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

Abstract

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.

Keywords: Jahn-Teller distorsion; X-ray structure; density functional calculations; magnetism; manganese (III) high-spin.