JKAU:

Sci., vol. 8, pp. 69-80 (1416 A.H./1996 A.D.)

Optical Absorption Spectra of Pr3+ Chelates with2- Amino-l- Phenylethanol

A.H. QUSTI* and A.G.M. AL-SEHEMI*Depal1ment of Chemistry, Faculty of Science. leddah; and

Teacher College at Abha, Abha, Saudi Arabia

ABSTRACT. Trivalent Pr3+ chelates of the type Pr(PhCHOHCH2NH2)4 havebeen synthesised by the direct reaction of 2-amino-l-phenylethanol with

Pr(NO3)3.5Hp. Spectral studies reveal the presence of a 1:4 (metal-ligand)stoichiometry. Various spectroscopic parameters have been evaluated from theUV. Vis. and near i.r. spectra.

Introduction

As a part of our program on the spectral studies of the Pr3+ ion in solution,ll-3] wereport the synthesis of praseodymium (III) nitrate and chloride chelates with 2-amino-l-phenylethanol. These complexes are characterized by electronic and vibrational spec-tral studies. The energy levels of the 4f2-configuration of the Pr3+ ions have beenanalysed in arc spectral4], o-hydroxyacetophenone oximel5], PGClj:SnCI416], and crystalPrCI317]. Surna et ai.IS] have studied the absorption spectrum of Pr + in haloacetate solu-

tions. Lakshman and Buddhudul9] reported the Slater-Condon, configuration, spin-orbit, nephelauxetic, bonding, and Judd-Gfelt parameters of Pr3+ in the acetates ofpraseodymium complexes in the presence of magnesium, calcium, and cadmium com-plexes. Buddhudu and BadullO] reported the Racah and Judd-Gfelt parameters for Pr3+ion in methyl, butyl, isopropyl and amyl alcohols. In general, Semiempirical calcula-tions based in the Judd-Gfelttheory were not satisfactory for the Pr3+ ionlll]. Recently,Misra and Sommererll2] have studied the UV-Vis. bands of Pr3+ complexes in 50lution.Their values of the T 2 parameter are mainly negative.

*The author to whom all the correspondence should be addressed.

69

70 A.H. Qusli & A.G.M.AI-Sehenli

Experimental

Materials and Chemicals :

The chemicals used were praseodymium nitrate pentahydra~e of 99.9% purity(Fluka), praseodymium chloride hexahydrate 99.9% purity (Aldrich), dimethylsulphox-ide (DMSO), acetic acid (BDH) and 2-amino-l-phenylethanol which was prepared.

Preparation of 2-amino-l-phenylethanolMandelonitrile (6 g) (ca 0.045 mole) in dry THF (73 ml) was added dropwise to a

sullry of LiAIH4 (5.8 g), (ca 0.150 mole) in dry THF (290 ml). The mixture was stirredand cooled at O°C during the addition, for 6 hr. After completion of the addition, thereaction mixture was left at room temperature overnight. The reacti9n mixture was thenrefluxed for 4 hr, then decomposed with water (8 ml), followed by aqueous sodiumhydroxide (20%, 15 ml), and finally water (8 ml). The product obtained was refluxedfor 30 min., then filtered hot and washed with hot THF. The filtrate was dried overanhydrous K2CO3 .Evaporation under reduced pressure. afforded an oily product(3.96g, 57.3%) m.p. 41°C which was identified as 2-alBino-l-phenylethanol. The IH-nmr in (CDCI3) spectrum showed the following signals: 2.8 (2H,d,'J = 6Hz, methyleneprotons), 3-3.i (3H, broad, OH, NH2 exchanged with D20), 4.6 (tH, J = 6Hz, methineprotons), and 7.3-7.5 (5H, m, Arh) ppm.

