Synthesis of Tellurium Sorption Complexes in Fully Dehydrated and Fully Ca²⁺-exchanged Zeolites A and X and their Single-crystal Structures

Abstract

Single crystals of fully dehydrated and fully Ca2+-exchanged zeolites A (|Ca6|[Sii2Ali2O48]-LTA) and X (|Ca46| [SiiooAl92O384]-FAU) were brought into contact with Te in fine pyrex capillaries at 623 K and 673 K, respectively, for 5 days. Crystal structures of Te-sorbed Ca2+-exchanged zeolites A and X have been determined by single-crystal X-ray diffraction techniques at 294 K in the cubic space group Pm 3 m (a = 12.288(2) A) and Fd 3 (a = 25.012(1) A), respectively. The crystal structures of pale red-brown |Ca6Tes|[Si12Al12O48]-LTA and black coloured |Ca46Te8| [Si1ooAl92O384]-FAU have been refined to the final error indices of R1/WR2 = 0.1096/0.2768 and R1/WR2 = 0.1054/ 0.2979 with 204 and 282 reflections for which Fo > 4°(F。)，respectively. In the structure of |Ca6Tes|[Si12Al12O48]-LTA, 6 Ca2+ ions per unit cell were found at one crystallographic positions, on 3-fold axes equipoints of opposite 6-rings. In |Ca46Te8|[Si10()Al92O384]-FAU, 46 Ca2+ ions per unit cell were found at four crystallographically distinct positions: 3 Ca2+ ions at Ca(1) fill the 16 equivalent positions of site I, 21 Ca2+ ions at Ca(2) fill the 32 equivalent positions of site I'，10 and 12 Ca2+ ions at Ca(3) and Ca(4), respectively, fill the 32 equivalent positions of site II. The Te clusters are stabilized by interaction with cations and framework oxygen. In sodalite units, Te-Te distances of 2.86(10) and 2.69(4) A in zeolites A and X, respectively exhibited strong covalent properties due to their interaction with Ca2+ ions. On the other hand, in large cavity and supercage, those of 2.99(3) and 2.76(11) A in zeolites A and X, respectively, showed ionic properties because alternative ionic interaction was formed through framework oxygen at one end and Ca2+ cations at the other end.

Optical study of Te8 ring clusters: comparison with density functional theory and a step towards materials design using nanoporous zeolite space

“…An XRD study of ∼60 micron size LTA-Te single crystals was performed in ref. 52. The XRD analysis suggested the interaction of Te atoms with the zeolite oxygen atoms and cations, while it showed low occupancy and high temperature factors for Te atomic sites.…”

“…At room temperature, the libration amplitudes are, probably, quite strong as well. This explains high temperature factors observed for Te sites, 52 which complicates the XRD analysis of LTA-Te. In contrast, this effect does not cause any trouble for polarization–orientation Raman spectroscopy, which appears to be a very fruitful method of zeolite-confined cluster study providing information on the cluster structure with distortions, orientation and interaction with zeolites.…”