Neutron diffraction of crystals

They are derived from x-ray and neutron diffraction of crystals, and from electron diffraction and spectroscopic measurements with microwave, infrared and Raman techniques on the gaseous phase. For optimization of PEFs on small molecules, gas-phase structures are used. They are rather numerous, and they are all calculated... 

Here Sp means by infrared or ultraviolet spectroscopy and M by microwave spectroscopy. Similar values, in general somewhat less reliable, have also been obtained for many molecules by x-ray diffraction of crystals, neutron diffraction of crystals, electron diffraction of gas molecules (ED), or analysis of vibrational frequencies. 

X-ray crystallographic analysis of the sodium thiosulfate pentahydrate [10102-17-7] crystal indicates a tetrahedral stmcture for the thiosulfate ion. The S—S bond distance is 197 pm the S—O bond distance is 148 pm (5). Neutron diffraction of a barium thiosulfate monohydrate [7787-40-8] crystal confirms the tetrahedral stmcture and bond distances for the thiosulfate ion (6). 

It is found that the tetra-isoamylphosphonium cation does not take a roughly spherical shape but accommodates an iodide ion 480 pm from the phosphorus atom. Neutron diffraction of phosphonium bromide crystals shows no evidence of hydrogen-bonding. The ructures of bis(trimethylphosphine)silicon tetrachloride and the iridium salt (134) are also reported. 

Neutron diffraction by crystals has been found valuable for locating hydrogen atoms (especially deuterium atoms, which scatter neutrons strongly), for studying the arrangement of magnetic moments, and for other special purposes. A summary is given by G. E. Bacon, Neutron Diffraction, Clarendon Press, Oxford, 1955. 

Box 3.2. Comparison of X-ray and Neutron Diffraction Single Crystal Analysis X-ray diffraction Neutron diffraction... 

Table 7.11. O-H -O Hydrogen-bond lengths from neutron diffraction of carbohydrates, and from combined (normalized) X-ray and neutron diffraction data from 43 monosaccharide crystal structures...

Boucherle, J. X., Gillon, B., Maruani, J. and Schweizer, J. (1987). Crystal structure determination neutron diffraction of 2,2-diphenyl-1-picrylhydrazyl (DPPH) benzene solvate (1/1). Acta Crystallogr C, 43, 1769-73. [203]... 

Another experimental technique to study the self-association of phenols is to investigate how molecules of phenols pack together in the crystalline state. This type of analysis is made possible by the availability of the computer-based CSD. The CSD contains unit-cell dimensions of more than 230,000 (April 2001 release) three-dimensional crystal-structure determinations that have been studied by X-ray or neutron diffraction. Each crystal structure is identified by a unique six-letter code, called its REFCOD, with an additional two digits for duplicate structures and measurements. 

Taylor, J. C., Mueller, M. H., Hitterman, R. L., Crystal stracture of thorium nitrate pentahydrate by neutron diffraction, Acta Crystal-logr., 20, (1966), 842-851. Cited on page 315. 

Neutron diffraction of K[BD4] shows a tetrahedral array ofhydrogen atoms about the boron atom with a B-H distance of 0.1219nm [95] and the crystal is face-centered cubic at room temperature [96]. 

Single-crystal neutron diffraction of U(BH4)4 was more informative in this respect - showing that each U is surrounded by six BHr ions, four being terdentate and two bidentate. Thus the U is fourteen-co-ordinate. The space group is F432i2, tetragonal, with a = 7.49, c = 13.24 A mean interatomic distances were as follows r(UH) 2.38(2), / (BH) 1.29(4) A. ... 

Recently, Bau et al have determined the neutron diffraction single crystal structure of [N(CH3)4]3[(//5-H)2Rhi3(CO)24] and found that five-coordinate hydrogen atoms are located in the square pyramidal cavities on the surface of the Rhis cluster in positions that are almost coplanar with the Rh4 faces of the cluster. Again, through a comparison with neutron diffraction studies of related rhodium complexes, Bau et al. have shown a correlation between the Rh—H... 

Supplementary Structure Investigations by Neutron Diffraction. Single-crystal X-ray structure analysis cannot determine the positions of hydrogen atoms in many cases. Even with error-free measurements, there are essentially two reasons ... 

Diffraction of X-rays or neutrons by crystals have provided very rich material on inter-nuclear distances R. If explicit determination of angles is not required, electron diffraction of gaseous molecules, or X-ray and neutron diffraction of vitreous materials, solutions, etc. may many times provide acceptable R values. If one asks for the distribution of distances from a given point in a gas of geometrical points, the density in a shell between R and R -1- dR is jaroportional to 4nR dR = P. This is also valid in actual compounds and alloys for very long R, but not at all for short R. Fig. 1 is a qualitative probability distribution of R values (normalized by division with P) for nuclei of a given element, or for a combination of two definite elements Zj and Zj. Contrary... 

Recently, lida measured the neutron diffraction of a single crystal of LuFe204 (lida et al. 1988). In an experiment at 14 K, he observed a weak Hne at [0,1, /],... 

D) DIFFRACTION OF NEUTRONS FROM NONMAGNETIC AND MAGNETIC CRYSTALS... 

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