RESIDUAL MANGANESE(II) ENTRAPPED IN SINGLE-LAYER-HYDRATE MONTMORILLONITE INTERLAYERS

Electron paramagnetic resonance (EPR) and Fourier transform infrared ( FTIR) spectroscopy in combination with X-ray diffractometry and therma l methods were used to determine the coordination of residual exchange able Mn(II) in an untreated sample of Wyoming montmorillonite. At room temperature, Mn(II) in a single-layer-hydrate interlayer was proposed to be coordinated directly with oxygen ions of the siloxane surface o n one layer and to form water bridges to the oxygens on the siloxane s urface of the opposite layer. Dehydration and collapse of the interlay er entrapped and thereby stabilized the partially solvated Mn(II) up t o 600 degrees C. A change to Mn(II) in highly symmetric coordination o ccurred during dehydroxylation of the montmorillonite structure betwee n 600 degrees C and 700 degrees C. Manganese(II) remained coordinated at the surface but positioned in a bicapped trigonal antiprism formed by oxygens of the silicate structure. This coordination was metastable at 800 degrees C when the structural decomposition of the clay minera l began.