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$1. 70 441 VERJIONT (*11W BURLINGTON DEPT OF CHEMISTRY FF6 7/3SYNTHESIS. ELECTRICAL CONDUCTIVITY. AND MAGNETISM OF * NEW MOtE—ET C(U)a. 79 .i T WROBLESI(I. 0 B BROWN N0001’4—75—C—O756

&* CLASSIFIED TR—16 IlL

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LE VEfrOFYICE ~9~ —~NA~VAL RESEARCH

Contr 4-Z~±~7 1

~~~ Task No. NR 356—593

I:’. ? TECHNICAL BEPá~~ IO. 16

~~~ ~~~~~ hesis, Electric Con~uctj vity , and Magnetism of a New oleculàr Metalj

~~ L_~ __~_ ’~~~~(~~~~~~~~~~~~~7~

robleaki~~~~~David B1 Brown i 0 0

r

Prepared for publication in the

Journal of the Am erican Chemical Society

C..) University of Vermont

Department of Chemistry

I~i... Burlington, Vermont 05405

1/ jjL Jun~~~~ *79 (

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Reproduction in whole or in part is permitted for any purpose of theUnited States Government.

This document has been approved for public release and sale; its distributionis unlimited.

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SE CUR I T Y CI..A*SIFICATION OP THIS PAGE (IThai 0.1. En*oisd)

oc~~e~~~r ~~I k?tI~~~ ~~~~~~~ READ INSTRU CTION SIl~~~~iJI,’L.s’I • ~~~~~~ ‘I”- BEFORE COMPLETING FORM

I. REPORT NUMBER 2. GOVT ACCESSION NO 3. RECIPIENT’S CATALOG NUMBER

164. TITLE (aid SubeSli.) 5. rv~~ or ~~~owr 4 PERIOD COVERED

“Synthesis, Electrical Conductivity, and Tec~~ica1 ReportMagnetism of a New Molecular Metal ,1C2 [Ni(l ,2—dithiooxalate) 2]110” ~~~~~~~~~ ORG. REPORT NUMBER

7. AUTHOR(.) S. CONTRACT OR ORAllY NUMSER(S)

James T. Wrobleski and David B. Brown N00014—75—C—0756

S. PERFORMING ORGANIZATION NAME AND ADDRESS — to. PROGRAM ELEMENT. PROJECT. TASKDepartment ot Chemistry AREA S BORIC UNIT NUMBERS

University of VermontBurlington, Vermont 05405

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IS. SUPPLEMENTARY NOTES

Submitted for publication in the Journal of the American Chemical Society

19. KEY WORDS (Continu. on r.v .r.. .id. if n.c•.~~~y aid td.nd~ ’ b~ block nomb.r)

Molecular metal , electrical conductivity, solid—state oxidation,stacked metal complex

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SO. AUSTRAC 1 (Cons Sin,, an v.v~r.. .ld. II sroc...ay aid Idsntlfr by block nomb.r)

Samples of K~,(Ni(DTO)23I1 ~~ (DTO — 1,2—dithiooxalate) have been

prepared by either solid—state oxidi~ion of K2(Ni(DTO) I with excess 1

2 at

130—140°c or electrolysis of K,(Ni(DTO),] in methanol iolution saturated withtetrasthylasmonium iodide. This material exhibits metal—like electricalconductivity (a300K 500 cr1 cm’~~) which, for one sample (sample A), persiststo the lowest temperature at which data were obtained (20. K). Other samplesof K2 [Ni(DTO ) 2]110 undergo a metal—to— insulator transition at temperatures

DO P.;~~:tti,~ 1473 £01 lION or I NOV SI IS OBSOLETE

S/N O1O2•OI4- 6IO~ ___________________________________________SECURITY CI.AUIPICATIOM OP THIS PAGE (* D~. ~~~~~~~

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as high as 190 K. Variable—temperature (20—300 K) magnetic susceptibilitydata for sample A were obtained . The effective magnetic moment for sample Adecreases from 2.4~~ at 295 K to 2.2u~ at 40 K. Below 40 K the value of

increases and ~eccses field dependent. A bonding model for this materiali~ proposed.

