p o l a r i z e r (M )

E ^ ( v )

+ 0 . 0 1 5 V .

i d 0 * a )

@70 cm Hg

T y p e o f C o n t r o l o f E l e c t r o d e

P r o c e s s

A p p r o x . # o f e i n v o lv e d a s

c a l c ’ d f r o m

b

R e v e r s i b i l i t y

1 ) NO 0 .0 5 M (C 2 H 5 ) 4K C 1 0 4 ? - 0 . 8 7 5 , - 1 .3 8 5 v a r i a b l e ? ? i r r e v . ( 0 . 3 ) i r r e v . ( 0 . 6 )

0 .1 M (C 3 l L , ) 4 l f C I O 1 . 0 x 1 0 " 3 - 0 . 8 4 4 , - 1 . 2 3 4 2 . 9 , 2 . 8 d i f f . , d i f f . 1 , 1 r e v . ( 1 . 0 ) r e v . ( 1 . 0 )

2 ) [ ( C 3 K 7 ) u N ] 2 F e ( C N ) 5NO 0 .0 5 M (C 2 H 5 ) 4 N+ C 1 0 4 1 . 0 x 1 0 " 3 - 0 . 8 9 4 , - 1 . 2 2 1 2 . 9 , 2 . 7 d i f f . , d i f f . 1 , 1 i r r e v . ( 0 . 8 ) r e v . ( l . l )

3 ) [ ( C 6 H5 ) 4 P ] 2 F e ( C N ) 5MO 0 . 1M ( C ^ ) ^ B r " 1 . 0 x 1 0 " 3 - O . 8 2 5 , - 1 .2 0 8 3 . 1 , 3 - 2 d i f f . , d i f f . 1 , 1 r e v . ( 1 . 0 ) r e v . ( 0 . 9 )

0 .0 5 M (C 2 H 5 ) 4 N+ C 1 0 4 1 . 0 x 1 0 " 3 - 0 . 8 8 4 , - 1 .1 8 6 2 . 7 , 2 . 5 d i f f . , d i f f . 0 . 9 , 0 . 9i r r e v . ( 0 . 8 )

r e v . ( 1 . 0 )

4 ) [ ( C 6 H 5 ) 4 P ] 3M n (C N )^ N O *

SHgO

(C 3^ ) 4 N , (C 2 H 5 ) 4 C1 0 4 , 1 . 0 x 1 0 " 3 n o w a v e s

5 ) [ ( C 6 H 5 ) 4 P ] 3 C r ( C N ) 5NO*

4 1 ^ 0

( c 2 h 5 ) 4 n , ( c 2 h 5 ) 4 c i o 4 ,

( c ^ ) 4 P

1 . 0 x 1 0 " 3 no w a v e s - - - -

6 ) [ F e ( C O ) 3 SCH3 ] 2 0 .0 5 M (C 2 I I 5 ) 4 N+ C 1 0 4 1 . 0 x 1 0 " 3 - 1 . 3 9 7 7 . 6 k i n e t i c 2 . 5 i r r e v . ( 0 . 8 )

0 . 1M (C 3E J 4 N+ B r ‘ l . O x . O " 3 - 1 .3 2 8 1 0 . 4 k i n e t i c 3 . 4 i r r e v . ( 0 . 6 )

7 ) [ F e ( N 0 ) 2 l ] 2 0 .0 5 M (C 2 H5 ) 4 N+ C 1 0 4 3 . 0 x 10™4 - 0 . 1 7 1 , - O . 7 3 4 , - 1 . 4 8 6

2 . 6 , 2 . 6 , 3 . 4

k i n e t i c , k i n e t i c , k i n e t i c

1 . 5 , 2 . 5 , 5

i r r e v . ( 0 . 7 ) i r r e v . ( 0 . 6 ) i r r e v . ( 1 . 2 )

8 ) HC1 0 .0 5 1 4 ( c 2 h 5 ) 4 n+ c i o 4

0 .0 5 1 4 ( C ^ L ^ N B r "

1 . 8 6 x 1 0 " 3

1 . 1 5 x 1 0 " 3

- 1 . 1 3 0

- 0 . 9 0 0

1 2 . 0

3 . 6

n o t d e t e r m in e d

n o t d e t e r m in e d

2

1

i r r e v .

i r r e v .

9 ) [ ( C 6 H 5 ) 4 P ] 2 F e ( C N ) 5NO 0 .1 0 M (C 3H7 ) 4 N+ B r " 1 . 0 x 1 0 " 3 i n [ F e ( C N ) 5N 0 ]2 " - 0 . 4 5 0 6 . 0 n o t d e t e r m in e d 0 . 6 i r r e v .

+ K C 13 . 3 x 1 0 “ 3 i n H C l

Treble H I Oxldixtivo Pol^.rcprnpliy in D ichlorcnctM ne

Cone, ofCompound E le c tro ly te D epolarizer (m)

1) MO 0.05M (C2H5) 4N+ C104 ?

