Understanding the function of Mn ions in biological and chemical redox catalysis requires precise knowledge of their electronic structure. X-ray emission spectroscopy (XES) is an emerging technique with growing application to biological and biomimetic systems. Here, we report an improved, cost-effective spec-trometer used to analyze two biomimetic coordination compounds: [MnIV(OH)2(Me2EBC)]2+ and [MnIV(O)(OH)(Me2EBC)]+, the second of which contains a key MnIV=O structural fragment. Despite having the same formal oxidation state (MnIV) and tetradentate ligands, XES spectra from these two compounds demonstrate different electronic structures. Experimental measurements and DFT calculations show differ-ent localized spin densities for the two complexes resulting from MnIV-OH conversion to MnIV=O. The rele-vance of the observed spectroscopic changes is discussed for applications in analyzing complex biological systems such as photosystem II. A model of the S3 intermediate state of photosystem II containing a MnIV=O fragment is compared to recent time-resolved x-ray diffraction data of the same state.