Multicenter bonding as key to the kagome halides and other correlated cluster materials

Correlated electron materials based on transition metal clusters in a solid, including trimer kagome halides (Nb₃Cl₈, Nb₃Br₈) and higher-order cluster compounds (lacunar spinels, Chevrel phases), exhibit exotic phenomena including quantum spin liquid behavior, 2D multiferroicity, and novel device functionalities (e.g., Josephson diodes, unconventional transistors). Despite growing interest, bonding within these materials remains poorly understood. Here, we apply electron localization function (ELF) topological analysis to probe their electronic structure and bonding. We show that these systems are characterized by multicenter bonding, deviating from conventional ionic or covalent models of correlated electron materials. A key signature is the presence of interstitial electron basins, indicating that anionic charge is transferred not to individual metal centers but to shared cluster sites. This highlights the unique nature of the electronic structure in this broader materials’ family and provides new guidelines for materials’ design.