Synthesis and crystal structure of Cu6[Ge6O18]*6 H2O, a dioptase-type cyclo-germanate

H.-J. Brandt, H. Otto
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引用次数: 10

Abstract

Cu 6 [Ge 6 O 18 ]. 6 H 2 O is obtained from aqueous solution as a crystalline, greenish-turquoise powder, having space group R3, lattice parameters a =15.0347(4) A and c = 7.9493(2) A, with Z = 18 CuGeO 3 H 2 O formula units per unit cell. The density is d x = 3.88 g cm -3 . X-ray powder diffraction data revealed a crystal structure isotypic with that of the mineral dioptase, Cu 6 [Si 6 O 18 ]. 6 H 2 O. The structure was refined by the Rietveld method to a final residual of R F = 0.036 (R p = 0.067, R wp = 0.088). It consists of sandwiched rings with empty channels down [001]. Isolated and less expanded rings of six corner-sharing GeO 4 tetrahedra alternate vertically with crown-shaped rings of six hydrogen-bonded water molecules. The two ring systems are bonded together by Cu 2+ ions in elongated octahedral coordination of four oxygen atoms and two more distant water molecules. Water can be degassed by heating, leaving Cu 2+ in at least square planar coordination. Once water is removed completely, the less dense compound with lattice parameters a = 14.8763(6) A and c = 7.9761(8) A shows reversible thermochromism from denim-blue at room temperature to rich green at high temperatures, a color which can be frozen by rapid cooling. A crystal-chemical comparison is drawn between Cu 6 [Ge 6 O18]. 6 H 2 O and Cu 6 [Si 6 O 18 ]. 6 H 2 O (dioptase) as well as Pb 6 [Ge 6 0 18 ]. 6 H 2 O, which represents the first example observed with pure [Ge 6 O 18 ] 12- single sechser rings.
二光型环锗酸盐Cu6[Ge6O18]* 6h2o的合成与晶体结构
Cu 6 [ge6o18]。水溶液中得到的6h2o为绿松石状结晶状粉末,其空间群为R3,晶格参数为a =15.0347(4) a和c = 7.9493(2) a,每单元格的公式单位为Z = 18 cugeo3h2o。密度为dx = 3.88 g cm -3。x射线粉末衍射数据显示其晶体结构与矿物铜6 [Si 6 O 18]的晶体结构相同。采用Rietveld法对结构进行细化,最终残差R F = 0.036 (R p = 0.067, R wp = 0.088)。它由夹层环和空通道组成[001]。由6个共用角的GeO - 4四面体组成的孤立的和扩展较小的环与6个氢键水分子组成的冠状环垂直交替。这两个环系是由Cu 2+离子以四个氧原子和两个更远的水分子的八面体配位连接在一起的。水可以通过加热脱气,使cu2 +至少保持平面的平方配位。一旦水完全除去,晶格参数a = 14.8763(6) a和c = 7.9761(8) a的密度较低的化合物表现出可逆的热变色,从室温下的斜纹蓝到高温下的富绿色,这种颜色可以通过快速冷却而冻结。对cu6 [ge6o18]进行了晶体化学比较。6 h2o和Cu 6 [Si 6 O 18]。6 h2o (dioptase)和pb6 [ge60 18]。这是第一个用纯[ge6o18] 12-单环观察到的例子。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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