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Synthe. , Electrical Conductivity, and Magnetism of a New Molecular Metal ,

K2[ N i( ,2—dithiooxalate)2] 110

Sir :

Mixed—valence, linear—chain polymers which possess relatively high electrical

conductivity have been prepared from square—planar ~/transition~metal complexes which

contain C, N, 0, or S donor groups. ~.~Zmamples of these highly—conducting compounds are

K2 (Pt(CN)4]Br0 3 •3H2O~ (C donor), ~~i’~ h~~~1ocyanine) ] (I 3)0 3 3

2 (N donor),

K181(P t(C204)21 ’2R20

3 (0 donor), and NH4 (N~ (i~~~) 2 I x R2O4 (S donor). Of these compounds ,

only K2(P t(CN)4

] Br0 3 3H20 and (Ni(phthalocyanii~~1<~~~033 exhibit metal—like electrical

conductivity (aa/aT<O) . Although several organic donor b~~ptor complexes which

contain sulfur (TTF—TCNQ is an example) 5 possess metal—like con~�~e~~~~ty near room

temperature, no transition—metal complex with an organic sulfur ligand~~~s.p~~viously

been reported to possess metal—like conductivity.6

As part of our overall effort to synthesize new, highly—conducting transition—

metal complexes we have recently prepared samples of K2 (Ni(DTO) 2]110 (DTO — S, S’ — 1,2—

dithiooxalate dianion) which show metal—like conductivity in the temperature range

20-400 K. These samples were prepared by reacting three—times recrystallized

K2 (Ni(DTO) 2]7 with a two—fold excess of 12 in an evacuated , sealed glass tube for five

day s at 130— 140°C. After this time the unreacted 12 was removed under vacuiml at 90°C.

The copper—colored compound prepared in this manner reacts slowly with water if stored in

air below 90°C. Chemical analysis8 of freshly—prepared samples were consistent with the

foriNila Z~ fNi (DT0)2]I1~~~00 5 . Although we have reproduced this preparation several

times, these reaction conditions do not always produce a product with metallic

conductivity. In fact, our succesr tate with this process has been three metal—like

• products In 24 attempted syntheses under (apparently) identical conditions . We have

been unabl. to explain this marked irreproducibility. In the preparations which did

not yield a product with metallic conductivity , 12 uptake by K2 (Ni(DTO) 2 ) occurs only

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ •

r~

to the extent of 0.25 — 0.65 I per Ni. These “I deficient” products have room—5 —1 —1temperature electrical conductivities near 1 x 10 ~ cm

The electrical conductivity of K2 [Ni (DTO)2 ] I is significantly higher than that which

has been reported for other stacked transition-metal complexes , with’ compaction conduct—

• ivities at room temperature on the order of 500 ~~~ cm 1.

Figure 1 illustrates the temperature—dependence of the electrical conductivity

• of several samples of K2 (Ni(DTO)2)I. These data were obtained by using pressure contacts

on pressed pellet specimens. The four contacts were arranged in the van der Paw

configuration9 and supported in a specially—constructed low—temperature cell made of

Teflon. Dc electrical conductivities were calculated from the following expression

a(~~~ cm~~’) — 0.2206 iJ~!

in which I is the applied current , V is the observed voltage drop across the sample ,

and t is the sample thickness in cm. AU the metallic samples of K2(Ni (DTO) 2]I displayed

ohmic behavior under the experimental conditions (I — 10—90 mA) . Data set A in Figure 1

was obtained with a freshly—prepared samp le of K2t~~~DT0) 23t powder which had been kept

at 90°C prior to ut~b {ng the measurements. The conductivity of this sample increased

• slowly in the temperature range 373 to 250 K then increased more rapidly to 24 K. No

metal—to—insulator transition was observed for this sample at T > 24 K. In contrast , the

conductivity of sample B (Figure 1) ma~{m{zts near 190 K. Sample B was stored at room

temperature in air for several days prior to making the measurements. Below 190 K the

conductivity of sample B dropped rapidly to approximately 1L~~~cm~~ at 80 K. A low—

temperature maximum in the conductivity vs. T curve was also observed for sample C

(Figure 1). This sample was a compaction of small (< lOOii) , copper—colored crystals of

K2 [Ni (DTO)21110. These crysta ls were obtained at a platinum anode by electrolysis

(1.5 V) of a concentrated methanolic solution of K2[Ni(DTO) 2 ] and tetraethyla onium

iodide. This sample showed metal—like conductivity in the temperature range 300 to 90 K.

