The interlayer structure of La-vermiculite

The structure of the interlayer cation-water system in La-vermiculite with a unit cell of a = 5.33(5), b = 9.18(6), c = 15.13(9) Angstrom and beta = 9 6.82(7)degrees has been determined in space group C2/m. Under ambient condi tions, the interlayer La cations are distributed on a 3a x b superlattice w hich disappears on dehydration but returns on rehydration. The basal spacin g does not change during the dehydration/rehydration process. The character of the superlattice spots indicate that the cation-water system, at ambien t conditions, is ordered over relatively large domains. The La cations are surrounded by 8 neighboring water molecules in a distorted cubic arrangemen t. The spaces between the La-water clusters are occupied by triads of water molecules that are relatively mobile.