1:1 Correlation between 27Al and 29Si chemical shifts and correlations with lattice structures for some aluminosilicate sodalites

Abstract

High-speed spinning 27Al and 29Si MAS n.m.r. experiments have been performed for five lithium and sodium halide aluminosilicate sodalites. Accurate 27Al and 29Si chemical shifts, 27Al quadrupolar coupling parameters, and 29Si spin-lattice relaxation times are reported and discussed. A 1:1 linear correlation between the 27Al and 29Si chemical shifts ( R L = 0.9998) covering a range of at least 12 ppm is observed. Linear correlations between δ( 27Al) [or δ ( 29Si)] and the cubic unit cell a-axis, the Si O Al bond angles (θ), and previously proposed functions describing the local framework geometry and based on θ [e.g. Σd TT = 13.48sin (θ/2)] are observed. The results indicate δ( 27Al) as alternative to δ( 29Si) for correlating MAS n.m.r. data with structure parameters at least for aluminosilicates with a ratio Si/Al= 1. The 27Al second-order quadrupolar effect seems to be influenced by the nature of the anions to a higher degree than by the framework geometry and cations in these systems.