IR SPECTROMETRY, CALORIMETRY AND H-1,P-31,LI-7 NMR OF CYCLOTETRAPHOSPHATE - NALI[NH3-(CH2)2-NH3]P4O(12)CENTER-DOT-3H2O

According to the previous single-crystal X-ray structure determination the cyclotetraphosphate NaLi[NH3-(CH2)2-NH3]P4O12 · 3H2O belongs to the Pcca (D82h) space group (M. Bdiri and A. Jouini, J. Solid State Chem. 83, 350 (1989)); there are four anions per unit cell at a C2 symmetry site. A vibrational spectroscopy is expected to give real information about the geometry of the P4O12 group since its symmetry determines the number of normal vibration modes and their IR and Raman activities. According to the IR spectrum and a theoretical group analysis, symmetry of the ring anion P4O4-12 is found to be idealized from C2 to C2v symmetry site. An assignment of observed bands at room temperature is proposed. Thermodynamic parameters of dehydration, ΔH and Ea, are determined by differential scanning calorimetry (DSC). Experimental NMR absorption lineshapes, for 1H, 31P, and 7Li nuclei in the solid state, at temperatures between 170 and 300 K, have been carefully examined. Analysis of 1H data indicates the rigid character of CH2 groups and the reorientation motion of proton in H2O and NH3. Analysis of static and MAS absorption lineshapes for the 31 P (I = 1/2) and 7Li (I = 3/2) resonance in the title compound leads to two tetrahedral atomic sites for phosphorous and to one for lithium, in agreement with the X-ray crystallographic studies. The 7 Li NMR spectrum obtained at low temperature suggests a static distribution so that only half of the Li general positions is occupied. © 1994 Academic Press, Inc.