The morphology of all-silica sodalite is calculated using surface simulation techniques, and is found to compare favourably with the experimentally observed morphology.

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Ab initio spin-coupled calculations have been carried out on MH and MH+ species to investigate the electronic structure of systems containing transition metal atoms in low oxidation states; results are presented for VH, where the bonding can be understood in terms of the overlap between a 'bonding hybrid' on vanadium and a distorted Is function on hydrogen.

The ab initio spin-coupled model, which is one of the most useful formulations of modern valence bond theory, has been used to study the general characteristics of, and the variations in, the chemical bonding in MCH 2 + (M ) Sc-Co) systems. The covalent metal-methylene interaction, characteristic of Schrock complexes, exhibits simultaneously a metal to ligand σ electron donation and a ligand to metal π electron donation. The degree of σ donation decreases and that of π donation increases monotonically from ScCH 2 + to CoCH 2 + in parallel with the decreasing dipole moment of the system and the increasing electronegativity of the M + center. The metal-methylene interactions are found to be well described by a balance between two resonant Lewis structures: a dominant doubly bonded closed-shell + MdCH 2 form and a much less important diradical-like, singly bonded form, + M • s • CH 2 . The importance of this last, which accounts for the triplet character in the π (and σ) interaction(s), grows with the number of unpaired nonbonding electrons on the metal. Such trends may be easily understood in terms of the preservation of intraatomic exchange energy and are consistent with a general decrease in the intrinsic bond strength from ScCH 2 + to MnCH 2 + , and vice versa from MnCH 2 + to CoCH 2 + . In addition, the sequential filling of nonbonding orbitals across the series is found to originate from a compromise between the minimization of repulsive electrostatic interactions between them and with bonding pairs, and the maximization of the intraatomic exchange energy.

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