Hydrogen-bonded networks based on [M(H2biim)3]2+ anion receptors with chiral recognition guests [M(H2biim)2phen]2+ (H2biim = 2,2′-biimidazole, phen = 1,10-phenanthroline)

Abstract

Reactions of transition metal(II) nitrate with 2,2′-biimidazole and 1,10-phenanthroline generated three new isostructural complexes, [Co(H2biim)3][Co(H2biim)2(phen)](NO3)4·2CH3OH·H2O (1), [Ni(H2biim)3][Ni(H2biim)2(phen)](NO3)4·3.5H2O (2), and [Zn(H2biim)3][Zn(H2biim)2(phen)](NO3)4·4H2O (3) (H2biim=2,2′-biimidazole, phen=1,10-phenanthroline). These complexes were characterized by single-crystal X-ray diffraction, elemental analysis, luminescent spectra and thermogravimetric analysis. The crystal packing of the complexes show that cationic [M(H2biim)3]2+ fragments are self-assembled to construct the 2-D supramolecular networks by hydrogen bonding and π–π interactions. The guest molecule [M(H2biim)2phen]2+ is well recognized by the N–H⋯O and O–H⋯O hydrogen bonds. In complexes 1–3, chiral guest molecules recognize the chirality of the host cations [M(H2biim)3]2+, which are assembled into 2-D nets with alternating Δ and Λ chirality resulting in the structure of racemates. The data observed in this paper suggest that the diverse hydrogen bonding modes between the nitrate and H2biim ligand identified here play a crucial role in the formation of 1–3.