The geometries and vibrational patterns of LiClO 3 and NaClO 3 ion pairs: an ab initio SCF study

Abstract

Ab initio SCF calculations at the 3-21G* and 6-31G* HF-SCF level were performed on LiClO 3 and NaClO 3. Tridentate, bidentate and monodentate coordination models were examined and the bidentate and tridentate structures were characterized as the two lowest-energy minima on the corresponding potential energy surfaces. In particular, bidentate LiClO 3 is favoured by ≈ 24 kJ mol −1 at the 6-31G* level with respect to the tridentate isomer. On the contrary, the tridentate NaClO 3 isomer is more stable than the bidentate by ≈ 7 kJ mol −1. Correlation energies were calculated via Møller—Plesset perturbation theory carried to the second and third order on the bidentate and tridentate energy minima of the two molecules and the bidentate structures of LiClO 3 and NaClO 3 were determined to be more stable by ≈ 17 and ≈ 3 kJ mol −1, respectively with regard to the corresponding tridentate models. The results of MP2/6-31G * and MP3/6-31G* calculations and the effect of zero-point energy on the stability of the bidentate and tridentate molecules are discussed. Calculated harmonic frequencies of the stable isomers of LiClO 3 and NaClO 3 and 37Cl and 18O frequency shifts are reported.