Neutron diffraction transition metal hydride complexes

Figure 5.14 Neutron diffraction structure of the transition metal hydride complex (Me3P)4lr(OH)H. (Reproduced with permission from ref. 19.)...

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

Prior Neutron Diffraction Work on Transition Metal Hydride Complexes... 

X-ray diffraction is a standard method employed by chemists to determine the structure of new complexes. In the case of transition metal hydride and dihydrogen complexes, precise location of metal-bound hydrogen atoms by X-ray diffraction is very difficult. Superior structural information is provided by neutron diffraction, but the requirement for large well-formed single crystals has limited this method to a small subset of the known complexes.118... 

The first hydride complex investigated by the neutron diffraction technique was K2[ReH9] containing the terminal M—H linkage. Many examples of complexes containing the terminal hydride ligands are now known for virtually all d-block transition elements. Binary transition-metal hydrides are rather few and the majority are stabilized by carbonyl, phosphine, or other ancillary ligands. 

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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