Proton Conduction and Long-Range Ferrimagnetic Ordering in Two Isostructural Copper(II) Mesoxalate Metal-Organic Frameworks

Two compounds of formula {(H3O)[Cu-7(Hmesox)(5)(H2O)(7)].9H(2)O}(n) (<bold>1a</bold>) and {(NH4)(0).(6)(H3O)(0).(4)[Cu-7(Hmesox)(5)(H2O)(7)].11H(2)O}(n) (<bold>1b</bold>) were prepared and structurally characterized by single-crystal x-ray diffraction (H(4)mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are crystalline functional metalorganic frameworks exhibiting proton conduction and magnetic ordering. Variable-temperature magnetic susceptibility measurements reveal that the copper(II) ions are strongly ferro- and antiferromagnetically coupled by the alkoxide and carboxylate bridges of the mesoxalate linker to yield long-range magnetic ordering with a T-c of 17.6 K, which is reached by a rare mechanism known as topologic ferrimagnetism. Electric conductivity, measured by impedance methods, shows values as high as 6.5 x 10(-5) S cm(-1) and occurs by proton exchange among the hydronium/ammonium and water molecules of crystallization, which fill the voids left by the three-dimensional copper(II) mesoxalate anionic network.