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The study analyzes bonding interactions in tetra‑manganese carbonyl clusters with chalcogen bridges E 2 Mn 4 (CO) 12 2− (E = S, Se, and Te) using electron density ( ρ b ) and electron localization function (ELF) techniques. The results reveal that the tellurium-bridged cluster (Cluster 3 ) exhibits a localized Mn Mn bond with low electron density (0.212 eÅ −3 ), characterized by distinct bond critical points (BCPs) and bond paths. In contrast, sulfur-bridged (Cluster 1 ) and selenium-bridged (Cluster 2 ) clusters lack these BCPs and paths. The adaptive natural density partitioning (AdNDP) analysis shows localized seven 6c–2e bonds in all three clusters, each with well-defined electron occupancy. In contrast, the delocalization index (DI) reveals more delocalized bonding interactions, indicating 6-center–10-electron interactions in clusters 1 and 2 , and a 6-center–11-electron interaction in cluster 3 . By combining AdNDP and DI, we gain a comprehensive understanding of the bonding, highlighting the importance of bridging atoms in stabilizing the nanocluster cores and enhancing electron delocalization. Source function analysis indicates that tellurium atoms contribute significantly to electron density at Mn Mn bonds, while carbonyl ligand atoms contribute minimally. Delocalization indices δ(Mn…O CO ) confirm the presence of strong π-back donation involving the carbonyl ligands and manganese centers in all clusters. The study highlights the role of bridging atoms and carbonyl groups in shaping transition metal bonding across the chalcogen series. • Quantum Chemical Analysis: ELF and ρb topologies clarify Mn–Mn bonding in chalcogen-bridged clusters. • Metal-Metal Bonding: Te-bridged cluster exhibits the weakest Mn–Mn bond (ρb = 0.212 eÅ⁻³). • Bridging Atom Effect: Bridging atoms modulate electron density and Mn–Mn bond characteristics. • Delocalization: 6c–10e and 6c–11e interactions confirmed for S/Se and Te clusters. • CO Ligand: π-back-donation from CO ligands stabilizes Mn–Mn interactions.
Hassan et al. (Mon,) studied this question.