One-dimensional oxalato-bridged copper(II) complexes with 3-hydroxypyridine and 2-amino-4-methylpyridine

Two new one-dimensional oxalato-bridged copper(II) compounds of formula [Cu(ox)L-2](n) (1) and {[Cu-2(ox)(2)L'(3)].L'}(n) (2) [ox = oxalate dianion, L = 3-hydroxypyridine (pyOH) and L' = 2-amino-4-methylpyridine (ampy)] have been synthesized and characterized by FT-IR spectroscopy, variable-temperature magnetic measurements and single-crystal X-ray diffraction. The crystal structure of 1 comprises chains of copper atoms in which cis-[Cu(pyOH)(2)](2+) units are sequentially bridged by asymmetric bis-bidentate oxalato ligands with an intrachain copper-copper separation of 5.548(1) Angstrom. Each copper atom is six-coordinated: four oxygen atoms belonging to two bridging oxalato ligands and two nitrogen atoms from two 3-hydroxypyridine ligands build a distorted octahedral environment around the metal atom. As in 1, the structure of compound 2 is made up of chains of copper atoms bridged sequentially by bis-bidentate oxalato ligands. Two types of copper(II) ion, one being six-coordinated (Cu(1)) and the other five-coordinated (Cu(2)), alternate regularly within the chain. The environment around Cu(1) is elongated octahedral with two cis-coordinated pyridine-nitrogen and two oxygen atoms from two oxalate ligands building the equatorial plane, the apical positions being filled by two oxalate-oxygen atoms. The environment around Cu(2) is distorted square pyramidal with four oxalato-oxygen atoms in the basal plane, and the pyridine nitrogen atom from one aromatic base in the apical position. Magnetic susceptibility data in the temperature range 2.0-300 K reveal regular ferromagnetic (J = +1.3 cm(-1)) and alternating antiferromagnetic (J = -66.6 cm(-1), alphaJ = -58.6 cm(-1)) chain behaviours for 1 and 2. The nature and magnitude of the magnetic coupling through the oxalato bridge in 1 and 2 are analysed and discussed in the light of the available structural data. (C) 2001 Elsevier Science B.V. All rights reserved.