Single crystal neutron diffraction study of the natural zeolite barrerite in its ND (sub 4) -exchanged form

Barrerite single crystals from Kuiu Island (Alaska) were treated in a ND (sub 4) Cl aqueous solution to obtain the ND (sub 4) -exchanged form. The crystal structure of the exchanged barrerite (Na (sub 0.85) K (sub 0.24) Mg (sub 0.38) Ca (sub 1.30) Ba (sub 0.02) (ND (sub 4) ) (sub 10.52) Al (sub 15.01) Si (sub 56.99) O (sub 144) .41D (sub 2) O, a = 13.601 Aa, b = 18.232 Aa, c = 17.810 Aa, 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 (sub 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 (sub 2) O molecules and in ND (sub 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 (sub 2) O and ND (sub 4) groups highly probable.