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

Abstract

Two Schiff bases, N-[(pyridin-2-yl)formylidene]benzylamine (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⁻, 2; 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…O hydrogen bond, π…π and C-H…π interactions. The complexes 1-4 exhibit d-d transition and n-π*/π-π* charge transfer transition. Electrochemical electron transfer study reveals copper(II)-copper(I) reduction in methanolic solutions. High-energy intraligand ¹(π-π*) fluorescence at room temperature and intraligand 3(π-π*) phosphorescence in glassy solutions (MeOH at 77 K) and in solid states are seen in all the complexes.