Montmorillonite and beidellite intercalated with tetramethylammonium cations

Molecular mechanics simulations, combined with X-ray powder diffraction and infrared spectroscopy, have been used in structure analysis of montmorillo nite and beidellite intercalated with tetramethylammonium cations. A comple x structure analysis provided us with the detailed structure model, includi ng characterization of the disorder, the total sublimation energy and a cha rge distribution in the structure of intercalates. The calculated basal spa cings (14.36 Angstrom for TMA-montmorillonite and 14.12 Angstrom for TMA-be idellite) are in good agreement with the experimental values (14.31 Angstro m for TMA-montmorillonite and 14.147 Angstrom for TMA-beidellite). Both int ercalated structures exhibit positional and orientational disorder in the a rrangement of TMA cations, and consequently disorder in layer-stacking. In the present work we analyse the effect of octahedral and tetrahedral substi tutions in a 2:1 silicate layer on the arrangement of tetramethylammonium ( TMA) cations in the interlayer space of montmorillonite and beidellite. The most significant difference between TMA-montmorillonite and TMA-beidellite is in the charge distribution on the TMA cations and silicate layer. The T MA-beidellite structure is highly polarized, the total charge on one TMA ca tion is +0.167 e(-), while the total charge on the TMA cation in montmorill onite is +0.050 e(-).