Characterization of transition-metal molecular hydrogen complexes by solid-state proton NMR

Hydrogen adsorption onRuO2(110): Density-functional calculations

“…The latter findings resemble much more the data from organometallic complexes: For so-called 2 -H 2 (dihydrogen) single metal atom complexes, in which the H u H bond remains intact, 46 TM-H 2 bond energies in the range of 0.1-0.3 eV/ H 2 are estimated, 47 significant redshifts of the stretch frequency 47,48 and bond elongation up to 0.9 Å are reported. 49,50 In fact, neutron scattering experiments furthermore indicate rapid rotation of 2 -H 2 ligands with an activation energy of less than about 10 meV, 49 just as we find for the molecular hydrogen at Ru cus . Even the donation/ backdonation bonding model is analogously discussed for the TM complexes.…”

Orientations of the principal components of electric field gradients and internal motions in dihydrogen ligands from the 2H T1 NMR relaxation data in solution

“…9 If the internal motions are slow on the ω D timescale, such dihydrogen ligands are static and their relaxation behavior corresponds to Eqn (1) or (2).…”

“…In contrast to classical hydrides, the Á 2 -H 2 ligands are very mobile even in the solid state at low temperatures. 2,3 The H atoms are spatially unfixed and their motions are varied and fast. For this reason, characterization of these compounds is not a simple task.…”

“…Note, however, that parameters of static quadrupolar tensors at D, reported for similar dihydrogen complexes, 5,6 are in poor agreement for several reasons. First, 2 H relaxation rates or 2 H lineshapes depend strongly on the type of internal D 2 motions, static DQCC values and orientations of principal components of the electric field gradients (EFGs). Second, the static DQCC has reliably been measured thus far for only one dihydrogen complex.…”

Chemical bonding of hydrogen molecules to transition metal complexes

“…An x-ray structure [13] of a rhenium complex with three classical hydrides and a dihydrogen ligand showed an H-H distance of 1.06 A, although x-ray determined distances are not reliable and must be confirmed by neutron diffraction. Solid state lH NMR experiments by Zilm at Yale [14] also indicate distances near 1.0 A for ruthenium-H2 complexes. These same experiments showed H-H to be 0.89 A in our tungsten complex, a distance 0.07 A longer than in the neutron structure.…”