Five new cobalt(II) and copper(II)-1,2,4,5-benzenetetracarboxylate supramolecular architectures: syntheses, structures, and magnetic properties
Résumé
1,2,4,5-Benzenetetracarboxylic acid (H4btec) and a combination of N-donor coligands, such as 4-aminopyridine (4-apy), pyrazine (pyz), 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), and 4,4'-bipyridine (4,4'-bipy) with transition metal ions Co(II) and Cu(II), give rise to five coordination complexes namely, [{Co(H2btec)(H2O)4}·4-apy·(H2O)2]n(1), [{Cu(btec)(4-apy)2}·(4-Hapy)2·(H2O)4]n(2), [{Cu(H3btec)2(pyz)·(H2O)2}·H2O]n (3), [Co(tptz)(H2O)2(H2btec)]·(H2O)2(4), and [{Co2(4,4'-bipy)2(H2O)8}·(btec)·(H2O)2]n(5). All these complexes form supramolecular frameworks through ligand-based hydrogen bonding interactions. They have been characterized by a combination of analytical, spectroscopic, and crystallographic methods. These highly crystalline complexes have been obtained under different pH conditions at room temperature and the btec binding mode differs in these five complexes. Complex 1 is a one-dimensional (1D) layered solid consisting of alternating neutral metal-organic coordination polymeric chains, [Co(H2btec)(H2O)4]n, and amines whereas the molecular structure of 2 is made up of alternating layers of anionic [Cu(btec)(4-apy)2]2-n coordination polymers and 4-apy cations (4-Hapy). In both 1 and 2, btec links the metal centers. Complex 3 is composed of zigzag 1D copper chains, and complex 4 is a mononuclear cobalt complex. In both 3 and 4, btec binds as a monodentate ligand. In the crystal structure of 5, btec4- is present unbound in the lattice and linked to 1D chains of [Co(4,4'-bipy)(H2O)4]2+ through strong hydrogen bonding interactions. The magnetic properties of the polymers were investigated in the temperature range 300-2 K. The values for the spin coupling constant J were estimated to be -0.60, -0.50, -0.79, and -5.72 cm-1 for 1-3 and 5, respectively, indicative of antiferromagnetic interactions.