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 Cs_3.5K{[W₃Te₇(CN)₆]Br}Br_1.5·4.5H₂O (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}I_1.5·4.5H₂O (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 TeSe^2- ligand. The complexes were characterized by IR, Raman, electronic, and ⁷⁷Se and ¹²⁵Te NMR spectra and by ESI mass spectrometry.