From cubane-assembled Mn-oxo clusters to monodispersed manganese oxide colloidal nanocrystals

The assemblies of [M₄O₄] (M = metal) cubanes represent a fascinating class of materials for a variety of application fields. Although such a structural characteristic is relatively common in small molecules and in extended bulk solids, high nuclearity clusters composed of multiple [M₄O₄] units as their backbones are rare. In this work, we report two new Mn-oxo clusters, Mn^II ₈Mn^III ₁₀O₁₀(OOCMe)₁₂(OMe)₁₄(py)₂ ([Mn₁₈-Ac]) and Mn^II ₄Mn^III ₁₄O₁₄(OOCCMe₃)₈(OMe)₁₄(MeOH)₅(py) ([Mn₁₈-Piv]), whose core structures are assemblies of either 6- or 7-cubanes in different packing patterns, which have been unambiguously revealed by single crystal X-ray diffraction technique. The cubane-assembled structural features can be deemed as the embryonic structures of the bulk manganese oxide. Herein, this report demonstrates the first case study of utilizing Mn-oxo clusters as precursors for the preparation of manganese oxide nanocrystals, which has never been explored before. Through a simple colloidal synthetic approach, high-quality, monodisperse Mn₃O₄ nanocrystals can be readily prepared by employing both precursors, while their morphologies were found to be quite different. This work confirms that the structural similarity between precursors and nanomaterials is instrumental in affording more kinetically efficient pathways for materials formation, and the structure of the precursor has a significant impact on the morphology of final nanocrystal products.