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, 1a 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 1a adopts a tetragonal lattice.
The unit cell dimensions are, for 1a, a = 8.095(1) Å, b = 8.095(1) Å, c = 46.283 (6) Å, α = 90°, β = 90°, and
γ = 90° (space group P43212, Z = 4), for 1b, a = 22.774(2) Å, b = 11.375 (1) Å, c = 22.533(2) Å, α = 90°,
β = 104.15(1)°, and γ = 90° (space group P21/c, Z = 4), for 2a, a = 17.657(6) Å, b = 18.709(4) Å,
c = 21.044(6) Å, α = 90°, β = 108.68(3)°, and γ = 90° (space group, C2/c, Z = 8), and, for 2b, a = 11.025(5)
Å, b = 15.139(4) Å, c = 11.443(4) Å, α = 90°, β = 97.48(3)°, and γ = 90° (space group P2/n, Z = 2). In all
the complexes 1a, 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 Å, respectively.