Structural and Motional Features of a Layered Sodium Hydrous Silicate as Revealed by Solid State NMR

Abstract

An approach for the investigation of layered alkali metal polysilicate hydrous materials is presented by choosing complementary multinuclear NMR methodologies. New insights into the structural and motional features of magadiite, a layered sodium silicate hydrate, have been gained using 1H, 2H, 29Si and 23Na one- and two-dimensional NMR experiments. Complementary 1H MAS single- and double-quantum studies have proven to be powerful tools in a clear recognition of the nature of hydrous species involved in hydrogen bonding. 1H and 2H MAS experiments permitted us to determine the extent of the mobility of water molecules and provided corroborating evidences of an intralayer, strongly hydrogen bonded character of silanol groups. On the basis of a novel strategy in the analysis of the cross polarization dynamics, it appeared that magadiite contains two types of structurally different Q(3) tetrahedra, as well as two types of sodium ions. The strategy applied in this work might be useful to obtain structural and motional information in the related layered alkali metal silicates, as well as in other classes of nanoporous materials.