The shapes of three hypervalent systems of first-row atoms FH3, H4o, and F3H

Abstract

Musher's theory of hypervalent molecules (2) accounts for the shape of numerous molecules containing second- and third-row atoms of groups V, VI, and VII. In an attempt to examine the hypervalent bonding mechanism in a system free of competing d orbital effects, we consider three hypervalent systems of first-row atoms, H4O, FH3, and HF3. Gaussian computations employing very small lobe-representations of Slater-type aos indicate that H4O assumes a typical hypervalent geometry, with two colinear weak OH bonds and two covalent OH bonds in a normal plane. This prediction survives an improvement in basis. Our crudest computation indicates a D3h geometry for FH3, but an improved basis leads to a T-shaped molecule consistent with the theory of hypervalent molecules. F3H does not possess a stable hypervalent geometry; it is computed to be unstable relative to rare gas structure F+3 + H-. The reliability of our small basis in a system with three fluorines is questionable.