Neutron diffraction hydrates

Naphthoic acid, 3-hydroxy-7-sulfonato-metal complexes structure, 482 1,8-Naphthyridine metal complexes, 92,93 Neoeupferron metd complexes, 509-512 Neptunium complexes cupferron, 510 Neutron diffraction hydrates... 

In general, anions are less strongly hydrated than cations, but recent neutron diffraction data have indicated that even around the halide ions there is a well defined primary hydration shell of water molecules, which, in... 

Protein crystals contain between 25 and 65 vol% water, which is essential for the crystallisation of these biopolymers. A typical value for the water content of protein crystals is 45% according to Matthews et al. l49,150). For this reason it is possible to study the arrangement of water molecules in the hydration-shell by protein-water and water-water interactions near the protein surface, if one can solve the structure of the crystal by X-ray or neutron diffraction to a sufficiently high resolution151 -153). 

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 structure of [H2Wi2O42]10 (paratungstate B) has been determined in at least eight different compounds (Fig. 20). This polyanion is not very soluble and is easily crystallized from aqueous solutions at pH 6-7 with cations such as Na+, K+, NH4, and Mg2+ (158). The role of hydrated cations in the stabilization and crystallization of this polyanion has been discussed (159). The position of the protons has been located by neutron diffraction as internally bound (159, 160) as predicted on the basis of crystallographic work (158b). 

At this time diffraction data for ion-ion distributions in aqueous solutions of moderate concentration are beginning to become available. In aqueous NiCl2 solutions very refined neutron diffraction studies indicate that the Ni2+-Cl pair correlation function has a peak near 3.l8 under conditions in which the Cl does not penetrate the Ni(H20)g2+ unit. (J+2 ) It is reported that EXAFS studies give the same result. (1 3) While the information is most welcome it is puzzling because a geometrical calculation indicates that the closest center to center distance for the Ni2+ and a Cl that does not penetrate the hydration shell is closer to 3.98. (7)... 

J. P. Hunt and H. L. Friedman, Prog. Inorg. Chem. 30, 359 (1983). This review is concerned with the structure of hydration complexes of ions and includes a discussion of the x-ray or neutron diffraction method for determining structure of ions in solution. 

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... 

Neutron diffraction examination of CsFe (S04)2 12H20 and CsFe (Se04)2 12H20 at 15 K showed a small but significant difference between Fe—O bond distances, 1.994(1) A in the sulfate, 2.002(1) A in the selenate. This difference is attributed to the different tilt an s of the coordinated water, 0.6° and 18.6°, respectively. A XRD structure determination on CsFe (8004)2 I2H2O gave Fe—0= 1.989(4) A (at room temperature). This selenate has the a-alum structure, whereas the corresponding sulfate has the /3-alum structure. These results have been placed in the context of X-ray and neutron diffraction studies of structures of hydrated cations in aqueous solution. ... 

Kuhs, W.F. Chazallon, B. Radaelli, P.G. Pauer, F. (1997). Cage Occupancy and Compressibility of Deuterated N2-Clathrate Hydrate by Neutron Diffraction. J. lncl. Phen. Microcyclic Chem., 29, 65-77. 

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. 

Ramsey theory, 22 201-204 Random-fragmentation model, Szilard-Chalmers reaction and, 1 270 Random-walk process, correlated pair recombination, post-recoil annealing effects and, 1 288-290 Rare-earth carbides, neutron diffraction studies on, 8 234-236 Rare-earth ions energy transfer, 35 383 hydration shell, 34 212-213 Rare gases... 

Macchi P, Casati N, Marshall WG, Sironi A (2010) The a and p forms of oxalic acid di-hydrate at high pressure a theoretical simulation and a neutron diffraction study. CrystEngComm 12 2596-2603... 

Starting with [Cr(OH2)6]3+, the nature of the second hydration shell has been probed with a variety of techniques including IR, XRD, EXAFS, and neutron diffraction (4). Surprisingly consistent results have been obtained, with n = 13 1 in [Cr(OH2)6]3+ (H20) and a Cr— distance of 4.02 A for the water molecules in the second hydration shell. 

X-ray and neutron diffraction methods and EXAFS spectroscopy are very useful in getting structural information of solvated ions. These methods, combined with molecular dynamics and Monte Carlo simulations, have been used extensively to study the structures of hydrated ions in water. Detailed results can be found in the review by Ohtaki and Radnai [17]. The structural study of solvated ions in lion-aqueous solvents has not been as extensive, partly because the low solubility of electrolytes in 11011-aqueous solvents limits the use of X-ray and neutron diffraction methods that need electrolyte of -1 M. However, this situation has been improved by EXAFS (applicable at -0.1 M), at least for ions of the elements with large atomic numbers, and the amount of data on ion-coordinating atom distances and solvation numbers for ions in non-aqueous solvents are growing [15 a, 18]. For example, according to the X-ray diffraction method, the lithium ion in for-mamide (FA) has, on average, 5.4 FA molecules as nearest neighbors with an... 

Aqueous solutions of nickel(II) salts in the absence of strong coordinating species are usually green because of the [Ni(H20)ft]2+ cation.1447 The number of coordinated water molecules in the inner-shell complex is now well ascertained in the temperature range -30 to 30 °C by means of electronic and both 170 and LHNMR spectra.1448-1451 The most recent value of the coordination number is 5.85 0.2.145 Neutron diffraction studies of NiCl2 in D20 solution led to estimates of the Ni—O bond distance within the [Ni(D20)6]2+ cation in the range 195-220 pm.1452 A second hydration sphere of about 15 water molecules has also been proposed. 

Cation X-Ray diffraction EXAFS Neutron diffraction Crystal hydrates Ionic radii ... 

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