The d orbitals of second‐row elements

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 SF 6 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 XO 4 species are also considered. Positive energies are found for d orbitals in isolated anions.