New Mn(III) complexes with tetradentate cis-N₂O₂, acacen-type ligands. Synthesis and characterization, single-crystal X-ray diffraction and DFT studies

One of the challenges of manganese(III) magnetochemistry is the design and synthesis of new building block systems to study and develop molecular magnets. In this context, two new Mn(III) complexes were synthesized using new tetradentate cis-N₂O₂ acacen ligands from the condensation of 1-anisyl-1,3-butanedione and 1,2-diaminoethane (2:1 ratio). All compounds were fully characterized by conventional spectroscopic techniques, such as FT-IR, HRMS, and UV–Vis, and rationalized with DFT and TD-DFT studies. The resulting cationic complexes were composed of N₄O₂ coordination spheres using a tetradentate ligand (N₂O₂²⁻) in the equatorial plane and two axial pyridines with general formulae as [Mn^III(L)(Py)₂](X) (X = BF₄⁻; ClO₄⁻). Single-crystal X-ray diffraction revealed that both complexes are isostructural with typical axial anisotropy due to the Jahn-Teller effect by tetragonal distortion. A complete analysis of the crystalline structures revealed a nonclassical intermolecular interaction of C[sbnd]H···F and C[sbnd]H···O. Supported by Hirshfeld surfaces and 2D- fingerprint plots, it was possible to isolate and calculate the contribution of intermolecular interactions in the supramolecular arrangement. For both complexes, the magnetic susceptibility confirmed a high spin state (HS) with 4.8 µ_B and 4.9 µ_B related to the spin-only contribution to the magnetic moment.