Embrace interlocking of dipyrazinylpyridine complexes involving N⋯π interactions

Fe(II) and Ni(II) complexes of 4-p-tolyl-2,6-di(2-pyrazinyl)pyridine (tdpzpy) have been synthesized and characterized. The N⋯π interaction involving the uncoordinated pyrazinyl N atom, which is stronger than the corresponding C–H⋯π hydrogen bonding in a similar 4-p-tolyl-2,2′:6′,2″-terpyridine complex, was distinguished as a supramolecular motif. It acts as an edge-to-face force in assembling cations of [Fe(tdpzpy)2]2+ or [Ni(tdpzpy)2]2+ into chains via embrace interlocking. C–H⋯π hydrogen bonds further link the chains into higher dimension net. The electronic absorption and emission properties of [Fe(tdpzpy)2]2+ and [Ni(tdpzpy)2]2+ are largely ligand-centered. [Fe(tdpzpy)2]2+ displays an MLCT absorption at 567 nm. The fluorescence of [Ni(tdpzpy)2]2+ is different markedly in methanol and acetonitrile. The ligand-based fluorescence is quenched to some extent by coordination to the d-orbital unfulfilled Fe(II) or Ni(II) atom.