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).

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