At 90 K the conductivity of the sample began to decrease , reaching a value of 40 fl~~ cm~~

at 22 K. We have as yet been unable to prepare single crystals of K2[Ni(DTO)2]I which are

A • _____________ ~~~~~~~~~~~~

—~~ — ~~~~~~~~ ~~~-w__ ~~~~~~~~~~~~~~~~~~~~~~~~

~~~~~~~~~~~~~~~ ,r.R~~~~~_ r

large enough for single—crystal X—ray diffraction or for measurements of the anisotropy

of conductivity.

Samples of K2 (Ni(PTO) 211 with. metal—like conductivity are paramagnetic , as

compared to highly—purified K2 (Ni(DTO) 2] which, is diamagnetic. The variable—temperature

magnetic susceptibility and effective magnetic moment per Ni of highly—conducting sample

A are shown in Figure 2. The value of 1~eff /’~~ decreases from 2•6~

t B at room temperature

to approximately 2.21I~ at 40 K. Below 40 K the magnetic moment increases and becomes

field dependent . This low—temperature behavior indicates the onset of ferromagnetic

order in the material. In contrast to sample A, samples B and C behave as normal para—

magnets over this entire temperature range ~~eff 2 4 U B at 300 K and 2•1UB at 25 K.)

We observe no magnetic anomaly for samples B and C in the vicinity of their metal—to—

insulation transition temperatures (190 and 90 K, respectively.)

Although detailed analysis of the properties of K2 (Ni (DT0) 2 ]1i.o must await a

single—crystal structural determination, our present conception of the bonding in this

molecular metal involves localized magnetic states (molecular orbitals) of comparable

energy to a partially—filled band formed by direct overlap of either ~~ 2 or ligand it

orbitals on adjacent stacked Ni (DTO) 2 units. It is interesting to speculate that the

metallic electrical conductivity of K2(Ni(DTO)2] I io may arise through formation of a

band which is a strong admixture of both ligand and metal orbitals and that this strong

intrachain bonding gives rise to enhanced stability of the metallic state in this

compound.

Acknowledgement: This work was supported in part by the Office of Naval Research.

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• References and Notes

(1) Krog.airn , K.; Heusen, H.D. Z. Anorg . ~~~ Chem. ~~~~ 358, 61.

(2) Schra , C.J.; Stojakovic, D.R.; Hoffman, B.M.; Marks , T.J. Science 1~%7~, ~QQ•, 47.

(3) Kobsyashi, A.; Sasaki, Y.; Shirotani, I.; Kobayaahi, H. Sol. State Comanm.

~~~~~~~ 653.

(4) mat is the l,2—dicyauoethylenedithiolate dianion: Perez—Albuerne, E.A.; Isett, L.C.;

Ha iler, R.K. 3. Chem. Soc. Chem. Comau~. I~,%J2,

417 and Miller, J.S.; Epstein, A.J.

.1. Coord. Chea. ~2%’ 8, 191.

(5) Kistenmacher , T.J.; Phillips, T.J.; Cowan, D.O. Acts Cryst. 3~%7~, 130 , 763.

(6) “Ionic” mixed—valence metal suif ides such as KCu4S3 are , however , known to possess

high, metal—like, electrical conductivity (a 4~~~ 6x105 f l~~cm~~) : Brown, D.B .;

Zubieta, J.A.; Valla, P.A. ; Wrobleski , J.T.; Watt, T.; Hatfield, W.E.; Day, P.

In preparation.

(7) Prepared from N1CL2•6R20 and K2DTO(Eastinan): Cox, E.G. ; Vardlaw, W.; Webster , K.C.

3. Chea. Soc. ~~~~ 1475.

(8) C,H, and I analyses by Integral Microanelytica] Laboratories, Raleigh, N.C.

(9) Van der P aw, L.J. Phillips Re.. Rpts. ~~~~

k~’ 1.

James T. Wrobleski and David B. Brown*

Depar tment of Chemistry

University of Vermont

Burlington, Vt 05405

~~~~~~~~~~~~~~~~~~

jir ~~~~~1_ TT~~~~~~~~~~H

iiFigure Captiona

Figure 1. Plot of dc electrical conductivity vs tempe~ature for three samples of

K2 (Ni (DTO) 2]I.

Figure 2. Molar magnetic susceptibility (0) and effective magnetic moment per Ni (~~

)

for highly—conducting ~~~~~~~~~~~

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• •~~~ ~~~-- •~~ - ~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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