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

The incoherent contribution to the tunnelling exchange of hydrogen pairs in NbH3cp′2 (cp′ = C5 H3(Si(CH3)3)2) was investigated by 1H-NMR line-shape analysis and two-dimensional 1H-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.