An X-Ray Diffraction Study of Aqueous Thallium(I) Malonate Solutions

Abstract

As a part of the structural investigation of highly concentrated aqueous solutions of thallium( I ) carboxylates, the so called heavy liquids, X-ray scattering experiments wer e performed at 25°C on aqueous thallium( I ) malonate solutions with different thallium concentrations(0.6, 3.0, 6.0, and 9.0 mol·dm^-3). Raman spectra were also measur ed for both aqueous solutions and crystals of thallium( I ) malonate. The radial distribution functions (Figs.2, 3, and 5) and Raman spectra (Table 2) indicate that in the 9.0 mol·dm^-3 malonate solution thallium( I ) ions are bridged via malonate ion, forming polynuclear species (Fig.7). With increasing water content, the polynuclear species tend to decompose in aqueous solutions. The T1( I )-T1( I ) distances in the complex are estimated to be 404-460 pm, consistent with the values found in the crystal structures of Tl( I ) salts. The oxygen coordination around T1( I ) ion is characterized by their T1-0 distances of 262 pm ( × 2), 296 pm( × 2), and 366 pm ( × -2), indicating the existence of a stereochemically active lone pair of electrons of the Tl( I ) ion in the solution. The bond valences proposed by Brown are calculated for the obtained T1-0 distances, the result showing that the model in Fig.7 is appropriate.