Synthesis, structural characterization, photoluminescence and thermal properties of [(Ph₃P)₂cu(μ-SeC{O}R)₂Cu (PPh₃)]

A number of neutral unsymmetrical dimers [(Ph₃P)₂Cu(μ-SeC{O}R)₂Cu (PPh₃)] (R = C₆H₅ (1), C₆H₄-Me-4 (2), C₆H₄-OMe-4 (3), C₆H₄-Cl-4 (4), C₆H₄-F-4 (5) and CH₃ (6)) were synthesized in moderate yield, and characterized by analytical and spectroscopic techniques including ³¹P NMR. Variable temperature ³¹P NMR experiments appear to indicate that the molecular structure is retained in solution. X-Ray structure determination of 2 and 6 confirmed the molecular geometry of the unsymmetrical dimer. In 2 the two 4-MeO-C₆H₄C=O groups have anti stereochemistry with respect to the Cu₂Se₂ ring while MeC=O groups have syn configuration in 6. A weak C-H⋯O=C intramolecular hydrogen bond present between the two selenoacetato ligands appears to dictate the syn geometry in 6. This hydrogen bonding is also responsible for the non-planarity of the Cu₂Se₂ ring. These compounds are photoemissive in CH₂Cl₂ solution. Thermogravimetry and pyrolysis experiments in nitrogen atmosphere show that 1-6 are good single source precursors to copper selenide bulk materials. Preliminary experiments show that these compounds are good single source molecular precursors for cubic phase Cu_2-xSe nanoparticles with an average size of 75 ± 15 nm.