Coordination polymers built from Cu(II) and pyrazine-2,3,5,6-tetracarboxyl ate or pyridine-2,4,6-tricarboxylate: Structural and magnetic studies

摘要

Room temperature reaction of Cu(NO3)(2)center dot 6H(2)O and pyrazine-2,3,5,6-tetracarboxylic acid (ptecH(4)) in the presence of pyridine (py) in water-methanol (1:1) mixture results in the formation of {[Cu-2(ptec)(.)(py)(2)(.)(H2O)(3)](.)4H(2)O}(n) (1). With pyridine-2,4,6-tricarboxylic acid (pytcH(3)) and Cu(NO3)(2)(.)6H(2)O, crystals of {[Cu(pytc)](.)1/2[Cu(H2O)6](H2O)-H-.}(N) (2) could be obtained hydrothermally at 180 degrees C. The structure of 1 consists of 2D polymeric sheets. These sheets are stacked on top of one another due to strong C-H...pi interactions forming an overall 3D structure. The structure of 2, on the other hand, consists of twin-chain coordination polymers. The void spaces between two polymeric chains are occupied by [Cu(H2O)(6)](2+) ions which are H-bonded to the polymeric chains. The variable temperature magnetic measurements for 1 and 2 show weak antiferromagnetic interaction between Cu(II) centers. The EPR spectra of the compounds are consistent with their structures. (c) 2005 Elsevier B.V. All rights reserved.