2) ((C3H7 )4N]2Fe(CN)5NO 3.0x10™3 1.0x10™3 3.3x10™4

3) [(C6H5) 4P]2Fe(CN)5MO 11 1.0x10™3

4) [(C6H5) 4P]3Mn(CN)5NO 11 1.0x10™3-43.3x10 4

5) [(C6H5) 4P]Cr(CN)5NO 1.0x10™33.3x10™4

6) [Fe(C0)3SCH3l 2 1.0x10™3

7) [Fe(N0)2l ] 2 1.0x10™3

Approx. # of e in

, x of Control volved asd o f E lectrode c a lc ’d from Reversi-

E^y2 (v) @70 cm Hg Process i d b i l i t y

no waves

+0.305, ~0 .700 O.55 , %i.o quasi k in e t ic 1/ 18 , y e i r r e v . , i r re v .

+ 0 .2 8 0 , 0 . 6 0 0 0 . 5 , 0 .5 quasi k in e t ic 1 / 6 , y e i r r e v . , i r re v .

+0.285, +0.645 0 . 32 , 0.40 quasi k in e tic 1/ 3 , 1/3 i r r e v . , i r re v . (0.7, 2.8)

+ 0.285, +0 .655 0 TT 0 xn quasi k in e t ic 1/ 9, n / 6 i r r e v . , irre v .

- 0 . 134, +0.245 2 .5 , 0.6 d i f f . , quasi k in e t ic 1, l /6 i r r e v . , irre v .-0 .135, +0.250 1 .1 , 0 .4 d i f f . , quasi k in e t ic 1, l /3 i r r e v . , i r re v .__________________________________________________________ (017)_

-195 0 .4 quasi k in e t ic 1/9 irre v .-235 0 .4 quasi k in e t ic 1/3 i r re v .

+0.700 3.4 d i f f . 1 rev . (? ) , (1.2)

+0.300 2 .2 k in e tic , 2 i r r e v . , (curve,0.6 G 0.9)

RESULTS

P re p a ra tio n o f th e N itro s y l Complexes

The re d u c tio n s o f [Fe(CN)^WO] ~ were a ttem p ted b e fo re th e20p u b lic a t io n o f a s u c c e ss fu l method appeared . As th e s e were un

s u c c e ss fu l in p roducing a p u re compound, th e y w i l l be d e a l t w ith

b r i e f l y .

The p o tass iu m amalgam re d u c tio n o f [ ( C^H ,̂)^2\fl^Fe ( CN) ,-NO, as

d e sc rib e d above, r e s u l te d in a m ix tu re o f p ro d u c ts . When th e re d u c tio n

was c a r r ie d o u t w ith more amalgam, o r f o r a lo n g e r tim e , i t m erely r e

s u l te d in th e fo rm atio n o f th e w h ite im p u rity , which appeared to cause

decom position o f th e b lu e p ro d u c t, [ ( ] ^Fe ( CN) ^MOK. Thus th e

re d u c tio n was stopped when th e band a t i 860 cm ^ f i r s t appeared in th e

in f r a r e d spectrum . P u r i f i c a t io n o f t h i s a i r - s e n s i t i v e m ix tu re was

a ttem p ted by c a r e fu l r e c r y s t a l l i z a t i o n from ace to n e , from ace to n e / e th y l

a c e ta te , and from 2 -bu tanone; by s e le c t iv e p r e c ip i t a t i o n w ith t r i s -

ethylenediam m ine c o b a l t ( i l l ) io d id e and t r i s -ethylenediam m ine

ch rom ium (ill) te tra p h e n y lb o ra te and by an ae ro b ic chrom atography w ith

alum ina, s i l i c a g e l , c e l l e x Ae, c e l le x T, and Dowex 21K columns. None

o f th e se methods produced any a p p re c ia b le s e p a ra tio n o f th e m ix tu re .

S ev era l p e n ta c y a n o n itro sy l complexes were t r e a t e d w ith hydrogen

c h lo r id e to y ie ld p ro d u c ts which cou ld n o t be unam biguously id e n t i f i e d .

Thus, th e d e s c r ip t io n o f th e se compounds i s in c lu d ed below r a th e r th a n

in th e ex p erim en ta l s e c tio n .

21

22

When HC1 i s bubb led th rough a d e a e ra te d CH^Cl^ s o lu tio n o f

[ ( C g H ^ ) ^ P ] ^ C r ( C N ) ^ H O * a ye llow a i r - s e n s i t i v e p r e c ip i t a t e form s.

