Effect of the Spinning Motion of the Dihydrogen Ligand on the Properties of an Elongated Dihydrogen Complex. A Theoretical Study of the trans-[Os(H···H)Cl(H₂PCH₂CH₂PH₂)₂]⁺ Complex

We present in this paper an electronic structure and quantum nuclear dynamics study of a modeled version of trans-[Os(H···H)Cl(dppe)2]+, an elongated dihydrogen complex classified as being between the fast and slow H2 spinning limits and whose J(H,D) coupling constant increases on increasing temperature. We have found that the librational potential energy barrier for the motion of the H2 unit is quite low, in agreement with the spinning regime of the H2 unit reported from experiment. Additionally, while the electronic structure study does not manage to describe the experimentally reported geometry obtained through neutron diffraction experiments, the quantum nuclear motion study reproduces the experimental findings very satisfactorily. Finally it is seen that only when the librational motion of the H2 unit is taken into account in an explicit way in the quantum nuclear motion calculations the temperature dependence of the J(H,D) 1H NMR coupling constant is also correctly accounted for.