Homo- and hetero-metallic manganese citrate complexes: Syntheses, crystal structures and magnetic properties

A series of Mn citrate coordination polymers [NaMn(Hcit)](n) (1, H(4)Cit = citric acid), [MnCa2(Hcit)(2)(H2O)(4)](n) (2), [{Mn(Hcit)(H2O)(2)}(2)Mn(H2O)(4)](n) (3) and [{Mn(Hcit)(H2O)(2)}(2)Mn(H2O)(2)](n) (4) have been synthesized by the solvothermal method and the conventional solvent method. 1 and 2 represent novel examples of bimetallic Mn citrate complexes with 3-D architectures. In the structure of 1, Mn(mu-O)(3)Na and Mn(mu-O)(mu-OCO)Na units are alternately fused via edge-sharing to form Mn...Na...Mn chains and the citrate trianion links between the chains by terminal carboxylate groups. In the structure of 2 the Ca ions are correlated by carboxylate bridges to create a two-dimensional Ca-citrate layer at the a-c face and the Mn(II) ions form a helix chain along the a axis by carboxylate bridges. Each citrate trianion links 9 and 8 hetero-metal ions in 1 or 2, respectively, through component carboxylate and hydroxyl groups. In 3 and 4 both the Mn(Hcit)(H2O)(2) units are coupled to form centrosymmetrical dimer units, which construct the one-dimensional chain structure of 3 and the 3D network architecture of 4. Infrared spectra and the magnetic properties are also discussed, being associated with the bridging coordination mode of the carboxylate group. (c) 2005 Elsevier Ltd. All rights reserved.