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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Structure, charge and spin density in Na2Ni(CN)(4)center dot 3H(2)O at 295 and 30 K
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Structure, charge and spin density in Na2Ni(CN)(4)center dot 3H(2)O at 295 and 30 K

机译：Na2Ni（CN）（4）中心点3H（2）O在295和30 K时的结构，电荷和自旋密度

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摘要

The earlier reported structure of the title compound, disodium tetracyanonickelate(II) trihydrate, Na2Ni(CN)(4).3H(2)O, has been found to be incorrect and has now been redetermined. The charge distribution has been determined by multipole refinements against single-crystal X-ray diffraction data. In the refinement based on 30 K data a comparison was made between the results obtained using hydrogen positions and displacement parameters from X-ray diffraction with those using the values determined by neutron diffraction. The spin density was investigated by polarized neutron diffraction at 1.6 K. Crystal data: at T = 30 K: a = 7.278 (4), b = 8.856 (5), c = 15.131 (8) Angstrom, alpha = 89.32 (5), beta = 87.39 (4), gamma = 83.61 (4)degrees; at 295 K: a = 7.392 (4), b = 8.895 (4), c = 15.115 (8) Angstrom, alpha = 89.12 (2), beta = 87.46 (2), gamma = 84.54 (2)degrees. The structure contains practically square planar Ni(CN)(4)(2-) ions, which are stacked on top of each other in almost linear chains along the a direction. The separation between the Ni(CN)(4)(2-) planes is rather large, with Ni-Ni distances around 3.7 Angstrom. The six crystallographically independent water molecules are each coordinated to two sodium ions, approximately in the tetrahedral (lone-pair) directions, and the polarizing influence of these sodium ions also appears to be reflected in the deformation density in the lone-pair plane. The charge density based on the deformation functions of all atoms in the structure is compared with the individual densities calculated from the deformation functions of only nickel or the separate water molecules. In this way the effects of simple superposition of the individual densities have been studied. In the planar Ni(CN)(4)(2-) ion the individual deformation density of nickel is in qualitative agreement with that expected from crystal-field theory. As the repulsion from the electrons is much weaker perpendicular to the Ni(CN)(4)(2-) plane than within this plane, the deformation density is considerably larger in the perpendicular direction. However, the largest maxima in the individual deformation density around nickel are not found precisely in the planes defined by nickel and the four cyanide ligands or in the perpendicular direction just mentioned, which illustrates that it is necessary to consider the crystal field due to the whole crystalline environment. [References: 23]
机译：发现标题化合物的早期报道的结构为三水合四氰基甲磺酸二钠（II）Na2Ni（CN）（4）.3H（2）O，这是不正确的，现已重新确定。电荷分布已通过针对单晶X射线衍射数据的多极精细化确定。在基于30 K数据的改进中，将使用氢位置和X射线衍射的位移参数的结果与使用中子衍射确定的值的结果进行了比较。通过在1.6 K下极化中子衍射研究了自旋密度。晶体数据：在T = 30 K时：a = 7.278（4），b = 8.856（5），c = 15.131（8）埃，alpha = 89.32（5） ，beta = 87.39（4），gamma = 83.61（4）度;在295 K时：a = 7.392（4），b = 8.895（4），c = 15.115（8）埃，alpha = 89.12（2），beta = 87.46（2），γ= 84.54（2）度。该结构包含几乎为正方形的平面Ni（CN）（4）（2-）离子，它们沿a方向几乎成线性链状相互堆叠。 Ni（CN）（4）（2-）平面之间的间距相当大，Ni-Ni距离约为3.7埃。六个在晶体学上独立的水分子每个都与两个钠离子配位，大约在四面体（孤对）方向上，这些钠离子的极化作用似乎也反映在孤对平面的变形密度中。将基于结构中所有原子的变形函数的电荷密度与仅根据镍或单独的水分子的变形函数计算出的单个密度进行比较。通过这种方式，已经研究了单个密度简单叠加的效果。在平面Ni（CN）（4）（2-）离子中，镍的单个变形密度与晶体场理论所预期的密度定性一致。由于来自电子的排斥力垂直于Ni（CN）（4）（2-）平面要比在该平面内弱得多，因此变形密度在垂直方向上要大得多。然而，在镍和四个氰化物配体所定义的平面内或在刚刚提到的垂直方向上，并未精确地发现镍周围的最大形变密度最大值，这说明有必要考虑整个晶体场。晶体环境。 [参考：23]

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