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)-1,3-dithiole-2-ylidene}-1,3-dihtiole-4,5-dithiolate(2-), C8H4S6O22- : 2-{(4,5-ethylenedioxy)-1,3-dithiole-2-ylidene}-1,3-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 [(Bu4N)-N-n][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 (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).