Synthesis and Reactivity of W<sub>3</sub>Te<sub>7</sub><sup>4+</sup> Clusters and Chalcogen Exchange in the M<sub>3</sub>Q<sub>7</sub> (M = Mo, W; Q = S, Se, Te) Cluster Family

Heating WTe<sub>2</sub>, Te, and Br<sub>2</sub> at 390 °C followed by extraction with KCN gives [W<sub>3</sub>Te<sub>7</sub>(CN)<sub>6</sub>]<sup>2-</sup>. Crystal structures of double salts Cs<sub>3.5</sub>K{[W<sub>3</sub>Te<sub>7</sub>(CN)<sub>6</sub>]Br}Br<sub>1.5</sub>·4.5H<sub>2</sub>O (<b>1</b>), Cs<sub>2</sub>K<sub>4</sub>{[W<sub>3</sub>Te<sub>7</sub>(CN)<sub>6</sub>]<sub>2</sub>Cl}Cl·5H<sub>2</sub>O (<b>2</b>), and (Ph<sub>4</sub>P)<sub>3</sub>{[W<sub>3</sub>Te<sub>7</sub>(CN)<sub>6</sub>]Br}·H<sub>2</sub>O (<b>3</b>) reveal short Te<sub>2</sub>···X (X = Cl, Br) contacts. Reaction of polymeric Mo<sub>3</sub>Se<sub>7</sub>Br<sub>4</sub> with KNCSe melt gives [Mo<sub>3</sub>Se<sub>7</sub>(CN)<sub>6</sub>]<sup>2-</sup>. Reactions of polymeric Mo<sub>3</sub>S<sub>7</sub>Br<sub>4</sub> and Mo<sub>3</sub>Te<sub>7</sub>I<sub>4</sub> with KNCSe melt (200−220 °C) all give as final product [Mo<sub>3</sub>Se<sub>7</sub>(CN)<sub>6</sub>]<sup>2-</sup> via intermediate formation of [Mo<sub>3</sub>S<sub>4</sub>Se<sub>3</sub>(CN)<sub>6</sub>]<sup>2-</sup>/[Mo<sub>3</sub>SSe<sub>6</sub>(CN)<sub>6</sub>]<sup>2-</sup> and of [Mo<sub>3</sub>Te<sub>4</sub>Se<sub>3</sub>(CN)<sub>6</sub>]<sup>2-</sup>, respectively, as was shown by ESI-MS. (NH<sub>4</sub>)<sub>1.5</sub>K<sub>3</sub>{[Mo<sub>3</sub>Se<sub>7</sub>(CN)<sub>6</sub>]I}I<sub>1.5</sub>·4.5H<sub>2</sub>O (<b>4</b>) was isolated and structurally characterized. Reactions of W<sub>3</sub>Q<sub>7</sub>Br<sub>4</sub> (Q = S, Se) with KNCSe lead to [W<sub>3</sub>Q<sub>4</sub>(CN)<sub>9</sub>]<sup>5-</sup>. Heating W<sub>3</sub>Te<sub>7</sub>Br<sub>4</sub> in KCNSe melt gives a complicated mixture of W<sub>3</sub>Q<sub>7</sub> and W<sub>3</sub>Q<sub>4</sub> derivatives, as was shown by ESI-MS, from which Ê<sub>3</sub>[W<sub>3</sub>(μ<sub>3</sub>-Te)(μ-TeSe)<sub>3</sub>(CN)<sub>6</sub>]Br·6H<sub>2</sub>O (<b>5</b>) and K<sub>5</sub>[W<sub>3</sub>(μ<sub>3</sub>-Te)(μ-Se)<sub>3</sub>(CN)<sub>9</sub>] (<b>6</b>) were isolated. X-ray analysis of <b>5</b> reveals the presence of a new TeSe<sup>2-</sup> ligand. The complexes were characterized by IR, Raman, electronic, and <sup>77</sup>Se and <sup>125</sup>Te NMR spectra and by ESI mass spectrometry.