Equilibria and thermodynamic quantities for the reactions of molybdenum(VI) and tungsten(VI) with mandelate (α-hydroxybenzeneacetate)

Abstract

The complex formation of molybdate and tungstate with mandelate [PhCH (OH)CO,-] have been investigated in the range pH, 7.5-1.5 by potentiometric, spectrophotometric and enthalpimetric titrations at 25 "C in 1.0 mol dm-3 NaCI. The potentiometric data were treated with the computer program SUPERQUAD taking into account the side-reactions of molybdate and tungstate with hydrogen ions. For both systems the 'best' reaction model comprises only one major complex and a number of minor complexes. Thermodynamic quantities have been determined for each of the major complexes. For the molybdenum(vt) complex [MOO,(C,H,O,),]~-. log p, , , = 15.93, AH" = -78.2 and TAS" = 12.7 k J mo1-l respectively and for the tungsten(v1) complex, [W02(C6HS03)2]2-, log p, , , = 17.59, A H = -86.3 and TAS" = 14.1 k J mol-l. The equilibrium constant and the enthalpy change for the protonation of mandelate have also been determined, log K = 3.1 5 and AH = -0.05 k J mot l. The energetics of complexation is discussed in terms of the thermodynamic quantities.

Vanadium(V) Complexes of Polydentate Amino Alcohols: Fine-Tuning Complex Properties

“…Third, for interpretation of the thermodynamic parameters for the complexes it is important that the corresponding parameters for H 2 VO 4 - be available under the conditions of the study. In the case of H 2 VO 4 - , we expect that the T Δ S ° term will dominate over the enthalpic component on the basis of the study reported at lower ionic strength 39a. However, since some differences are likely based on the differences in conditions of the studies, it is necessary to redetermine these parameters in about 0.40 M KCl.…”

Enantiomeric and mesomeric mandelate complexes of molybdenum – on their stereospecific formations and absolute configurations

“…For those ligands having only one a-hydroxyl and one a-carboxylic acid group, the preferred stoichiometry appears to be 1:2 [22,29]. The related mononuclear cisdioxo complexes have been isolated in the solid state and their structures determined by single crystal X-ray analyses [12,16,18,[34][35][36][37].…”

“…The solution chemistry of molybdenum(VI) and tungsten(VI) with mandelic acid has been previously investigated [19][20][21][22][23]. On the base of the results of spectrophotometric, potentiometric, enthalpimetric titration and NMR studies, it is concluded that coordination behaviour of mandelic acid groups towards molybdenum(VI) in 1:2 metal:ligand complexes are much more stable than that of 1:1 ratio.…”

cis-Dioxo-tungsten(VI) and -molybdenum(VI) complexes with N2O2 tetradentate ligands: synthesis, structure, electrochemistry and oxo-transfer properties

“…Reactions employing this reagent appear to be susceptible to the pH of the reaction mixtures. 25 The complex WO 2 Cl 2 possesses a polymeric structure which renders it insoluble in most organic solvents. 1b Although its derivative [WO 2 (acac) 2 ] has better solubility, its preparation is not always reproducible.…”