Syntheses and characterizations of copper(II) polymeric complexes constructed from 1,2,4,5-benzenetetracarboxylic acid

Four polymeric complexes with rectangular grids or channels, [Cu-2(btec)(H2O)(4).2H(2)O](n) (2), [Cu-2(btec)(4/4){Cu(Hbtec)(2/2)-(4,4'-Hbpy)(H2O)(2)}(2).4H(2)O](n) (3), [Cu-2(btec)(hmt)(H2O)(4).8H(2)O](n) (4), and [Cu-3(btec)(OH)(2)](n) (5), were designed and constructed from Cu(II) ion and 1,2,4,5-benzenetetracarboxylic acid along with auxiliary ligands (where H(4)btec = 1,2,4,5-benzenetetracarboxylic acid, 4,4'-Hbpy = monoprotonated 4,4'-bipyridine, and hmt = hexamethylenetetramine). Complexes 2, 3, and 4 have rectangular pores with the size of 6.5 Angstrom x 4.5 Angstrom, 6 Angstrom x 7 Angstrom, and 10.1 Angstrom x 11.8 Angstrom, respectively, while 5 has a channel of 7.4 Angstrom x 9.6 Angstrom. The complexes show interesting magnetic properties due to the different coordination modes of the carboxylate groups and the presence of auxiliary ligands. On lowering the temperature, the magnetic interactions in 2 are changed from antiferromagnetic to ferromagnetic. For 3, the antiferromagnetic interactions weaken sharply at low temperature. Complex 4 shows ferromagnetic interactions while 5 is antiferromagnetic.