This paper presents an analysis of the crystal structure and the charge density, p(r), for lithium bis(tetramethylammonium) hexanitrocobaltate(III) determined by the rigid pseudoatom model from accurate X-ray data measured at l13K. This compound has also been investigated by an ab initio Hartree-Fock fully periodic approach. A comparison of the topological properties between the experimentally and theoretically derived density is also given. A notable agreement between experiment and theory is observed in the topological properties of the metal-ligand interaction and a close parallel between the orbital model description and the shape of the Laplacian distribution around the Co atom is outlined. The results confirm the typical 3d-electron distribution of octahedral Co nI complexes in a low-spin state and the presence of four C--H...O hydrogen bonds in the crystal structure. Important differences between experiment and theory remain for the Laplacian and the parallel curvature (23) values at the C--N and N--O bond critical points. The atomic charges derived from the Quantum Theory of Atoms in Molecules are remarkably close to the formal values.Ohba, Saito & Miyamae (1991), were based on the analysis of the deformation density (DD). These studies were mainly aimed at the determination of the asphericity of nonbonding 3d-electrons around the octahedrally coordinated transition-metal atom and of the electron-density distribution in the nitro group.In this work we perform a topological analysis (Bader & Essen, 1984;Bader, 1990) and a comparison of the total experimental density with suitable theoretical densities in order to characterize the interaction between atoms in the title crystal. By proceeding in this way experiment and theory are directly compared in terms of the properties of an observable, using an approach (Bader, 1990) rooted in quantum mechanics. Some of the problems (Ruedenberg & Schwarz, 1990) inherent to DD studies are a priori avoided; neither the choice of the most appropriate promolecule density nor the resort to a given orbital model as an interpretative tool is needed in this framework.Our study mainly focuses on the analysis of the aspherical 3d-electron distribution around the Co atom, the metal-ligand interaction, the bond nature in the coordinated NO~-group and the characteristics of the C--H.• .O interactions.

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The metallacyclopentanes [ Ph{CH,CH (R)CH ( RxH,}(q5-C5Me5) (PPh,)] [ ( I b

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