EXPERIMENTAL DETERMINATION OF TOPOLOGICAL FEATURES IN METALS AND INORGANIC MATERIALS. B.B. Iversen and F. Krebs Larsen, Department of Inorganic Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark

Accurate X-ray diffraction data allow the electron density distribution (ED) of crystals to be determined. Recently, Iversen et al. (1) derived the ED in metallic Be using both the maximum entropy method and the multipole refinement method. The high resolution of the ED allowed a critical point network for the beryllium hcp structure to be proposed. The detailed information about the topology of beryllium suggested new explanations for some of the interesting physical properties of hcp metals. To see if these findings were general properties of hcp metals we have sub-sequently determined the ED of metallic Mg from 8 K AgK[[alpha]] X-ray diffraction data. Overall the topology resembles that of Be, but the valence features are sharper. This corroborates, according to the theory of atoms in molecules (2), the fact that Mg is a poorer conductor than Be. If accurate diffraction data are measured at very low temperatures detailed topological features of transition metal complexes can also be mapped. We have studied Ni(ND₃)₄(NO₂)₂ from 9 K AgK[[alpha]] X-ray diffraction data, and based on the properties of the Laplacian at the bond critical points the interaction between the metal and the ligands can be studied. As an example the topological analysis reveals a larger pi contribution to the bonding for the nitro group than for the amine group, but overall the metal-ligand bonding is dominated by electrostatic interactions.

1. B.B. Iversen, F.K. Larsen, M. Souhassou, M. Takata. Acta Cryst. B51 (1995) 580-592.

2. R.F.W. Bader. Atoms in Molecules. A Quantum Theory. Oxford University Press (1991).