Synthesis of Praseodymium (III)-2-amino-l-phenylethanol chelatesA series of solutions were prepared and analysed according to Job's[13.14] method. A

solution of Pr(NO3)3' 5H20 0.1 M (100 ml) in (DMSO) was prepared. A solution ofPhCHOHCH2NH2 (ligand) O.IM in (DMSO, 100 ml) also was prepared. In each ofnine flasks a mixture of metal salt and the ligand was stirred (the sum of the total con-centration of the metals salt and the ligand is kept constant, while the mole fractions ofthe reactants are varied).

Absorption SpectraAll UV, Visible, and near IR spectra of the samples and of the solvents were recorded

with a Cary D- 17 spectrophotometer or a UV-260 spectrophotometer. Optical cells withpathlengths of 5 mm or 10 mm were used in the absorption measurements. All absorp-tion spectra were recorded at room temperature (22-24°C). L = PhCHOHCH2NH2'M = Pr3+ : Pr(NO3)3 .5H2O

Results and Discussion

To study the complexation of Pr3+ with PhCHOHCH2NH2 (L)in (DMSO) a seriesof solutions were prepared in which the total concentration of Pr3+ and 2-amino-l-phenylethanol is constant, but their proportion is varied, i.e., [Pr3+] + {L] = constant.

The data obtained for Pr3+ PhCHOHCH2NH2 complexes in DMSQappropriate to Job'smethod are listed in Table (1). A plot of absorbance versus mole naction of the ligand(XL) is shown in Fig. (I). The maximum absorbance is always at mole fraction of XL =0.8. This indicates that the formula of the complex is [PrL4]3+. A tentative structure issuggested in Fig. (2). :Ii;

Optical Absorption Spectra of.

Data of Pr3+ -PhCH(OH)CH2NH2 complexes in dimethylsulphoxide for Job's method.

(:)

0

~

0.6 0.7 0.8 0.9 1

FIG.Xl

Plots of absorbance (0.0) versus mole fraction of ligand (XPr3+-PhCH(OH)CH2NH2 complex.

at different time for

72

A.H.

Qusti & A.G.M.AI-Seheuli

OH

NH2

2. The tentative structure (II) for [Pr(PhCHOHCHzNHZ)4P+ complex is suggesteed. and (I) the structureof ligand vaz; 2-amino-l-phenyIethanoI. '

The absorption spectrum of 2-amino-l-phenylethanol in the UV -Visible regionshowed a single absorption band in the spectral range of 220-400 mn and maximum at)., = 263 nm. Therefore, there is no overlapping between this band and that of the Pr3+ion in the visible region. The absorption spectra of Pr3+ -L of the compositions (5: 5)and (6:4) are shown in Fig. (3). These spectra show the four UV-Vis bands of Pr-'+namely: 3H4 ~ lDz, 3H4 ~ 3po, 3H4 ~ 3PI' and 3H4 -73pZ' plus a new band due tocomplexation with i -m -X at 356 mn. The intensity of the new band increases withincreasing the molar ratio of the ligands and reaches a maximum value at (Pr3+ : L) of

(0.2 : 0.8).

The fact apparent from this work and pre.vious studies on spectroscopy of Pr3+ arethe position of the terms in the free ion and in the ionic host are the same within a fewhundred wavenumber. The 4f electrons are obviously not the outer most ones, andhence they are "shielded" from external fields by two electronic shells with larger radi-al extensions (5s and 5p). Therefore, the 4f-electrons are only weakly perturbed by thecharges of the surrounding ligands. The observed ultraviolet-visible and near i.r. spec-tra of Pr3+ -PhCHOHCHzNHz complexes are shown in Figs. (4,5). The energy EJ of

the Jtb level, written in a Taylor series is :

,.., dEJ AI:: dEJ A :;-tirK+-L.1<X+-d<x

dE,

b J = EOJ + L dFKK=2.4.6

Where EOJ is the zero-order energy of the Jih level and (dEJ/dFK); (dEJ/da); (dEJ/d[3);(dEJ/d~4f) are the partial derivatives. The values of the zero-order energies and partialderivatives are taken from tables of Wong[15J. The observed energy values were substi-tuted for EJ' in the Taylor-series expansion to evaluate changes in F2' F4' F6' a, [3 and~4f. A least-squares fit was employed to evaluate these parameters. The Slater-Condon(F2' F4 and F6)' configurational interaction (a and [3) and spin-orbin (~4f) parameters for

dE] rd~ + -d~4f

d~4f

Optical Absorption Spectra of.. 73

FIG. 3. Absorption spectra (a) (5:5) Pr3+ -PhCH(OH)CH2NH2; (b) (5:5) Pr3+DMSO.

