Triple M as Manganese: Medicine, magnetism and macrocycles. Seven-coordinate Mn(II) complexes with pyridine-based macrocyclic ligands

Manganese, or more accurately manganese(II) complexes, are extensively used in various scientific and research fields. In this work, we present the preparation and characterization of three manganese(II) complexes with three structurally-new pyridine-based macrocyclic ligands, which differ from each other by functional group in pendant arms. The ligands' backbone consists of a parental 17-membered macrocycle (L-diProp) containing pyridine and piperazine rings, which are part of the macrocyclic scaffold. The original aliphatic NH groups in L-diProp were successively substituted with three different pendant arms - benzyl (bn(2)-L-diProp), 2-pyridylmethyl (py(2)-L-diProp) and 2-aminoethyl ((NH(2)et)(2)-L-diProp). A series of manganese(II) complexes with structural formulas [Mn(bn(2)-L-diProp)Cl-2]center dot CH3OH (1), [Mn(py(2)-L-diProp)] (ClO4)(2)center dot 0.5CH(3)CN center dot 0.35H(2)O (2) and [Mn((NH(2)et)(2)-L-diProp)](ClO4)(2) (3) were subsequently prepared. In all cases, the presence of coordination number seven with a close to pentagonal bipyramid geometry was confirmed by X-ray diffraction analysis. The axial positions were occupied by chlorido coligands (1) or nitrogen atoms of the pendant arms (2 and 3). The pentagonal bipyramidal coordination sphere was distorted in case of all complexes 1-3 and axially compressed for 2 and 3. The equatorial Mn-N-aliphatic bond distances were significantly lengthened up to 2.61 angstrom. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

In this work, the preparation and characterization of three manganese(II) complexes with structurally-new pyridine-based macrocyclic ligands are presented. X-ray diffraction analysis confirmed a coordination number seven with a close to pentagonal bipyramid geometry for all complexes studied.