Synthesis of a tetradentate piperazine ligand and a structural study of its coordination compounds

A tetradentate ligand N,N'-bis(2-pyridylmethyl)piperazine (L1) and seven structures of its transition metal coordination compounds are described. Most of the compounds an of the general formula [M(L1)(NO3)(2)], with M=Cu2+, Co2+, Mn2+ and Cd2+. Ln addition, a dimeric copper(II) compound, [Cu-2(L1)(Ac)(4)](H2O)(3), and polymeric silver(I) compounds, [Ag(L1)](n)(NO3)(n)(EtOH)(n) and [Ag(L1)](n)(SO3CF3)(n), were formed. The overall structure of L1 in the metal complexes A-G varies with the size and electronic properties of the metal ions. Mononuclear complex A is a five-coordinated, B is a six-coordinated, and C and D are eight-coordinated metal complexes. The dinuclear Cu complex, E, is four-coordinated, as are the polymeric Ag complexes, F and G. The polymeric Ag complexes contain meso-helical subunits and the anions are clathrated between the metal-ligand strands. (C) 1999 Elsevier Science Ltd. All rights reserved.