Structural Studies on Synthetic A2−x[M2(TeO3)3]·nH2O Phases (A = Na, K, Rb, Cs; M = Mn, Co, Ni, Cu, Zn) with Zemannite-type Structures

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Abstract
During a systematic study on formation conditions of new compounds with zemannite-type structures, crystals of ten new oxidotellurate(IV) phases were grown under hydrothermal conditions, partially with a drastic reduction of the water content. The crystal structures of the obtained phases were determined by single-crystal X-ray diffraction. Na2[Ni2(TeO3)3]·2.5H2O, K2[Ni2(TeO3)3]·H2O, K2[Zn2(TeO3)3]·2H2O, Rb1.25[Co2(TeO3)3]·1.5H2O and Rb1.24[Mn2(TeO3)3]·2H2O exhibit a unit-cell with hexagonal symmetry (Z = 2, a ≈ 9.3 Å, c ≈ 7.7 Å), in which most of the other compounds with a zemannite-type structure are known to crystallize. Relative to this unit-cell, K2[Cu2(TeO3)3]·2H2O exhibits a twofold superstructure, K2[Co2(TeO3)3]·2.5H2O a twofold superstructure with an additional incommensurate modulation, Na2[Cu2(TeO3)3]·1.5H2O a threefold superstructure, and Rb1.5[Mn2(TeO3)3]·1.25H2O and Cs[Mn2(TeO3)3]·H2O a fourfold superstructure. Disorder of the alkali metal cations and crystal water molecules in the channels as well as variable water contents complicate modelling and structure refinement.