Electronic Structure and Magnetic Properties of a High‐Spin Mn(III) Complex: [Mn(mesacac)(3)] (mesacac=1,3‐Bis(2,4,6‐trimethylphenyl)‐propane‐1,3‐dionato)

Metal acetylacetonates of the general formula [M(acac)(3)] (M(III)=Cr, Mn, Fe, Co) are among the best investigated coordination compounds. Many of these first‐row transition metal complexes are known to have unique electronic properties. Independently, photophysical research with different β‐diketonate ligands pointed towards the possibility of a special effect of the 2,4,6‐trimethylphenyl substituted acetylacetonate (mesacac) on the electron distribution between ligand and metal (MLCT). We therefore synthesized and fully characterized the previously unknown octahedral title complex. Its solid‐state structure shows a Jahn‐Teller elongation with two Mn−O bonds of 2.12/2.15 Å and four Mn−O bonds of 1.93 Å. Thermogravimetric data show a thermal stability up to 270 °C. High‐resolution mass spectroscopy helped to identify the decomposition pathways. The electronic state and spin configuration of manganese were characterized with a focus on its magnetic properties by measurement of the magnetic susceptibility and triple‐zeta density functional theory (DFT) calculations. The high‐spin state of manganese was confirmed by the determination of an effective magnetic moment of 4.85 μ(B) for the manganese center.