Domenico De Marco

Thermodynamics of complex formation of Ag(I). VI: Ag(I)-thiocarbonyl ligand systems in aqueous solution

Abstract The formation of complexes between Ag(I) and substituted thioureas has been studied by potentiometric measurements in aqueous solution at μ = 0 and various temperatures. Under these experimental conditions, three-coordinated complexes are formed with all the ligands. The influence of the substituents is mainly an “external” effect and causes a more positive Δ H and Δ S value for the formation of complexes with substituted thioureas compared to those with thioureas.

Formation of ferrocyanides—IV: Th(IV), Nd(III), UO2(II) and Hg(II)

The stoichiometry of the reaction between ferrocyanide and thorium, neodymium, uranyl ion and mercury(II) has been investigated. The first three give single products irrespective of the order of addition of the reagents, but the last does not. If mercury(II) is added to ferrocyanide Hg(2)Fe(CN)(6) is obtained, but if ferrocyanide is added to mercury(II) various cyanide complexes of mercury are formed. The K(sp) values for the precipitates are reported.

Formation and thermodynamic properties of mixed complexes of Cd(II) with SCN2H4 and C−, Br−, I− as ligands☆

Abstract Thermodynamic parameters for in-water-formation of mononuclear complexes of cadmium-halide-thiourea systems, calculated by means of potentiometric measurements at different temperatures and at μ = 1 for KNO 3 , are reported.

Formation and thermodynamic properties of Ag(I) complexes with S2O32−, SCN2H4 and SCN− as ligands

Abstract Changes in thermodynamic functions ΔG°, ΔH° and ΔS° for the formation of Ag(I) complexes of general formulae: Ag ( S 2 O 3 ) n ( SCN 2 H 4 ) m ( SCN ) p 1−2 n − p and the diagrams defining the range of existence of the following complexes: Ag ( SCN 2 H 4 ) m ( SCN ) p 1− p and Ag ( S 2 O 3 ) n ( SCN ) p 1−2 n − p in an aqueous medium at μ = 1 for KNO 3 , are reported. The relations between thermodynamic parameters for coordination or displacement of S 2 O 3 2− , SCN − or SCN 2 H 4 ligands are discussed.

Formation of ferricyanides-I silver(I), copper(II) and cadmium(II).

With potassium ferricyanide copper(II) forms KCu(10),[Fe(CN)(6)](7) quantitatively in 0.5M potassium nitrate medium. Cadmium forms Cd(3)[Fe(CN)(6)](2) if the ferricyanide is added to the cadmium solution in absence of extra potassium, and KCd(10)[Fe(CN)(6)](7) if potassium is added first, or if the cadmium solution is added to the ferricyanide. Silver forms Ag(3)Fe(CN)(6) only.

Thermodynamics of complex formation of Ag(I). Part 10. Investigations on complex equilibria between Ag(I) and thioureas in ethanol

Abstract The complex equilibria between Ag(I) and thiourea or N -alkyl-substituted thioureas have been investigated in ethanol by potentiometry at different temperatures in the range 0–45°C. The free energy, enthalpy and entropy changes at 25°C and ionic strength μ = 0 for the formation of mono-, bi- and tri-coordinate compounds are given. The investigated alcohols favour the complex formation, but specific factors operate on the transfer of each reaction from water to methanol to ethanol. Interaction between tetramethylthiourea and Ag(I) involves a different mechanism compared with the other thioureas owing to the different electronic structure of the ligand. The ranked affinity sequences of the ligands follow different orders according to the coordination level of the substratum.

Thermodynamics of complex formation of Ag(I). Part 9. Investigations on Ag(I)—thiourea—thioacetamide—halide systems in aqueous solution

Abstract Complex formation in the three-ligand systems Ag(I)-SCN 2 H 4 -SCN − −X (X = Cl − , Br − ,I − ) has been investigated by potentiometry in aqueous solution at ionic strength μ = 1 using KNO 3 and different temperatures. Enthalpy and entropy changes have been evaluated from the free energy change dependence on temperature. Predominance diagrams for the two-ligand systems Ag(I)-SCN − -X (X = Cl − , Br − , I − ) and the three-ligand systems Ag(I)-SCN 2 H 4 -X (X = Cl − , Br − , I − ) at 25°C and μ = 1 for KNO 3 are shown. The free energy changes for the coordination reactions of thiourea or thiocyanate indicate higher affinities for the dicoordinated substrata than for the monocoordinated ones. The ionic charges of both the substrata and the entering group are not the main factors in determining the affinity sequences. The parameters of the Gibbs equation are interrelated, though in different ways, in both the overall and stepwise complex formation.

Additional thermodynamic relationships on complexation equilibria in various solvents

Abstract Complex formation in solution comes from the displacement reactions of solvent molecules through donor-acceptor interactions. Δ H and Δ S parameters are due to interactions between substrates and to solvent action, so that enthalpy and entropy changes depend on the same process (at least partially). Compensative and, in some cases, cooperative interdependence between Δ H and Δ S for several complexation equilibria in various solvent media are shown.

Thermodynamic relationships of complex formation: Part 5. Isoequilibrium relationships in soft-soft interactions in hard solvents

Abstract The inspection of the Δ H -Δ S patterns for reactions between Ag(I) complex substrata and various entering ligands discloses linear interplay between the two parameters. The actual Δ H (Δ S ) values demonstrate that soft-hard interactions can produce favourable enthalpy changes coupled to unfavourable entropy changes, and confirm that soft-soft interactions can yield unfavourable enthalpy changes coupled to favourable entropy changes. These results, together with the already published enthalpy-entropy interplays, which show negative values of both Δ H and Δ S for hard-hard interactions in aqueous solution, demonstrate that in this solvent soft-soft (hard-hard) interactions do not necessarily produce Δ H H > 0) coupled to Δ S S > 0) because their values also descend from the role of the solvent molecules in the specific reaction. The coordinated solvent produces a sort of ‘shielding’ or ‘levelling’ of the acceptor and donor abilities.

Thermodynamics of complex formation of Ag1: VII. Ag1-Thilocarbonyl ligand systems in methanol

Abstract Complex formation between Ag 1 and some alkyl-substituted thioureas in methanol has been studied at ionic strength μ = 0 and in the temperature range 0–40°C. In all cases, step-wise formation of tris-coordinated complexes was found. The behaviour of the investigated systems does not suggest any notable differences between water and methanol. Very strict free energy or enthalpy relationships between the step-wise reaction series in the two solvents were not found. The step-wise complex formation reactions in methanol form a series of “homologous” reactions for which there are very strict enthalpy-entropy linear relationships. The corresponding isoequilibrium temperatures in methanol are a little lower than in water. Tetramethylthiourea behaves differently in comparison with the other ligands.