Determination of the charge of Al13 Keggin oligocations intercalated into synthetic hectorite

Abstract

Abstract Applying a nematic liquid crystalline phase of a synthetic Na-hectorite with layer separations >100 nm, the reaction time for pillaring with Al13 Keggin oligocation could be reduced to seconds ensuring that cation exchange is controlled by thermodynamics. With this material at hand we are able to resolve the long-standing dispute regarding the charge of intercalated Keggin oligocations. Micropore sizes as determined by physisorption isotherms, adsorption isotherms obtained via elemental analysis, and results of 27Al solid-state NMR and pyridine probe IR spectroscopy favor a charge of +7 for the Al13 pillars intercalated into hectorite unaltered.