On the low-temperature behavior of the zeolite gobbinsite: a single-crystal X-ray diffraction study

The crystal structure, crystal chemistry and low-temperature (LT) behavior of a natural gobbinsite [(Na4.97K0.07Ca 0.48)Σ5.52[Al5.62Si10.29] Σ15.91O32·11.9H2O, Z = 1, a = 10.1185(4), b = 9.8035 (4), c = 10.1692(4) and V = 1008.75(10) 3, space group Pmnb] have been studied by in situ LT single-crystal X-ray diffraction. Five structural refinements were conducted on the basis of intensity data collected at 293 (room conditions), 250, 200, 150 and 100 K. Reflection conditions confirmed that the space group Pmnb is maintained within the T-range investigated. At room temperature, the same extra-framework population described by Gatta et al. [7] was found, with one site partially occupied by Na, one site partially occupied by Ca, and five sites partially occupied by water. At low-T a partial dehydration, likely induced by the N 2-flow, was observed, with a significant rearrangement of the extra-framework configuration. Low-T induced deformations of the 8- and 4-membered rings were observed, and the relationships between the main deformation mechanisms of the tetrahedral framework and the contraction along the unit-cell edges are discussed.