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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Neutron diffraction study of [Pt(en)_2][Pt(en)_2I_2](ClO_4)_4 at 20 K: structure and evidence of a new phase transition
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Neutron diffraction study of [Pt(en)_2][Pt(en)_2I_2](ClO_4)_4 at 20 K: structure and evidence of a new phase transition

机译：[Pt（en）_2] [Pt（en）_2I_2]（ClO_4）_4在20 K下的中子衍射研究：结构和新相变的证据

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摘要

The structure at 20 K of fully deuterated [Pt(en)2]-[Pt(en)2I2](Cl04)4, where en = ethylenediamine, has been determined by neutron diffraction on a single crystal. It is shown that the symmetry is monoclinic with cell parameters a =16.650(7), b = 5.760(2), c= 14.751(2) A and fi = 99.19(1)°, that is, with respect to the previously reported room-temperature structures, a doubling of the c parameter is observed. The space group is C2/c and the refinements lead to an R value of 0.0374. All the bond lengths (C-C, C-N, C-D, N-D and CI-O) and angles are consistent with the expected values and the main difference with respect to the previously reported room-temperature structures results in an ordering of the stacking of the ethylenediamines. The iodines are distributed over two sites, which gives two Pt-I distances, 2.712(3) A, attributed to the PtIV-I bond, and 3.048 (3)A, attributed to Pt11-I. Actually, very weak diffraction peaks that provide evidence for an additional doubling of the a and b parameters are also observed and a space group Cl is therefore proposed. This could result from a very slight ordering of the chains with respect to one another, but, due to the weakness of such signals and the large number of atoms to be considered, no reliable refinement has been obtained in C2. On the other hand, on heating the crystal the diffraction peaks with / odd greatly decrease in intensity between 150 and 160 K, which unambiguously argues for the existence of a phase transition presumably connected to an order-disorder of the ethylenediamines.
机译：完全氘化的[Pt（en）2]-[Pt（en）2I2]（Cl04）4在20 K时的结构（其中en =乙二胺）已通过中子衍射在单晶上确定。结果表明，对称性是单斜的，单元参数为a = 16.650（7），b = 5.760（2），c = 14.751（2）A和fi = 99.19（1）°，即相对于先前报道的在室温结构中，观察到c参数加倍。空间组为C2 / c，细化导致R值为0.0374。所有键长（C-C，C-N，C-D，N-D和CI-O）和角度均与预期值一致，并且相对于先前报道的室温结构的主要差异导致乙二胺堆积的顺序。碘分布在两个位点上，这两个点给出两个Pt-I距离，归因于PtIV-1键的距离为2.712（3）A，归因于Pt11-I的距离为3.048（3）A。实际上，还观察到非常弱的衍射峰，这些衍射峰为a和b参数的加倍提供了证据，因此提出了空间群Cl。这可能是由于链彼此之间的排列顺序非常微小，但是由于这种信号的弱点和要考虑的大量原子，在C2中尚未获得可靠的改进。另一方面，在加热晶体时，具有/奇数的衍射峰的强度在150和160K之间大大降低，这明确地证明存在可能与乙二胺的无序连接的相变。

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