A VALENCE-BOND PERSPECTIVE ON THE MOLECULAR SHAPES OF SIMPLE METAL ALKYLS AND HYDRIDES

Many chemists use qualitative valence bond concepts to rationalize mol ecular structures and properties, particularly for main group elements . Extension of Pauling's valence bond concepts to transition metal com pounds dominated by covalent bonding leads to simple prescriptions for determining bond hybridizations and molecular shapes. As a result, tr ansition metal structures can be discussed in the familiar terminology of Lewis structures. lone pairs, hybrid orbitals, hypervalence, and r esonance. A primary feature of these prescriptions is the relative imp otence of valence p-orbitals in the formation of covalent bonds at tra nsition metals: sd(n) hybridization dominates. This feature is consist ent with detailed analyses of high level quantum mechanical computatio ns. Unlike Pauling's original treatments of hypervalency, rationalizat ion of empirical structures and high level electronic structure comput ational results requires consideration of multiple resonance structure s. Valence bond theory constitutes a compact and powerful model that a ccurately explains the often unexpected structures observed for simple metal alkyls and hydrides.