Stabilisation of unusual metal co-ordination geometries using an oxo-cubane ligand; syntheses and structures of [{Sn4(NtBu)3O}3LiCl]·3thf and [{Sn4(NtBu)3O}3FeCl2]·3thf

Abstract

Complexation of LiCl and FeCl₂ with the oxo-cubane [Sn₄(N^tBu)₃O] 1 (3 equivalents) gave [{Sn₄(N^tBu)₃O}₃LiCl]· 3thf 2 and [{Sn₄(N^tBu)₃O}₃FeCl₂]·3thf 3, respectively; the co-ordination of three sterically demanding, ‘ether-like’ [Sn₄(N^tBu)₃O] ligands to the Li⁺ and Fe²⁺ centres of 2 and 3 results in unusual geometries for these metals. The geometry in 2 can be described as a distorted trigonal bipyramid with one vertex missing, while in 3 it is trigonal bipyramidal. Model semi-empirical calculations combined with the structural findings stress that although sterically encumbered 1 is a highly effective ligand for oxophilic metals.