And neutron diffraction

The specific surface area of a solid is one of the first things that must be determined if any detailed physical chemical interpretation of its behavior as an adsorbent is to be possible. Such a determination can be made through adsorption studies themselves, and this aspect is taken up in the next chapter there are a number of other methods, however, that are summarized in the following material. Space does not permit a full discussion, and, in particular, the methods that really amount to a particle or pore size determination, such as optical and electron microscopy, x-ray or neutron diffraction, and permeability studies are largely omitted. 

As with other diffraction techniques (X-ray and electron), neutron diffraction is a nondestructive technique that can be used to determine the positions of atoms in crystalline materials. Other uses are phase identification and quantitation, residual stress measurements, and average particle-size estimations for crystalline materials. Since neutrons possess a magnetic moment, neutron diffraction is sensitive to the ordering of magnetically active atoms. It differs from many site-specific analyses, such as nuclear magnetic resonance, vibrational, and X-ray absorption spectroscopies, in that neutron diffraction provides detailed structural information averaged over thousands of A. It will be seen that the major differences between neutron diffraction and other diffiaction techniques, namely the extraordinarily... 

Neutron Diffraction and Its Application in Inorganic Chemistry G. E. Bacon... 

In the case of selective oxidation catalysis, the use of spectroscopy has provided critical Information about surface and solid state mechanisms. As Is well known( ), some of the most effective catalysts for selective oxidation of olefins are those based on bismuth molybdates. The Industrial significance of these catalysts stems from their unique ability to oxidize propylene and ammonia to acrylonitrile at high selectivity. Several key features of the surface mechanism of this catalytic process have recently been descrlbed(3-A). However, an understanding of the solid state transformations which occur on the catalyst surface or within the catalyst bulk under reaction conditions can only be deduced Indirectly by traditional probe molecule approaches. Direct Insights Into catalyst dynamics require the use of techniques which can probe the solid directly, preferably under reaction conditions. We have, therefore, examined several catalytlcally Important surface and solid state processes of bismuth molybdate based catalysts using multiple spectroscopic techniques Including Raman and Infrared spectroscopies, x-ray and neutron diffraction, and photoelectron spectroscopy. 

Baron, V., Gillon, B., Plantevin, O. et al. (1996) Spin-density maps for an oxamido-bridged Mn(II)Cu(II) binuclear compound. Polarized neutron diffraction and theoretical studies, J. Am. Chem. Soc., 118, 11822-11830. 

The neutral Irv complex, cp Ir(H)2(SiEt3)2, has been studied by neutron diffraction and its structural characteristics compared to those of the isomorphous Rh analogue.6 The significant differences are longer metal-ligand distances and larger bond angles for the Ir species. 

Although X-ray and neutron diffraction and scattering methods give only approximate estimates of hydration numbers they can provide precise measures of ion-water distances in solution. In calcium chloride and bromide solutions of various concentrations, Ca-0 distances of between 2.40 and 2.44 A have been reported (167,168,171,172) Ca-0 — 2.26A was claimed in an early X-ray investigation of molar calcium nitrate solution (167,186). EXAFS and LAXS studies showed a broad and asymmetric distribution of Ca-0 distances centered on a mean value of 2.46 A (174). 

The solid curves below 7 A are calculated accurately for a model (Section 4) that fits the osmotic coefficient data. The curves above 7 A are merely schematic, showing in exaggerated form the oscillations that appear in gab at large r when the concentration is large, even for the models in Section 4. The dashed curve indicates the location and intensity of the peak in g+. (r) identified in aqueous NiCle in neutron diffraction and EXAFS studies, as reviewed in Section 5. 

Figure 57 The molecular structure of [Fe(dppe)2(H2) (H)]+. The H-H bond length is 0.82 A at the neutron diffraction and 0.87 A at X-ray diffraction, respectively...

Determinations of epr fine structure and paramagnetic susceptibilities are most often used. For characterization of higher spin orders, neutron diffraction and other physical methods may be useful. On the other hand, a successful measurement of normal high-resolution nmr spectra would serve as good evidence for singlet ground states of the chemical entities at issue. 

Since these early X-ray diffraction experiments, several other crystals have been subjected to analysis by X-ray and neutron diffraction and the F bond length has remained virtually unchanged. The location of the proton has been the point at issue. Early ir studies on KHF2 were interpreted as evidence for a double minimum potential well (Ketelaar, 1941 Glocker and Evans, 1942), but later studies questioned this (Pitzer and Westrum, 1947 Cote and Thompson, 1951 Newman and Badger, 1951) and led to a revision of earlier opinions (Ketelaar and Vedder, 1951). 

Also, in support of the Litt model, Plate and Shibaev observed that hydrated membranes behave in a fashion as brushlike polymers. This suggested to these authors that Nafion has a multilayer structure such that water forms aggregates in lamellar domains,and this view was said to be supported by the results of the neutron diffraction and Moss-bauer specroscopic experiments of Timashev. ... 

Biochemistry and chemistry takes place mostly in solution or in the presence of large quantities of solvent, as in enzymes. As the necessary super-computing becomes available, molecular dynamics must surely be the method of choice for modeling structure and for interpreting biological interactions. Several attempts have been made to test the capability of molecular dynamics to predict the known water structure in crystalline hydrates. In one of these, three amino acid hydrates were used serine monohydrate, arginine dihydrate and homoproline monohydrate. The first two analyses were by neutron diffraction, and in the latter X-ray analysis was chosen because there were four molecules and four waters in the asymmetric unit. The results were partially successful, but the final comments of the authors were "this may imply that methods used currently to extract potential function parameters are insufficient to allow us to handle the molecular-level subtleties that are found in aqueous solutions" (39). 

A primary hydration number of 6 for Fe + in aqueous (or D2O) solution has been indicated by neutron diffraction with isotopic substitution (NDIS), XRD, 16,1017 EXAFS, and for Fe " " by NDIS and EXAFS. Fe—O bond distances in aqueous solution have been determined, since 1984, for Fe(H20)/+ by EXAFS and neutron diffraction, for ternary Fe " "-aqua-anion species by XRD (in sulfate and in chloride media, and in bromide media ), for Fe(H20)g by neutron diffraction, and for ternary Fe -aqua-anion species. The NDIS studies hint at the second solvation shell in D2O solution high energy-resolution incoherent quasi-elastic neutron scattering (IQENS) can give some idea of the half-lives of water-protons in the secondary hydration shell of ions such as Fe aq. This is believed to be less than 5 X I0 s, whereas t>5x10 s for the binding time of protons in the primary hydration shell. X-Ray absorption spectroscopy (XAS—EXAFS and XANES) has been used... 

Thompson, H. Soper. A.K. Buchanan, P. Aldiwan, N. Creek, J.L. Koh, C.A. (2006). Methane hydrate formation and decomposition Structural studies via neutron diffraction and empirical potential structure refinement. J. Chem. Phys., 124 (16), Art. No. 164508. 

It is usually assumed that the dominant defect species responsible for nonstoichiometry is constituted by oxygen vacancies (rather than metal interstitials). This assumption can be justified on the basis of X-ray and neutron diffraction and density measurements . ... 

In the case of PuP, Psat is unkown, but from neutron diffraction the easy axis is (100) thus Psat = 1.27 Ppowder 0-6 Pb and not 0.42 pg. This correction is important because the difference between Poid = 0.77 ps obtained by neutron diffraction and Ppowder = 0.42 Pb has been attributed to a huge conduction electron polarization of - 0.35 Pb Although important, this term should in reality reach only half this value (- 0.17 pb). 

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