Synthesis, structure and photoluminescence properties of naphthalene-based chiral zinc(II) complexes

Abstract Two novel chiral zinc(II) complexes containing naphthalene moieties, namely [Zn(CMN)Cl2] (1) and [Zn(CBN)Cl2] (2), were obtained through the reaction of zinc(II) chloride with, respectively, (1R,2R)-N1-(naphthalen-2-ylmethyl)cyclohexane-1,2-diamine (CMN) and (1R,2R)-N1,N2-bis(naphthalen-2-ylmethyl)cyclohexane-1,2-diamine (CBN) in ethanol. The ligands CMN and CBN were characterized via infrared, nuclear magnetic resonance and absorption spectroscopic analyses. As regards to the two complexes, a comprehensive single crystal X-ray diffraction investigation showed that in both cases the zinc(II) ion is surrounded by two N atoms of CMN/CBN and two chloro groups, and has a distorted tetrahedral structure, though 2 also contains an additional naphthalene group. The photo-physical properties of 1 and 2 were examined based on their electronic absorption and photoluminescence spectra. Both complexes exhibited ultraviolet emissions (both at 335 nm in CHCl3; 336 and 385 nm for 1 and 337 nm for 2 in their solid states) under 278-298 nm excitation. Synopsis We have synthesized the monomeric complexes 1 and 2 based on chiral bidentate ligands containing monosubstituted and disubstituted naphthalene groups. The complexes exhibited significant UV emissions via the excitation of intraligand transitions; in particular, 1 showed two big emission bands at 336 and 385 nm in the solid state but only one at 335 nm in solution.