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

## TL;DR

This paper reports the synthesis and characterization of new rhenium cluster complexes with substituted phenylacetylide ligands and explores how these substitutions affect their electrochemical and optical properties.

## Contribution

The study introduces new [Re6Se8]2+ cluster complexes with para-substituted phenylacetylide ligands and reveals unique substituent effects on their spectroscopic and electrochemical behavior.

## Key findings

- The Hammett parameter σp correlates with the [Re6Se8]3+/2+ redox couple, showing substituent effects on electrochemistry.
- The reversibility of the oxidative process is influenced by the nature of the para-substituent.
- Substituents affect photophysical properties, but the emission trend is opposite to that seen in benzonitrile ligand studies.

## Abstract

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.