The elem ental analyses ob ta ined fo r t h i s m a te r ia l do no t d is tin g u ish

between th e compounds {[ ((y i^ )^P ] (H+)>Cr(CN^H^CONC) and

{[(CgH5 )itP](H+)2 }Cr(CN) HO-HgO. The anion [Cr(CN )^(H gO )m f ~ has beenOC v 0_

p o s tu la te d as an in te rm e d ia te in th e a q u a tio n o f [Cr(CtT)^NO] in

a c id ic w a ter s o lu t io n s , so t h i s su p p o rts th e f i r s t fo rm u la tio n . The

in f r a r e d fre q u e n c ie s have been s h i f te d in a manner which would be ex p ec ted

f o r th e exchange o f te traphenylphosphonium fo r a sm a lle r c a tio n such as

a p ro to n y e t th e s h i f t s a re n o t g r e a t enough to in d ic a te t h a t a p ro to n

i s bonded d i r e c t l y to a cyanide o r n i t r o s y l group. The p e r t in e n t

fre q u e n c ie s a re :

Compound ̂ VGN“ ^cm ^

{[(C6H5 )^P](H+ )}Cr(CN)5 (H20)N0 (? ) l680 2149, sh2150,

sh2 l 6 0 , 2170

K Cr(CN) NO 1675 2150

[(C6H5 ) 1+P ]3Cr(CN)5NO 4 ^ 0 l6 4 0 2100

VThen d ich lorom ethane s o lu tio n s o f [ ( ) ^P] ^Mh( CN)^N0e SH^O

and [ (C^H^)^P]2Fe(CN)^N0 were t r e a t e d w ith hydrogen c h lo r id e , p r e

c i p i t a t e s were a lso formed which decompose in th e p re sen c e o f a i r o r

w a ter. The manganese compound y ie ld s a p in k s o l id which has th e

fo l lo w in g - in f ra re d bands: VqN“ = 2170 , 2130 cm \ = 1800 cm”1 ,

w h ile th e s t a r t i n g m a te r ia l has v ^ - = 212 0 , 2080 cm 1 , = 1700 cm 1 ,

and th e tr ip o ta s s iu m s a l t has vq̂ ** = 2130 , 2100 cm”1 , = 1730 cm”1 .

23

The p ro to n a te d compound a lso has a l a r g e , b ro ad band a t 655 cm”'1" which

i s much s tro n g e r th a n i s found w ith th e o th e r c a t io n s . The s t a r t i n g

m a te r ia l has sharp cyanide and n i t r o s y l in f r a r e d b an d s, w h ile th e p ro

d u c t has b ro ad b an d s, in d ic a t iv e o f a m ix tu re . The e lem en ta l a n a ly s is

may a lso be e x p la in ed as a m ix tu re : Found, C, U3 . 57; H, 2 .9 4 ; 0 , 7 .75 .

C a lc u la te d f o r {[ ( ] (H+ )2> Mn ( C$t)^NO 2H20 :

C, 5 9 .0 ; H, 4 .1 ; 0 , 8 .1 .

C a lcu la te d f o r ( H ^ m ( C N ) ^ O : C, 2 7 .5 ; H, 1 .4 ; 0 , 7 .4 . The

p o s i t io n s o f th e cyanide bands in th e p ro to n a te d sp e c ie s and p o tassium

s a l t a re v e ry s im ila r and th e s h i f t s o f th e cyanide bands may be ex

p la in e d by th e exchange o f te traphenylphosphonium c a tio n s f o r p ro to n s .

However, th e n i t r o s y l frequency i s 70 cm ^ h ig h e r in th e p ro to n a te d

compound th an in th e po tass iu m s a l t . T his can be in te r p r e te d as a

p ro to n a tio n o f th e n i t r o s y l group. T his ty p e o f b eh av io r has been r e - 20p o r te d f o r a s im ila r iro n compound, b u t th e s h i f t i s much la r g e r :

FeC CN ^O 3" , Vjjq = 1568 cm"1 ; Fe(CK) UOH2 " , = 1746 cm"1 .

When a d ich lorom ethane s o lu tio n o f [ ( C^H^) l ^Fe ( CH)^NO was

t r e a t e d w ith hydrogen c h lo r id e , a w h ite p r e c ip i t a t e formed im m ediately .

T his a i r - s e n s i t i v e m a te r ia l had an in f r a r e d spectrum which showed a

b roaden ing o f th e cyanide and n i t r o s y l b ands, b u t no s h i f t o f th e se

bands compared to th e spectrum o f th e s t a r t i n g m a te r ia l . The compound

decomposed to a brown s o l id b e fo re an e lem en ta l a n a ly s is cou ld be p e r

formed. The compound may a ls o have decomposed w h ile th e KBr d isk was

b e in g p re p a re d f o r th e in f r a r e d spectrum . In th e p re sen ce o f w a te r , th e

24

w h ite compound becomes y e llo w , p o s s ib ly due to th e fo rm atio n o f

[Fe(CN)5 (H20 ) ] 3".

P o larography

When n i t r i c ox ide was in tro d u ce d in to th e p o la ro g ra p h ic s o lu t io n

i t y ie ld e d two re d u c tio n waves, th e f i r s t o f which was l a r g e r th an th e

second. As th e scan was re p e a te d , th e second wave grew a t th e expense

o f th e f i r s t and th e sum o f th e h e ig h ts fo r b o th waves d ecreased slow ly .

