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

Treatment of α,ω-dithiols HS(CH₂)_nSH, n = 4 or 5, with tris[(triphenylphosphine)aurio]oxonium tetrafluoroborate affords the corresponding S,S,S′,S′-tetrakis[(triphenylphosphine)aurio]-α,ω- alkanediylbis(sulfonium) bis(tetrafluoroborates) of the type {[(Ph₃P)Au]₂S(CH₂)_nS[Au(PPh ₃)]₂}²⁺2BF₄^-. 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[(Ph₃P)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 {[(Ph₃P)-Au]SCH₂CHS[Au(PPh₃)]CH ₂S[Au(PPh₃)]₂}⁺BF₄ ^- 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{PPh₃)]₃}⁺ with its strong intramolecular Au-Au contacts. A similar structure is proposed for the monocation {CH₂(CH₂S)_2- [Au(PPh₃)]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.