127I, 185Re and 187Re Solid State NMR Measurements on (CH3)4AsIO4 and (CH3)4AsReO4

Abstract

Tetramethylarsonium-metaperiodate shows 127I solid state NMR signals without any visible quadrupole splitting. Due to the very large nuclear quadrupole moments of the rhenium isotopes 185,187Re, the analogous Re compound exhibits the expected second order quadrupole NMR effects. The measured 185,187ReRe NMR powder spectra contain superimposed signals arising from two different types of ReO- 4 tetrahedra, indicating that part of the ReO4 - anions deviate only slightly from tetrahedral symmetry, while the other part are nearly undistorted ReO4 - anions. The temperature dependence of the solid state NMR spectra reveals phase transitions for both compounds, which are confirmed also by DSC analyses. Furtherm ore, the DSC analysis of the Re compound again proves the existence of the two different types of ReO4 - tetrahedra in the lattice of the high temperature modification.