Synthesis and chromotropism study of a copper complexes containinghemilabile tridentate and pseudo halide ligands

There is an interesting interchange between oxygen and nitrogen binding of amide group to metal ions in coordination compounds. Metal ions have tendency to interact onlyweakly with the oxygen atom of the carbonyl moiety of the amide group but it is strengthened if it is attached to an anchoring group with coordinating atom(s) so that achelate ring can form that stabilizes the resultant complex due to chelate effect. However, the deprotonated amide nitrogen is a much stronger metal binding site; a condition that turn into more favorable at higher pH. Using appropriate metal ion, this phenomenon appears with distinct color change due to change in ligand field strength around the metal ion [1]. The reversible change in color of a substance under differing physical or chemical conditions such as pH and solvent, temperature, ion is called chromotropism [2]. In this work we prepared two copper(II) complexes with the general formula of [Cu(L)(X)](ClO4), where L =3-((pyridin-2ylmethyl)amino)propanamide, X= N3 -, SCN-were synthesized and characterized by elemental analyses, IR, UV-Vis spectroscopy techniques, molar conductance measurements and X-ray crystal analysis. The chromotropism (halo-, solvato- and ionochromism) of both complexes were studied using visible absorption spectroscopy. The complexes are found to be soluble in water and organic solvents and displayed reversible halochromism due to the flexible and sensitive nature of the amide group with changing pH values (Scheme 1). The complexes were ionochromic and exhibited high-sensitive and selective towards CN- and N3 - anions in presence of other halide and pseudo-halide ions.