Diffusion phenomena and metal complex formation equilibria. Part 1.—CdII–thiourea systems in aqueous and mixed-solvent media

Abstract

Changes in polarographic diffusion current of the cadmium(1r) aquo complex when consecutively complexed with thiourea and substituted thioureas are directly related to commonly used polynomial functions of free-ligand concentration involving overall formation constants. Pseudoformation curves are defined and their analysis exploited as a means of obtaining formation-constant data; these are essentially in agreement with those generated by more conventional methods when these are applicable. It is shown that the average diffusion coefficient of a system of metal complexes in equilibrium depends upon the free-ligand concentration in a manner which is a function of both the nature of the ligand and the solvent medium.

Cadmium(II) Complex Formation with Selenourea and Thiourea in Solution: An XAS and 113Cd NMR Study

“…The resulting β y values obtained for the solvated Cd(TU) y 2+ (y = 1 – 4) species in methanol at 203 K (β 1 = 2.0·10 4 , β 2 = 2.0·10 7 , β 3 = 5.0·10 9 and β 4 = 2.5·10 12 ) differ considerably from those previously reported from a polarographic study for similar complexes in aqueous solution at 298 K (β 1 = 20, β 2 = 140, β 3 = 260 and β 4 = 1200). 16 …”

“…The resulting β y values obtained for the solvated Cd(TU) y 2+ (y = 1−4) species in methanol at 203 K (β 1 = 2.0 × 10 4 , β 2 = 2.0 × 10 7 , β 3 = 5.0 × 10 9 , and β 4 = 2.5 × 10 12 ) differ considerably from those previously reported from a polarographic study for similar complexes in aqueous solution at 298 K (β 1 = 20, β 2 = 140, β 3 = 260, and β 4 = 1200). 16 By increasing the thiourea concentration from 0.4 mol dm −3 in T4 to 1.0 mol dm −3 in T7 (C Cd(II) = 0.1 mol dm −3 ), the single 113 Cd NMR peak became more shielded, shifting from 515 ppm in T4 to 423 ppm in T7. The latter value can be An attempt to evaluate the speciation of the higher Cd(II)− thiourea complexes was made by fitting the LT EXAFS spectra for solutions T6 and T7 (TU/Cd(II) mole ratios 8.0 and 10.0, respectively) with linear combinations of EXAFS oscillations simulated for CdS 4 and CdS 6 coordination.…”

“…15 In aqueous solution cadmium(II) complexes with up to four thiourea ligands have been reported with the formation constants β 1 = 20, β 2 = 140, β 3 = 260 and β 4 = 1200 (Figure S-1), based on a polarographic study. 16 …”

“…15 In aqueous solution, cadmium(II) complexes with up to four thiourea ligands have been reported with the formation constants β 1 = 20, β 2 = 140, β 3 = 260, and β 4 = 1200 (Figure S-1 of the Supporting Information), based on a polarographic study. 16 CdS semiconducting nanoparticles (NPs) and thin films have promising photoelectrochemical applications, for example, in solar cells. 17 Highly luminescent water-soluble CdS NPs can be prepared by thermal decomposition of Cd(II) and thiourea mixtures.…”

“…The structures of many metal–thiourea complexes, in which the thiourea molecule is coordinated to the metal center via its S atom, are available in the Cambridge structural database (CSD), such as the four-coordinated [Cd(TU) 2 Cl 2 ] and [Cd(TU) 4 ](NO 3 ) 2 , and the six-coordinated [Cd(TU) 2 (NO 3 ) 2 ], [Cd(TU) 2 (HCOO) 2 ], and [Cd(TU) 6 ](ReO 4 ) 2 complexes . In aqueous solution, cadmium(II) complexes with up to four thiourea ligands have been reported with the formation constants β 1 = 20, β 2 = 140, β 3 = 260, and β 4 = 1200 (Figure S-1 of the Supporting Information), based on a polarographic study …”