3d Orbitals and bonds of second-row atoms. Part I. σ Bonds
The effect of molecular environment on valence shell orbitals of second-row atoms is considered for a series of molecular systems in which the second-row elements appear to be in excited valence states. An electrostatic calculation shows that electronegative environments contract diffuse 3d orbitals and also reduce 3d promotion energies, so overcoming the main objections to 3d participation in bond formation. The influence of interatomic exchange is estimated for SF6, based on the octahedral valence state of sulphur, and confirms that sulphur 3d orbitals contribute substantially to bonding. Comparisons are made with a series of hypothetical molecules of sexivalent sulphur.