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Crystal structure determination and analysis have been carried out for the two spin-crossover compounds [Fe(teeX)6](BF4)2 (teeX is haloethyltetrazole; X = I: teei; X = Br: teeb), in both their high-spin (near 300 K) and their low-spin states (T = 90 K), using high-resolution powder-diffraction data collected at the ESRF (Grenoble, France) and SPring8 (Japan) synchrotron radiation facilities. The structures of teei have been solved using various direct-space structure determination techniques (grid search, genetic algorithm and parallel tempering) and refined with the Rietveld method using geometrical restraints. In the case of teeb, a structural model was found but a full refinement was not successful because of the presence of a significant amount of an amorphous component. Analysis of the structures (space group P21/c, Z = 2) and diffraction data, and the absence of phase transitions, show the overall structural similarity of these compounds and lead to the conclusion that the gradual spin-crossovers are likely to be accompanied by small structural changes only. [ABSTRACT FROM AUTHOR]

The crystal structures of β-1,2,3-tris(pentadecanoyl)glyceroI (β-C15C15C15), β-1,2,3-tris(heptadecanoy1)glycerol (β-C17C17C17) and β-1,2,3-tris(nonadecanoyl)glycerol (β-C19C19C19) have been determined from high-resolution X- ray powder diffraction data. Grid search and Rietveld refinement have been used to determine and refine the structures, respectively. As in β-1,2,3-tris(tridecanoyl)glycerol (β-C13C13C13) and the even-numbered mono-acid triacylglycerols, all three odd-numbered monoacid triacylglycerols crystallize in space group P&macr1; with Z = 2 in an asymmetric tuning-fork conformation and have a lateral acyl chain packing resulting in a layered structure. [ABSTRACT FROM AUTHOR]

Reports findings of a study where the structure of the coordination compound [Fe9teec)[sub 6]](BF[sub 4])[sub 2], hexa[(2-chloroethyl)tetrazole]iron(II)di(borotetrafluoride) were determined using the grid-search techniques of the program suite MRIA. Crystal structure at room temperature showing the existence of two symmetry-equivalent iron(II) ions in the high-spin state.

The crystal structures of the β' phase of CLC (1.3-didecanoyl-2-dodecanoylglycerol) and MPM (1.3-ditetradecanoyl-2-hexadecanoylglycerol) have been determined from single-crystal X-ray diffraction and high-resolution X-ray powder diffraction data, respectively. Both these crystals are orthorhombic with space group Iba2 and Z = 8. The unit-cell parameters of β'-CLC are a = 57.368 (b), b = 22.783 (2) and c = 5.6945 (6) Å and the final R value is 0.175. The unit-cell parameters of β'-MPM are Rp value is 0.057. Both the β'-CLC and β'-MPM molecules are crystallized in a chair conformation, having a bend at the glycerol moiety. The zigzag planes of the acyl chains are orthogonally packed, as is typical for a β' phase. Furthermore, unit-cell parameters of some other members of the CnCn+2n-type triacylglycerol series have been refined on their high-resolution X-ray powder diffraction pattern. Finally, the crystal structures are compared with the currently known structures and models of triacylglycerols. [ABSTRACT FROM AUTHOR]

A complete isothermal phase-transition scheme of cocoa butter under static conditions is presented, based on time-resolved X-ray powder diffraction experiments. In contrast to what is known from literature, not only β V, but also β VI can be obtained directly through transformation from β′. Another remarkable result is that β′ exists as a phase range rather than as two separate phases. Within this β′ phase range no isothermal phase transitions have been observed. More detailed information concerning the observed cocoa butter polymorphs was obtained by determination of melting ranges, using time-resolved X-ray powder diffraction. Also standard X-ray powder diffraction patterns of the γ, the α, and the two β phases and parts of the β′ phase range have been recorded. The observed phase behavior of cocoa butter has been explained based on the concept of individual crystallite phase behavior of cocoa butter [ABSTRACT FROM AUTHOR]

From a homologous series of C nCn+2Cn ( n = even) triacylglycerols which are β′-stable, Guinier X-ray powder diffraction photographs were used to determine cell parameters and space groups. The powder diffraction patterns are consistent with a pseudo-orthorhombic unit cell with space group lc2a. Only one axis is changing as a function of chain lengthening. The experimental results were used to propose a β′-crystal packing for triacylglycerols. In contrast to earlier proposed β′-crystal structures, the acyl chains of this structure are not tilted with respect to the methyl-end group plane. Furthermore, with only one molecule in the asymmetric unit, overall orthogonal chain packing is obtained when the intramolecular acyl zigzag planes are parallel. [ABSTRACT FROM AUTHOR]

The melting behavior of twelve different cocoa butter samples, in the β-phase, has been investigated with real-time X-ray powder diffraction. The melting trajectory of each sample is characterized by three temperature values: a starting point, a point of maximum melting, and a point of complete melting. These points are determined by an analysis of the subsequent X-ray diffraction patterns. A least-squares analysis has been developed which allows the observed melting points to be related to the composition of the cocoa butter. This analysis shows that the melting behavior of cocoa butter can be described as a function of certain binary combinations of its major components. [ABSTRACT FROM AUTHOR]

The crystallization behavior of cocoa butter has been investigated by means of real-time X-ray powder diffraction. Two procedures have been followed: cooling from 60°C at a constant rate until maximum solidification has taken place; and cooling from 60°C in 2 min to a constant solidification temperature. It appears that all polymorphic forms of cocoa butter, with the exception of the β form, can be formed from liquid. The solidification temperature appears to be the most important crystallization parameter. [ABSTRACT FROM AUTHOR]

Direct β-crystallization of different samples of cocoa butter has been investigated. The influence of the thermal history of cocoa butter on its phase behavior is defined as a memory effect. The chemical composition of cocoa butter has been related to the occurrence of the short-term β-memory effect via statistical analysis of the results. We explain how this effect can be attributed mainly to stearic acid and its related triacylglycerols. The total phase behavior of cocoa butter is discussed on the basis of the results obtained from the series of three papers of which this is the last. [ABSTRACT FROM AUTHOR]