Complexation between molybdenum(VI) and citrate: a potentiometric and calorimetric investigation
The molybdenum(VI)-citrate system has been investigated in the pHc range 7.5-2.0 by potentiometric and enthalpimetric titrations at 25°C in 1 M NaCl. The potentiometric data were treated with the computer program MINIQUAD taking into account side reactions of molybdate and citrate with hydrogen ions. A reaction model comprising the complexes (1,1,1)4-,(1,1,2)3-,(1,1,3)2-,(2,1,4)3- and (2,1,5)2- gave a satisfactory description of the data; the numbers refer to the values of p, q and r in the general formula (MoO2-4)p(Cit3-)q(H+)r. The enthalpy and entropy changes for the formation of these complexes were calculated from the enthalpimetric data using the values of the now known formation constants. Equilibrium constants as well as enthalpy and entropy changes for the successive protonations of citrate have also been determined. © 1986.