A tridentate insitu generated ligand that directs the self-assembly of a transition metal complex: Synthesis and structural characterization of cis-dichloro[1-(2-aminoethyl)biguanide]copper(II) monohydrate

One mononuclear penta-coordinated Cu(II) complex, [CuLCl2] · H2O (1), where L is a tridentate ligand H2N–(CH2)2–NC(NH2)–NH–C(NH2)NH [=1-(2-aminoethyl)biguanide], has been synthesized and characterized crystallographically. In an attempt to prepare bis(ethylenediamine)bis(biguanide)Cu(II), it resulted in a different product, [CuLCl2] · H2O (1), where Cu(II) was found to occupy the base of a square pyramid formed by N3Cl2 coordination. The ligand L is believed to be generated in situ in presence of Cu(II), since neither L can be prepared independently nor it can be removed from complex 1. Similar attempts with Ni(II) Co(II), Zn(II), Fe(II) or Fe(III) salts failed, and we conclude that Cu(II) acted as a template for the formation of 1. The solid-state structure of 1 is interesting because one monomeric unit, i.e. [CuLCl2] self-recognizes other monomeric unit centrosymmetrically to form a supramolecular dimer through N–H···Cl hydrogen bonding. The single lattice water molecule played an important role in the formation of 2D supramolecular sheets involving these dimers and become an integral part of such self-assembled structure. The EPR spectrum of complex 1 in the frozen state is consistent with a typical monomeric tetragonal Cu(II) environment. Electrochemical study of 1 in aqueous medium showed an irreversible reductive response at –0.65 V versus SCE, which can be assigned to CuII/CuI redox couple.

A tridentate ligand that can be prepared insitu in the presence of Cu(II) leads to an interesting crystalline solid. The single lattice water molecule played an important role in the formation of 2D supramolecular sheets and become an integral part of such self-assembled structure.Figure optionsDownload as PowerPoint slide