Copper(II), iron(II), and manganese(II) complexes of 2-methyl-2-(2-pyridinyl)-1,3-propanediamine

Abstract

Copper(II), iron(II), and manganese(II) complexes of 2-methyl-2-(2-pyridinyl)-1,3-propanediamine (ppda) were synthesized and characterized. The reaction of copper(II), iron(II), or manganese(II) salts with ppda yields complexes [Cu(ppda)Cl2] (1), [Cu(ppda)2](OTf)2 (2), [Fe(ppda)2](OTf)2 (3), and [Mn(ppda)2](OTf)2 (4). Complex 1 is square pyramidal with one molecule of ppda coordinated in a tridentate fashion with the amine N atoms and with chlorido ligands in the basal plane, and the pyridyl N atom in the axial position. Six-coordinate, C2-symmetrical complex 2 contains two ppda ligands with the pyridyl rings from two separate ppda ligands cis to each other in a tetragonally compressed square bipyramidal structure. The axial amine Cu–N bond distances are about 0.2Å shorter than the equatorial bonds. Solution EPR spectra of 2 at 77 and 298K display typical axial signals suggesting a tetragonally elongated structure in solution. Librational disorder of the solid state structure points to crystal packing disorder in the solid state that leads to the slight axial compression, while the molecular structure in solution is the more typical dx2-y2 ground state of an axially elongated structure. Complexes 3 and 4 are isostructural with 2 in terms of the disposition of the two ppda ligands. However, the bond distances for 3 are all very similar to each other (2.00±0.04Å), and for 4 they are even more alike (2.25±0.01Å).