Metal ion size and coordination mode in complexes of a β-diketiminate ligand with pendant quinoline arms

A suite of late first row transition metal complexes has been synthesized using a monoanionic nitrogen donor β-diketiminate ligand with quinolyl pendant arms, BDIQQH (1). BDIQQNiOTf (2), BDIQQCuCl (4), BDIQQZnCl (5) were prepared from the reaction of 1 with Ni(OTf)2, CuCl2·2H2O and ZnCl2, respectively. BDIQQNiCl (3) was synthesized from an anion exchange of 2 with nBu4NCl. Reaction of 1 and CoI2 afforded the unexpected [(BDIQQ)2Co]+I− (6). Through density functional theory (DFT) calculations, ligand geometries in BDIQQ complexes were investigated and it was found that smaller ionic radius and higher charge destabilize 1:1 metal–ligand complexes relative to alternative 1:2 complexes like 6 owing to significant conformational strain in 1:1 complexes involving metals with small ionic radii. Synthesis and characterization of these complexes, including crystal structures of 4 and 5, are reported, in addition to the results of DFT calculations.

A suite of first row transition metal complexes has been synthesized using a monoanionic nitrogen donor β-diketiminate ligand with quinolyl pendant arms. Through density functional theory calculations, ligand geometries were investigated and it was found that smaller ionic radius and higher charge destabilize 1:1 metal–ligand complexes relative to 1:2 complexes.Figure optionsDownload as PowerPoint slideResearch highlights
► Complexes with a β-diketiminate with pendant quinoline donors were prepared.
► Complexes demonstrate tri- and tetradentate binding.
► The effect of ionic radius on ligand distortion was estimated using DFT calculations.
► A highly fluorescent zinc complex was prepared.
► Its luminescence was found to be quenched in the presence of Cu2+ and Co2+.