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 Ca 2+ -exchanged zeolites A (|Ca 6 |[Si 12 Al 12 O 48 ]-LTA) and X (|Ca 46 | [Si 100 Al 92 O 384 ]-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 Ca 2+ -exchanged zeolites A and X have been determined by single-crystal X-ray diffraction techniques at 294 K in the cubic space group Pm3m (a = 12.288(2) A) and Fd 3 (a = 25.012(1) A), respectively. The crystal structures of pale red-brown |Ca 6 Te 3 |[Si 12 A 12 O 48 ]-LTA and black coloured |Ca 46 Te 8 | [Si 100 Al 92 O 384 ]-FAU have been refined to the final error indices of R 1 /wR 2 = 0.1096/0.2768 and R 1 /wR 2 = 0.1054/ 0.2979 with 204 and 282 reflections for which F o > 4σ(F o ), respectively. In the structure of |Ca 6 Te 31 |[Si 12 Al 12 O 48 ]-LTA, 6 Ca 2+ ions per unit cell were found at one crystallographic positions, on 3-fold axes equipoints of opposite 6-rings. In |Ca 46 Te 8 |[Si 100 Al 92 O 384 ]-FAU, 46 Ca 2+ ions per unit cell were found at four crystallographically distinct positions: 3 Ca 2+ ions at Ca(1) fill the 16 equivalent positions of site I, 21 Ca 2+ ions at Ca(2) fill the 32 equivalent positions of site I', 10 and 12 Ca 2+ 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 Ca 2+ 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 Ca 2+ cations at the other end.