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 Cu^II ions. In 2, mononuclear Cu^II 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.