Krawczyk J, Pietraszko A, Kubiak R, Łukaszewicz K
Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-950 Wrocław, Poland.
Acta Crystallogr B. 2003 Jun;59(Pt 3):384-92. doi: 10.1107/s0108768103004804. Epub 2003 May 23.
Crystals of uranium iodine phthalocyanine present an example of a disordered commensurate modulated structure of the intergrowth type. The short-range order of both uranium ions and iodine chains I(3)(-) has been analysed by Reverse Monte Carlo (RMC) simulation of X-ray diffuse scattering. The diffraction pattern of uranium iodine phthalocyanine contains diffuse superstructure reflections. In the routine crystal structure analysis diffuse superstructure reflections may be either omitted or measured and classified along with other Bragg reflections. The crystal structure of uranium iodine phthalocyanine is an example of such ambiguity. The crystal structures of two specimens of [U(1-x)Pc(2)]I(2-y) with slightly different composition have been published in the literature with different space groups and unit cells. We have shown that the structure of both specimens differs only in the degree of short-range order and is isostructural with [YbPc(2)]I(2). We have also shown that while the omission of diffuse reflections results in the average crystal structure, the treatment of these reflections as normal Bragg reflections is incorrect and produces the structure averaged over a limited small range.
铀碘酞菁晶体是共生型无序调制结构的一个例子。通过对X射线漫散射的反向蒙特卡罗（RMC）模拟，分析了铀离子和碘链I(3)(-)的短程有序性。铀碘酞菁的衍射图案包含漫散射超结构反射。在常规晶体结构分析中，漫散射超结构反射可能会被忽略，或者与其他布拉格反射一起进行测量和分类。铀碘酞菁的晶体结构就是这种模糊性的一个例子。文献中已发表了两种成分略有不同的[U(1-x)Pc(2)]I(2-y)样品的晶体结构，它们具有不同的空间群和晶胞。我们已经表明，这两种样品的结构仅在短程有序程度上有所不同，并且与[YbPc(2)]I(2)同构。我们还表明，虽然忽略漫反射会得到平均晶体结构，但将这些反射当作正常布拉格反射来处理是不正确的，并且会产生在有限小范围内平均的结构。
