Gismondine; the detailed x-ray structure refinement of two natural samples

Gismondine from different localities and with Si/Al ratios of 1.06 and 1.15 are monoclinic, space group P21/c, with a 10.0198, b 10.360, c 9.830 Å, and β 92.536°; Z = 1. The final Rw = 3.9% and Rw = 3.3%, resp. The ordered Si-Al distributions and T-O distances agree with the compositional data. Details of the Si-Al distributions in the T sites were obtained by electrostatic energy calcns. One partially occupied H2O site not previously reported for gismondine was located in both crystals. Six H atoms pertaining to 3 fully occupied H2O sites were located at the proper H bond distances between H2O and framework atoms. The rest of the zeolitic H2O (∼1.4 mols. per formula unit) partially occupies, on a statistical basis, 4 more sites. All H2O mols. are at coordination distances from the only extraframework cation site. Both structures, although with a highly ordered framework, do not display the degree of ordering for the H2O mols. that one would expect, esp. for the 1st sample.