A study on a modeled version of the complex [Ru(H ... H)(C5Me5)(dppm)](+) has been performed both at electronic structure level and including quantum treatment of nuclei. Density functional theory (DFT) electronic structure calculations alone fail to reproduce the experimentally reported geometry of the elongated dihydrogen ligand of the complex, even though the rest of the complex is satisfactorily described. Quantum nuclear motion calculations manage to correctly explain the geometries found experimentally by means of neutron diffraction measurements. Isotopic effects are predicted for the hydrogen-hydrogen distance of the elongated dihydrogen ligand depending on its isotopic composition. Moreover, the temperature dependence of the J(H,D) coupling constant is also interpreted successfully on the grounds of varying population of the vibrational excited states of the Ru-H-2 unit.