When hydrogen c h lo r id e was in tro d u ce d in to th e s o lu t io n , th e f i r s t wave

d isap p ea red and th e h e ig h t o f th e second wave in c re a se d . O x idative

p o la ro g rap h y d id n o t y ie ld any d i s t i n c t w aves, a lth o u g h th e re i s a

p o s s i b i l i t y t h a t a wave began to appear j u s t b e fo re th e dropping m ercury

e le c tro d e i s o x id iz e d (+0.9 v . ). The c o n c e n tra tio n o f NO in th e p o la ro

g rap h ic s o lu t io n s was n o t determ ined.2_

P e n ta c y a n o n it r o s y lf e r r a te , [Fe(CN)^N0] ” , i s p o la ro g ra p h ic a l ly

reduced in two s in g le e le c t r o n , d i f f u s io n c o n tro l le d , s te p s

(E^y^ = -0 .9 , - 1 .2 ) . Using (C^H^)^N+Br as an e l e c t r o l y t e , b o th waves

a re r e v e r s ib le , w hereas, w ith (C^H )^N+d O ^ o n ly th e second wave i s

r e v e r s ib le . A lso , th e half-w ave p o te n t i a l o f th e f i r s t wave i s about

50 mv. more n e g a tiv e w ith th e (CgHc)^N^dO^ e le c t r o ly te th a n w ith

(C^Hr-,)|+N+Br , w h ile th e second wave o ccu rs a t e s s e n t i a l l y th e same

p o te n t i a l w ith b o th e le c t r o ly te s (T able I I ). Hydrogen c h lo r id e i s r e - (

duced in d ich lorom ethane in one i r r e v e r s ib l e wave which has a more

n e g a tiv e half-w ave p o te n t i a l ( - 1 .1 3 0 v. ) w ith th e (C2H^)^N+C10j+

e le c t r o ly te th an w ith (CgH^)]+N+Br (E^y^ = 0 .900 v. ). When 1 .0 x 10 ^ M

[ ( C^gHt-)^Pl^Fe( C N ) i s a^ded to a s o lu t io n which i s 3*33 x 10""^ M in

hydrogen c h lo r id e and 0 .1 0 M in (C^H^)^N+Br*‘) th e h e ig h t o f th e p ro to n

re d u c tio n wave i s low ered by an amount co rrespond ing to 1 .2 moles H+ p e r2 „

mole o f [Fe(CN)c_N0 ] and i t s p o te n t i a l i s s h i f te d by +0.450 v.

= -0 .4 5 0 v . ) . The p o la ro g ra p h ic o x id a tio n o f [Fe(GN)^N0]2"* y ie ld s

two sm all waves (E^y^ = +0 . 2 6 5 , +0 . 6 1 5 ) whose h e ig h t i s e s s e n t i a l ly con-_Q

c e n tr a t io n independent from 3 .0 x 10 M to 3*33 x 10 M. These waves

a re i r r e v e r s ib l e and may be d e sc r ib e d as q u a s i - k in e t ic a l ly c o n tro l le d ,

as th e p lo t o f h1/ 2 v s . i ^ g iv e s th e in te r c e p t s ( i^ = 0 , h1^2 = 2 .9 cm"̂ /2 ,

and i ^ = - 0 . 3n&, h^ /2 = 0 ) , which a re in te rm e d ia te betw een th o se expec ted

f o r a c le a r ly k in e t i c p ro c e ss and a w e ll behaved d i f f u s io n c o n tro l le d

p ro c e ss .

The an ions [Mn(CN)j-N0]^ and [ C r( Ctt)^NO] ^ a re n o t reduced in

th e range a v a i la b le in d ich lorom ethane (+0. 9 v. to -1 .5 v . ). However,

b o th compounds g iv e sm all o x id a tiv e waves a t about +0 .2 0 0 v. which

behave s im i la r ly to th e o x id a tiv e waves d e sc rib e d above f o r th e 2 _

[Fe(CN)^H0] an ion (T able I I I ) . The manganese compound a lso d isp la y s

a d if f u s io n c o n tro l le d , i r r e v e r s i b l e , one e le c tro n o x id a tio n wave a t

= "0.135 v.

The s u l f u r b r id g e d dim er, ^ [Fe(C0)^SCH^]2 , y ie ld s one k i n e t i

c a l ly c o n tro l le d re d u c tio n wave a t about - 1 .3 5 v. whose h e ig h t and

h alf-w ave p o te n t i a l i s dependent upon th e e le c t r o ly te com position. T his

i s p ro b ab ly an i r r e v e r s ib l e two e le c tro n re d u c tio n , b u t t h i s cannot be

d e f in i t e ly concluded, s in ce th e wave i s n o t d if f u s io n c o n tro lle d . This

dimer g iv e s one o x id a tio n wave (E , - +0 .7 v . ) which i s d if f u s io n

26

c o n tro l le d and p ro b ab ly r e v e r s ib le . The c e r ta in ty o f r e v e r s i b i l i t y

must be q u a l i f ie d s in ce th e p lo t o f E v s . lo g g iv e s a s t r a ig h tv 1 .

l i n e w ith a s lo p e o f 0 .048 and an "n" v a lu e o f 1 .2 . The "n" v a lu e f o r

a r e v e r s ib le p ro c e ss i s no rm ally .betw een 0 .9 and 1 . 1 .

