Composés d'addition des halogénures de niobium(V) et de tantale(V): VI. Réactions d'échange des composés du chlorure de niobium(V) avec quelques nitriles

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Abstract
The ligand exchange reactions NbCl5·ŘN + RCN* ⇄ NbCl5 · RCN* + RCN are studied by NMR. spectroscopy for R = Me3C, Me, FCH2, CICH2, BrCH2, ICH2. The reaction is of zero order in RCN and of first order in NbCl5 · RCN and thus a dissociative mechanism is suggested for all the ligands studied. The enthalpies and entropies of activation are determined over 50° to 90° temperature ranges. There is a linear correlation between ΔG≠ and the free enthalpy of formation of NbCl5 RCN. However this correlation is shown to hold only for series of adducts having the same donor group.