Triple M as Manganese: Medicine, magnetism and macrocycles. Seven-coordinate Mn(II) complexes with pyridine-based macrocyclic ligands
Abstrakt
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)].CH3OH (1), [Mn(py(2)-L(diProp))] (ClO4)(2).0.5CH(3)CN .0.35H2O (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 Å.