The halogen b rid g e d dim er, [FefN O )^!]^, was found to g ive th r e e

re d u c tio n waves (E^y^ = - 0 . 171*, - 0 .0 3 4 , -1 .4 8 6 v. ) a l l o f which a re

k i n e t i c a l l y c o n tro l le d . I t i s re a so n a b le to assume t h a t th e se a re one,

tw o, and fo u r e le c t io n i r r e v e r s ib l e w aves, r e s p e c t iv e ly , a lth o u g h th e

k in e t ic c o n tro l o f th e s e waves ag a in p re c lu d e s d e f in i t e co n c lu s io n s .

The d in i t r o s y l i ro n io d id e dim er a ls o g iv e s a k i n e t i c a l l y c o n tro l le d

o x id a tio n wave (E^y^ = +0 . 3 v. ) which ap pears to r e s u l t from th e

i r r e v e r s ib l e lo s s o f two e le c tro n s .

i

DISCUSSION

The re d u c tiv e p o la ro g rap h y o f d is so lv e d n i t r i c o x id e , NO, may

be e x p la in ed by a t t r i b u t i n g th e f i r s t wave to th e r e a c t io n :

N0° + e -> NO , and th e second wave t o : NOH+ + e ” -> NOH°. The

h e ig h t o f th e second wave in c re a s e s w ith tim e due to th e a b s t r a c t io n

o f a p ro to n from th e so lv e n t by NO to g iv e NOH+. T his i s s u b s ta n t ia te d

by th e observed in c re a s e in h e ig h t o f th e second wave and d isap p earan ce

o f th e f i r s t wave on a d d it io n o f hydrogen c h lo r id e . The h e ig h t o f th e

f i r s t wave d e c rea se s r a p id ly w ith tim e due to p ro to n a tio n o f NO as w e ll

as lo s s o f NO from th e s o lu t io n . T his lo s s o f NO in to th e n itro g e n

atm osphere above th e s o lu t io n i s re s p o n s ib le fo r th e d ecrease o f th e sum

o f b o th wave h e ig h ts w ith tim e. T his d ec rease p re v e n ted a c c u ra te d e te r

m in a tio n o f th e change o f d if f u s io n c u r re n t w ith r e s p e c t to th e h e ig h t

o f th e column o f m ercury.

An o x id a tiv e wave r e s u l t in g from N0° - ( e ” ) -> N0+ would be

ex p ec ted , b u t does n o t occu r b e fo re th e o x id a tio n o f th e dropping

m ercury e le c tro d e ta k e s p la c e .p_

The two s te p re d u c tio n o f [Fe(CN)^NO]- may be a t t r i b u t e d to th e

r e a c t io n s [Fe(C N )^N of ~ + e~ [Fe(CN)^N0]3~, [Fe(GN)^NO]^” + e “ 5= = ^

[Fe(CN)^NO] ̂ . I t was p re v io u s ly p o s t u l a t e d ^ th a t th e s e waves a re n o t

r e v e r s ib le in w a ter due to p ro to n a tio n o f [Fe(CN)^NO]^ to g ive a sp e c ie s

in a c t iv e to back o x id a tio n . The r e v e r s ib le waves o b ta in e d in d ic h lo ro -

methane w ith th e tetrapropylam m onium brom ide e l e c t r o ly te su p p o rt t h i s

27

28

p rem ise . The f i n a l p ro d u c t o f t h i s p o la ro g ra p h ic re d u c tio n ,

[Fe(CN)cjNO] , i s p ro b a b ly u n s ta b le , as th e p ro d u c ts o f a long term

re d u c tio n o f [Fe(CN)^l'IO]^ in l i q u id ammonia have been re p o r te d to be

[F eC at^N O ]3" and [ F e ( C N ) ^ 0 ] ^ " .^ When [Fe(CN),-II0]2~ was added to a

s o lu t io n c o n ta in in g HC1, i t was found to r e a c t w ith one p ro to n to g ive

a p o la ro g ra p h ic a l ly in a c t iv e sp ec ie s which f a c i l i t a t e s re d u c tio n o f th e7

rem ain ing p ro to n s . S ince i t has been argued th a t th e re d u c tio n o f 2 _

