Distribution of Si and Al in Clintonites: A combined NMR and Monte Carlo Study.

The distribution of silicon and aluminum atoms over the tetrahedral sheets of clintonites (aluminum-rich phyllosilicates 2:1) has been studied by 29Si and 27Al magic-angle-spinning NMR spectroscopies. According to the 29Si NMR spectra, no silicon atoms are present in adjacent tetrahedra; however, several environments have been detected in the 27Al NMR signal, proving that these aluminosilicates do not adhere to Loewenstein's rule. The atom distribution has been simulated by a Monte Carlo procedure. From the results of these simulations, a further dispersion of silicon atoms over the tetrahedral sheets has been found, indicating a homogeneous dispersion of the electrostatic charge over the phyllosilicate layers. In contrast, a maximum dispersion of charges must be discarded in the layers of studied clintonites. Finally, an analysis of structural factors controlling this kind of cation distribution is given