Crystal structures of organic salts of chloranilic acid and 2,2′-bi(3-hydroxy-1,4-naphthoquinone) acting as proton donors to 4,4′-Bipyridine and 1,4-Diazabicyclo[2.2.2]octane: 3D networks with bifurcated N+-H···O−/O or N+-H···O/Cl synthons

Abstract

Five organic salts were prepared by proton transfer from organic acids to nitrogenous bases using chloranilic acid (H2CLA) or the Lawsone dimer (H2LD) as proton donors and 1,4-diazabicyclo[2.2.2]octane (DABCO) or 4,4′-bipyridine (BPY) as proton acceptors, viz., [(H2BPY)(CLA)]⋅4H2O, [(HDABCO)2(CLA)]⋅2H2O, [(HDABCO)2(CLA)]⋅6H2O, [(H2DABCO)(HCLA)2]⋅2H2O, and [(H2DABCO)(LD)]⋅H2O. The molecular crystal salts were characterized by elemental analysis, single-crystal X-ray diffraction (SCXRD) analysis, infrared spectroscopy and TG-DSC measurements. The SCXRD studies revealed that the molecular crystals studied herein are all hydrates with extensive and diverse hydrogen bonds of the N+−H⋅⋅⋅O−/O, N+−H⋅⋅⋅O/Cl, Ow−H⋅⋅⋅O−/O, Ow−H⋅⋅⋅Cl, Ow−H⋅⋅⋅N, Ow−H⋅⋅⋅Ow, and C–H⋅⋅⋅N type, which in some cases were accomplished by π–π, Cl⋅⋅⋅Cl or Cl⋅⋅⋅O contacts. Common to all crystal structures is the presence of cation-anion aggregates formed through bifurcated N+−H⋅⋅⋅O−/O or N+−H⋅⋅⋅O/Cl hydrogen bonds. All compounds constitute infinite 3D supramolecular networks based essentially on hydrogen bonding or a combination of hydrogen bonding and π-π interactions.In addition, ecofriendly preparative methods were tested for the preparation of the organic molecular crystal salts studied herein, viz., neat grinding, liquid-assisted grinding, slurry and precipitation.