Neutron diffraction studies, transition metal

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 first isolable transition metal complex containing a coordinated H2 molecule is W(CO)3[P(CHMe2)3]2(H2). X-ray and neutron diffraction studies and a variety of spectroscopic methods have confirmed that it possesses a i72-H2 ligand, as shown in Fig. 11.5.1. 

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]. 

Morris, R.H. Sawyer. J.F. Single crystal x-ray and neutron diffraction studies of an r -dihydrogen transition-metal 28. complex Trans-[Fe(ri -H2)(H)(PPh2CH2CH2 PPh2)2]BPh4. 

The rare earth perovskites are usually treated in terms of a two-sublattice model with a rare earth ion on the A site and a transition metal ion on the B site. Early neutron diffraction studies (Koehler et al., 1960) Indicated that there was little interaction between the two sublattices. This is also suggested by the respective ordering temperatures for example, in the orthoferrifes the iron lattice orders around 700 K and the rare earth lattice only at a few degrees kelvin. An advantage of the low ordering temperature of the rare earth sublattice is that studies can be made well above Tn without much effect from the thermal vibrations of the lattice. 

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