The role of acid in the formation of hydrogen-bonded networks featuring 4,4′-dicarboxy-2,2′-bipyridine (H2dcbp): Synthesis, structural and magnetic characterisation of {[Cu(H2dcbp)Cl2]·H2O}2and [Cu(H2dcbp)(NO3)2(H2O)

Abstract

Reported herein are the synthesis, structural and magnetic characterisation of two hydrogen-bonded networks featuring the 4,4′-dicarboxy-2,2′-bipyridine (H2dcbp) ligand: {[Cu(H2dcbp)(Cl)2]·H2O}2 1 and [Cu(H2dcbp)(NO3)2(H2O)] 2. Compounds 1 and 2 result from the reaction of CuCl2 and Cu(NO3)2, respectively, with H2dcbp under hydrothermal conditions in the presence of either HCl or HNO3. The acid ensures that H2dcbp remains protonated and provides the anions required for charge balance irrespective of Cu(II) precursor. Within 1 and 2 the H2dcbp ligand performs a dual role of Cu(II) coordination, via the 2,2′-bipyridine moiety, and propagates the formation of chains through hydrogen-bonding involving the peripheral 4,4′-dicarboxylic acid functionalities. Additional hydrogen bonding between the 4,4′-dicarboxylic acid groups, metal bound chloride and nitrate anions, in 1 and 2 respectively, and water molecules generate 3D networks. Variable temperature magnetic susceptibility measurements reveal very weak antiferromagnetic coupling between the Cu(II) centres across the chloride bridges in 1 (J = −3.02 cm−1).