Cooperative Ternary Assemblies Involving Anion-π/π-π/Anion-π Assemblies and Unconventional ClMIDLINE HORIZONTAL ELLIPSISCl Interactions in Cu(II) Coordination Compounds: Experimental and Theoretical Studies

Two coordination compounds of Cu(II), namely, [Cu (phen)(2)Cl](NO3)center dot H2O (compound 1) and [Cu-2(mu-Cl-2)Cl-2(Hdmpz)(4)] (compound 2), where phen = 1,10-phenanthroline and Hdmpz = 3,5-dimethylpyrazole, were synthesized at room temperature and characterized using elemental analysis, TGA, spectroscopic techniques (FT-IR and electronic) and single-crystal X-ray diffraction studies. The cooperative anion-pi/pi-pi/anion-pi assemblies involving the coordinated phen, along with the uncoordinated nitrate moieties, played pivotal roles in the stabilization of the crystal structure of compound 1. Unconventional type I ClMIDLINE HORIZONTAL ELLIPSISCl interactions involving the coordinated Cl atoms provided reinforcement to the crystal structure of compound 2. We theoretically explored the supramolecular assemblies observed in the crystal structures of compounds 1 and 2 using DFT calculations, MEP surface analysis and combined NCI plot/QTAIM computational tools. Theoretical analysis revealed that the antiparallel pi-stacking interactions in compound 1 and the N-H center dot center dot center dot Cl H-bonds in compound 2 were the strong structure-guiding non-covalent synthons which stabilized the compounds. In the anion-pi/pi-pi/anion-pi assembly observed in compound 1, the anion-pi interaction reinforced the pi-stacking by reducing the electrostatic repulsion between the metal-coordinated electron-deficient phen rings.