Assembling giant heterometallic cyclic coordination clusters {MnII 2LnIII 2} n (n = 6 and 8) for efficient photocatalytic hydrogen production.

Heterometallic Mn-rare earth metal clusters with exceptional catalytic activity remain scarcely explored. Herein, two nanosized oxo/alkoxo-bridged cyclic coordination clusters (CCCs), namely {Mn12Ln12} and {Mn16Ln16}, were successfully isolated. These elegant supramolecular aggregates represent rare examples of Mn(ii)-containing 3d-4f clusters, as Mn(ii) ions are highly susceptible to aerial oxidation under alkaline conditions. Notably, {Mn16Ln16} constitutes the largest such cluster reported to date in terms of nuclearity. Interestingly, both CCCs are composed of repetitive {Mn2Ln2O4} structural units, and their structures have certain similarities to some characteristics of the cubic {CaMn4O5} oxygen-evolving center in photosystem II. Crucially, these clusters exhibit excellent stability in solvents and function as highly efficient homogeneous photocatalysts for H2 production. Specifically, {Mn12Gd12} achieves an outstanding photocatalytic hydrogen production rate of 2778 µmol g-1 h-1, surpassing that of many reported covalent organic frameworks (COFs) and precious-metal-free inorganic photocatalysts. This superior catalytic performance stems from its suitable energy levels, high charge-transfer efficiency, and abundance of active oxygen sites. This work offers new mechanistic insights and design principles for the rational development of highly active manganese-cluster-based photocatalysts.