HEXAMERIC LITHIUM PHENOLATE - CRYSTAL-STRUCTURES AND LI-7 QUADRUPOLE COUPLING IN SOLID AND SOLUTION PHASES

Whereas lithium phenolate in dioxolane coexists as a mixture of compar able amounts of a hexamer and tetramer, together with minor amounts of less aggregated species, in THF the predominant species is the tetram er. Two crystalline forms of lithium phenolate have been obtained from THF and THF/hexane solutions, and X-ray crystallographic studies show that they consist of very similar hexagonal prismatic hexamers of lit hium phenolate with one THF molecule bound to each lithium cation. The Li-7 nuclear quadrupole coupling constant (QCC = e2Qq(zz)/h = 67 +/- 1 kHz) and the asymmetry parameter (eta = 0.77 +/- 0.05) have been obt ained from line shape analysis of the powder spectrum of one of the cr ystalline samples. Proton decoupling was used to remove H-1/Li-7 dipol e-dipole interactions, and samples diluted with Li-6 were employed to estimate the contribution of the Li-7/Li-7 interaction to the line sha pe. These data give a value (73 kHz) for the quadrupole splitting cons tant [QSC = (1 + eta2/3)1/2(e2Qq(zz/h)] in agreement with that (72 +/- 10 kHz) determined for hexameric lithium phenolate in dioxolane from spin-lattice relaxation data. The values of QSC for the tetrameric spe cies in THF and dioxolane are 46 +/- 0.5 and 59 +/- 6 kHz, respectivel y. CP-MAS C-13 NMR spectroscopy is of limited value for characterizing solid samples of the aggregates.