Coherent D-2 rotational tunneling and incoherent D-2 dynamics in a solid non-classical RuD2 complex studied by H-2 solid state NMR spectroscopy

The H-2 solid state NMR spectra and T-1 relaxation data of a transition met al eta(2)-dideuterium complex, namely trans-[Ru(D-2)Cl(PPh2CH2CH2PPh2)(2)]P F6, have been measured in the temperature regime from 5.4 to 320 K. In the Ru-D-2 sample, coherent and incoherent exchange processes on the time scale of the quadrupolar interaction have been found, leading at low temperature s to a tunnel splitting of the H-2 NMR spectrum. With increasing temperatur e a slight increase of the tunnel splitting is observed, in conjunction wit h a strong increase of the incoherent exchange process, which finally, at t emperatures above 20 K, destroys the tunnel splitting and determines the sp ectral line shape. For the description of the experimental spectra a Liouvi lle formulation of the Alexander-Binsch NMR line shape theory, adapted for exchanging deuterons, is employed. It is shown that the whole evaluation of the H-2 magnetization takes place in four 2D and two 4D subspaces of the 8 1D Liouville space, leading to a drastic simplification of the numerical ef forts in the simulation of the spectral line shapes. The height of the tunn el barrier calculated from the value of the tunnel splitting is 270 meV (6. 22 kcal mol(-1)). The incoherent exchange rates extracted from the spectra and from T-1 relaxation data are analyzed in terms of a Bell tunneling mode l, with a temperature dependent effective potential.