A single-crystal neutron diffraction analysis along with density functional calculations and incoherent inelastic neutron scattering studies has conclusively shown that the dihydrogen adduct of [P2N2]Zr(mu-eta(2)-N-2)Zr[P2N2] (1) (where P2N2 = PhP(CH2SiMe2NSiMe2CH2)(2)PPh) is [P2N2]Zr(mu-eta(2)-N2H)(mu-H)Zr[P2N2] (2), the complex with a bridging hydride and a N-N-H moiety, and not the dihydrogen complex [P2N2]Zr(mu-eta(2)-N-2)(mu-eta(2)-H-2)Zr[P2N2] (3), as was proposed on the basis of X-ray crystallographic data. In addition, DFT calculations show that the reaction of 1 with both H-2 and SiH4 is exothermic while an endothermic reaction is found for the reaction of 1 with CH4.