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STUDIES OF INTERMOLECULAR INTERACTIONS IN 1

PLANAR METAL COMPLEXES III BIS(ETHYLENE-1,2DITHIOLENE) COMPLEXES OF NICKEL, PALLADIUM, AND PLATINUM K. W. Browall & L. V. Interrante Published online: 13 Dec 2006.

To cite this article: K. W. Browall & L. V. Interrante (1973) STUDIES OF INTERMOLECULAR INTERACTIONS IN PLANAR METAL 1

COMPLEXES III BIS(ETHYLENE-1,2-DITHIOLENE) COMPLEXES OF NICKEL, PALLADIUM, AND PLATINUM, Journal of Coordination Chemistry, 3:1, 27-38, DOI: 10.1080/00958977308073784 To link to this article: http://dx.doi.org/10.1080/00958977308073784

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J. Coord. Chem., 1973, Vol. 3, pp. 27-38

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STUDIES OF INTERMOLECULAR INTERACTIONS IN PLANAR METAL COMPLEXES IIIl BIS(ETHYLENE-1,2-DITHIOLENE) COMPLEXES OF NICKEL, PALLADIUM, AND PLATINUM K. W. BROWALL and L. V. INTERRANTE (Received December 4, 1972; in final form February 9, 1973)

The synthesis and characterization of nineteen new bis-dithiolene metal complexes of the type A, t [MS4C4Hdn-1, where A various organic cations, M = Ni, Pd, Pt, and n = 0, 1 , are described. The results of redox, infrared, electronic spectral, and NMR measurements on these complexes support a monomeric, planar structure for the complex units both in solution and, with the exception of the neutral MS4C4H4 (M = Pd, Pt) derivatives, in the solid state. However, evidence for intermolecular interactions in these solids has been found on the basis of fourprobe conductivity measurements. The conductivities of these complexes range from less than 10-JO ohm-] cm-1 to 10 -5 ohm -1 cm-.-land depend markedly on the nature of A+, M and n. On the basis of these measurements, empirical generalizations relating conductivity and the structural parameters A-+and M are derived. In addition, information regarding the dependence of the conductivity on the spacial relationship of the complex units in the solid is obtained from measurements on single crystals of NiS&H4 and PtS4C4H4 as a function of crystallographic direction. The implications of these results with regard to the electron transport mechanism in such solids are discussed. +

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INTRODUCTION Considerable attention has been focused recently on the unusual electrical properties exhibited by certain square-planar metal complexes. For example, the d8 metal complexes, Pt(NH3),PtC14 and Ir(CO),(acac), have been found to exhibit highly directional conductivity behavior with room temperature electrical conductivities as high as 10- ohm-' cm-l in the preferred conductivity d i r e c t i ~ n . Although ~?~ the metal dithiolene complexes, M(S2C2R2)"-2.3, where M = Ni, Pd, Pt, Mo, Fe, Cu, V, W, Re, Cr, Co and R = CN, CH3, CF3, C6H5,etc, are probably best known for their unique molecular properties, such as their reversible redox behaviour and highly delocalized ground state electronic c~nfiguration,~ several bis- and tris-complexes of this type have also been found to exhibit significant electrical conductivity in the solid state.5 In contrast to the aforementioned dx metal complexes, where direct metal-metal interactions are possible and the ligand groups apparently only moderate these interactions, it is likely that in the bisdithiolene complexes the extended Telectron system of the molecular units plays an important role in the electron transport process. The present investigation centers on complexes of the unsubstituted ethylenedithiolate ligand, 27

H2C2S2,-, of the type A,-1-[MS4C4H4" ] where A-+ = monopositive cation, M = Ni, Pd, Pt, and n = 0,l. These complexes were chosen for study because of the small size of the hydrogen substituent on the ligand and the availability of stable oxidation states with low net charge, thus facilitating both close intermolecular packing and electron transfer between complex units. Following the synthesis of the H2CzS22- ligand in 1964,6 a number of neutral and monoanionic bis- and triscomplexes were described. 7,x With the exception of the NiS4C4H4"- complexes, however, little additional information on bis complexes of this ligand has been reported. The recent synthesis of the [MS4C4H4],M = Pd and Pt, compounds and the discovery of their unusual dimeric structure'*10 has generated renewed interest in these materials. We now wish to report the full details regarding their molecular properties and electrical conductivity in the solid state. EXPERIMENTAL Starting Materials Sodium ethylene- 1,Zdithiolate (Na2S2C2H,) was prepared by the method of Schroth and PescheF and stored in a N2-filled dry-box until used.