-PhCH(OH)CH2NH2 in

A.H. Qu,ri & A.G.M.AI-Sehemi74

14

~.-.;

2

12 3 3~ +- H4-cOJ.-u.---OJ0vC0.-uC.-)(OJL-a0~

10

B

6

it

O+-3H2 -

it

2

016000 20000 2200018000

-1Wavtlonumbtlor(Cm )

Fit;. 4. Absorption spectrum of (6:4) pr-1+ .PhCH(OH)CH2NH2 in DMSO at room temperature.

...c:III'u"£III0Uc:0

:;;uc:...><III'-

..Q0~

45

40

35

30

25

2015

10

5

0680058004800

-1Wavenumer(Cm)

FI(;. 5. Near lR absorption spectrum' of (6:4) PrJ+ -PhCH(OH)CH2NH2 in DMSO at room temperature.

Optical Absorption Spectra of 75

Pr3+ complexes are presented in Table (2). It is interesting to note that the hydrogenicF4/FZ and F6/FZ ratio are equal to -0.16 and 0.016, for Pr3+ -L at various ratios and arenearly the same for this ion in different environments, which suggests that the radialproperties of tripositive Praseodymium ion remains unchanged in different systems.Experimental and calculated energy levels of Pr3+ -PhCHOHCHzNHz complexes arelisted in Table (3). A good agreement between experimental and calculated energies is

apparent,

TABLE 2. Slater-Condon (F2' F 4' and F6) Racah (EI, E2 and E3), spin-orbit (~4r) and configuration interaction

(a, (3) parameters and (FjF4 and F2/F6) ratios of the Pr3+-PhCHOHCH2NH2 complex in dimethyl-sulphoxide at room temperature.

Mole ratio of p3+ -PhCHOHCH2NH2Parameter

(0.9: 0.1)

313.60

51.60

5.02

! 4880

21.55

473

773.71

19.98

-886.38

0.165

I 0.016

~313.10

51.49

5.02

4874

21.53

472.42

I 774.89~-886.37,

0.164

0.016

(0.7: 0.3)

315.00

51.32

5.02

4884

21.80

475.30

771.39

19.30

-791.59

0.163

0.016

(0.6: 0.4)

314.48

51.32

5.02

4880

21.74

474.47

774.8

19.374

-886.31

0.163

0.016

(0.5 : 0.5) ,pr-l+ in solvent

314.27

51.44

5.02

4882

21.68

474.36

775.03

19.38

~ 896.36

0.164

0.016

314.54

52.89

5.10

4938

21.29

475.31

726.43

12.68

-801.23

0.168~

0.016

F2

F4

F6

~E

E2

EJ

~4r

<X

13

F4/F2

F6/F2

TABLE 3. Experimental and calculated energy levels of Pr3+ complex with PhCHOHCH2NH2 in dimethyl

sulphoxide.

Pr-1+. L

(0.8: 0.2)Pr-\+ -L

(0.7 :0.3)

Pf-1+ .L

(0.6:0.4)

Prl+-L

(0.5: 0.5)

