Vanadium thermodynamic parameters

It has been suggested that an increase in the coordination number of vanadium from 4 to 5 already takes place in the second protonation step, i.e. when [H2V04] is formed (21). For reactions (1) and (2), however, the protonation constants and thermodynamic parameters are comparable with those reported for P04 and As04 , providing firm evidence that reaction (2) is not accompanied by incorporation of water in the vanadate ion (15, 17). Further, the estimated thermodynamic quantities for reaction (6), AH° = -39 kJ/mol and AS0 = —51 J/(mol K), obtained by extrapolation from the experimental values for reactions (1) and (2) and those for the three protonation steps of P04 and As04 , are not typical of a simple protonation reaction (17). For such a reaction the entropy change is normally a positive quantity often amounting to 100 50 J/(mol K) and the enthalpy... 

Thiosalicylic acid forms a green 2 1 complex with V02+ in aqueous ethanol442 (log K1 = 10.24, log K2 = 8.39). Addition of pyridine causes a more than 10-fold increase in the molar extinction coefficient and a yellow shift affording a chloroform extractable complex which can be used for the analysis of vanadium. The thermodynamic parameters for the 2 1 complex of furfurylmercaptan and V02+ are (35 °Q log K, 8.18 AH° = - 8.18 kcal mol"1, AG°, - 23.31 kcal mol"1 AS°, + 49.12 e.u 443 Stepwise formation constants of the V02+ complex of p-(mercaptoacetamide)chloro-benzene have been determined.444... 

The solid-state and solution chemistry of triethanolamine complexes has been investigated. While the solid-state structure was maintained in organic solvent (38), a different structure was observed in aqueous solution.262 170 NMR spectroscopy was used to demonstrate that the two oxo groups were different and in combination with H and 13C NMR data, defined the structure as (39).262 Speciation studies and a detailed characterization of this class of compounds were important because the ligand is a commonly used buffer in biology and the complexes are model systems for interactions with proteins.61,263 The thermodynamic parameters were determined for several derivatized diethanolamine ligand-vanadium(V) complexes, and represent some of the few vanadium complexes for which such parameters are known.62 The structure of (nitrilotriacetato)dioxovanadate was reinvestigated.2 4... 

Table 2 Thermodynamic parameters for oxidation of organic substrates by vanadium(v) from ref 9, Introduction and references therein)...

During recharging, the reactions occur in the opposite direction. As stated earlier, the values cited for the thermodynamic parameters of the reactions refer to the situation where the concentrations of the vanadium ions in the higher and lower oxidation states are equal. 

Table 1 Rate constants and thermodynamic parameters for reduction of metal complexes by chromium(ii), vanadium(ii), iron(ii), and europium(u). Second-order rate constants are quoted in 1 mol s at T = 25 "C unless stated. The units of AH and AS are kcal mol and cal deg mol respectively...

Papathanassopoulos and Wenzl made a similar set of measurements on films ( 500oA) of vanadium. They were able to extract thermodynamic parameters of the films and they comment that their thin film results are comparable to bulk. The kinetics for hydrogen absorption and desorption by the vanadium was enhanced by the evaporation of a thin palladium film ( 100-500A) immediately following the evaporation of the vanadium. 

Thermodynamic Parameters The thermodynamic values determined for the phases and species of vanadium(III) are listed in Table 11.3. 

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