Properties and structural characterization of copper(II) mixed complexes with 2,2′:6′,2″-terpyridyl and iminodiacetate or pyridine-2,6-dicarboxylate

Abstract

The crystal structure and a visible optical and e.s.r. spectroscopic study of the two mixed complexes of copper(II), [Cu(terpy)(pydca)](1) and [Cu(terpy)(ida)](2)(pydca = pyridine-2,6-dicarboxylate, ida = iminodiacetate, and terpy = 2,2′:6′,2″ terpyridyl) are reported. Crystals of (1) are triclinic, space group P, with a= 10.964(7), b= 13.209(8), c= 9.724(6)Å, α= 98.3(1), β= 112.9(1), γ= 102.2(1)°, and R= 0.041. Crystals of (2) are monoclinic, space group P2₁/n, with a= 23.41 (1), b= 10.538(7), c= 8.372(6)Å, β= 91.3(1)°, and R= 0.044. Complex (1) consists of [Cu(terpy)(pydca)] units linked together by water molecules. The copper atom is co-ordinated by terpy and pydca units which act as tridentate ligands in a distorted octahedral environment. The e.s.r. and visible spectra indicate that the solid-state stereochemistry is preserved in solution. In crystals of (2) Cu(terpy) units are bridged by ida units which act as unidentate ligands. The polymeric configuration in (2) is similar to that found for the analogous [Cu(terpy)(tda)](tda = thiodiacetate). The copper atom is found to be in a distorted trigonal-bipyramidal geometry. It is significant that this stereochemistry is not preserved in solution. In fact the frozen solution e.s.r. (130 K) and visible absorption spectra of (2) agree with a six-co-ordinated environment about the copper(II) ion.