Tripodal ligands: Design of distorted coordination polyhedra in biomimetic metal complexes. Crystal structures of [Zn(SCN)(ntb)](SCN) · iPrpOH and [Fe(acac)(ntb)](ClO4)2 · 2 CH2Cl2 · iPrpOH, ntb = N-tris(2-benzimidazolylmethyl)amine

Article abstract of DOI:10.1002/zaac.19966220221

The tripodal ligand N-tris(2-benzimidazolylmethyl)amine (ntb) was used for the preparation of zinc(II) and iron(III) complexes, [Zn(SCN)(ntb)](SCN) · ⁱPrpOH (1) and [Fe(acac)(ntb)](ClO₄)₂ · 2 CH₂Cl₂ · ⁱPrpOH (2). 1 has a highly distorted trigonal-bipyramidal ZnN₅ coordination geometry. The donor atoms are nitrogens of one amine, three benzimidazoles and one SCN^-. A striking feature of the complex is the length of the Zn-N_amine bond of 2.539(6) A. The octahedral N₄O₂ coordination sphere of the iron in 2 is less distorted than that of the zinc in 1. The metal is surrounded by an amine and three benzimidazole nitrogens of the ligand and two oxygens of the bidentate acetylacetonate co-ligand. The Fe-O bond lengths differ by about 0.1 A. As for the unusual long Zn-N bond in 1 this is a result of a trans effect. 1 crystallizes in the space group P1 with: a = 9.530(1) A, b = 13.402(1) A, c = 13.578(2) A, α = 98.83(1), β = 95.19(1), γ = 101.21(1)°, Z = 2; 2 is also triclinic, space group P1, with: a = 9.875(6) A, b = 12.929(10) A, c = 18.635(15) A, α = 94.95(8)°, β = 101.01(6)°, γ = 111.09(4)°, Z = 2. Johann Ambrosius Barth 1996.