Ray and Neutron Diffraction

JIT-Ray and Neutron Diffraction.— X-Ray studies have been reported for arsatriptycene (2) and phosphatriptycene (3), and also for substituted arsatrip-tycenes and phosphatriptycenes. The structures of the [4 + 2] cyclo-adduct (4) and the [6 + 4] cyclo-adduct (5) of A -ethoxycarbonyl-l//-azepine with 

van Rooyen-Reiss and C. H. Stam, Acta Crystallogr., Sect. B, 1980,36,1252 F. Smit and C. H. Stam, ibid., p. 1254. 

5-dimethoxycarbonyl-3,4-diphenylcyclopentadienone and of the photoadduct (6) of furan with 1-cyanonaphthalene have been defined by X-ray methods. Cycloaddition of furan with fumaryl chloride proceeds in good yield and makes the bromo-lactone (7) readily available. The X-ray structural determination of (8), obtained via several steps from (7), has been reported. [2, 3] Sigmatropic rearrangement of the ylide (9) affords the vinyl ether (10), which was characterized by X-ray analysis. Further studies concern 4-(trimethylstan-nyl)quinuclidinium perchlorate, 3-ethyl-3-azabicyclo[3.2.1 ]octane-8-spiro-5 -hydantoin, and 1 -bromo-3,5,7-trimethyl-1,3,5,7-tetrasila-adamantane. The conformational equilibria in bicyclo[3.3.1]nonanes have attracted much attention, and a variety of techniques have been used for studies in solution (see below for recent studies), but X-ray analysis has been frequently used to study conformations in the solid state. Energy differences in this series are sufficiently small that different conformations may be adopted in solution and in the crystal. Structures have now been reported for eleven bicyclo[3.3.1]nonanes, including a number of heterocyclic examples. In most cases the chair-chair structure is adopted in the crystal, but examples have been found for preference of the chair-boat structure. 

Further X-ray analyses have been reported in later references (refs. 58, 67, 105, 108, 121, 155, and 191). 

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The structure of a fluid is characterized by the spatial and orientational correlations between atoms and molecules detemiiued through x-ray and neutron diffraction experiments. Examples are the atomic pair correlation fiinctions (g, g. . ) in liquid water. An important feature of these correlation functions is that... 

The main problem with x-ray (and neutron) diffraction is that the infonnation it is made to yield is essentially... 

F H, O Kennard, D G Watson, L Brammer, A G Orpen and R Taylor 1987.1 ables of Bond Lengths determined by X-ray and Neutron Diffraction. 1. Bond Lengths in Organic Compounds. Journal of he Chemical Society Perkin Transactions 11 51-519. 

The stmcture of Pmssian Blue and its analogues consists of a three-dimensional polymeric network of Fe —CN—Fe linkages. Single-crystal x-ray and neutron diffraction studies of insoluble Pmssian Blue estabUsh that the stmcture is based on a rock salt-like face-centered cubic (fee) arrangement with Fe centers occupying one type of site and [Fe(CN)3] units randomly occupying three-quarters of the complementary sites (5). The cyanides bridge the two types of sites. The vacant [Fe(CN)3] sites are occupied by some of the water molecules. Other waters are zeoHtic, ie, interstitial, and occupy the centers of octants of the unit cell. The stmcture contains three different iron coordination environments, Fe C, Fe N, and Fe N4(H20), in a 3 1 3 ratio. 

A detailed account is given in Reference 20. The techniques giving the most detailed 3-D stmctural information are x-ray and neutron diffraction, electron diffraction and microscopy (qv), and nuclear magnetic resonance spectroscopy (nmr) (see Analytical methods Magnetic spin resonance X-ray technology). 

Silver in the +3 oxidation state, including silver peroxide, ie, black oxide, marketed as AgO, is obtained by the action of the vigorous oxidising agent S20 g on Ag20 or other Ag compounds. X-ray and neutron diffraction analyses show the nominal AgO unit cell to be Ag20 Ag202- Both Ag" and Ag " are present. Another compound of potentially important commercial value is Ag O, which has a unit cell of two Ag and two Ag ions. Its preparation is as follows ... 

H2 could be quantitatively removed at room temperature either by partial evacuation or by sparging the solution with argon. Definitive confirmation that the complexes did indeed contain 7J--H2 came from X-ray and neutron diffraction studies on the bisftri t-propylphosphine) analogue at —100°, which revealed the side-on coordination of H2 as shown in Fig. 3.2. During the past decade many other such compounds have been prepared and studied in great detail, and the field has been well reviewed. ... 

Figure 3.2 The geometry of iner-/ran.v-[W(CO)3-(ij--H2)(Pf 3)2l from X-ray and neutron diffraction data r(H-H) 84pm (compared with 74.14 pm for free H2), I(W-H) 175 pm. Infrared vibration spectroscopy gives v(H-H) 2690cm compared with 4159cm (Raman) for free Hj.

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. 

We wish to thank Dr. Raymond G. Teller for the x-ray and neutron diffraction results and Prof. Edward Kostlner for fruitful discussions. 

X-ray and neutron diffraction analysis of the Ca -ATPase of sarcoplasmic reticulum... 

Blasie and his colleagues have determined the separate profile structures of the lipid bilayer and of the Ca transport ATPase molecule within the sarcoplasmic reticulum membrane to 11 A resolution by a combination of X-ray and neutron diffraction techniques [128,140,187-199]. 

Benzoylacetone was studied using both X-ray and neutron diffraction. Four X-ray data sets at four different temperatures were collected, namely at room temperature, 160, 20 and 8 K. Furthermore a neutron data set was collected at 20 K. 

The most well-characterized metalla-/3-diketone is 10 in that both X-ray and neutron diffraction structures have been determined (11 and 12) (26). 

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 crystal structure of /3-Be(OH)2 has been determined using both X-ray and neutron diffraction (101). It is very similar to the structure of /j-crystabolite in that Be(OH)4 tetrahedra are linked by corner shar-... 

According to X-ray and neutron diffraction structures [3, 4] the binding of CO to the heme leads to a bent FeCO unit. The Fe-C-O angle is, however, found to be linear in synthetic models of the protein (hiomimetic molecules). Because of this, it was originally thought that the FeCO distortion was responsible for the well known discrimination of the protein against CO - the affinity ratio C0/02 is lower in the protein than in biomimetic systems [1]. In... 

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