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 K2(SSS) in methanol. While
mononuclear components (R3P)AuCl with R3 = Ph3, Ph2Py, or Me3 (1−3) gave open-chain complexes, the dinuclear
components ClAu(Ph2P−E−PPh2)AuCl with E = (CH2)6, (C5H4)Fe(C5H4), or 1,4-CH2C6H4CH2 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 [(CH2Cl2)2] and 2
(CH2Cl2) 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 (CH2Cl2) with smaller tertiary
phosphine ligands, the molecules are aggregated via short [3.0089(3) and 3.1048(5) Å] and probably strong
aurophilic bonding to give a two-dimensional network with tetranuclear units formed from four (Me3P)AuS moieties
of four different molecules as the connecting elements. In these tetranuclear units [(Me3P)AuS−]4, the P−Au−S
axes are rotated against each other (“crossed swords”) by 108.5° (P2−Au2···Au2‘−P2‘) or 116.9° (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)° and P2−Au2−S2 = 165.52(8)°. 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) Å]. 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°.