Low-Temperature Syntheses and Characterization of Novel Layered Tellurites, A<sub>2</sub>Mo<sub>3</sub>TeO<sub>12</sub> (A = NH<sub>4</sub>, Cs), and “Zero-Dimensional” Tellurites, A<sub>4</sub>Mo<sub>6</sub>Te<sub>2</sub>O<sub>24</sub>·6H<sub>2</sub>O (A = Rb, K)

1998-08-29T00:00:00Z (GMT) by Vidyavathy K. Vidyasagar
Hydrothermal synthetic investigations to prepare new A<sub>2</sub>Mo<sub>3</sub>TeO<sub>12</sub> (A = NH<sub>4</sub>, Cs, Rb, K) compounds are described. Novel noncentrosymmetric layered tellurites, (NH<sub>4</sub>)<sub>2</sub>Mo<sub>3</sub>TeO<sub>12</sub> (<b>1</b>) and Cs<sub>2</sub>Mo<sub>3</sub>TeO<sub>12</sub> (<b>2</b>), have been synthesized by hydrothermal methods. Their structures contain two-dimensional hexagonal tungsten oxide related (Mo<sub>3</sub>TeO<sub>12</sub>)<sup>2-</sup> anionic layers interleaved with NH<sub>4</sub><sup>+</sup>/Cs<sup>+</sup> ions. New “zero-dimensional” tellurites, Rb<sub>4</sub>Mo<sub>6</sub>Te<sub>2</sub>O<sub>24</sub>·6H<sub>2</sub>O (<b>3</b>) and K<sub>4</sub>Mo<sub>6</sub>Te<sub>2</sub>O<sub>24</sub>·6H<sub>2</sub>O (<b>4</b>), containing discrete centrosymmetric (Mo<sub>6</sub>Te<sub>2</sub>O<sub>24</sub>)<sup>4-</sup> anionic aggregates and alkali metal ions have been synthesized by simple refluxing of stoichiometric reactants in water. In this hexamolybdoditellurite anion, the Mo<sub>6</sub>O<sub>24</sub> flat hexagonal ring, formed from edge sharing of six MoO<sub>6</sub> octahedra, is capped by tellurium on both sides. The two types of anions have the same empirical formula. Cs<sub>2</sub>Mo<sub>3</sub>TeO<sub>12</sub> (<b>2</b>) 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 <b>1</b>, hexagonal space group <i>P</i>6<sub>3</sub>, <i>a</i> = 7.332(2) Å, <i>c</i> = 12.028(4) Å, <i>Z </i>= 2; for <b>2</b>, hexagonal space group <i>P</i>6<sub>3</sub>, <i>a</i> = 7.3956(10) Å, <i>c</i> = 12.186(2) Å, <i>Z</i> = 2; for <b>3</b>, monoclinic space group <i>P</i>2<sub>1</sub>/<i>c</i>, <i>a</i> = 10.0564(14) Å, <i>b</i> = 9.877(8) Å, <i>c</i> = 15.724(3) Å, β = 109.988(11)°, <i>Z</i> = 2; for <b>4</b>, monoclinic space group<i> P</i>2<sub>1</sub>/<i>c</i>, <i>a</i> = 9.878(3) Å,<i> b</i> = 9.724(4) Å, <i>c</i> = 15.301(3) Å, β = 108.57(2)°,<i> Z</i> = 2. Low-temperature syntheses, structure, and powder X-ray diffraction, spectroscopic, and thermal studies of compounds <b>1</b>−<b>4</b> are described.