Syntheses and structures of three chiral complexes derived from nucleophilic addition of L-proline to di-2-pyridyl ketone

In the presence of nickel acetate, a chiral ligand, (S)-Hdphp ((S)-N-[di(2-pyridyl)-hydroxymethyl]- proline), was synthesized in situ by nucleophilic addition of L-proline to di-2-pyridyl ketone. Based on this ligand, three chiral mononuclear complexes, {Ni[(S)-dphp](DMF)(H2O)}(ClO4) (1), {Ni[(S)-dphp](H2O)(2)}(ClO4)(H2O)(1.5) (2), and {Ni[(S)-dphp](SCN)(H2O)} (3), have been obtained and characterized by single-crystal X-ray diffraction, elemental analyses, and infrared spectra. By virtue of charge-assisted O-H center dot center dot center dot O hydrogen-bonding interactions, all the complexes possess double chain structures. The double chains were connected into 2-D networks via pi center dot center dot center dot pi stacking and CH center dot center dot center dot pi interactions in 1. For 2, O-H center dot center dot center dot O hydrogen-bonding interactions between free water molecules and other oxygens as well as pi center dot center dot center dot pi stacking and CH center dot center dot center dot pi interactions extend the chains into a 3-D network. Complex 3 exhibits 3-D structure via O-H center dot center dot center dot S interactions.