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

1998-08-29T00:00:00Z (GMT) by Vidyavathy K. Vidyasagar
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 14 are described.