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DOI: 10.1039/A700264E (Paper) Reference Section for: J. Chem. Soc., Dalton Trans., 1997, 1925-1930

Tungsten(VI) complex formation. Equilibria and thermodynamic quantities for the reactions with malate

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Johannes J. Cruywagen, Leon Krüger and Elisabeth A. Rohwer

Abstract

Complex formation between tungstate and malate has been investigated in the range pH 1.5–8.5 by potentiometric and enthalpimetric titrations at 25 °C in 1.0 mol dm-3 (Na)Cl. The ‘best’ reaction model comprises mono-, di- and tetra-nuclear complexes. The formation constants of the complexes, denoted by βpqr, where the subscripts p, q and r refer to the stoichiometric coefficients in the general formula [(WO4)p(mal)qH r], have the values: log β111 = 8.85, log β112 = 14.78, log β113 = 17.26, log β122 = 17.20, log β123 = 21.70, log β124 = 25.61, log β213 = 23.07, log β222 = 18.87, log β223 = 25.72, log β224 = 31.88 and log β4411 = 73.60. Enthalpy and entropy changes for complexes occurring in sufficiently high concentrations were calculated from the calorimetric data using these formation constants: ΔH°111 = -64, ΔH°112 = -65, ΔH°113 = -67, ΔH°122 = -86.0, ΔH°123 = -92, ΔH°124 = -91, ΔH°222 = -115, ΔH°223 = -121, ΔH°224 = -120 and ΔH°4411 = -240 kJ mol-1.

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