Synthesis and coordinating properties of the functionalized macrocyclic ligand 1,4-bis(1-methylimidazol-2-ylmethyl)-7-carboxymethyl-1,4,7-triazacyclononane. Crystal structures of cobalt(III), nickel(II) and zinc(II) complexes

Abstract

The synthesis of the new unsymmetrically derivatized macrocycle 1,4-bis(1-methylimidazol-2-ylmethyl)-7-carboxymethyl-1,4,7-triazacyclononane (LH) is reported. The potentially hexadentate ligand yields cobalt(III), nickel(II) and zinc(II) complexes of formulae COL (PF 6) 2 ( 1), NiLPF 6 · CH 3OH ( 2) and ZnLClO 4 · H 2O ( 3), which have been isolated in the solid state and characterized. The nickel complex is remarkably stable towards ligand dissociation in water solution even in the presence of a large excess of CN −. The structures of the complexes have been determined by single-crystal X-ray analyses. Compound 1 crystallizes in the triclinic space group P1, a = 7.397(2), b = 10.960(4), c = 17.420(5) Å, α=101.51(3), β = 91.85(4), γ = 98.24(3)°, Z = 2. Compound 2 is monoclinic P2 1/ a, a = 14.094(15), b = 11.045(4), c = 16.905(5) Å, β = 105.54(7)°, Z = 4; 3 is triclinic P1, a = 7.903(4), b = 9.218(5), c = 16.996(10) Å, α = 98.51(6), β = 96.76(8), γ = 101.98(7)°, Z = 2. In each complex cation the metal atom is six-coordinated, being surrounded by the three macrocycle nitrogens, the two imidazole nitrogens and one carboxylate oxygen atom, with a coordination geometry which is approximately trigonal antiprismatic in 1 and 2 and trigonal prismatic in 3.