Cluster Core Controlled Reactions of Substitution of Terminal Bromide Ligands by Triphenylphosphine in Octahedral Rhenium Chalcobromide Complexes

Reactions of rhenium chalcobromides Cs₄[{Re₆(µ₃-S)₈}Br₆]^.2H₂O, Cs₃[{Re₆(µ₃-Se)₈}Br₆]^.2H₂O, Cs₃[{Re₆(µ₃-Q)₇(µ₃-Br)}Br₆]^.H₂O (Q) S, Se), and K₂[{Re₆(µ₃-S)₆(µ₃-Br)₂}Br₆] with molten triphenylphosphine (PPh₃) have resulted in a family of novel molecular hybrid inorganic-organic cluster compounds. Six octahedral rhenium cluster complexes containing PPh₃ ligands with general formula [{Re₆(µ₃-Q)_8-n(µ₃-Br)_n}(PPh₃)_4-nBr_n+2] (Q ) S, n ) 0, 1, 2; Q ) Se, n ) 0, 1) have been synthesized and characterized by X-ray single-crystal diffraction and elemental analyses, ³¹P{¹H} NMR, luminescent measurements, and quantum-chemical calculations. It was found that the number of terminal PPh₃ ligands in the complexes is controlled by the composition and consequently by the charge of the cluster core {Re₆Q_8-nBr_n}ⁿ⁺². In crystal structures of the complexes with mixed chalcogen/bromine ligands in the cluster core all positions of a cube [Q_8-nBr_n] are ordered and occupied exclusively by Q or Br atoms. Luminescence characteristics of the compounds trans-[{Re₆Q₈}(PPh₃)₄Br₂] and fac-[{Re₆Se₇Br}(PPh₃)₃Br₃] (Q ) S, Se) have been investigated in CH₂Cl₂ solution and the broad emission spectra in the range of 600-850 nm were observed.