First systematic investigation of C-H•••Cl hydrogen bonding using inorganic supramolecular synthons:: Lamellar, stitched stair-case, linked-ladder, and helical structures

Using a group of six neutral (MCl2)-Cl-II-containing coordination compounds as building blocks, the first systematic investigation of C-H...Cl hydrogen-bonding interactions was performed. Single-crystal X-ray structural analyses of four new compounds (pseudo-tetrahedral Con and Zn-II; distorted trigonal bipyramidal Zn-II) authenticate the metal coordination geometry. To provide a unified view of the presence of noncovalent interactions in this class of compounds, we have re-examined the packing diagram of two previously reported compounds (a distorted square-pyramidal Cu-II complex and a trans-octahedral Co-II complex). The organic ligands of our choice comprise bidentate/tridentate pyrazolylmethylpyridines and an unsymmetrical tridentate pyridylalkylamine. This systematic investigation has allowed us to demonstrate the existence of versatile C-H...Cl2M interactions and to report the successful application of such units as inorganic supra- molecular synthons. Additional noncovalent interactions such as C-H...O and O-H...Cl hydrogen bonding and pi-pi stacking interactions have also been identified. Formation of novel supramolecular architectures has been revealed: 2D lamellar (p-cyclophane) and 3D lamellar, 3D "stitched staircase" (due to additional hydrogen-bonding interactions by water tetramers, with an average O-O bond length in the tetramer unit of 2.926 Angstrom, acting as "molecular clips" between staircases), 3D linked ladder, and single-stranded 1D helix.