Transition metal hydrides neutron diffraction studies

Neutron diffraction studies have shown that in both systems Pd-H (17) and Ni-H (18) the hydrogen atoms during the process of hydride phase formation occupy octahedral positions inside the metal lattice. It is a process of ordering of the dissolved hydrogen in the a-solid solution leading to a hydride precipitation. In common with all other transition metal hydrides these also are of nonstoichiometric composition. As the respective atomic ratios of the components amount to approximately H/Me = 0.6, the hydrogen atoms thus occupy only some of the crystallographic positions available to them. 

Neutron Diffraction Studies of Tetrahedral Cluster Transition Metal Hydride Complexes HFeCo3(CO)9-(P(OCH3)3)3 and H3Ni4(C5H5)4... 

The formation of transition metal hydrides using atomic hydrogen has been studied 242), and there is evidence for transient volatile hydrides of Co, Ag, and Au. The only well-defined solid hydride is CuH (dec. > 60°) 196), which neutron diffraction studies show to have the wurtzite structure... 

It is interesting that the hydrogen bond with transition metal atoms as well as that with hydride ligands of boron hydrides (see below) also displays a linear arrangement for the X-H -M and X-H—H(B) fragments. The linearity of the ionic hydrogen bonds N-H+ - [Co]- and N-H+ -[Pt]- was proven by neutron diffraction studies of the corresponding salts [22a,b]. 

Hydrides. According to X-ray and neutron diffraction and metallographic studies of the Nb-H system,524 the H may be considered a lattice gas with phase transitions. In the a-, a -, j6-, and -phases of the system, H occupies tetrahedral interlattice positions. Whereas direct reaction between niobium metal and hydrogen occurs only after repeated activation of the metal by hydrogen absorption at ca. 7 atm and 350 °C, NbH2 is formed at temperatures as low as 22 °C in mixtures of LaNi5H6 7 and Nb.525 The extraordinary catalytic effect of the lanthanum-nickel complex is attributed to the presence of surface-absorbed atomic hydrogen species which are able to diffuse into the niobium lattice. There has been a review of the T a-H system.526... 

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