Neutron diffraction study

The example in Fig. 7.5 shows a setup used for measurements of the structure factor of liquid cesium (Winter et al., 1987 Winter and Boden-steiner, 1988) along the coexistence line up to about 1700 °C. The sample 

In order that the high-pressure neutron window be as thin as possible while maintaining the necessary mechanical strength, it is necessary that it remain cool. This is achieved by water cooling that keeps the window at room temperature even when the sample temperature reaches 

1700 °C. All the electrical feedthroughs for thermocouples and heaters are brought through the bottom flange of the autoclave. 

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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. 

Ca(I) sites have been shown to be responsible for most of the observed luminescence, whereas emission from the Mn " ions on the Ca(Il) sites occur only for higher Mn concentrations. Neutron diffraction studies have also confirmed these results (10). 

Conformation. Neutron diffraction studies of sucrose revealed the presence of two strong intramolecular hydrogen bonds 0-2—HO-1 and 0-5—HO-6 in the crystal form (7,8). These interactions hold the molecule in a weU-ordered and rigid conformation. The two rings are disposed at an angle close to 90°, with the glucopyranosyl and fmctofuranosyl residues adapting chair and T" twist conformations, respectively. 

Physical Properties. Table 3 contains a summary of the physical properties of L-ascorbic acid. Properties relating to the stmcture of vitamin C have been reviewed and summarized (32). Stabilization of the molecule is a consequence of delocalization of the TT-electrons over the conjugated enediol system. The highly acidic nature of the H-atom on C-3 has been confirmed by neutron diffraction studies (23). 

Discussion of neutron diffraction studies of superconductors was largely taken from J. D. Jorgensen and D. G. Hinks. Neutron News. 24,1, 1990. 

Pings [106], and a neutron diffraction study by Mildner and Carpenter [107], both concluded that there is no clear evidence for sp carbon and that the radial distribution functions can be satisfactorily indexed to a hexagonal arrays of carbon atoms. A similar conclusion was reached in a recent neutron diffraction study of activated carbons by Gardner et al [108]. 

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. ... 

High-temperature neutron diffraction studies have shown that this latter phase has the cubic ordered Re03-type structure (p, 1047) with octahedral coordination of both types of Sn atoms by F (Sn -F 229 pm, Sn" -F 186 pm). The fi-phase also features octahedral coordination in a structure closely related to that of rhombohedral LiSbF6. 

Definitive proof of the structure of porphine in the solid state awaits a variable-temperature crystallographic (X-ray or neutron diffraction) study the analysis of the anisotropic displacement factors (ADP) should disclose any rotational motion or its absence as well as determine the positions of the inner hydrogens. A search in the September 1998 version of the Cambridge Structural Database [CSD (91MI187)] showed that the only structures of porphine (codename PORPIN) were obtained in 1965 and 1972. 

A.I. Kolesnikov, A.M. Balagurov, I.O. Bashkin, V.K. Fedotov, V.Yu. Malyshev, G.M. Mironova, E.G. Ponyatovsky, A Real-Time Neutron Diffraction Study of Phase Transitions in the Ti-D System after High Pressure Treatment, J. Phys. Condensed Matter 5 5045 (1993). 

O-H bond length was 1.08A, a value similar to that previously reported by Szy-tula et al. in a neutron diffraction study of Ni(OH)2 [23]. The O-H bond is both well crystallized and as precipitated materials is parallel to the c-axis. The difference between well-crystallized and as precipitated material is important since the well-crystallized material is not electrochemi-cally active. The differences between the materials are attributed to a defective structure that accrues from the large concentration of surface OH ion groups in the high-surface-area material [22]. These are associated with absorbed water. This is a consistent with an absorption band in the infrared at 1630cm 1. This is not seen in the well-crystallized material. 

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. 

As a consequence of the molecular orbital interactions, ferrocene adopts an axially symmetrical sandwich structure with two parallel Cp ligands with a distance of 3.32 A (eclipsed conformation) and ten identical Fe-C distances of 2.06 A as well as ten identical C-C distances of 1.43 A [12]. Deviation of the parallel Cp arrangement results in a loss of binding energy owing to a less efficient orbital overlap [8]. All ten C-H bonds are slightly tilted toward the Fe center, as judged from neutron-diffraction studies [13]. 

Takusagawa F, Koetzle TF (1979) A neutron diffraction study of the crystal structure of ferrocene. Acta Crystallogr B 35 1074-1081... 

Baron, V., Gillon, B., Kahn, O. et al. (1993) Spin density in a bimetallic magnetic chain MnCu(pba)(H20)3. 2H20 a polarised neutron diffraction study, Mol. Cryst. Liqu. Cryst., 233, 247-256. 

Warren, P., Forsyth, J.B., McIntyre, GJ. et al. (1992) A single-crystal neutron diffraction study of the magnetization density in Fe2Zx, J. Phys. Cond. Mat., 4, 5795-5800. 

Gukasov, A., Wisniewski, P. and Henkie, Z. (1996) Neutron diffraction study of magnetic structure of U3Bi4 and U3Sb4, J. Phys. Cond. Mat., 8, 10589-10600. 

Papoular, R.J. and Delapalme, A. (1994) Model-free polarised neutron diffraction study of an acentric crystal metamagnetic UCoAl, Phys. Rev. Lett., 72(10), 1486-1489. 

Moze, O., Caciuffo, R., Gillon, B. et al. (1994) Polarised-neutron diffraction study of the magnetisation density in hexagonal Y2Fe17, Phys. Rev. B, 50(13), 9293-9299. 

An important lesson learned from the studies of naphtazarin [2], benzoylacetone [8] and nitromalonamide has been that the detailed structure of these types of compounds can only be reliably determined by introducing results of low-temperature neutron diffraction studies in the analysis of the low-temperature X-ray diffraction data. Furthermore it has been found that information about the bonding of the enol hydrogen can be extracted from the thermal parameters of the enol hydrogen. This underlines the importance of the neutron diffraction study in these cases. 

The long-known K2Hg(CN)4 and related compounds are still the object of structural studies. Thus, a neutron-diffraction study confirmed the spinel structure of K2Hg(CN)4 at room temperature (298 K) with exactly tetrahedral anions, Hg(CN)42 (r(Hg—C) 215.2, r(C—N) 114.9 pm).112... 

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