[Fe(CN)jJtfO]~ p r im a r i ly in v o lv e s th e n i t r o s y l group, i t would be

re a so n a b le to assume th a t th e p ro to n a tio n o f th e n i t r o s y l cou ld g r e a t ly

a l t e r th e re d u c tio n p ro c e sse s . The s h i f t in p ro to n re d u c tio n p o te n t i a l

d e sc r ib e d above cou ld be due to k in e t i c f a c i l i t a t i o n by a t r a n s p o r t

mechanism in v o lv in g th e [Fe(CN)^HO] io n , b u t no c le a r e x p la n a tio n can

be p o s tu la te d from th e d a ta a v a i la b le . The two sm all o x id a tiv e waves2 —a re due to th e r e a c t io n o f [Fe(CN)^NO] w ith im p u r it ie s in th e so lv e n t

o r e l e c t r o l y t e , th u s t h e i r wave h e ig h t i s independen t o f th e c o n cen tra -,2-t i o n o f [Fe(CN)^NO]‘

The io n [Cr(CN)^NO] 3 g iv e s no o x id a tio n o r re d u c tio n waves ingo

d ich lo rom ethane, a lth o u g h i t i s known to g ive a r e v e r s ib le , one

e le c tro n wave in w a te r . However, in w a te r , t h i s wave o ccu rs a t aboutP —th e same p o te n t i a l as th e t h i r d re d u c tio n wave f o r [Fe(CN)jJTO] ” , and

i t has been n o ted above t h a t th e so lv e n t i s reduced b e fo re t h i s p o te n t i a l

i s reached in d ich lo rom ethane.

The [Mn(CN)j-NO]3’’ an ion g iv e s no re d u c tio n waves and one i r r e

v e r s ib le s in g le e le c t ro n o x id a tio n wave, which i s id e n t i c a l to th e r e s u l t s

re p o r te d in w a ter.

29

I t shou ld be n o ted t h a t t h i s o x id a tio n occu rs f a i r l y e a s i l y ,

El / 2 = "0 .135 v.

Both [Cr(CIT)^NO]^ and [Mn(GIT)_NO]^ d is p la y a sm all o x id a tio no _

vra-ve which i s analogous to th e [F e ((21)^110] o x id a tio n m v e s and i s

a t t r i b u t e d to th e p re sen ce o f im p u r i t ie s in th e p o la ro g ra p h ic s o lu tio n .

The s u l f u r b r id g e d dim er, [Fe(CO)^SCH^]^, has been re p o r te d ^1

as g iv in g a r a d ic a l an io n , [Fe(C0 )^SCH^]2 , upon re d u c tio n in dim ethoxy-

e th an e . However, in d ich lorom ethane i t appears to i r r e v e r s ib ly ta k e up

two e le c tro n s . The sh o r t Fe-Fe bond d is ta n c e ( 2 . A) in t h i s compound

has le d to th e p o s tu la t io n o f m e ta l-m e ta l bond in v o lv in g an u n p a ired

e le c tro n from each i ro n atom. I t i s v e ry l i k e l y t h a t t h i s i r o n - i r o n

bond undergoes a two e le c tro n re d u c tio n which c lea v e s th e m olecule.

T his dim er a lso undergoes a one e le c t r o n o x id a tio n which i s p ro b ab ly th e

r e v e r s ib le fo rm atio n o f th e c a t io n ic complex, [Fe(CO)^SCH^]p. A s im ila r

s p e c ie s , [(*-C^Iy)Fe(CO)SCH^]g, has been g e n e ra te d in d im e th y o x y e th an e .^

The th re e re d u c tio n waves o f th e halogen b r id g e d dim er,

[Fe(NO)^!]^? may be e x p la in ed by th e fo rm atio n o f a r a d ic a l an ion ,

[Fe(NCOgllg? which th e n a cc e p ts two e le c tro n s to reduce th e m e ta l-m e ta l

bond, th e n ta k e s on fo u r e le c tro n s in a re d u c tio n o f th e n i t r o s y l groups.

R ad ica l an ions have been produced from a number o f ca rb o n y l and n i t r o s y l31 —com plexes, " so th e p o s tu la t io n o f [Fe(NO)^!]™ i s n o t u n reaso n ab le . A l

though [F e(N 0 )g l]2 has a r a th e r lo n g m e ta l-m e ta l d is ta n c e ( 3.05 A ),

37th e re i s ev idence f o r i r o n - i r o n bonding in t h i s complex and i t s second

re d u c tio n may be co n sid e red to be analogous to th e so le re d u c tio n wave

g iven by [FeCCCO^SCH^lg.

30

This complex, [Fe(N O )^!]^, a lso g iv e s a two e le c t ro n o x id a tio n

wave which i s p ro b ab ly due to th e o x id a tio n o f th e m eta l atom s, a lth o u g h

i t cou ld a ls o be a t t r i b u t e d to o x id a tio n o f th e io d id e b r id g e s .

