Thermal parameter , anisotropic

The structure was refined by block-diagonal least squares in which carbon and oxygen atoms were modeled with isotropic and then anisotropic thermal parameters. Although many of the hydrogen atom positions were available from difference electron density maps, they were all placed in ideal locations. Final refinement with all hydrogen atoms fixed converged at crystallographic residuals of R=0.061 and R =0.075. 

The structure was refined with block diagonal least squares. In cases of pseudo-symmetry, least squares refinement is usually troublesome due to the high correlations between atoms related by false symmetry operations. Because of the poor quality of the data, only those reflections not suffering from the effects of decomposition were used in the refinement. With all non-hydrogen atoms refined with isotropic thermal parameters and hydrogen atoms included at fixed positions, the final R and R values were 0.142 and 0.190, respectively. Refinement with anisotropic thermal parameters resulted in slightly more attractive R values, but the much lower data to parameter ratio did not justify it. 

Crystal data and parameters of the data collection (at -173°, 50 < 20 < 450) are shown in Table I. A data set collected on a parallelopiped of dimensions 0.09 x 0.18 x 0.55 mm yielded the molecular structure with little difficulty using direct methods and Fourier techniques. Full matrix refinement using isotropic thermal parameters converged to R = 0.I7. Attempts to use anisotropic thermal parameters, both with and without an absorption correction, yielded non-positive-definite thermal parameters for over half of the atoms and the residual remained at ca. 0.15. 

Data was then coTTected on a smaller crystal. The residuals improved, but several non-hydrogen anisotropic thermal parameters converged to non-positive-definite values. There was no evidence for... 

Carbon and oxygen atom positions were refined with anisotropic thermal parameters. Hydrogen atoms were not located. Figure 3 shows the molecular structure and the atom numbering scheme utilized for the x-ray data presented in the supplementary material for heritiana acetate. Coordinates, bond length, and bond angles for compound III acetate are available as supplementary material. 

The final refinement used anisotropic thermal parameters for all positions except 0(5), for which only isotropic values were used. The largest peak (x = 0.21, = z H, height 1.6 eX 3) on the final difference Fourier function (esd = 0.13 eX 3 at a general position) was unstable in least-squares refinement. The structure of partially dehydrated Bag-A is shown in Figure 1. 

ORTEP were used to draw the structures. The final refinement included atomic positions for all the atoms, anisotropic thermal parameters for all the non-hydrogen atoms, and isotropic thermal parameters for the hydrogen atoms. The aromatic hydrogen atoms for I—III, methylene hydrogen atoms of the DABCO unit (for IV), and ethylenediammonium ion (for V) were introduced in the... 

Table 12. Final anisotropic thermal parameters (Ax 100) with e.s.d. s for SPM...

Anisotropic thermal parameters are of the form exp (—2it2(Unh2a 2 +. .. + 2U23klb c ))... 

The figures represent isotropic F atoms, since the anisotropic thermal parameters given in Tables I and III may not be realistic. The data for the structures were not of high quality and, furthermore, the descriptions of the crystals for the absorption corrections were less exact than we would have liked. 

Crystals of Xe(OSeFs)2 are rhombohedral, space group R3m. At 23.5 C the hexagonal axes are fl - 6 = 8.588 (3) and c - 11.918 (3) A Z = 3, da cd = 3.345 g cm"3, and V = 761.23 AL The molecule lies on a threefold axis, and there is orientational disorder of the oxygen and fluorine positions. X-ray diffraction data obtained with an automatic diffractometer were analyzed on the basis of a molecular model with some constraints based on chemical considerations to reduce the number of independent parameters of the poorly resolved oxygen and fluorine atoms. For 122 unique reflections with > a(F ) and with anisotropic thermal parameters, R = 0.064. Bond distances are Xe-0 2.12 (5), Se-0 1.53 (5), and Se-F = 1.70 (2) A (uncorrected) and Se-F = 1.77 A (corrected for thermal motion). 

A Fourier synthesis revealed ten major peaks, in addition to the two Rh atom peaks in the asymmetric unit. These ten peaks were assigned as F atoms and refinement, employing isotropic thermal parameters, yielded a final conventional R =0.067. Three cycles of least-squares refinement, in which anisotropic thermal parameters were permitted for the rhodium atoms, resulted in an R factor of 0.049. 

The final positional, isotropic, and anisotropic thermal parameters are given in Table 2, together with their stand-... 

Final positional parameters (fractional) with standard deviations (A), final isotropic thermal parameters (A X 10 XJ = BjSn ). and final anisotropic thermal parameters (A x 10 )... 

Table III. Distances and angles for f -NiF3 at 2 and 295 K, refined in R3 (the Ni atoms were modelled with anisotropic thermal parameters in the 2 K refinement, but isotropically for the 295 K).

In simulating the observed diffraction pattern, however, large values of anisotropic thermal parameters (l/i,) were necessary for As and F atoms. The temperature dependence of the pattern obtained by the Guinier-Simon method (Fig. 8) indicates that the pattern essentially does not change up to 390 K. This hinted that there prevails considerable disorder already at room temperature. The fine structure at 300 K shown in Fig. 8(/>)... 

Fig. II Observed Guinier-Simon X-ray powder diflraetion pattern (Cu-Kaj) of the nestled Ci.AsF. at 300 K and the dependence of simulate pattern on the anisotropic thermal parameters U,(As) and...

Table 5 Anisotropic thermal parameters (xlOO) used for the calculations...

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