Non-empirical analysis of unusual chemical bonds. Part III. [LiBH(NH)2)2]+

The geometry and electronic structure of H 2XO radicals have been investigated by means of non-empirical UHF and MNDO HE methods. The results show that σ radicals invariably have a planar equilibrium geometry, while π radicals are characterized by a variable degree of pyramidalization. The MNDO method and the STO-3G basis set provide unreliable geometric parameters, while 4-31G results are in good agreement with experimental data and more refined ab initio computations. The effect of the electronegativity of X and the number of valence electrons on the geometry of H 2XO radicals is rationalized in terms of the PMO model.