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

Crystals of [Au(ppy)(S-S)]2[Q][Solvent]n [ppy− = C-deprotonated-2-phenylpyridine(−); S-S = C8H4S82−: 2-{(4,5-ethylenedithio)-l,3- dithiole-2-ylidene}-l,3-dihtiole-4,5-dithiolate(2−), C8H4S6O22−: 2-{(4,5-ethylenedioxy)-l,3-dithiole-2-ylidene(-l,3-dihtiole-4,5-dithiolate (2−); Q = PF6−, BF4− AsF6− and TaF6−; 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 [Bun4N][Q] as electrolyte. These salts exhibit two types of unique columnar structures. The one (S-S = C8H4S82−, Q = PF6−/S-S = C8H4S6O22−, Q = BF4−) contains the two-fold head-to-head stacking of cation radicals while the other (S-S = C8H4S82−, Q = AsF6−, TaF6−) is based on the stacking of tetramers of cation radicals. [Au(ppy)(C8H4S8)]2[PF6] shows semiconductive behavior (Ea = 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 (Ea = 0.11–0.15 eV).