Coordination Polymers of Ni(II) with Thiophene Ligands: Synthesis, Structures, and Magnetic Properties

Two new metal-organic frameworks [Ni(btdc)(bipy)(H2O)(2)] (I) and [Ni(azobipy)(H2O)(4)](btdc) (II) (H(2)btdc is 2,2'-bithiophene-5,5'-dicarboxylic acid, bipy is 4,4'-bipyridyl, and azobipy is 4,4'-azobipyridyl) are synthesized under the solvatothermal conditions. The structures and compositions of the compounds are determined by single-crystal X-ray structure analysis (CIF files CCDC nos. 2068945 (I) and 2068946 (II)) and confirmed by X-ray diffraction, elemental, and thermogravimetric analyses and IR spectroscopy. The structure of compound I is a rare example for mutual interlacing of the network motifs in two independent directions. Compound II is ionic and consists of the alternating cationic [Ni(azobipy)(H2O)(4)](2+) and anionic btdc(2-) fragments. The magnetic susceptibility and effective magnetic moment are measured for compound I in a temperature range of 1.77-300 K in the magnetic fields up to 10 kOe. The value of mu(eff) is 3.08 mu(B) at 300 K, which is close to the spin-only value for the isolated high-spin Ni2+ ion with S = 1 (2.83 mu(B)) with allowance for the orbital moment contribution. Weak antiferromagnetic interactions are observed between the Ni2+ ions at the temperatures T < 10 K.