A 6-31G* chemistry of isoelectronic tetrahedral XL4ε and YL4ε (X = Li to F; Y = Na to Cl; L = H, F, Cl) species. Part 2. Energies, bond lengths, and critical radii

Abstract

The 6-31G* ab initio treatment of isoelectronic tetrahedral species now covers the complete XL4ε and YL4ε series (X = Li to F; Y = Na to Cl; L = H, F, Cl). The optimized equilibrium molecular parameters comprise the total electronic energy E, bond lengths, critical radii rc, MO energy levels, net charges, and electron densities at the bond critical points; only the first four are discussed in this part. The stability in terms of E, of the tetrahedral species relative to some competing systems, is examined. The energy requirements associated with the transfer of electronic charge from L to the central atom are reflected in the variation of the critical radii with the oxidation state m of X and Y, with important differences between the first- and the second-row elements. In an appendix it is shown that the E~HF limit energies of isoelectronic He-core (Li+ ff.), Ne-core (Na+ ff.), and Ar-core (K+ ff.) series of ions can be represented analytically by quadratic polynomials in m to an accuracy of ~0.0023% of the E~HF limit range or better, and that these approximations for the three series are qualitatively of the type E = −a(Z − b)2.