Structural features of the congruently melting compounds MLi (NO3)2 (M = K, Rb, Cs) inferred from their Raman spectra

Raman spectroscopy was applied to interpret the structure of the congruently melting compounds KLi(NO3)(2), RbLi(NO3)(2) and CsLi(NO3)(2). They have similar Raman spectra in both the external and internal vibrational regions, indicating the same structure of the crystals and the same coordination environment of the nitrate ion. The two peaks of comparable intensity in the non-degenerate nu(1) region suggest two crystallographically different sites of the nitrate ion. These compounds appeared to have the same Li-NO3 complexes as in molten LiNO3: lithium ions and are tetrahedrally coordinated to nitrate ions to form polymeric complexes in which the nitrate ions act as either unidentate or bidentate ligands. This work confirms that KLi(NO3)(2) is a congruently melting compound. (C) 1999 Elsevier Science Ltd. All rights reserved.