Ligand-Driven Electrochemical Tuning of Co6Se8 Chevrel Clusters

Molecular “Chevrel-type” clusters of the formula Co6Se8L6 (L = neutral ligand) are a well-studied class of clusters due to their utility as molecular analogues to the Chevrel extended solid phase and their application as subunits in hierarchical materials. However, their solution and optical properties remain relatively underexplored. Aiming to develop the fundamental relationships between the molecular and electronic structures of these clusters and their electrochemical and photophysical properties, this work reports the preparation of a series of Co6Se8(P(C6H4R)3)6-type clusters with R = Cl (1), F (2), H (3), CH3 (4), and OCH3 (5) via a stepwise synthetic approach. Solution and solid-state experimental characterization and density functional theory calculations reveal that the Co6Se8 cores of 1–5 maintain consistent electronic and structural properties despite the variation of the triarylphosphine ligand para-substituent Hammett parameters (σp). However, cyclic voltammetry measurements indicate that the electron transfer energetics of 1–5 are strongly influenced by ligand substitution, with the E1/2 of a given redox event spanning ∼0.5 V depending on the triarylphosphine ligand’s σp. These findings support the characterization of Co6Se8 clusters as atomically precise nanoclusters with both the structural robustness and the electrochemical tunability needed to act as components in larger charge transfer assemblies.