Beta-diketonate complexes of first row transition metals have been investigated for many years. Due to the wide variety of possible oxidation states, manganese is an interesting metal center in coordination chemistry and there are many reports on acetylacetonate complexes in the literature. For the most part only the readily available beta-diketonate ligands with alkyl substituents have been used, in some cases also the 1,3-diphenyl-1,3-propanedionato ligand, but rarely the sterically very demanding 1,3-bis(2,4,6-trimethylphenyl)propane-1,3-dionato (mesacac) ligand. Recently the surprising effects of that ligand on the electronic structure of the resulting metal complexes was found in photophysical research. Therefore we became interested in the effect of the mesacac ligand on the electronic structure of a manganese complex. We were able to synthesize and characterize the previously unknown manganese(III) mesitylacetylacetonato complex. The solid state structure of the complex unequivocally confirmed the geometry proposed by DFT calculations. The strong Jahn-Teller distortion as predicted for the high spin structure is very obvious from the experimentally determined bond lengths. The predicted high-spin electronic structure was confirmed by measurements in a SQUID-magnetometer, a magnetic moment of 4.5 μB was experimentally found on the metal center.

Synthesis and characterization of an octahedral mesityl-substituted manganese(III) acetylacetonate complex [Mn(mesacac)3]

ACS Spring 2022

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