The d orbitals of second-row elements

Abstract

Atomic SCF calculations for second-row elements with configurations involving d electrons show that under favourable conditions of spin alignment d atomic orbitals may sometimes be of a suitable size for engaging in molecular bonding. The orbital energies, however, are very small, and “simple-minded” combination with oxygen or fluorine ligand orbitals is therefore questionable. The participation of d orbitals in bonds is possible if their energies are substantially lowered by the ligands. The Craig–Zauli electrostatic treatment of SF6 is reconsidered and it is found that the neutral penetration integrals are large. Although this method neglects important terms, it suggests a possible mechanism for d-orbital participation by second-row elements and illustrates the need for extreme caution in semiempirical MO calculations. Tetrahedral XO4 species are also considered. Positive energies are found for d orbitals in isolated anions.