Antimony centre in three different roles: does donor strength or acceptor ability determine the bonding pattern?

Abstract

A set of antimony(III) compounds containing a ligand (Ar) with a pendant guanidine function (where Ar = 2-[(Me₂N)₂CN]C₆H₄) was prepared and characterized. This includes triorgano-Ar₃Sb, diorgano-Ar₂SbCl and monoorgano-ArSbCl₂ compounds and they were characterized by ¹H and ¹³C NMR spectroscopy and by single-crystal X-ray diffraction analysis (sc-XRD). The coordination capability of Ar₃Sb and Ar₂SbCl was examined in the reactions with either cis-[PdCl₂(CH₃CN)₂] or PtCl₂ and complexes cis-[(κ²-Sb,N-Ar₃Sb)MCl₂] (M = Pd 1, Pt 2) and [(κ³-N,Sb,N-Ar₂SbCl)MCl₂] (M = Pd 3, Pt 4) were isolated, while their structures were determined by sc-XRD. Notably, the ligands Ar₃Sb and Ar₂SbCl exhibit different coordination modes – bidentate and tridentate, respectively – and the antimony exhibits three distinct bonding modes in complexes 1–4, which were also subjected to theoretical studies.