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

Four new organometallic [Re₆Se₈]²⁺-based cluster complexes containing <i>para</i>-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 σ_p and the [Re₆Se₈]^3+/2+ couple. The reversibility of this oxidative process is also significantly impacted by the nature of the <i>para</i>-substituent. The photophysical properties of these phenylacetylide cluster complexes (including <i>cis</i>- and <i>trans</i>-[Re₆Se₈(PEt₃)₄(CC-C₆H₅)₂]) in solution and in the powder-phase are reported. Our findings confirm <i>para</i>-substituent effects on emission; however, the trend is opposite to that found in previous studies involving [Re₆Se₈]²⁺ clusters containing <i>para</i>-substituted benzonitrile ligands.