Di-2-pyridyl ketone-based ligands as evergreen “trees” in the “forest” of manganese chemistry: Mononuclear Mn(III) complexes from the use of MnF3

Abstract The syntheses, crystal and electronic structures are reported of three new mononuclear Mn(III) complexes with the formulae [Mn{(py)2C(OMe)(O)}2(MeOH)2](PF6) (1), [Mn{(py)2C(OMe)(O)}2](PF6) (2) and [Mn{(py)2C(OMe)(O)}2](ClO4) (3), where (py)2C(OMe)(O)− is the monoanion of the hemiacetal form of di-2-pyridyl ketone, (py)2CO. They were obtained from the reactions of (py)2CO with MnF3 in the presence of (NH4)PF6 (1, 2) or NaClO4 (3) in refluxing MeOH. The complex cations are centrosymmetric pseudo-octahedral with a rhombic arrangement of the donor atoms; the anion (py)2C(OMe)(O)− behaves as a N,O-bidentate chelating (η1:η1) ligand in 1 and as a N,O,N-tridentate chelating (η1:η1:η1) ligand in 2 and 3. The 3D architectures of 1–3 are characterized by hydrogen-bonded chains of the cations surrounded by columns of the counterions and are formed through an extensive network of cation–anion hydrogen bonds. The three compounds are the first structurally characterized Mn(III) complexes with (py)2CO-based ligation. Variable-temperature magnetic susceptibility, magnetization isotherms and X-band EPR spectra of 1 and 2 reveal high-spin MnIII atoms (S = 2), anisotropy effects and a positive value of ~ +4 cm−1 of the zero--field splitting parameter D; moreover, EPR spectroscopy indicates the contribution of rhombic and/or higher order terms.