Oxo-bridged manganese polynuclear complexes have applications in a variety of technologies, such as single-molecule nanomagnets, catalysis and photosynthetic redox chemistry. The reason that these types of compounds are capable of such important and varied technologies is thought to be because they possess ground states with large spin values. However, the electronic, structural and magnetochemical relationships are not well understood and need to be thoroughly investigated to adequately explain why Mn is such an integral part of so many useful processes. X-ray photoemission spectroscopy was used to study the Mn 3p, 3s and valence band electronic behavior as a function of Mn cluster structural properties, where the cluster size and nuclearity are systematically varied. Results show a chemical shift of the Mn 3p3/2,1/2 spin-orbit pair related to the cluster size and nuclearity. Also, the Mn 3s 7S and 5S final state multiplet components shift since they involve the binding energy of a ligand valence electron. In addition, the branching ratio of the 7S:5S states is related to the 3s–3d electron correlation. Specifically, in the 7S state, the remaining 3s electron is well correlated with 3d electrons of parallel spin, while in the 5S state the two spins are antiparallel. Changes in this electron correlation are clearly observed in the 7S:5S branching ratio as a function of cluster size and ligand electronegativity.