A new approach to the distortion of the tetrahedral geometry at E in the E(ZXY(2))(4) compounds

Density functional theory calculations have been used to study the structur al features of a variety of tetrahedral E(ZXY(2))(4) compounds. In these co mpounds, the six Z-E-Z angles deviate from the ideal tetrahedral geometry i n such a way that they are either four smaller and two larger (4s2l), or fo ur larger and two smaller (4l2s). A simple cubic model has been used to exp lain such structural distortions. Within this cubic model, the stability of the D-2d and S-4 conformers of E(ZXY(2))(4) compounds can be understood in terms of the homophobic and heterophilic nature of the substituents on the Z atoms. The hyper-conjugation effect has also been emphasized for compoun ds when the Z atoms have lone pairs of electrons.