ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The kinetics of formation and dissociation of [V(H2O)5NCS]2+ have been studied, as a function of excess metal-ion concentration, temperature, and pressure, by the stopped-flow technique. The thermodynamic stability of the complex was also determined spectrophotometrically. The kinetic and equilibrium data were submitted to a combined analysis. The rate constants and activation parameters for the formation (f) and dissociation (r) of the complex are: kf298/M-1 · S-1 = 126.4, kr298/s-1 = 0.82; ΔHf≠ /kJ · mol-1 = 49.1, ΔHr≠/kJ · mol-1 = 60.6; ΔSf≠/ J·K-1·mol-1= -39.8, ΔSr≠J·K-1·mol-1 = -43.4; ΔVf≠/cm3·mol-1 = -9.4, and ΔVr≠/cm3 · mol-1 =-17.9. The equilibrium constant for the formation of the monoisothiocynato complex is K298/M-1 = 152.9, and the enthalpy and entropy of reaction are ΔH0/kJ · mol-1 = - 11.4 and ΔS0/J. K-1mol-1 = +3.6. The reaction volume is ΔV0/cm3· mol-1 = +8.5. The activation parameters for the complex-formation step are similar to those for the water exchange on [V(H2O)6]3+ obtained previously by NMR techniques. The activation volumes for the two processes are consistent with an associative interchange, Ia, mechanism.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19890720816
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