Diversity in the structural chemistry of (phosphine)gold(I) 1,3,4-thiadiazole-2,5-dithiolates (bismuthiolates I)

A series of dinuclear (phosphine)gold(I) complexes of the ambidentate 1,3,4-thiadiazoledithiolate ligand (SSS) were prepared in high yield from the corresponding (phosphine)gold(I) chlorides and K(2)(SSS) in methanol. While mononuclear components (R(3)P)AuCl with R(3) = Ph(3), Ph(2)Py, or Me(3) (1-3) gave open-chain complexes, the dinuclear components ClAu(Ph(2)P-E-PPh(2))AuCl with E = (CH(2))(6), (C(5)H(4))Fe(C(5)H(4)), or 1,4-CH(2)C(6)H(4)CH(2) afforded cyclic complexes (4-6). The products have been characterized by analytical and spectroscopic methods, and the crystal structures of 1-4 have been determined by single-crystal X-ray techniques. Crystals of 1 [(CH(2)Cl(2))(2)] and 2 (CH(2)Cl(2)) contain the molecules aggregated in strings with long and probably very weak intermolecular Au.S contacts. The P-Au-S groups are aligned parallel head-to-tail and shifted in opposite directions to reduce steric conflicts, thus ruling out aurophilic Au...Au bonding. By contrast, in crystals of 3 (CH(2)Cl(2)) with smaller tertiary phosphine ligands, the molecules are aggregated via short [3.0089(3) and 3.1048(5) A] and probably strong aurophilic bonding to give a two-dimensional network with tetranuclear units formed from four (Me(3)P)AuS moieties of four different molecules as the connecting elements. In these tetranuclear units [(Me(3)P)AuS-](4), the P-Au-S axes are rotated against each other ("crossed swords") by 108.5 degrees (P2-Au2...Au2'-P2') or 116.9 degrees (P2-Au2...Au1'-P1'), respectively, to minimize steric conflicts. There is also significant bending of the P-Au-S axes to bring the metal atoms closer together: P1-Au1-S1 = 171.88(8) degrees and P2-Au2-S2 = 165.52(8) degrees. In the crystals of the cyclic complex 4 which contain no solvent molecules, the molecular units are aggregated in strings with short closed-shell interactions between the gold atoms of neighboring molecules [3.1898(3) A]. Because of the metallocyclic structure, the shielding of the gold atoms is reduced to allow aurophilic bonding as the P-Au-S groups are rotated against each other (crossed) by a dihedral angle P-Au...Au-P of 74.6 degrees.