Synthesis and structural characterisation of germanium(II) halide complexes with neutral N-donor ligands

Abstract

The Ge(II) complexes [GeX2(L–L)] (L–L = 1,10-phen (X = Cl, Br); L–L = Me2N(CH2)2NMe2, 2,2¢-bipy (X = Cl)), [GeX(L–L)][GeX3] (L–L = 2,2¢-bipy (X = Br); L–L = pmdta (MeN(CH2CH2NMe2)2) (X = Cl, Br)) have been prepared and their crystal structures determined. The crystal structure of [GeCl2{Me2N(CH2)2NMe2}] shows a weakly associated centrosymmetric dimer based upon distorted square-pyramidal coordination at Ge(II) and containing asymmetrically chelating diamine ligands. The structure of [GeCl2(2,2¢-bipy)] contains a chelating 2,2¢-bipy ligand and forms a zig-zag chain polymer via long-range intermolecular Ge ◊◊◊ Cl bridging interactions, leading to a very distorted six-coordinate environment at Ge. [GeCl2(1,10-phen)] adopts a weakly associated dimeric structure similar to that in [GeCl2{Me2N(CH2)2NMe2}], whereas [GeBr2(1,10-phen)] is again a zig-zag polymer similar to [GeCl2(2,2¢-bipy)]. [GeBr(2,2¢-bipy)][GeBr3] contains a pyramidal cation with a chelating 2,2¢-bipy and a terminal Br ligand and with long-range contacts involving the three Br atoms in the anion. [GeX(pmdta)][GeX3] (X = Cl or Br) show discrete cations and anions, with no significant long-range interactions. The bonding in these systems can be described as covalent, with longer range interactions to other ligands involving the 4p orbitals of Ge. DFT calculations performed on [GeCl2(2,2¢-bipy)] show that the geometry of the monomer unit in the experimental crystal structure does not correspond to the global minimum of the isolated molecule, but to a higher energy minimum. In contrast, the calculated structure of the tetramer shows some of the main structural characteristics observed in the crystal structure.