Proton conduction and long-range ferrimagnetic ordering in two isostructural Copper(II) mesoxalate metal-organic frameworks.

Two compounds of formula {(H3O)[Cu7(Hmesox)5(H2O)7]·9H2O}n (1a) and {(NH4)0.6(H3O)0.4[Cu7(Hmesox)5(H2O)7]·11H2O}n (1b) were prepared and structurally characterized by single-crystal X-ray diffraction (H4mesox = mesoxalic acid, 2-dihydroxymalonic acid). The compounds are crystalline functional metal-organic 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 Tc 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 × 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.