The half-w ave p o te n t i a l s found in aqueous s o lu t io n s v s . a

s a tu r a te d calom el re fe re n c e e le c tro d e a re p lo t t e d (F ig u re l ) vs. th e

half-w ave p o te n t i a l s found in d ich lorom ethane w ith an aqueous 1 .0 M LiC lo _

re fe re n c e e le c tro d e . As d isc u sse d above, th e re d u c tio n o f [Fe(CN)^N0]

i s in f lu e n c e d by p ro to n a v a i l a b i l i t y due to th e p ro to n a tio n o f th e r e

duced s p e c ie s , [F e (d ’T)^N0]^ , to form th e sp ec ie s [Fe(CN)^N0H]2” which

i s in a c t iv e to back o x id a tio n . However, p ro to n a v a i l a b i l i t y should n o t

in f lu e n c e th e re d u c tio n o f HC1 o r NOH. The o x id a tio n o f [Mn(CN)^H0]^”28 2— in w a ter i s known to produce [Mn((2l)t-N0 ] so t h i s r e a c t io n would n o t

be expec ted to be in f lu e n c e d by p ro to n a v a i l a b i l i t y e i th e r . Thus th e

p o in ts fo r H d , NOH, and [Ifo(CN)j-NO]^ f a l l on a s t r a ig h t l i n e , w h ile

th o se f o r th e two re d u c tio n s o f [Fe(CH)^N0 ]^ f a l l to th e l e f t o f t h i s

l i n e . The p o s i t io n o f th e p o in t due to th e f i r s t re d u c tio n [ F e ( l ) ] may

be ex p la in ed by p o s tu la t in g th a t in b o th so lv e n ts th e r e a c t io n

[F e(d l)^N 0]2 ’" + e~ [Fe(CN)^N0]^” ta k e s p la c e , w h ile in H^O, b u t n o t

in CHgCl^, t h i s i s fo llo w ed by th e r e a c t io n [Fe(CN)

[Fe(CN)^N0H]^ . Thus in H^O th e c o n c e n tra tio n (C^) o f th e reduced

s p e c ie s , [Fe(CN)^N0]^ , i s l e s s th an in CH^Cl^. When t h i s i s a p p lie d to

th e e q u a tio n E , = E° -0 .059 lo g C /C (where E . = En /o when. x d.m. e. r o d.m. e. 1 /2

Cr = Co ) , i t can be seen t h a t E^y^ vriill be more p o s i t iv e in H^O th a n in

31

E,(v.) in H20 2

- 1.0 --

[F e(C N L N 0 ]5"NOH + e

[Fe(CN)5NO]2™ +-0 .4 - -

HCI + e- 0.2 - -

— 0.2 —0 .4 —0.6 y^O.8 - 1.0 - 1.2 -1.4+ 0.2

40.2 - -

+ 0.4 •"

[Mn(CN) NO]+ 0.6 - -

F ig u re 1 . w ith SCE R eference E lec tro d e v s . E^y^ in Cl^Clg

w ith Aqueous 1 .0 M LiCl R eference E lec tro d e

r e l a t i v e to th e same re fe re n c e e le c tro d e . For th e second r e

d u c tio n , th e r e a c t io n in w a ter may be p o s tu la te d as ( l ) [Fe(GN)^N0H]2’”

+ e~ -> [Fe(CN)^lTOH]3"’ and in CHgCl^: (2 ) [Fe(m )^N O ]3'" + e~

[Fe(GN)^NO]^ . Using th e eq u a tio n above, assuming j u s t i f i e s th e

p o s i t io n o f th e p o in t F e(2 ) in F ig u re 1.

CONCLUSION

The most ambiguous a sp e c ts o f m e ta l - n i t r o s y l com plexes, th e

fo rm al o x id a tio n s t a t e o f th e m e ta l, can be c l a r i f i e d by an a ly z in g th e

p o la ro g ra p h ic d a ta d isc u sse d above.

I f a c o o rd in a ted n i t r o s y l were s im ila r to th e f r e e m olecu le ,

th e n a co o rd in a ted N0° group should g iv e one re d u c tio n wave a t -0 .9 v .

o r g r e a te r due to s t a b i l i t y by c o o rd in a tio n , an N0+ group would be r e

duced a t a l l p o t e n t i a l s , w h ile an NO** group would g iv e an o x id a tiv e wave

a t - 0 .9 v. o r l e s s due to s t a b i l i z a t i o n , in th e p o la ro g ra p h ic system

d isc u sse d above. Thus th e fo u r e le c tro n re d u c tio n a t -0 .4 8 6 v. o f

[Fe(N0)2 l !2 can be a t t r i b u t e d to th e re d u c tio n o f fo u r N0° groups to

NO , which im p lie s F e ( l ) . I r o n ( l ) in a low sp in d^ c o n f ig u ra tio n would

a llow th e u se o f one e le c tro n from each m eta l atom to form th e m e ta l-

met a l bond p o s tu la te d f o r t h i s complex. I t i s i n t e r e s t i n g to n o te t h a t

th e carbony l lig a n d s in th e complex [Fe(C0 )^SCH^]2 , and in o th e r com-

p le x e s do n o t g iv e any p o la ro g ra p h ic waves and th u s CO i s n o t e l e c t r o -+ch em ica lly s im ila r to NO , a lth o u g h th e y a re i s o e le c t r o n ic .

