Non-aqueous solutions of lithium and sodium perchlorates have been investigated by IR and Raman spectroscopy. The 35C104 and 37C10, isotopomers induce an asymmetry or a splitting of v3 and v, bands. All spectra are interpreted by assuming that the bands of possible solvent-separated species are at the same wavenumbers as if they were free ions ('spectroscopically free ions'). In ionizing solvents (dimethylsulfoxide, N,N-dimethylformamide, acetonitrile or acetone) these perchlorates are partly or completely dissociated into free ions while in associating solvents (esters, cyclic ethers or nitromethane) LiClO, is in part dimerized. In nitromethane, LiClO, ion pairs are slightly dissociated into free ions at low concentrations and dimerized at high concentrations. The coordination of ClO, in the ion pairs is either monodentate (LiClO,) or bidentate (NaClO,). Both ClO, groups in the LiClO, dimer are linked by two lithium bridges into a centrosymmetrical structure.

Abstract

Non-aqueous solutions of alkaline-earth metal perchlorates M(ClO,), (M = Ba, Sr, Ca, Mg) have been investigated by IR and Raman spectroscopy. The association of M 2 + and ClO,-into mononuclear species M(ClO,), (x = 1 or 2) depends on the cation and on the solvent. In a given solvent the association extent decreases from Ba to Mg. In all cases it has been possible to find at least one associating solvent (ester, cyclic ether) where the association into M(ClO,), is complete. In the associated species the coordination of ClO, can be monodentate (C3,) or bidentate (C,,). The monodentate coordination is the only mode in Mg(C10,), while bidentate coordination is predominent with the other cations. In that case there is a minor proportion of monodentate ClO, groups which decreases from Ca to Ba. The two kinds of coordination are distinguished by the shift Av, of v1 relative to free ClO, -which is either positive (monodentate) or negative (bidentate). This criterion has been established by the investigation of the other vibrational modes of ClO,. Wavenumber shifts and splittings have been correlated to the cation polarizing power. Force constant variations calculated on BaC10, + and LiClO, are correctly interpreted by Lewis structures.

No abstract

The dimerization of the ion pairs MNCS (M = Li, Na, K) has been investigated in tetrahydrofuran (THF) and in 1,3-dixolane (DXL) solutions by infrared and Raman spectroscopy. The mixed dimer LiNa(NCS)2 and the triple cations Li2NCS+ and Na2NCS+ have also been characterized. The three dimers (MNCS)2 have the same rhombic structure. Dimerization reactions exhibit a nonideal behavior which mostly comes from ion pair-ion pair interactions. The dimerization is more pronounced for NaNCS and KNCS than for LiNCS, In all cases these reactions are athermic or endothermic, i.e., entropy controlled. The upward curvature which is observed when the logarithm of the solubility of MSCN is plotted against the reciprocal of the temperature is explained by the dimerization and by ion pair-ion pair interactions.

No abstract

No abstract

No abstract