Terminally bifurcated tetraaurio-alpha,omega-bis(sulfonium) salts as building blocks for auriophilicity-determined coordination polymers

Treatment of alpha,omega-dithiols HS(CH2)(n)SH, n = 4 or 5, with tris[(triphenylphosphine)aurio]oxonium tetrafluoroborate affords the corresponding S,S,S',S'-tetrakis[(triphenylphosphine)aurio]-alpha,omega-alkanediylbis(tetrafluoroborates) of the type {[(Ph(3)P)Au]S-2(CH2)(n)S[AU(PPh(3))](2)}(2+)2BF(4)(-). The crystal structure of the species with n = 5 has been determined by single crystal X-ray diffraction studies. In the lattice the unfolded dications are linked into chains through short double Au-Au contacts between the terminal bifurcated diauriosulfonium centers. The analogous reactions with (racemic) 1,2-dithioglycerol and 1,2,3-trithioglycerol also give tri- and tetranuclear complexes with a varying distribution of the metal atoms over the chalcogen(ium) centers. As again demonstrated in a single crystal X-ray diffraction study, the dications {HOCH2HCS[(Ph(3)P)Au]2CH2S[Au(PPh(3))](2)}(2+) of the dithioglycerol compound form only dimers through auriophilicity-determined pairing of the bifurcated ends, while the open ends are shielded by the dangling hydroxyl group. The trinuclear complex of 1,2-dithioglycerol is fluxional in solution; the crystal structure has not been determined but is expected to be similar to that derived for the analogous dithioglycol complex. The tetranuclear, trithioglycerol-based dications of {[(Ph(3)P)-Au]SCH2CHS[Au(PPh(3))]CH2S[Au(PPh(3))](2)}(BF4-)-B-+ are isolated in the lattice and feature an unsymmetrical complexation, which is an extension of the structure of the trinuclear dithioglycol analogue {(CH2S)(2)[Au(PPh(3))](3)}(+) with its strong intramolecular Au-Au contacts. A similar structure is proposed for the monocation {CH2(CH2S)(2)-[Au(PPh(3))](3)}(+) obtained from propane-1,3-dithiol. The structures of these cations are also fluxional in solution, however, as shown by variable-temperature NMR studies.