From mono- and dinuclear to polynuclear cobalt(II) and cobalt(III) coordination compounds based on o-phthalic acid and 2,2′-bipyridine:: Synthesis, crystal structures, and properties

The reaction of o-phthalic acid (H(2)Pht) and 2,2'-bipyridine (bpy) with cobalt(II) carbonate at different temperatures results in the isolation of three types of new cobalt(II) and cobalt(III) compounds. The mononuclear cobalt(III) complex [Co(CO3)(bpy)(2)](2)(Pht)-16H(2)O (1) is obtained when the reaction is run at 60 degrees C. Crystallographic analysis revealed that 1 contains two crystallographically independent [Co(CO3 (bpy)2](+) cations, a Pht(2-) anion, and sixteen solvate water molecules. The latter form a wall of channels with the oxygen atoms of the carboxylate groups of the Pht2- anions, which are occupied by pairs of cations. Increasing the temperature of the reaction to 80 degrees C leads to the formation of the open dinuclear cobalt(II) complex [(bpy)(2)Co(Pht)H(Pht)Co(bpy)(2)]-(HPht)(H(2)Pht)center dot 2H(2)O (2), which crystallizes in two polymorphic modifications 2a and 2b. Compound 2a consists of a centrosymmetric dinuclear [(bPY)(2)CO(Pht)H(Pht)Co(bPY)(2)](+) cation, an HPht(-) anion, an H(2)Pht molecule, and two solvate H2O molecules. In 2b, a small alteration in the crystal structure leads to an increase of the unit-cell volume. The asymmetric unit of 2b contains six crystallographically independent Co-II complexes, which combine into four [(bpy)(2)CO(Pht)H(Pht)-Co(bpy)(2)](+) units. The main structural unit of the cyclic dinuclear complex [Co(Pht)(bpy)(H2O)](2)center dot 2H(2)O (4) is neutral and cenrosymmetric, with the two Coll atoms linked by two phthalate ligands to form a 14-membered cycle. A further temperature increase results in the isolation of both the mononuclear complex [Co(Pht)(bpy)(H2O)3]center dot 3H(2)O (3) and the polynuclear helical coordination polymer [Co(Pht)(bpy)-(H2O)](n) (5). Extended hydrogen bonding networks as well as aromatic pi-pi stacking interactions stabilize multidimensional supramolecular architectures in all compounds. Magnetic susceptibility measurements have been performed for complexes 1, 2, 3, and 5. Simulations gave the following parameter sets: for complex 2 vertical bar D vertical bar = 70 cm(-1), g = 2.55 and J = -0.1 cm(-1); for complex 3 vertical bar D vertical bar = 80 cm(-1), g = 2.6, and for complex 5 vertical bar D vertical bar = 65 cm 1, g = 2.45. Complex 1 is diamagnetic. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.