Structures and electrical conductivities of cation radical salts based on unsymmetrical [Au(III)(C-N)(S-S)] type dithiolate complexes

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Crystals of [Au(ppy)(S-S)] 2[Q][Solvent] n [ppy − = C-deprotonated-2-phenylpyridine(−); S-S = C 8H 4S 8 2−: 2-{(4,5-ethylenedithio)-l,3- dithiole-2-ylidene}-l,3-dihtiole-4,5-dithiolate(2−), C 8H 4S 6O 2 2−: 2-{(4,5-ethylenedioxy)-l,3-dithiole-2-ylidene(-l,3-dihtiole-4,5-dithiolate (2−); Q = PF 6 −, BF 4 − AsF 6 − and TaF 6 −; solvent = PhCl and PhCN; n = 0–0.5] type cation radical salts were prepared by constant current electrolysis of benzonitrile or chlorobenzene solutions of unsymmetrical [Au(ppy)(S-S)] type metal complexes with [Bu n 4N][Q] as electrolyte. These salts exhibit two types of unique columnar structures. The one (S-S = C 8H 4S 8 2−, Q = PF 6 −/S-S = C 8H 4S 6O 2 2−, Q = BF 4 −) contains the two-fold head-to-head stacking of cation radicals while the other (S-S = C 8H 4S 8 2−, Q = AsF 6 −, TaF 6 −) is based on the stacking of tetramers of cation radicals. [Au(ppy)(C 8H 4S 8)] 2[PF 6] shows semiconductive behavior ( E a = 0.03 eV) under ambient pressure. Interestingly, it shows metallic behavior under high pressure (>0.8 GPa). To our knowledge, this is the first example of the metallic cation radical salt based on the unsymmetrical metal complex. Other radical cation salts show insulating or semiconducting behavior ( E a = 0.11–0.15 eV).