Coordination Polymers Based on Phthalic Acid and Aminopyrazine Ligands: On the Importance of N⁻H···π Interactions

Two new Co(II) and Cu(II) coordination polymers, {Co(HL₁)₂(μ-L₂)(H₂O)₂} (1) and {[Cu(HL₁)₂(μ-L₂)H₂O]·H₂O} (2) (H₂L₁ = Phthalic acid and L₂ = 2-aminopyrazine), have been synthesized by slow evaporation of solvent and characterized by IR spectroscopic, elemental, single-crystal X-ray diffraction and thermal analysis. X-ray results indicate that in both the polymers, phthalate acts as a monodentate ligand and the aminopyrazine ligand is responsible for the formation of the infinite one-dimensional chain structure. The solid-state structures are stabilized through hydrogen bonds and N‒H···π interactions by generating two-dimensional layered structures. Finally, the non-covalent interactions have been studied energetically and using Bader's theory of atoms in molecules by means of Density Functional Theory (DFT) calculations. The influence of the metal coordination on the strength of the interaction has been studied using molecular electrostatic potential surface calculations.