Abstract

Barrerite single crystals from Kuiu Island (Alaska) were treated in a ND4Cl aqueous solution to obtain the ND4-exchanged form. The crystal structure of the exchanged barrerite (Na0.85K0.24Mg0.38Ca1.30Ba0.02(ND4)10.52 Al15.01Si56.99O144 ·41D2O, a = 13.601 Å, b = 18.232 Å, c = 17.810 Å, 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 NH4-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 D2O molecules and in ND4+ 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 D2O and ND4 groups highly probable.

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