Prol+ -L

(O.9:0.1iP1'1+ in solvent

DMSOLevels

3H4

3F-L-3F3-3F4 I~~

EEXP I ECAt. ~~-I-~~-I EcAt E""p I. ~AL. EEXP I EcAL I EEXP EcAL I

22420 I 22490 122420 I 22460 122420 I 22530 ! 22470 I 22520 I 22500 I 22510 I 22420 I 22120 I

21230 I 21290 I 21190 I 21260 121280 I 21340 ~ 21280 I 21320 I 21280 I 21320 I 21280 I 20970 1

20700 I 20620 120660 I 20590 I 20700 I 20670 I 20660 I 20650 ~ 20660 I 20640 I 20700 I 20400 I

16840 I 16820 116840 116810 116870 I 16880 , 16860 I 16g60 ~ 16840 I. 16840 I 16840 I 16550

..5147 I 5119 i 5147 I 5120 I 5155 I 5140 5147 I 5112 5155 I 5142 ~ 5155 5110

6077

6612

~

6849

6392 I 641{) I 6393 I 6431 I 6328 6423 1 6394 ! 6431 I 6400 \ 6439

I

6829 I 6849 I 6828 I 6859 I 6809 6849 I 6819 I 6846 I 6824 ~ 6863

51.72 48.09 11.81 31.79 28.54 32.61

A.H. Qu'ti & A.G.M.Al-Sehemi76

The int~nsity of an absorption band is measured by its oscillator strength which isdirectly proportional to the area under the absorptive curve. The experimental oscillatorstrength (P exp.) of the band is evaluated from the formula.

-9fV2 Pexp. = 4.32 x 10 V1E(V)dv

where E is the molar absorptivity, v is the energy of the transition in wavenumber and

J E(v)dv is the area under absorption curve.

The intensity of a band can be affected by electric dipole, magnetic dipole, and elec-tric quadrupole transitions. The bands of lanthanide ions essentially arise from electricdipole transitions. But some magnetic dipole character will be present in some transi-tions. The electric quadrupole and magnetic dipole component are very small in this

case and can be neglected.

Iudd-Ofelt[16.17] have independently shown that the oscillator strength of an inducedelectric dipole transition may be related to the energy of transition(v) and the square ofthe matrix elements of the unit tensor operatofU" connecting the initial and final states('Plj 4 'PIt> via three phenomenological parameters T,,(t.. = 2, 4, 6). These three para-meters are complex expressions relating the ~adial wave functions of the state, therefractive index of the medium, and the ligand field parameters which characterize theenvironmental field. According to Iudd-Ofelt theory the induced electric dipole oscilla-

tor strength (P ed) is given by :

~where 13

~ =.!.l v complex

n V aqua

where v (cm-l) is the mean energy of the transition (\fJi ~ \fIr>, UA is the unit tensoroperator of rank A, and sum extends over 1..(2,4 and 6). The experimental and calculatedspectral intensities for seven observed bands using component UA for (3PI + 116) aregiven in Table (4). This indicates a good fit between observed and calculated oscillatorstrength. Unlike most reported results, our values of the T2 parameter are positive. TheT2 parameter has been related to the hypersensitivity being more dependent on thecovalent metal-lig~nd.interactions, while T4 and T6 h~ve been c~nsid~red more depen-dent on the coordInation cluster symmetryLIS,-22]. A lInear relationship between (P expovalues) of the hypersensitive band (3H4 ~ 3F2) and T 2 for Pr3+ -L complexes is shown

in Fig. (6).

The energies at which the various bands appear are low as compared to the aquo ion.This red shift has been ascribed to a nephelauxetic effect[23]. The extent of the red shiftis related to covalence in the metal ligand bond. Sinhh[24] has proposed a scale toexpress this covalence.Sinha' s parameter, 0(%) is given by the relation -

O%=~XlOO

""0';(0~Co

]>.~~'5,S

N:I:Z

N:I:U:I:0:I:U~~+'

18"0f;Xe:.'"~'6IJc~'in5~'u'"0"E'iO-:;O

J-aO

J"0C..-acE'c8->

<U

J

~'"..J=<I-

~

oJ,",:,

0

i~.0.

oJ"!,0

+-..~003

oJ;;:;,0

+

..~

'- ~

8 ..J:;-,0

+ ..

~'" -C

Q.

.0,

oJ:;:;00

+ ..

