Synthesis of tellurium sorption complexes in fully dehydrated and fully Ca²⁺-exchanged zeolites A and X and their single-crystal structures

Single crystals of fully dehydrated and fully Ca²⁺-exchanged zeolites A (|Ca₆|[Si₁₂Al₁₂O₄₈]-LTA) and X (|Ca₄₆|[Si₁₀₀Al₉₂O₃₈₄]-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 Pm3 m (a = 12.288(2) Å) and Fd 3 (a = 25.012(1) Å), respectively. The crystal structures of pale red-brown |Ca₆Te₃|[Si₁₂Al₁₂O₄₈]-LTA and black coloured |Ca₄₆Te₈| [Si₁₀₀Al₉₂O₃₈₄]-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 F_o > 4σ(F_o), respectively. In the structure of |Ca₆Te₃|[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|[Si₁₀₀Al₉₂O₃₈₄]-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) Å 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) Å 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.