Ab initio study of ortho-meta isomerism of Li(4)AB(3)(+) nitrite and phosphite oxo and thio salt molecules (A = N, P; B=O, S)

Ab initio MP2/6-31G*//HF/6-31G* + ZPE(HF/6-31G*) and MP4SDTQ/6-31G*//MP2/6- 31G* + ZPE(MP2/6-31G*) calculations of potential energy surfaces (PESs) of Li4NO3+, Li4PO3+, Li4NS3+, and Li4PS3+ ions and Li3NO3 Li3PO3 , Li3NS3 and Li3PS3 AB(2) oxo and thio salt molecules with 26 valence electrons were per formed. Several low-lying local minima were localized for each of these ion s, including ortho structure (Li+)(4) . AB(3)(3-) (1) Of the C-3v Symmetry with the pyramidal triply charged AB(3)(3-) anion (three Li+ cations in thi s structure are coordinated bidentately and one cation, tridentately) and a series of meta structures similar to the L+ . AB(2)(-) . BLi3+ ion triplet (2 and 5) and the ion-pair AB(2)(-) BLi42+ structure (3 and 3a) of the C-2 v and C-s symmetry, metry, bearing onium OLi3+ and OLi42+ cartons or their into SLi3+ ana SLi42+ analogues. For phosphate, thiophosphite, and thionitr ite ions, ortho isomer 1 is more favorable. However, meta isomer 3 (C2v) Of Li4PO3+ with a planar six-membered cycle and another meta isomer 5 (C-s) o f Li4NS4+ are only 9 and 7 kcal/mol less stable than structure 1, respectiv ely. By contrast, the most favorable meta isomers 3 (C-2v), 3a (C-2v), and 5 (C-s) of Li4NO3+ are almost degenerate in energy, whereas ortho isomer 1 is about 10 kcal/mol less stable. The equilibrium geometrical parameters, r elative energies of isomers, energies of decomposition along different path ways, frequencies and intensities of normal vibrations, and characteristics of electron density distribution were calculated. The results of calculati ons were compared to those for neutral Li(3)AB(3) Salt molecules. The defor mation and polarization of AB(3)(3-) in Li(3)AB(3) salts and Li(4)AB(3)(+) ions and variation of the relative stability of isomers with the number of Li+ cations were considered.