Synthesis, crystal structure and magnetic properties of a one-dimensional Mn²⁺ complex constructed from (+)-dibenzoyltartaric acid and 2,2'-bipyridine

The self-assembly reaction of (+)-dibenzoyltartaric acid (D-H₂DBTA) with 2,2'-bipyridine (bpy) and Mn(CH₃CO₂)₂·4H₂O yielded a new coordination polymer, namely, catena-poly[[[diaqua(2,2'-bipyridine-κ²N,N')manganese(II)]-μ-2,3-bis(benzoyloxy)butanedioato-κ²O²:O³] dihydrate], {[Mn(C₁₈H₁₂O₈)(C₁₀H₈N₂)(H₂O)₂]·2H₂O}_n or {[Mn(DBTA)(bpy)(H₂O)₂]·2H₂O}_n, (I). Complex (I) has been characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis (TGA) and single-crystal and powder X-ray diffraction. It crystallizes in the orthorhombic space group P2₁2₁2₁. In the complex, the Mn²⁺ cation displays a distorted octahedral {MnO₄N₂} geometry, formed from two carboxylate O atoms of two DBTA^2- ligands, two cis-oriented N atoms from one chelating 2,2'-bipyridine ligand and two trans-oriented O atoms from coordinated water molecules. The polymer displays a 1D chain with an Mn...Mn distance of 9.428 (1) Å. Due to the presence of flexible polycarboxylate and rigid bipyridyl ligands in the molecular structure, a high thermal stability of the complex is attained. The magnetic properties of (I) were analyzed based on the mononuclear Mn²⁺ model due to the long intramolecular Mn...Mn distance. The zero field splitting (ZFS) contribution in the high-spin Mn²⁺ cation is almost negligible and there are weak antiferromagnetic couplings between 1D chains [zJ' = -0.062 (5) cm^-1], corresponding to an intermolecular Mn...Mn distance of 7.860 (2) Å.