Electronic structure and mechanistic understanding of electrochemical H2 evolving activity of metal-bis(dithiolenes)

Abstract

Dithiolenes are a unique class of non-innocent ligands known for their ligand-centered redox activity and ability to stabilize multiple oxidation states. Their electronic properties can be fine-tuned by varying the metal center, making metal-dithiolene complexes particularly versatile. This review focuses on the electronic structure of dithiolene complexes of first-row transition metals, highlighting their redox behavior and bonding characteristics. These insights are critical for designing systems with targeted electronic properties. In the context of clean energy, metal-dithiolene complexes have gained attention as electrocatalysts, particularly for the hydrogen evolution reaction (HER), a vital component of water splitting. These complexes, along with 1D, 2D, and 3D metal-organic frameworks (MOFs) or coordination polymers (CPs) incorporating dithiolenes, have demonstrated significant HER activity in both organic and aqueous media. We discuss key studies exploring their performance and delve into mechanistic insights that reveal how these materials facilitate hydrogen generation. Despite recent advances, the field faces challenges such as understanding the long-term stability of these systems, optimizing their activity under practical conditions, and exploring their scalability for industrial applications, as well as efforts to increase the conductivity of the standalone materials.