Synthesis and characterization of a series of N3O-ligated mononuclear Mn(II) halide complexes

Treatment of a N3O-donor chelate ligand (mpppa = N-methyl-N-((6-pivaloylamido-2-pyridyl)methyl)-N-(2-pyridylethyl)amine; bpppa = N-benzyl-N-((6-pivaloylamido-2-pyridyl)methyl)-N-(2-pyridylmethyl)amine) with equimolar amounts of Mn(ClO4)2 · 6H2O and Me4NX (X = Cl, Br, I) in methanol resulted in the production of a series of mononuclear Mn(II) halide complexes of the formula [(L)Mn-X(CH3OH)]ClO4 (L = mpppa or bpppa). X-ray crystallographic studies of [(mpppa)Mn-Cl(CH3OH)]ClO4 · CH3OH (2 · CH3OH), [(mpppa)Mn-Br(CH3OH)]ClO4 · CH3OH (4 · CH3OH), [(mpppa)Mn-I(CH3OH)]ClO4 · CH3OH (6 · CH3OH), and [(bpppa)Mn-I(CH3OH)]ClO4 · O2(CH2CH3)2 (7 · O(CH2CH3)2) revealed for each a mononuclear Mn(II) center having tetradentate coordination of the chelate ligand, one coordinated halide anion, and one molecule of coordinated methanol. An increase in the Mn-X distance through the halide series (Cl, Br, I) correlates linearly with the increase in the radius of the anion. The magnetic moment of each halide complex, measured via Evans method in methanol, is consistent with the presence of a high-spin distorted octahedral Mn(II) center. The EPR features of the halide complexes in methanol do not change as a function of the nature of the halide coordinated to the Mn(II) center.