~'-

or.Q

. 9-

cQ)

;>

°0~~

.-~..Jo+~'-

I'L

'" ':S

:o-o-o-~~

~.=

- 000000

'" x

-+""""~",,,,-

"'xxxXX

XtI:I:~

~'~

OQ

.-Q.-Q

."'E

""""""""",..J~

' ~

. ~

. ~

. -~

. ~

. ~

. ..E

- E

- E

- a

a a

:.:1

00 x

...'

"""--

'V

'I

r- -"" <

.

u ""

Q. :.;

j""~

~

~- -""'

<;;~ ~,,-;- ..:I~

<

.

u -.r

Q.

'"

IN

0.

Ir)

X

.,,-'" ~

'1

0- '<

or;

~

~P

. N

0-

~r-- 'I~

-0-<

.

,,~ ~

:.:Ir-

~

..,~

~

<;,)""

~"" Nor.,.,:'" 00~~.,..

""M

0-""""'

~-c \0~N r".0..,:

~f-i

or)

~""'

00N..j 0\...;

0-0-

~ N00

..r"'" ~ ~0

~0 .".Ir:0 \0r-.,.; 0-~,0 ~ ~M~ N~"" '"~ or\t-o; r-~N 'TII":

-0;.,., O

ptical Absorption S

peC1rt1 of

~""' ~,.; \CN ~N ~...,

NN"";

~.-. ~N"'; -00-,,; 0\"",...

a-"!"",,

0-r-:

-0'r\..,:

coco~ ~-ri

"""1~ ,...

~'" or)

r--:.,.,

""~~i

"T~,'; ,...~ """"'" ('I

6'" ~~M ~ ~ N0;-0 N,...

~-0 'C!

"" ~«i -0"'.'" ~ 0-~

~""'r.:

~or)

Nq0-

~00

~M ""..; r-.

~ Si r--N ~~~ -0 ~'"

'"r-:

roo~ci ..,~""'

00 or:...,

-0000

or;

""'~ ~"..;

0000,,;

...:N 00

""

~ l-t-:

l"-f":'" 0-r-.""'

Ir.Or)

c-;

""'~

~,,; a-N or.I-: ~r--:

N~'" N~r".

~~ r-Ir!~ N'r)

~ "'tor:0\or,

~0:r--

~0'"

r"'.N-0 'r\~'" ,.,0;~ ~~ 00"":"" ......r.'"'

-0r--:O

r)

Nq'" ~-0.q:

~M "!~ ~~

77

A.H. Qusti & A.G.M.A/.Sehemi178

1..00...><a.x

c..G.I

FIG. 6. Oscillator strength of the 3F2 ~ 3H4 transition (hypersensitive transition) as a function of the Judd-

Ofelt T 2 parameter of Pr:I+-PhCH(OH)CH2NH2 complex.

he bonding parameter, b1/2, the magnitude of which suggests the extent of involvementof the 4f orbital in the metal-ligand bond, is correlated to the nephelauxetic ratio (13) by

the expression:

OpTical Ah.'iorpTi(}n SpecTra (if: 79

The bonding parameters /3, 0(%) and bl/2 were calculated, and their values are present-ed in Table (5). The positive values of bonding parameters (Table 5), suggest the occur-rence of some covalent character in the metal-ligand bond. The magnitude of the para-meters reach maximum when the molar ratio of ligand: Pr3+ is (8:2). Thus, on the basisof the above evidence. it can concluded that the Pr3+ ion is surrounded by four neutralligand molecules each bound in a bidentate N, -0 fashion forming a coordination num-ber of eight. A suggested structure of the complex is shown in Fig. (2).

'ABU,S,

Nepheluxetic effect for Pr:l+-PhCHOHCH2NH2 complexes in dimethylsulphoxide.

