Synthesis and structural characterisation of a novel high-nuclearity gold–tin cluster compound, [Au8(PPh3)7(SnCl3)]2[SnCl6]

Abstract

The compound [Au₈(PPh₃)₇(SnCl₃)]₂[SnCl₆] has been synthesised from either [Au₈(PPh₃)₇][NO₃]₂ or [Au₉(PPh₃)₈][NO₃]₃ and excess of SnCl₂·2H₂O in acetone solution. Alternatively it can be synthesised in high yield from [Au₈(PPh₃)₈][NO₃]₂ and NEt₄SnCl₃ in acetone. The compound has been characterised by ³¹P-{¹H} n.m.r. and ¹¹⁹Sn Mössbauer spectroscopy and a single-crystal X-ray crystallographic determination. It crystallises in the monoclinic space group C2/c with a= 48.230(14), b= 16.831(7), c= 32.240(10)Å, and β= 96.50(3)°. The geometry of the gold atoms in the cluster closely resembles that observed previously in [Au₈(PPh₃)₇]²⁺ and corresponds to a fragment of a centred icosahedron. The SnCl₃ ligand is co-ordinated only to the central gold atom, with Au–Sn 2.625(3)Å, and does not interact significantly with the surface gold atoms to complete a hemispherical polyhedron. The distances from the central gold atom to those gold atoms on the surface lie in the range 2.633(2)–2.679(2)Å and are shorter than the distances between the surface gold atoms [2.847(2)–2.965(3)Å]. The relationship between the structure of [Au₈(PPh₃)₇(SnCl₃)]⁺ and those of related high-nuclearity gold cluster compounds with toroidal and spherical topologies has been explored using molecular-orbital calculations.