Synthesis, crystal structure and properties of manganese(II) complexes with the tripod ligand tris(2-benzimidazylmethyl) amine and α,β-unsaturated carboxylates

Two new ternary complexes of manganese(II) with tris(2-benzimidazylmethyl) amine (ntb), and two different alpha,beta-unsaturated carboxylates, {[Mn(ntb)(acrylate)](ClO4)}(2)(.)(H2O)(.)3(CH3OH) (1) and {[Mn(ntb)(alpha-methacrylate)](ClO4)}(2)(.)(H2O)(.)2(CH3OH)(2), have been synthesized and characterized by means of elemental analyses, thermal analyses, IR, UV and single crystal X-ray diffraction. In the two complexes, ntb functions as a tripodal tetradentate ligand, resulting in trigonal pyramidal geometry. In each complex, an additional ligand, acrylate anion, or alpha-methacrylate anion, is coordinated at the opened site trans to the apical nitrogen atom of the ntb ligand. The crystal structure of 1 shows two crystallographically independent but chemically identical [Mn(ntb)(acrylate)](+) cations. In 2, the crystal structure shows two crystallographically independent and chemically different [Mn(ntb)(a-methacrylate)](+) cations. Cyclic voltammograms of the manganese complexes indicate a quasireversible Mn3+/Mn2+ couple. The X-band EPR spectrum of the complexes exhibits a six-line manganese hyperfine pattern with g 2, A 97 (1) and 93G (2). The spectrum confirms that the material is high-spin Mn(II).