The o x id a tio n o f [Mn(CT0^N0]^ a t -0 .135 v . can be a t t r i b u t e d to

NO b e in g o x id iz e d to NO0 . The n i t r o s y l s t r e tc h in g freq u en cy fo r th eP— pR

o x id iz e d s p e c ie s , (CN)^NO] , i s 1885 cm which i s alm ost i d e n t i --1 p i

c a l to th e 1876 cm" freq u en cy o f f r e e NO, b u t i s much h ig h e r th a n

th e 1730 cm**1 v a lu e found f o r [Mn(CN)^N0]u". ^ P o s tu la t io n o f NO"

33

im p lie s M n (ll l) f o r [Mn(CN)^MO]^"", which ag rees w ith th e observed

diam agnetism o f th e compound.

P—However, th e two s te p re d u c tio n o f [Fe(GN)^HO] ** and th e s in g le

e le c tro n re d u c tio n o f [Cr(CN)^no]^ a t v e ry n e g a tiv e p o t e n t i a l s , cannot

be ex p la in ed by th e sim ple form alism o f ITO+, N0°, and NO”. These r e

d u c tio n s may be p a r t i a l l y e x p la in ed u s in g m o lecu lar o r b i t a l (M.0. )O'! p _

l e v e l s c a lc u la te d by Manoharan and Grey. For [Fe(CN)^NO] *" th e •

p e r t in e n t l e v e l s a re :

7e(jt*NO) ( - 6 5 ,560 cm"*1 )

Pbg(xy) (-8 6 ,1 0 0 cm™1 )

-16e (x z , yz) ( - 90 ,6 7 0 cm™ )

Thus, two re d u c tio n waves, a t s im ila r p o t e n t i a l s , would h a l f f i l l th e

7e le v e l . The p ro d u c t o f th e f i r s t re d u c tio n should be p a ram ag n e tic ,

and s in ce e le c tro n s a re b e in g p la c e d in a n tib o n d in g o r b i t a l s , th e r e

duced sp e c ie s should be l e s s s ta b le th a n th e s t a r t i n g m a te r ia l . S ince

th e Pbg o r b i t a l i s o f r e l a t i v e l y low energy , no o x id a tio n p ro c e sse s

should occu r. A ll th e se phenomena a re observed . A lthough t h i s d e f in e s

th e fo rm al charges as F e ( H ) and NO*1, d e ta i le d c a lc u la t io n s show th e"f* on i t r o s y l group to be in te rm e d ia te betw een NO and NO . I t has been in -

d ic a te d above t h a t th e re d u c tio n o f [Fe(CN)^NOH]_™ ta k e s p la c e a t a

le s s n e g a tiv e p o te n t i a l th a n th e re d u c tio n o f [Fe(CN)^NO]^™. With

re g a rd to th e M. 0. diagram above, t h i s may be in te r p r e te d as a low ering

o f th e 7e(it ) l e v e l in th e f i r s t compound as compared to th e second.20This i s in acco rd w ith th e re p o r te d h ig h e r n i t r o s y l bond o rd e r

(ca. 0 . 2 ) in th e f i r s t compound as compared to th e second.

35

I f [Cr(CN)^MO]^ i s fo rm a lly c o n sid e red as C r ( l l l ) and NO**,

which i s su p p o rted "by th e param agnetism and low n i t r o s y l s t r e tc h in g

freq u en cy (l645 cm th e n th e Ye le v e l has one e le c tro n . A one

e le c tro n re d u c tio n would h a l f f i l l th e Ye l e v e l , and f u r th e r re d u c tio n

would be d i f f i c u l t due to e le c t r o n - e le c t r o n re p u ls io n , which i s observed .

However, th e c o n f ig u ra t io n should be e a s i ly o x id iz e d , and t h i s i s

n o t observed . The param agnetism o f th e compound p re c lu d e s use o f th e

N0° fo rm alism , and th e N0+ form alism g iv e s th e c o n f ig u ra tio n 6e^2b‘L

which should be reduced a t much more p o s i t iv e p o te n t i a l s th a n i s observed .

A s im ila r problem a r i s e s in e x p la in in g th e o x id a tio n o f [Mn(CN)^NO]^**

w ith th e se M. 0. l e v e l s . A gain, a N0° form alism i s e lim in a te d by th e

m agnetism , w h ile a N0+ fo rm u la tio n would p r e d ic t two re d u c tio n waves2 — —( i s o e le c t r o n ic w ith [Fe(GN)^N0] ) and a NO form alism would p r e d ic t

2 —two o x id a tio n waves. Thus th e p o la ro g ra p h ic b eh av io r o f [Fe(CN)^N0]

can be e x p la in ed by M.0. c a lc u la t io n s , and th e fo rm u la tio n o f NO** in

[Mn(CN)

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