Tropolone as anionic and neutral ligand in lead(II) and bismuth(III) complexes: Synthesis, structure, characterization and computational studies

Abstract

Two new metal complexes, [Bi(trop)2(Htrop)(CF3SO3)] (1) and [Pb(trop)2(Htrop)] (2), have been synthesized by reaction of the respective metal triflates with an excess of tropolone (Htrop) in the concentrated methanol or dimethylsulfoxide solution. In addition, it was found that complex 1 crystallizes through the formation of unstable intermediate methanol solvated tris(tropolonato)bismuth(III) compound. The characteristic behavior of tropolone which coordinates both as the bidentate anion (trop−) and the monodentate neutral molecule (Htrop) has been revealed in 1 and 2. The crystal structures of studied compounds have been determined by single-crystal X-ray diffraction. The molecular structures of both complexes have been compared with their geometries received from DFT calculations giving a good correlation. The presented compounds show coordination number of metal ion equal to five in 2 and six in 1 and the presence of stereochemically active 6s2 lone electron pair. The complexes were characterized by FT-IR, NMR and UV–Vis techniques. IR and UV–Vis spectra of 1 and 2 were also simulated by DFT methods. TD-DFT predictions demonstrate the frontier HOMOs and LUMOs cover in the major part the tropolonate and(or) tropolone moieties which gives mainly ligand-to-ligand charge transfer (LLCT) and ligand centered (LC) character to the energy bands above 300 nm.