Synthesis and structural characterization of five-, six-, and seven-coordinate manganese(II) complexes of the tripodal ligand tris(2-benzimidazolylmethyl)amine

Abstract

A series of manganese(II) tris(2-benzimidazolyImethyl)amine (ntb) complexes were synthesized and characterized. In these complexes, ntb functions. as a tripodal tetradentate ligand, resulting in trigonal pyramidal geometry. The complexes have five- to seven-coordinate manganese(II) ions depending on the additional ligand used. In each complex, an additional ligand, chloride anion, acetate anion, or nitrite anion, is coordinated at the &apos;&apos;opened&apos;&apos; site trans to the apical tertiary nitrogen atom of the ntb ligand. Complex 1, Mn-II(ntb)Cl]Cl, has trigonal bipyramidal geometry. This geometry, corresponding to the active-site geometry of native manganese superoxide dismutase, was easily constructed using ntb as a tetradentate ligand and chloride as a monodentate ligand. Complex 2, [Mn-II(ntb)(OAc)]Cl, was synthesized using ntb as a tetradentate ligand and acetate as a chelating bidentate ligand. The seven-coordinate complex [Mn-II(ntb)(NO2)(2)], 3, was also synthesized using ntb as a tetradentate ligand and nitrites as both monodentate and bidentate ligands. In each case, up to three donor atoms could be accommodated by the &apos;&apos;opened&apos;&apos; site without significant disturbance to the trigonal pyramidal portion of the complex. Crystal data are as follows. [Mn-II(ntb)Cl]Cl . 2.5MeOH, 1: triclinic space group <P(1)over bar>; a = 13.388(2) Angstrom, b = 14.427(2) Angstrom, c = 17.595(3) Angstrom; alpha = 79.13(1)degrees, beta = 83.28(2)degrees, gamma = 66.02(2)degrees; V = 3046.3(8) Angstrom(3); Z = 4; R1 = 0.0786, wR2 = 0.2063 for reflections of I > 2 sigma(I). [Mn-II(ntb)(OAc)]Cl . 0.5MeOH . 3.25H(2)O, 2: triclinic space group <P(1)over bar>; a = 13.308(1) Angstrom, b = 14.689(2) Angstrom, c = 18.335(2) Angstrom; alpha = 75.48(1)degrees, beta = 79.21(1)degrees, gamma = 62.99(1)degrees; V = 3195.7(6) Angstrom(3); Z = 4; R1 = 0.0899, wR2 = 0.2594 for reflections of I > 2 sigma(I). Mn-II(ntb)(NO2)(2)]. 4MeOH, 3: monoclinic space group P2(1)/n; a = 14.484(14) Angstrom, b = 15.454(14) Angstrom, c = 14.925(11) Angstrom; beta = 114.86(6)degrees; V = 3031(5) Angstrom(3); Z = 4; R1 = 0.0748, wR2 = 0.1614 for reflections of I > 2 sigma(I)