Synthesis, structure and luminescence behaviour of copper(II)cyanato complexes containing bidentate N-donor Schiff bases

Two Schiff bases, N-[(pyridin-2-yl)formylidenelbenzylamine (pfba) and N-[(pyridin-2-yl)benzylidene]benzylamine (pbba) have been prepared and used to synthesize four pentacoordinated copper(II)cyanato complexes of type [Cu(L)(2)(NCO)X (1-4) [L = pfba, X = ClO4- 1; L = pfba, X = PF6-, 4; L = pbba, X = ClO4-, 3; L = pbba, X = PF6- ,4]. The complexes have been characterized on the basis of microanalytical, spectroscopic, magnetic, electrochemical and other physicochemical properties. Structure of [Cu(pbba)(2)(NCO)]ClO4 (3) has been solved by X-ray diffraction measurement. Structural analysis reveals that the copper(II) centre in 3 has a distorted trigonal bipyramidal geometry with a CuN5 chromophore coordinated through four N atoms of two bidentate pbba units and one N atom of terminal cyanate. 3 forms a one-dimensional chain through C-H... 0 hydrogen bond, pi...pi and C-H... pi interactions. The complexes 1-4 exhibit d-d transition and n-pi*/pi-pi* charge transfer transition. Electrochemical electron transfer study reveals copper(II)-copper(I) reduction in methanolic solutions. High-energy intraligand (1)(pi-pi*) fluorescence at room temperature and intraligand (3)(pi-pi*) phosphorescence in glassy solutions (MeOH at 77 K) and in solid states are seen in all the complexes.