Crystal structure of hydrated and partially NH4-exchanged heulandite

Crystal structure refinement of a hydrated and partially NH4-exchanged heul andite was carried out on single-crystal X-ray diffraction data. The space group is C (1) over bar [cell parameters a=17.668(5), b=17.881(5), c=7.413( 2) Angstrom, alpha=90.26(2), beta= 116.48(2), gamma = 89.61(2)degrees], and the structural refinement leads to R=0.08 and R-w=0.05. Eight H2O, two cat ion sites and one partially occupied NH4 site were localized. The symmetry lowering is ascribed to the asymmetrical distribution of the NH4 molecules. A micro-IR spectrum, compared with that of natural heulandite, confirms th at a few H2O molecules are involved in bonding to NH4 ions. (C) 1999 Elsevi er Science B.V. All rights reserved.