Syntheses of terpyridine-pyridylbenzothiazole linked ditopic ligands and their copper(II) complexes

Abstract

New binary ligands consisting of 2,2′:6′,2″-terpyridine and 2-(2-pyridyl)benzothiazole linked with polymethylene chains of various lengths (3a-d, n = 4–11, where n is the number of CH2 units) were synthesized. Cu(II) complexes of these ligands with both CuLCl2 (4a-d) and CuL2ClO4 (5a-d) composition were also synthesized. Single crystals of the chloride complex 4b and perchlorate complex 5b were obtained, and their crystal structures were determined using X-ray diffraction. Both compounds are mononuclear Cu(II) coordination compounds with five-coordinate distorted tetragonal pyramidal geometry in the chloride complex and six-coordinate octahedral geometry in the perchlorate complex. Only terpyridine moieties coordinate with the copper ion, while pyridylbenzothiazole fragments do not participate in the coordination. Cyclic voltammograms of complexes 4 and 5 showed a Cu(II) → Cu(I) reduction at approximately −0.15 V; the observed oxidation and reduction potentials were almost identical for complexes with (CH2)4 and (CH2)11 linkers. Complex 5b, based on cyclic voltammetry data, could be turned into a heteronuclear Rh(III)–Cu(II) complex by treatment with [S-(11-(4-([2,2′:6′,2″-terpyridin]-4′-yl)phenoxy)undecyl)ethanethioate]rhodium(III) trichloride.