X-N STUDY OF THE ELECTRON DENSITY DISTRIBUTION IN Ni(ND3)4(NO2)2 AT 9 K. F. Krebs Larsen and B.B. Iversen, Department of Inorganic Chemistry, University of Aarhus, DK-8000 Aarhus C, Denmark, and Brian N. Figgis, Department of Chemistry, University of Western Australia, Nedlands, WA 6009, Australia, Philip A. Reynolds, Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia, and A.J. Schultz, IPNS, Argonne National Laboratory, Argonne, IL 60439, USA
The electron density distribution (ED) of Ni(ND3)4(NO2)2 has been determined from 9 K AgK[[alpha]] X-ray diffraction data in combination with 13 K Time-of-flight (TOF) neutron diffraction data. Excellent agreement is obtained between positional and thermal parameters derived separately from the two experiments. This demonstrates that, also for complex systems, TOF neutron diffraction can produce structural parameters of a quality comparable to measurements with monochromatic neutrons. The valence orbital model used to model the ED in a previous study of Ni(ND3)4(NO2)2 (1) turned out to be inadequate for describing the more accurate very low-temperature data which extend to sin[[theta]]/[[lambda]]= 1.4 Å-1. Instead a multipole model with extra radial flexibility is used to obtain a satisfactory description of the data. The bonding in Ni(ND3)4(NO2)2 is discussed based on representations of the total ED. Topological analysis of the static model density is used to describe the metal-ligand interactions. Both ligands are bonded to Ni through closed shell interactions, but the ellipticity in the Ni-nitro bond is larger than in the Ni-ammine bond. This suggests larger pi-type contributions to the Ni-nitro bond than to the Ni-ammine bond.
1. B.N. Figgis, P.A. Reynolds, S.J. Wright, J. Am. Chem.Soc. 105 (1983) 434-440.