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A study was conducted to explore the interaction of molecular hydrogen with the small molecules HF, [H.sub.2]O, N[H.sub.3], and LiOH. The interaction energy for the simultaneous interaction of [H.sub.2] with two LiOH molecules has not exceeded the value obtained for the interaction with a single LiOH molecule.

Binuclear square planar Ni(II) complexes, formed by two tridentate ligands with two imine-nitrogens coordinating two nickel atoms, have presented new types of eidge-tile-like chiral compounds that are stable in the appropriate bent conformation. The new compounds with ridge-tile-like chiral topology are shown to be reasonably stable and hence their chemistry, physical properties and applications are analyzed.

The synthesis of [Si.sub.5][Mes.sub.6] (Mes = 2,4,6-trimethylphenyl) consisting of an archetypal [1.1.1] cluster core featuring two ligand-free, ' inverted tetrahedral' bridgehead silicon atoms, is described. Reactivity studies have provided evidence for both closed-shell and radical-type reactivity and have thus confirmed the unusual nature of the stretched silicon-silicon bond in the ' nonclassical' molecule.

The correlated coupled-cluster theory with singles and doubles (CCSD) approach is employed for the calculation of the reaction barrier height for hydrogen abstraction by the hydroperoxyl radical from methane. The reactions of the [C.sub.n][H.sub.2n+2], where n = 2-4 alkanes, are also studied.

The article describes the benchmark, near basis set limit fc-CCSD(T) equilibrium harmonic frequencies for a set of 12 closed-shell and five open-shell molecules, which is computed numerically by using the CCSD(T)-R12 method. The corrections due to core-valance correlation are used for assessing the accuracy of the benchmark data, along with corrections from scalar relativistic effects.

The effect of basis set on second order Moller-Plesset perturbation (MP2) of several hydrogen-bonded complexes is studied. The possibilities of utilizing basis set extrapolations for geometries and dissociation energies are discussed along with the results of R12 methods and density functional and local correlation methods.

An analytical, full-dimensional, and global representation of the potential energy surface of ammonia in the lowest adiabatic electronic state is developed, and parameters are determined by adjustment to ab initio data and thermochemical data for several low-lying dissociation channels. The representation is distinguished by giving a qualitatively correct description of the potential energy for very large amplitude displacements of the nuclei from equilibrium.

The larger aromatic systems should be favored over single benzene rings in order to increase the interaction of dihydrogen with aromatic systems. The investigations of different ways to store hydrogen are described.