Syntheses, crystal structures, spectral and thermal analysis and biological activities of copper(II)-pyridine-2,5-dicarboxylate complexes with 4-methylimidazole, imidazole, and 3,4-dimethylpyridine

In this study, three novel Cu(II)-pyridine-2,5-dicarboxylate (pydc) complexes with 4-methylimidazole (4-Meim), [Cu(pydc)(H2O)(4-Meim)(2)]center dot H2O (1), imidazole (im), {[Cu(mu-pydc)(im)(2)]center dot 2H(2)O}(n) (2), and 3,4-dimethylpyridine (dmpy), [Cu(mu-pydc)(H2O)(dmpy)](n) (3) have been synthesized. Elemental and thermal analyses, magnetic susceptibilities, IR and UV/vis spectroscopic studies have been performed to chatacterize the complexes. The molecular structures of mononuclear (1) and polynuclear (2 and 3) complexes have been determined by the single crystal X-ray diffraction technique. In 1 and 2, Cu(II) ions have distorted square planer geometry, while 3 has distorted octahedral coordination. The pyridine-2,5-dicarboxylate exhibits three different coordination modes namely bidentate (1), tridentate (2) and tetradentate (3). The complex I is further constructed to form three-dimensional framework by hydrogen bonding, C-H center dot center dot center dot pi and pi center dot center dot center dot pi stacking interactions. The adjacent chains of 2 and 3 are then mutually linked via hydrogen bonding, pi center dot center dot center dot pi and C-H center dot center dot center dot pi interactions, which are further assembled to form three-dimensional framework. 1 exhibits the magnetic moment value of 1.70 BM, which corresponds to one of the unpaired electron, while the polynuclear complexes 2 and 3 exhibit 1.58 and 1.46 BM, which is lower than the spin only value for one unpaired electron, indicates to anti ferromagnetic effect. The first thermal decomposition process of all the complexes is endothermic dehydration. This stage is followed by partial (or complete) decomposition of the neutral and pydc ligands. In the later stage, the remained organic residue exothermically burns. The final decomposition products which identified by IR spectroscopy were the CuO. (C) 2009 Elsevier Masson SAS. All rights reserved.