Synthesis and Structures of Bis- A nd Tris-(triphenylarsine)gold(i) Iodides

The title compounds [(Ph₃As)₂AuI] and [(Ph₃As)₃AuI] have been crystallized from equimolar solutions of Bu₄NAuI₂ and AsPh₃ in dimethylformamide and structurally characterized by single crystal X-ray diffraction studies. [(Ph₃As)₂AuI] crystallizes in space group C2/c, Z 4, and is isomorphous with other [(Ph₃E)₂MX] (MX = coinage metal(i) salt) arrays, with the Au-I bond being disposed on a crystallographic 2-axis: Au-I, As 2.7008(2), 2.4337(2) Å, As-Au-As, I 125.736(8)°, 117.132(4)° (153 K). [(Ph₃As)₃AuI] crystallizes as a triclinic phase in space group CH19340_IE1.gif, Z 4, and is isomorphous with [(Ph₃Sb)₃CuI] and [(Ph₃P)₃AgI]: Au-As 2.4847-2.5049(10), Au-I 2.8518(8), 2.8597(7) Å with As-Au-As, I 109.67(3)-115.97(3)°, 101.33(2)-106.85(3)°. A second '[(Ph₃As)₃AuI]' product was obtained as a co-crystalline phase in space group P2₁/n containing [(Ph₃As)₃AuI], and [(Ph₃As)₂AuI] accompanied by an additional unbound Ph₃As molecule, i.e. [(Ph₃As)₃AuI]·[(Ph₃As)₂AuI·Ph₃As], with structural parameters closely similar to those for the corresponding separate [(Ph₃As)₃AuI] and [(Ph₃As)₂AuI] complexes described above. Comparison of the bond lengths for these and related complexes show that they are generally consistent with the 'gold is smaller than silver' phenomenon caused by relativistic orbital contraction effects in gold, but the results also show that the magnitude of this effect is dependent on the nature of the metal-ligand bonds involved, and on changes in the metal coordination environment, which can in some circumstances yield trends in which the effect on particular bonds is partially masked or even reversed.