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 = C₈H ₄S₈^2-: 2-{(4,5-ethylenedithio)-l,3- dithiole-2-ylidene}-l,3-dihtiole-4,5-dithiolate(2-), C₈H ₄S₆O₂^2-: 2-{(4,5-ethylenedioxy)-l,3-dithiole-2-ylidene(-l,3-dihtiole-4,5-dithiolate (2-) ; Q = PF₆^-, BF₄^- AsF ₆^- 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 = C₈H₄S₈^2-, Q = PF ₆^-/S-S = C₈H₄S₆O ₂^2-, Q = BF₄^-) contains the two-fold head-to-head stacking of cation radicals while the other (S-S = C ₈H₄S₈^2-, Q = AsF₆ ^-, TaF₆^-) is based on the stacking of tetramers of cation radicals. [Au(ppy)(C₈H₄S ₈)]₂[PF₆] 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).