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

A set of antimony(III) compounds containing a ligand (Ar) with a pendant guanidine function (where Ar = 2-[(MeN)CN]CH) was prepared and characterized. This includes triorgano-Ar3Sb, diorgano-Ar2SbCl and monoorgano-ArSbCl2 compounds and they were characterized by H and C 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 -[PdCl(CHCN)] or PtCl and complexes -[(κ-Sb,N-Ar3Sb)MCl] (M = Pd 1, Pt 2) and [(κ-N,Sb,N-Ar2SbCl)MCl] (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.