Cocrystallized Mixtures and Multiple Geometries: Syntheses, Structures, and NMR Spectroscopy of the Re6 Clusters [NMe4]4[Re6(Te8-nSen)(CN)6] (n = 0−8)

Abstract

The mixed tellurium/selenium Re6 clusters [NMe4]4[Re6(Te8-nSen)(CN)6] (n = 0−8) have been prepared from the reactions of Re6Te15 with the appropriate stoichiometry of NaCN and Se at 600 °C, followed by cation exchange with NMe4Br. A typical anion comprises an Re6 octahedron with its eight faces capped by μ3-chalcogen atoms to form a pseudocube, and each Re atom has a terminal cyanide ligand. These anions have essentially idealized cubic symmetry. In the [Re6Te8(CN)6]4- anion, Re−Re bond distances range from 2.673(1) to 2.690(1) Å and Re−(μ3-Te) distances range from 2.683(1) to 2.705(1) Å. In the [Re6Se8(CN)6]4- anion the Re−Re and Re−(μ3-Se) distances range from 2.622(2) to 2.638(2) Å and 2.520(3) to 2.550(3) Å, respectively. The “[Re6Te4.34Se3.66(CN)6]4-” anion, with disordered Se/Te positions, displays intermediate bond distances with Re−Re distances ranging from 2.653(1) to 2.665(1) Å and Re−(μ3-Q) (Q = Se, Te) distances ranging from 2.581(1) to 2.673(1) Å. Whereas single-crystal X-ray diffraction results provide the barest indication of the complicated nature of the mixed Te/Se crystalline products, NMR spectroscopy indicates that they comprise cations and mixtures of geometric isomers of [Re6(Te8-nSen)(CN)6]4- anions (125Te NMR (δ, ppm): [NMe4]4[Re6Te8(CN)6], −1112; [NMe4]4[Re6Te7Se(CN)6], ≥10 peaks, −643 to −1231; [NMe4]4[Re6Te4Se4(CN)6], ≥18 peaks, −705 to −1234; [NMe4]4[Re6TeSe7(CN)6], ≥12 peaks, −648 to −1114. 77Se NMR (δ, ppm): [NMe4]4[Re6TeSe7(CN)6], ≥8 peaks, 928 to 966; [NMe4]4[Re6Se8(CN)6]·31/3H2O, 933).