Stretched H2 complex

According to the valence bond order concept as applied to the case of stretched H2 complexes by Limbach, there is a significant H-H bond order phh even at /hh = 1.6 A, implying that stretched dihydrogen complexes are not usefully considered as compressed dihydrides . 

Stretched H2 complexes are often poorly modeled in DFT work because the PES is very flat. Lluch and Lledos combined DFT with nuclear motion calculations to suggest that the time-averaged <7hh should be temperature dependent, explaining the unusual temperature dependence of the Jhd in [Cp Rn(H2)dppm]+, and the isotope dependence of Jht and Jdt valnes. ... 

Stretched H2 complexes with H—H distances above 1 A are less common for example, d(H—H) is 1.36 A (n diffraction) in 3.41. They are diflicult to distinguish from classical hydrides other than by neutron diffraction or H, D coupling. 

Stretched H2 complexes with H-H distances >1A are rare and difficult to distinguish from classical hydrides other than by neutron diffraction or /hd- For example, hh in [Re(H2)Hs P(o-tolyl)3 2] is 1.36A by neutron diffraction. 

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