Gaudin E, Petricek V, Boucher F, Taulelle F, Evain M
Laboratoire de Chimie des Solides, IMN, UMR C6502 CNRS, Universite de Nantes, 2 rue de la Houssiniere, BP 32229, 44322 Nantes CEDEX 3, France.
Acta Crystallogr B. 2000 Dec;56 (Pt 6):972-9. doi: 10.1107/s0108768100010260.
The crystal structure of the third polymorph of the Cu(7)PSe(6) argyrodite compound, alpha-Cu(7)PSe(6), heptacopper phosphorus hexaselenide, is determined by means of single-crystal diffraction from twinned crystals and X-ray powder diffraction, with the help of extensive NMR measurements. In the low-temperature form, i.e. below the last phase transition, alpha-Cu(7)PSe(6) crystallizes in orthorhombic symmetry, space group Pna2(1), with a = 14.3179 (4), b = 7.1112 (2), c = 10.1023 (3) A, V = 1028.590 (9) A(3) (deduced from powder data, T = 173 K) and Z = 4. Taking into account a twinning by reticular merohedry, the refinement of the alpha-Cu(7)PSe(6) structure leads to the residual factors R = 0.0466 and wR = 0.0486 for 127 parameters and 3714 observed, independent reflections (single-crystal data, T = 173 K). A full localization of the Cu(+)d(10) element is reached with one twofold-, one threefold- and five fourfold-coordinated Cu atoms. The observation of two phase transitions for Cu(7)PSe(6), to be compared with only one for Ag(7)PSe(6), is attributed to the d(10) element stability in a low coordination environment, copper being less prone to lower coordination sites than silver, especially at low temperature.
通过对孪晶进行单晶衍射和X射线粉末衍射，并借助大量核磁共振测量，确定了铜磷六硒化物（Cu₇PSe₆）第三种多晶型物α-Cu₇PSe₆（七铜磷六硒化物）的晶体结构。在低温形式下，即在最后一次相变温度以下，α-Cu₇PSe₆以正交晶系对称结晶，空间群为Pna2(1)，a = 14.3179 (4) Å，b = 7.1112 (2) Å，c = 10.1023 (3) Å，V = 1028.590 (9) ų（由粉末数据推导得出，T = 173 K），Z = 4。考虑到网状半面孪晶，对α-Cu₇PSe₆结构进行精修，对于127个参数和3714个观测独立反射（单晶数据，T = 173 K），残余因子R = 0.0466，wR = 0.0486。通过一个二重配位、一个三重配位和五个四重配位的铜原子实现了Cu⁺d¹⁰元素的完全定位。观察到Cu₇PSe₆有两次相变，而Ag₇PSe₆只有一次相变，这归因于d¹⁰元素在低配位环境中的稳定性，铜比银更不容易倾向于低配位位点，尤其是在低温下。
