Hydrogen determined from neutron

Table II. Mean Distances 1 (A) Involving the Interstitial Hydrogen Atoms Determined from Neutron Diffraction Studies of Compounds 3 and 4...

In 2002, Roimebro et alP explored the perovskite-related stmcture of Na3AlH6. These studies determined the positions of the hydrogen atoms from neutron diffraction data of a deuterated sample. It was found that the best fit data was for the monoclinic space group Pliln (no. 14). The structure was a distorted face-centered cubic (FCC) structure of [AlDg] units with sodium in all of the octahedral and tetrahedral sites. The complex anions were found to be distorted [AlFIg] octahedra. Selected interatomic distances and bond angles are reported in Table 14.2. The Al-D distances were 1.746,1.758, and 1.770 A,... 

Figure 13.2 Evolution of the anisotropic displacement parameter of the hydrogen atom in the 3,5-dinitrobenzoic acid homodimer in its binary complex with 4-dimethylaminobenzoic add determined from neutron diffraction data. A single, well-localized position is observed at 30 K...

For structure determination by neutron diffraction, deuterium is used instead of hydrogen. It is noted that the absorption-desorption curve for deuterium is slightly different from that of hydrogen (isotope effect see Fig. 3.23). 

Figure 5. Architecture of the [Ni 12(00)21-Hl2]2 dianion in Compound 3 with 20% isotropic ellipsoids of nuclear motion as determined from the neutron diffraction refinements. The two hydrogen atoms were found to occupy the two octahedral interstices.

Figure 2-1 Packing of molecules of suberic acid HOOC-(CH2)6-COOH in a crystal lattice as determined by neutron diffraction.2 Notice the pairs of hydrogen bonds that join the carboxyl groups at the ends of the molecules and also the close contact of hydrogen atoms between the chains. Only the positions of the hydrogen nuclei were determined the van der Waals radii have been drawn around them. However, the radii were originally determined from X-ray and neutron diffraction data obtained from many different crystalline compounds.

H from D would mean being able to determine which hydrogens are exchangeable. Neutron diffraction, it would seem, gives us a way to answer these questions. 

The most detailed structures have been obtained from neutron diffraction data, when isotopic substitution methods have been possible to use. Neutrons are strongly scattered by hydrogen atoms, making it possible to determine not only bond lengths and coordination number of the metal ion, but also the orientation of the water molecules in its first coordination sphere. A summary of results is given in Table II (19-31). 

Mallinson et al. [56,57] have carried out experimental and theoretical charge density determinations on a proton sponge compound, bis(dimethyamino)-napthalene (DMAN), in both pristine and protonated forms (Fig. 6). They used positional and thermal parameters of hydrogen atoms from an independent neutron diffraction experiment and treated the thermal... 

X-ray and time-of-flight (TOF) neutron diffraction and Raman spectroscopic measurements have been carried out at 25°C on concentrated aqueous sulfuric acid solutions, (H2S04),(H20),, x = 0, 0.25, 0.5, 0.75 and 0.86, in order to investigate the hydrogen-bonded intermolecular stmcture in the solutions. The intramolecular parameters for regular tetrahedral SO4 unit were determined from the least squares fit to observed X-ray and neutron interference terms in the range of Q S 8. The nearest neighbor... 

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