Mole ratio of Pr3+-PhCHOHCH~NH~

Parameter

13

/)(%)

bl/2

(0.9: 0.1)

0.9951

0.4956

0.0497

(0.8 : 0.2)

0.9940

0.6013

0.0547

(0.7: 0.3)

0.9960

0.3996

0.0446

(0.6 : 0.4)

0.9961

0.3959

0 .0444

(0.5: 0.5)

0.9959

0.4095

0.0452

References

[I] Qusti, A.H. and AI-Sehemi, A.G.M., In press.[2] Qusti, A.H. and Chrysochoose, J., J. Less. Common. Met.. 112,291 (1985).[3] Qusti,A.H. and Chrysochoose, J., J. Less Common. Met.. 126, 169 (1986).[4) Cheetham, A.K., Fender, B.E., Fuess, H. and Wright, A.F.,Acta. Cry.\'t.. 32,94 (1976).[5) Mohn, M., Tondon, J.P. and Gupta, N.S.,ltlIJrg. Chim.Acta..111, 187(1986).[6] Qusti, A.H., Ph.D Thesis. University of Toledo. U.S.A. (1986).[7) Sinha, S.P., Sy.~tematics and the Properties of the Lanthanide.\' (1982),316 p.[8] Surana, S.S.L., Singh, M. and Misra,S.N., ItlIJrg. Nucl. Chem.. 42,61 (1980).[9) Lakshman, S. V.J. and Buddhudu, S., Polyhedron. 2,403 (1983).[10] Buddhudu, S. and Babu, V.R., J. Quant. Spectrosc. Radiat. Transfer.. 37,415 (1987).[II] Weber, MJ., Phys. Rev.. 157,262 (1962).[12] Misra, S.N. and Sommerr, S.O., Can. J. Chem.. 70,46 (1992).[13) Job, P.,Anal. Chim.. 9, 113 (1928).[14] Christian, G.D. and Reilly, J.E., Instrumental Analysis. London (1986) p. 186.[15] Wong, E.Y.,J. Chern. Phy.\'. 35,544 (1961).[16] Judd, B.R.J., Phy.\'. Rev. 127,750 (1962).[17) Ofelt, G.S.,J. Chem. Phy.\'. 37,511 (1962).[18] Henrie, D.E., Fellows, R.L. and Chopin, G.P., Coord. Chem. Rev.. 27,223 (1979).[19] Jorgensen,C.K. and Judd, B.R., Mol. Phys.. 8,281 (1964).[20] Lucas, J., J. Le.\'.\' Common Metals. 112,27 (1985).[11] Ribeiro, S.J.L., Massabnal, A.M.G. and Stucchi, E.B.,lnorg. Chim. Acta.. 199,67 (1991).[22] Yatsimirkii, K.B. and Oavidenko, W.K., Coord. Chem. Rev. 27,223 (1979).[23] Jorgensen, C.K., Prog. Inorg. Chem.. 4, 73 (1962).[24] Sinha, S.P., Spectrochim. Acta.. 22,57 (1966).

80 A.H. Qu.I!i & A.C.M. AI-Sehemi

~\ ~)\ COPr3+(jy-~ ~.,...:JI vP~'l\ J~i..J;~l Jo:.;.- ,- .f-z41-"

"'~. .'* ..~I iJl;.I.$. illl-l.:'" J .-s:-J ~ illl-l.:'"

o~ '.,j:;.JI¥.J.U1I;""~, i #' i.:1S' ;.~I r.-"'" '*

4;.> ~I ~~I ~I -~i, ~I i.:1S' i #' r.-"'" '*'*

Pr (phCHOHCH2NHV ~I .:".- Pr3+ ..;..Jl.:SI? ~ ~ .~I

.Pr (NO3)3. 5H20 t" (Jy~l J.:;,~, -.f-o:"i- r).J ~L:l1 js-lA;J4 ~~J

~ 4: 1 ..;" r!:!l:.Il ~ )I..) ~ -pi ~.:,i ~1..;..JL..IJ~I..:..;.;;iJ

UV-Vis"-4k: } J;: 11 ~I.:".- ~1..;..J")L.L..lI.:".- -4J..J1 f-.I..4; ~

.r!:!l:.I\ ~~ .I~I ~ ~~I ~ ~J