Topological analysis of electron density for M-M Metal Bond Clusters (Fe, Ru)

The electron density and multicentre bonding in hexanuclear metal carbide carbonyl clusters is a subject of great controversy within the organometallic community. Closed shell highly reduced metals rarely obey the two-centre rule and so required a more sophisticated description. This paper details a real space description of the bonding in the two extremely stable clusters Fe₆C(CO)₁₇-3 and Ru₆C(CO)₁₇-3, which consist of a hexa-metal centre surrounded by a central carbide and stabilized by a very tight compact shell of carbonyls. These compounds, bearing a charge of −3, show extreme stability despite great distances between the charges in the clusters. Beyond their fundamental importance in understanding multicentre metal bonding, hexanuclear metal carbide carbonyl clusters may provide valuable insights for the development of metal-based therapeutic agents. In particular, ruthenium carbonyl systems have attracted attention due to their potential biological activity and their relevance in the design of carbon monoxide releasing molecules (CORMs), which are being explored for anti-inflammatory and cytoprotective applications. These electronic differences suggest distinct biomedical potentials. The localized electronic structure of the Fe₆ cluster may favor its use in stable drug delivery systems, while the higher electron delocalization in the Ru₆ cluster may enhance interactions with biological targets, supporting potential applications as anticancer and antimicrobial agents. Additionally, the presence of carbonyl ligands indicates their possible use as CO-releasing molecules (CORMs) with anti-inflammatory activity.