Synthesis, structures, and magnetic properties of four copper compounds with 2,2′-dinitrobiphenyl-4,4′-dicarboxylate

Four copper(II) coordination polymers of 2,2′-dinitrobiphenyl-4,4′-dicarboxylic acid (H2dnbpdc), with or without 4,4′-bipyridyl (bipy) as co-ligand, were synthesized under hydrothermal conditions and characterized crystallographically and magnetically. They are formulated as [Cu2(dnbpdc)(OH)2]n (1), [Cu(Hdnbpdc)2(bipy)]n·2nH2O (2), [Cu2(dnbpdc)2(bipy)(H2O)2]n·2nH2O (3) and [Cu3(dnbpdc)2(bipy)(OH)2(H2O)]n·nH2O (4). Compound 1 exhibits a 2D coordination network, in which infinite [Cu(μ-OH)(μ-COO)]n chains are linked by the backbones of the dnbpdc2− ligands. Magnetic studies indicated antiferromagnetic coupling through the mixed hydroxo and carboxylate bridges between CuII ions. In 2, mononuclear CuII centers are linked by Hdnbpdc− and bipy ligands into 2D grid-like layers. Compound 3 also consists of 2D grid-like coordination layers, which however are based on aqua-bridged Cu2(μ-OH2)2 units. Magnetic studies showed that the magnetic coupling through the double aqua bridges is antiferromagnetic. Compound 4 exhibits a 3D framework in which [Cu(OH)(COO)]n chains are linked by bipy and dnbpdc2− ligands. The chain has a complicated bridging network involving μ3-OH, μ2-OH and μ-COO, and magnetic studies revealed overall antiferromagnetic interactions within the chain.