Strukturuntersuchungen an Amminkomplexen und Hydroxiden von Übergangsmetallen

The crystal structures and IR-spectra of some ammoniakates, Co(OD) 2 , and Mn 2 (OH) 3 Cl have been determined with a view to study hydrogen bonding in these compounds. [Ni(NH 3 ) 6 ]SO 4 , [Cu(NH 3 ) 5 ]SO 4 and Mn 2 (OH) 3 Cl crystallize in the monoclinic space group P2 1 /c with a = 705.0(1), b = 1195.2(2), c = 1180.0(2) pm, β = 96.14(3)°, Z = 4, in the orthorhombic space group Pnma with a = 707.1(1), b = 1065.5(2), c = 1199.0(2) pm, Z = 4, and a = 650.02(2), b = 712.39(3), c = 953.10(3) pm, Z = 4, respectively. IR-spectra of microcrystalline Zn(NH 3 ) 2 Br 2 and Ni(NH 3 ) 2 X 2 (X = Cl, Br) and their isotopically diluted derivatives indicate that hydrogen bonds in these compounds are stronger than in the respective octahedral complexes. The broad range of N⋅⋅⋅O distances and OD stretching vibrations in [Ni(NH 3 ) 6 ]SO 4 and [Cu(NH 3 ) 5 ]SO 4 gives evidence for hydrogen bonds of very different strength. The predicted brucite type of Co(OD) 2 was confirmed (P-3m1, a = 317.79(4), c = 464.2(1) pm and Z = 1. In spectra of isotopically diluted samples two OD-stretching vibrations instead of the one expected were observed. The reason is found in the slow H/D exchange in these brucites with very low solubility, which leads to mixtures of fully and partially deuterated species. In Mn 2 (OH) 3 Cl both hydrogen atoms in positions directly between O and Cl take part in hydrogen bonding. A histogram of the O-H distances in brucite type hydroxides shows that the average distances are in the range 94-96 pm. Contrary to the lattice constants c the lattice constants a correlate well with the average O-H distances. The mean metal-oxygen distances of the first coordination sphere do not correlate withe the frequencies of the OH-stretching modes. Together with the red-shift of the OH valency modes with increasing pressures and the short O-H distances this is an indication for weak trifurcated hydrogen bridges in these compounds.