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K. W. BROWALL AND L. V. 1NTERRANTE

Tetrachloroplatinate (11) andl tetrachloropalladate (11) were obtained from Matthey Bishop and

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Research Organic/lnorganic Chemicals as the anhydrous salts. All other chemicals were of reagent grade quality and were used without further purification. Preparation of Complexes A [MS4C4H4 ] Complexes: Method I. The A [MS4C4H4 ] complexes were generally prepared by direct reaction of' Na2S2C,H2 with a stoichiometric amount of nickel chloride, sodium tetrachloropalladate (II), or sodium tetrachloroplatinate (11) at approximately -15"C.ll The reaction was allowed to proceed for a few minutes in the case of nickel, 4-6 hours for palladium, and overnight for platinum before an excess of the appropriate cation, A + , as the halide salt was added. Nickel and platinum mixtures were allowed to react overnight, and the palladium mixtures for 4-6 hours before the crude product was filtered off, washed with water and air-dried. The A [MS4C4H4 ] product was then extracted with acetone and the extract evaporated to dryness. After purification by precipitation from acetone solution with benzene, the products were obtained as dark solids in yields ranging from 80-90% for nickel complexes to 10-302, for palladium complexes to 2 0 4 5 o/, for platinum complexes. A [MS4C4H4 ] Complexes: Method II. Several of the nickel and platinum complexes were prepared from the CsMS4C4H4derivative by reaction with an excess of the salt A - X , where X = C1 or Br, in acetonitrile solution. After removing the precipated CsX by filtration, the solution was evaporated to dryness and the residue washed well with water to remove the excess A X salt. The crude product was then recrystallized from acetonitrile to yield the [A '][MS4C4H4 ] complex in 80-95 yield. Attempts to prepare the following compounds by the above methods were unsuccessful : [A7][MS4C4H4 ] where M = Ni and [A+] = NM = Pd and [A '1 = methyl-phenazinium; N-methylphenazinium, cesium, methyl-pyridinium, quinolinium, and morpholiinium; M := Pt and [A 1 ] = N-methylphenazinium, quinolinium, and morpholinium. Also, efforts 1 0 grow single crystals of the A MS4C4H4 compounds suitable for use in conductivity measurements were not successful. [MS4C4H4]' Complexes, M = Ni,Pd,Pt; These complexes were prepared by (oxidation of [(n-C3H,),N ][MS4C4H4 ] with I, in CH3CN

solution. Equimolar amounts of [(n-C3H7)4N'][MS4C4H4-] and I, were dissolved in minimum amounts of CH3CN and the solutions were filtered before being mixed at room temperature. The reaction mixture was evaporated to one-half its volume and the crude product was collected by filtration, washed with CH3CN, and air-dried. Recrystallization from CS, gave the purified complex as a dark solid in yields ranging from 60"/, to 70% for NiS4C4H4 and PtS4C4H4 t o t l o % for PdS4C4H4. Single crystals of NiS4C4H4 and PtS4C4H4were grown from CS, solution by slow evaporation. The NiS4C4H4crystals were obtained as large, thick needles, up to 5 mm long and 0.8 mm by 0.5 mm in cross section. The samples used for electrical measurements were all cut from one particularly large crystal and measured approximately 0.8 x 0.7 x 0.4 mm3 with approximate 90" angles between crystal edges. Single crystals of PtS4C4H4were typically -0.2 x 0.2 x 0.5 mm3. Elemental analyses of the compounds prepared in this work are given in Table I. Electrical Measurnzents : A four-electrode DC conductivity technique was used to measure the electrical conductivity of polycrystalline samples in the form of pellets pressed at 85,000 psi. Electrical contact to the sample was made with 5 mil platinum wires attached with silver conducting paste. Voltage measurements were made using a Keithley 610C electrometer. Measurements were carried out in ltacuo at pressures