Solvent-dependent coordination polymers:: Cobalt complexes of 3,5-dinitrobenzoic acid and 3,5-dinitro-4-methylbenzoic acid with 4,4′-bipyrdine

The synthesis, structure elucidation, and analysis of the self-assembly of Co(II) complexes of 3,5-dinitrobenzoic, acid and 3,5-dinitro-4-methylbenzoic acid with 4,4'-bipyridine have been reported. Formation of the complexes and the self-assembly in the three-dimensional structures have been found to be dependent on the solvents (such as acetone, dimethly sulfoxide, etc.) employed for the synthesis of the aggregates. 3,5-Dinitrobenzoic acid forms two coordination polymers, la and 1b, from methanol and a mixture of methanol and acetone solvents, respectively, with entirely different recognition patterns. Similarly, 3,5-dinitro-4-methylbenzoic acid also forms two coordination complexes, 2a and 2b, incorporating the solvent of the reaction medium into the crystal lattice. Complex 2a forms a solvated channel structure, whereas 2b gives a bilayered structure, with the layers being separated by solvent of crystallization (dimethyl sulfoxide) molecules. All the complexes have been characterized by single-crystal X-ray diffraction studies. Complexes 1b, 2a, and 2b crystallize in a monoclinic lattice, but la adopts a tetragonal lattice. The unit cell dimensions are, for 1a, a = 8.095(1) Angstrom, b = 8.095(1) Angstrom, c = 46.283 (6) Angstrom, (alpha = 90degrees, beta = 90degrees, and gamma = 90degrees (space group P4(3)2(1)2, Z = 4), for 1b, a = 22.774(2) Angstrom, b = 11.375 (1) Angstrom, c = 22.533(2) Angstrom, alpha = 90degrees, beta = 104.15(1)degrees, and gamma = 90degrees (space group P2(1)/c, Z = 4), for 2a, a = 17.657(6) Angstrom, b = 18.709(4) Angstrom, c = 21.044(6) Angstrom, alpha = 90degrees, beta = 108.68(3)degrees, and gamma = 900 (space group, C2/c, Z = 8), and, for 2b, a = 11,025(5) , b = 15.139(4) Angstrom, c = 11.443(4) Angstrom, alpha = 90degrees, beta = 97.48(3)degrees, and gamma = 90degrees (space group P2/n, Z = 2). In all the complexes la, 1b, 2a, and 2b, the basic interaction between Co(II) and 4,4'-bipyridine remains the same with the formation of linear Co-N dative bonds, but the carboxylates display various modes of interaction with Co(II). The average Co-N and Co-O distances are 2.161 and 2.108 Angstrom, respectively.