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

The Ge(II) complexes [GeX(2)(L-L)] (L-L = 1,10-phen (X = Cl, Br); L-L = Me(2)N(CH(2))(2)NMe(2), 2,2'-bipy (X = Cl)), [GeX(L-L)][GeX(3)] (L-L = 2,2'-bipy (X = Br); L-L = pmdta (MeN(CH(2)CH(2)NMe(2))(2)) (X = Cl, Br)) have been prepared and their crystal structures determined. The crystal structure of [GeCl(2){Me(2)N(CH(2))(2)NMe(2)}] shows a weakly associated centrosymmetric dimer based upon distorted square-pyramidal coordination at Ge(II) and containing asymmetrically chelating diamine ligands. The structure of [GeCl(2)(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. [GeCl(2)(1,10-phen)] adopts a weakly associated dimeric structure similar to that in [GeCl(2){Me(2)N(CH(2))(2)NMe(2)}], whereas [GeBr(2)(1,10-phen)] is again a zig-zag polymer similar to [GeCl(2)(2,2'-bipy)]. [GeBr(2,2'-bipy)][GeBr(3)] 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)][GeX(3)] (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 [GeCl(2)(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.