Neutron diffraction studies types

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. 

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. 

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. 

Thermodynamic (specific-heat) and transport (resisitivity) studies for the U(Pti xPdx)3 compounds have revealed magnetic transitions for x-values of 0.02 and higher, in contrast to the compounds below x = 0.01 that did not show anomalies in specific heat and resistivity that point to magnetic order. The sharpest transition in the specific heat studies is found for x = 0.05. For this compound, the resistivity v.v temperature curve exhibits a Cr-type of anomaly just below the magnetic ordering temperature suggesting the presence of a spin-density wave below TN. A few results from neutron diffraction studies are shown in fig. 6. 

Wollan, E. O. Koehler, W. C. 1955 Neutron diffraction study of the magnetic properties of the series of perovskite-type compounds [La xj, CajMn03. Phys. Rev. 100, 545-563. (doi 10. 1103/PhysRev. 100,545)... 

A special type of pseudo-polymorphism is that related to the proton transfer along an X-H Y interaction. The motion may not be associated with a phase transition, but may well imply the transformation of a molecular crystal into a molecular salt. Wilson [34] has discussed, on the basis of an elegant neutron diffraction study, the migration of the proton along an O-H O bond in a co-crystal urea-phosphoric acid (1 1) whereby the proton migrates towards the mid-point of the hydrogen bond as the temperature is increased, becoming essentially centred at T > 300 K. Wiechert and Mootz [35] isolated two crystalline materials composed of pyridine and formic acid of different composition. In the 1 1 co-crystal the formic acid molecule retains its proton and transfer to the basic N-atom on the... 

The crystal structure of sucrose has been established by X-ray diffraction and neutron diffraction studies. The packing of sucrose molecules in the crystal lattice is determined mainly by hydrogen bond formation between hydroxyl groups of the fructose moiety. As an example of the type of packing of molecules in a sucrose crystal, a projection of the crystal structure along the a axis is shown in Figure 4-15. The dotted square represents one unit cell. The crystal faces indicated in this figure follow planes between adjacent sucrose molecules in such a way that the... 

Table 9.5 b. The intramolecular hydrogen bonds in y5-cyclodextrin undecahydrate at 120 K are all of the three-center type, one is a flip-flop. Data taken from a neutron diffraction study [455]. (For atom numbering see Part IIB, Chap. 18)... 

Proton NMR cannot be used as an indication of the position occupied by hydrides in HNCC in solution as the range of chemical shifts observed is enormous (441). For example, all fully characterized carbonyl clusters that contain interstitial hydrides are listed in Table II, with chemical shifts from 23.2 6 in [Co6(CO)isH]- to -24(5 in [Nii2(CO)2iH] -. The octahedral [Rue(CO).8H]- was the first reported cluster for which an interstitial hydride was assigned on the basis of X-ray (30, 31) and solid-state infrared spectroscopy studies (33). However, because of the extremely low field position of the NMR signal (16.4 S), it was suspected to be of the formyl type (417). Its interstitial position was later unequivocally established by neutron diffraction studies (32). The observation of the satellites in the... 

The use of neutron diffraction provides structural information about fats in hquid and crystalline states through interactions of neutrons with atomic nucleus that is different from the information provided by X-ray diffraction. Neutron diffraction studies with selective deuteration of glycerine and fatty acid chains of a TAG indicated nematic-type liquid crystal organization of the TAG molecules in the liquid phase (21, 22). 

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