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

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 GeCl 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.