An NMR investigation of the incoherent tunnelling exchange in a niobium trihydride

The incoherent contribution to the tunnelling exchange of hydrogen pairs in NbH(3)cp(2) " (cp " = C5H3(Si(CH3)(3))(2)) was investigated by H-1-NMR line-shape analysis and two-dimensional H-1-NMR exchange spectroscopy. The experimental data were analysed by fitting them with simulated one-and two-dimensional spectra, taking into account the coherent and incoherent tunnelling contributions and nuclear cross relaxation. The dissipative exchange process shows an Arrhenius-like temperature dependence with an activation energy E-a = 69(2) kJ mol(-1) over the temperature range 246-341 K.