Zinc(II) complexes with an imidazolylpyridine ligand: luminescence and hydrogen bonding

ZnLCl and [H2L](2)[ZnCl4], based on 2-(1-hydroxy-4,5-dimethyl-1H-imidazol-2-yl)pyridine (HL), have been synthesized. There is a short intraionic O-H center dot center dot center dot N hydrogen bond between the hydroxyimidazolyl and pyridyl of H2L+ cations (N center dot center dot center dot O 2.608(2) angstrom) in the structure of [H2L](2)[ZnCl4]. The formation of this rather strong hydrogen bond is confirmed by IR spectroscopy through a broad band at 3200-2200 cm(-1) and a band at 1655 cm(-1). HL crystallizes in the form of a hemihydrate, HL center dot 0.5H(2)O. HL assemble into infinite helical chains due to N-H center dot center dot center dot O intermolecular hydrogen bonds between the NH of imidazole and O of the N-oxide (O center dot center dot center dot N 2.623(2) angstrom). An unusual mid-IR pattern with three broad bands at 3373, 2530, and 1850 cm(-1) is typical for strong hydrogen bonds, explained by resonance-assisted hydrogen bonding occurring in the helical chains. On cooling to 5 K, noticeable changes in the IR spectra of [H2L](2)[ZnCl4] and HL center dot 0.5H(2)O were observed. ZnLCl and [H2L](2)[ZnCl4] exhibit bright photoluminescence with maxima of emission at 458 nm (for ZnLCl) and 490 nm (for [H2L](2)[ZnCl4]).