Cocrystallized Mixtures and Multiple Geometries: Syntheses, Structures, and NMR Spectroscopy of the Re 6 Clusters [NMe 4 ] 4 [Re 6 (Te 8 - n Se n )(CN) 6 ] ( n = 0−8)

The mixed tellurium/selenium Re 6 clusters [NMe 4 ] 4 [Re 6 (Te 8 - n Se n )(CN) 6 ] ( n = 0−8) have been prepared from the reactions of Re 6 Te 15 with the appropriate stoichiometry of NaCN and Se at 600 °C, followed by cation exchange with NMe 4 Br. A typical anion comprises an Re 6 octahedron with its eight faces capped by μ 3 -chalcogen atoms to form a pseudocube, and each Re atom has a terminal cyanide ligand. These anions have essentially idealized cubic symmetry. In the [Re 6 Te 8 (CN) 6 ] 4 - anion, Re−Re bond distances range from 2.673(1) to 2.690(1) Å and Re−(μ 3 -Te) distances range from 2.683(1) to 2.705(1) Å. In the [Re 6 Se 8 (CN) 6 ] 4 - anion the Re−Re and Re−(μ 3 -Se) distances range from 2.622(2) to 2.638(2) Å and 2.520(3) to 2.550(3) Å, respectively. The “[Re 6 Te 4.34 Se 3.66 (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−(μ 3 -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 [Re 6 (Te 8 - n Se n )(CN) 6 ] 4 - anions ( 125 Te NMR (δ, ppm): [NMe 4 ] 4 [Re 6 Te 8 (CN) 6 ], −1112; [NMe 4 ] 4 [Re 6 Te 7 Se(CN) 6 ], ≥10 peaks, −643 to −1231; [NMe 4 ] 4 [Re 6 Te 4 Se 4 (CN) 6 ], ≥18 peaks, −705 to −1234; [NMe 4 ] 4 [Re 6 TeSe 7 (CN) 6 ], ≥12 peaks, −648 to −1114. 77 Se NMR (δ, ppm): [NMe 4 ] 4 [Re 6 TeSe 7 (CN) 6 ], ≥8 peaks, 928 to 966; [NMe 4 ] 4 [Re 6 Se 8 (CN) 6 ]·3 1 / 3 H 2 O, 933).