Structure and Homogeneous Chemical Equilibria of Lithium β-Diketonates in Dimethyl Sulfoxide

Abstract

Abstract The structure and the homogeneous chemical equilibria of lithium β-diketonates (LiL), viz., Li(dbm), Li(bzac), and Li(acac), in dimethyl sulfoxide (DMSO) were studied by means of 13C NMR, IR spectral measurements, and rotating disk voltammetry, where dbm−, bzac−, and acac− indicate the enolate anions of dibenzoylmethane, benzoylacetone, and acetylacetone, respectively. It was found by the 13C NMR and IR spectral measurements that LiL existed mainly as Li(uni-L) in DMSO, where uni- means that the ligand coordinates to the metal as unidentate. Since it is known that LiL dissociates slightly into ions in DMSO, LiL is involved in the following homogeneous chemical equilibrium: Li(uni-L)\ightleftharpoonsL++L− Furthermore, the apparent dissociation constant (logKapp) of LiL was obtained by rotating disk voltammetry in DMSO containing 0.1 mol dm−3 tetrabutylammonium perchlorate (TBAP), i.e., Li(dbm): −3.0±0.1, Li(bzac): −2.7±0.1, and Li(acac): −2.0±0.1, respectively. It was noted that the homogeneous chemical equilibria shifted more to the right in 0.1 mol dm−3 TBAP–DMSO than in DMSO alone. The behavior can be explained mainly in terms of the interaction between the π-electron system of Li(uni-L) and the cations of TBAP.