Discrete μ₄-Oxido Mn(II) Clusters with Controlled Nuclearity: On-Demand Synthesis, Molecular and Self-Assembled Structures

Discrete heterovalent manganese-oxido clusters are widely used as building blocks and precursors of modern functional materials, such as molecular magnets, polyoxometalates (POMs), metal-oxide nanocrystals, and metal-organic frameworks (MOFs). While access to various heterovalent Mn-(II)/Mn-(III) oxido clusters is well established, the rational synthesis of similar compounds composed exclusively of Mn-(II) centers remains a significant challenge. Herein, we present an on-demand synthesis of homovalent [Mn₄ ^II(μ₄-O)-L₆]-type clusters via a transmetalation/hydrolysis approach. Interestingly, by tuning the coordination properties of selected model organic ligands, we achieved control over the nuclearity of the resulting manganese oxide clusters, leading to the formation of either tetranuclear [Mn₄(μ₄-O)-(L^NN)₆] or octanuclear [Mn₄(μ₄-O)-(L^ON)₆]₂ clusters, depending on the use of <i>N</i>,<i>N</i>'- or <i>O</i>,<i>N</i>-bidentate ligands, respectively. Furthermore, a detailed analysis of the supramolecular structures of these new complexes, in comparison with selected examples of widely studied zinc-oxido clusters and to a lesser extent with Co-(II) and Fe-(II) analogues, provided deeper insight into the factors controlling solvation and noncovalent interaction-driven self-assembly.