Low-Temperature Syntheses and Characterization of Novel Layered Tellurites, A₂Mo₃TeO₁₂ (A = NH₄, Cs), and “Zero-Dimensional” Tellurites, A₄Mo₆Te₂O₂₄·6H₂O (A = Rb, K)

Hydrothermal synthetic investigations to prepare new A₂Mo₃TeO₁₂ (A = NH₄, Cs, Rb, K) compounds are described. Novel noncentrosymmetric layered tellurites, (NH₄)₂Mo₃TeO₁₂ (1) and Cs₂Mo₃TeO₁₂ (2), have been synthesized by hydrothermal methods. Their structures contain two-dimensional hexagonal tungsten oxide related (Mo₃TeO₁₂)^2- anionic layers interleaved with NH₄⁺/Cs⁺ ions. New “zero-dimensional” tellurites, Rb₄Mo₆Te₂O₂₄·6H₂O (3) and K₄Mo₆Te₂O₂₄·6H₂O (4), containing discrete centrosymmetric (Mo₆Te₂O₂₄)^4- anionic aggregates and alkali metal ions have been synthesized by simple refluxing of stoichiometric reactants in water. In this hexamolybdoditellurite anion, the Mo₆O₂₄ flat hexagonal ring, formed from edge sharing of six MoO₆ octahedra, is capped by tellurium on both sides. The two types of anions have the same empirical formula. Cs₂Mo₃TeO₁₂ (2) could be prepared by a solid state reaction as well. All four new tellurites have been structurally characterized by single-crystal X-ray diffraction studies. Pertinent crystal, data are as follows:  for 1, hexagonal space group P6₃, a = 7.332(2) Å, c = 12.028(4) Å, Z = 2; for 2, hexagonal space group P6₃, a = 7.3956(10) Å, c = 12.186(2) Å, Z = 2; for 3, monoclinic space group P2₁/c, a = 10.0564(14) Å, b = 9.877(8) Å, c = 15.724(3) Å, β = 109.988(11)°, Z = 2; for 4, monoclinic space group P2₁/c, a = 9.878(3) Å, b = 9.724(4) Å, c = 15.301(3) Å, β = 108.57(2)°, Z = 2. Low-temperature syntheses, structure, and powder X-ray diffraction, spectroscopic, and thermal studies of compounds 1−4 are described.