Synthesis and Reactivity of W₃Te₇⁴⁺ Clusters and Chalcogen Exchange in the M₃Q₇ (M = Mo, W; Q = S, Se, Te) Cluster Family

Heating WTe2, Te, and Br2 at 390 °C followed by extraction with KCN gives [W3Te7(CN)6]2-. Crystal structures of double salts Cs3.5K{[W3Te7(CN)6]Br}Br1.5·4.5H2O (1), Cs2K4{[W3Te7(CN)6]2Cl}Cl·5H2O (2), and (Ph4P)3{[W3Te7(CN)6]Br}·H2O (3) reveal short Te2···X (X = Cl, Br) contacts. Reaction of polymeric Mo3Se7Br4 with KNCSe melt gives [Mo3Se7(CN)6]2-. Reactions of polymeric Mo3S7Br4 and Mo3Te7I4 with KNCSe melt (200−220 °C) all give as final product [Mo3Se7(CN)6]2- via intermediate formation of [Mo3S4Se3(CN)6]2-/[Mo3SSe6(CN)6]2- and of [Mo3Te4Se3(CN)6]2-, respectively, as was shown by ESI-MS. (NH4)1.5K3{[Mo3Se7(CN)6]I}I1.5·4.5H2O (4) was isolated and structurally characterized. Reactions of W3Q7Br4 (Q = S, Se) with KNCSe lead to [W3Q4(CN)9]5-. Heating W3Te7Br4 in KCNSe melt gives a complicated mixture of W3Q7 and W3Q4 derivatives, as was shown by ESI-MS, from which Ê3[W3(μ3-Te)(μ-TeSe)3(CN)6]Br·6H2O (5) and K5[W3(μ3-Te)(μ-Se)3(CN)9] (6) were isolated. X-ray analysis of 5 reveals the presence of a new TeSe2- ligand. The complexes were characterized by IR, Raman, electronic, and 77Se and 125Te NMR spectra and by ESI mass spectrometry.