Rhenium Chalcogenide Clusters Containing para-Substituted Phenylacetylide Ligands: Synthesis, Characterization, and Investigation of Substituent Effects on Spectroscopic and Electrochemical Properties

Four new organometallic [Re6Se8]2+-based cluster complexes containing para-substituted phenylacetylide ligands, [Re6Se8(PEt3)5(C≡C–C6H4–X)](SbF6) where X = NO2, CO2Me, CH3, and OMe, have been synthesized and fully characterized using 1H, 13C{1H} and 31P{1H} NMR, IR, and UV–vis spectroscopy, HRMS, and elemental analysis. Three of these cluster complexes, [Re6Se8(PEt3)5(C≡C–C6H4–NO2)]+, [Re6Se8(PEt3)5(C≡C–C6H4–CO2Me)]+, and [Re6Se8(PEt3)5(C≡C–C6H4–CH3)]+ were also characterized via single-crystal X-ray diffraction. Electrochemical studies of these newly reported complexes, as well as the unsubstituted phenylacetylide complex, [Re6Se8(PEt3)5(C≡C–C6H5)](SbF6), reveal a correlation between the Hammett parameter σp and the [Re6Se8]3+/2+ couple. The reversibility of this oxidative process is also significantly impacted by the nature of the para-substituent. The photophysical properties of these phenylacetylide cluster complexes (including cis- and trans-[Re6Se8(PEt3)4(C≡C–C6H5)2]) in solution and in the powder-phase are reported. Our findings confirm para-substituent effects on emission; however, the trend is opposite to that found in previous studies involving [Re6Se8]2+ clusters containing para-substituted benzonitrile ligands.