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-benzimidazolylmethyl)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 "opened" 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)(NO(2))(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 "opened" 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&onemacr;; a = 13.388(2) Å, b = 14.427(2) Å, c = 17.595(3) Å; alpha = 79.13(1) degrees, beta = 83.28(2) degrees, gamma = 66.02(2) degrees; V = 3046.3(8) Å(3); Z = 4; R1 = 0.0786, wR2 = 0.2063 for reflections of I > 2sigma(I). [Mn(II)(ntb)(OAc)]Cl.0.5MeOH.3.25H(2)O, 2: triclinic space group P&onemacr;; a = 13.308(1) Å, b = 14.689(2) Å, c = 18.335(2) Å; alpha = 75.48(1) degrees, beta = 79.21(1) degrees, gamma = 62.99(1) degrees; V = 3195.7(6) Å(3); Z = 4; R1 = 0.0899, wR2 = 0.2594 for reflections of I > 2sigma(I). [Mn(II)(ntb)(NO(2))(2)].4MeOH, 3: monoclinic space group P2(1)/n; a = 14.484(14) Å, b = 15.454(14) Å, c = 14.925(11) Å; beta = 114.86(6) degrees; V = 3031(5) Å(3); Z = 4; R1 = 0.0748, wR2 = 0.1614 for reflections of I > 2sigma(I).