Single crystal neutron diffraction study of the natural zeolite barrerite in its ND4-exchanged form

Abstract

Barrerite single crystals from Kuiu Island (Alaska) were treated in a ND 4 Cl aqueous solution to obtain the ND 4 -exchanged form. The crystal structure of the exchanged barrerite (Na 0.85 K 0.24 Mg 0.38 Ca 1.30 Ba 0.02 (ND 4 ) 10.52 Al 15.01 Si 56.99 O 144 ·41D 2 O, a = 13.601 A, b = 18.232 A, c = 17.810 A, space group Fmmm ) was studied by single crystal neutron diffraction on data collected at 20 K at the D19 line at ILL (Grenoble). A comparison with a previously studied NH 4 -exchanged barrerite showed that the framework was identical in the two refinements, and that a substantial agreement occurred also in the extraframework content in the residual cations, in D 2 O molecules and in ND 4 + ions. Surprisingly, no evidence was found of D atoms either around nitrogen or around the oxygens of water molecules. This result could be interpreted as a consequence of the partial occupancy of the extraframework sites and the large distances of these sites from framework oxygens, with consequent weak hydrogen bonds, which make a disorder in the orientation of D 2 O and ND 4 groups highly probable.