AN NMR INVESTIGATION OF THE INCOHERENT TUNNELING EXCHANGE IN A NIOBIUM TRIHYDRIDE

The incoherent contribution to the tunnelling exchange of hydrogen pai rs 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 spec troscopy. The experimental data were analysed by fitting them with sim ulated one-and two-dimensional spectra, taking into account the cohere nt and incoherent tunnelling contributions and nuclear cross relaxatio n. The dissipative exchange process shows an Arrhenius-like temperatur e dependence with an activation energy E-a = 69(2) kJ mol(-1) over the temperature range 246-341 K.