Effects of existence form and concentration of PbO on the conductivity of choline chloride–urea deep eutectic solvent

Abstract

The effects of existence form and concentration of lead oxide (PbO) on the conductivity and viscosity of choline chloride (ChCl)-urea deep eutectic solvent (DES) were investigated. The ESI-MS and FT-IR analyses indicated that three-coordinated complexes are presented in the form of {[PbO∙CO(NH2)2]∙Cl−}−. It is deduced that the complex anions are formed through sp3 hybrid orbitals of Pb2+ ion and three sp hybrid orbitals are all filled with lone pair electrons which are donated by Cl−, O2− and O atoms of urea respectively. The raising of temperature leads to the electrical conductivity increases. With PbO concentration, however, the conductivity increases firstly and then decreases. The viscosity has an opposite change trend compared with the conductivity. These experimental phenomena can be explained by the formation of PbO-containing complexes and oligomers.