The structure of the complex trans-[Ru(η 2 -H 2 )(H)(dppe) 2 ][BPh 4 ] (1), dppe = PPh 2 CH 2 CH 2 PPh 2 , has been determined by single-crystal X-ray diffraction at 123 K and neutron diffraction at 12 K. The core of the complex has a distorted octahedral geometry about ruthenium with the dihydrogen ligand trans to hydride and eclipsing a trans-P-Ru-P axis that is bent away from the hydrogens with a P-Ru-P angle of 167.9(4)°. The crystallographically determined H-H distance is 0.83(8) (X-ray) or 0.82(3) (neutron) 9. The latter value, when corrected for the shortening caused by the torsional libration of the H 2 ligand, increases to about 0.94 9. The long Ru-(H 2 ) distance of 1.81(2) 9 (neutron), compared to the terminal hydride to ruthenium distance of 1.64(2) 9 (neutron), is consistent with the lability of the dihydrogen ligand, which is partially lost from the crystal by treatment with vacuum. The analogous iron complex trans-[Fe(η 2 -H 2 )(H)(dppe) 2 ][BPh 4 ] (2) has similar features except that the Fe-H(H 2 ) distances are much shorter and the H 2 ligand is correspondingly less labile. An inelastic neutron scattering study of the powder of 1 at 5 K reveals two broad inelastic peaks flanking the elastic peak. With the assumption that the dihydrogen librates in a double-minimum potential, the barrier to dihydrogen reorientation is calculated to be 1.0 to 1.4 kcal mol - 1 , depending upon which of the H-H distances is used. This barrier is less than that for the iron analog, determined for its BF 4 salt, therefore suggesting that there may be less d π → σ * backbonding in 1 than 2.