The crystal structure of K/NbF7, determined originally from two-dimensional X-ray data, has been refined by the method of least-squares with three-dimensional data. The refinement included adjustment of the scattering factors of niobium and potassium relative to the fluorine scattering factor. For potassium the new value 0.370_+0.004 cm-a2 was found. Effects of extinction were minimized by omittingfrom the final refinement a number of the observations, as suggested by systematic analysis of the quality of agreement between calculated and observed F2 values as a function of observed intensity. Shifts of atomic positions by as much as 0.15 A occurred in the refinement, but the general description of the structure, including the description of the NbF~-ion, remains unchanged. The standard errors of the coordinates are about 0.001 A for the niobium atom and 0.002 to 0.003 ,~ for the fluorine atoms and the potassium ions. Analysis of the anisotropic thermal parameters shows that the NbF, 2-ion is a nearly ideal case for use of the 'riding' model in calculating bond-length corrections, and the Nb-F bond lengths have been corrected accordingly. Exceptionally large vibrational displacements of two of the fluorine atoms seem plausible in view of the packing in the crystal.
die kurzen Absffmde von 3,09 bzw. 3,08 A hin, die zwischen dem Wassermolekiil 0(4) und seinen beiden C1-Nachbarn [C1(3) (x + 1, y-1, z) und CI(3) (-x, -y + 1, -z)] beobachtet werden. The effect of the integration limits on the measurement of intensities of cq, ~2 doublets is investigated and the minimum limits required to avoid errors due to the separation are defined.Errors can arise in the photometry of high angle integrated reflexions, due to ctz,ct2 separation, unless this factor is taken into account in setting the integrating ranges. Of course, if the doublet is treated as a single reflexion, and the greatest measurement across any doublet on a nonintegrating photograph is added to the diameter, b, of the photometer beam to give the integrating range in that direction, then there will be an area of diameter b, in the centre of the resulting integrated spot, whose uniform density will be proportional to the total energy in ~l+0Cz.
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