Abstract:Die siliciumreiche Käfigverbindung MgSi 5 wird durch Hochdruck-Hochtemperatur-Synthese erhalten. Die erste Bestimmung der Kristallstruktur durch Elektronendiffraktionstomographie schaffte die Basis für Phasenanalysen und damit für den Optimierungsprozess der Synthesebedingungen. Dieser Prozess ermçglichte letztendlich die Herstellung von Einkristallen, die für Rçntgendiffraktionsexperimente geeignet waren. Die Kristallstruktur von MgSi 5 (Raumgruppe Cmme, oS24, a = 4.4868(2) , b = 10.1066(5) und c = 9.0753(4) … Show more
“…Based on previous experience with structure solution from electron diffraction or PEDT data, − we tested the method on the product of an unusual topochemical reaction. This continues our investigations on the synthesis of new compounds by heterogeneous reactions including mass transport and structural transformations in the solid state. − The compounds obtained in this way are often, but not necessarily, metastable and cannot be produced by other methods.…”
The dark red semiconductor Cu(Sb 2 S 3 )Cl was obtained by leaching the layered precursor Cu(Sb 2 S 3 )[AlCl 4 ] in a 0.1 M aqueous HCl solution. The selective extraction of AlCl 3 yielded a mica-like lamellar product of poor crystallinity. Misalignment of lamellae down to the nanoscale prevented structure determination by conventional single-crystal X-ray diffraction, but a combination of transmission electron microscopy, selected area electron diffraction, and selected area electron precession diffraction tomography on a nanoscale spot with largely ordered crystalline lamellae revealed the crystal structures of two intergrown modifications. Orthorhombic o-Cu(Sb 2 S 3 )Cl and monoclinic m-Cu(Sb 2 S 3 )Cl have similar layers to the precursor and differ only in the stacking of the layers. These consist of uncharged Sb 2 S 3 strands, whose sulfide ions, together with chloride ions, coordinate the copper(I) cations. Only one chloride ion remained from the [AlCl 4 ] − group. DFT calculations confirm the structure solution for the orthorhombic form and suggest that the monoclinic structure is metastable against transformation to o-Cu(Sb 2 S 3 )Cl.
“…Based on previous experience with structure solution from electron diffraction or PEDT data, − we tested the method on the product of an unusual topochemical reaction. This continues our investigations on the synthesis of new compounds by heterogeneous reactions including mass transport and structural transformations in the solid state. − The compounds obtained in this way are often, but not necessarily, metastable and cannot be produced by other methods.…”
The dark red semiconductor Cu(Sb 2 S 3 )Cl was obtained by leaching the layered precursor Cu(Sb 2 S 3 )[AlCl 4 ] in a 0.1 M aqueous HCl solution. The selective extraction of AlCl 3 yielded a mica-like lamellar product of poor crystallinity. Misalignment of lamellae down to the nanoscale prevented structure determination by conventional single-crystal X-ray diffraction, but a combination of transmission electron microscopy, selected area electron diffraction, and selected area electron precession diffraction tomography on a nanoscale spot with largely ordered crystalline lamellae revealed the crystal structures of two intergrown modifications. Orthorhombic o-Cu(Sb 2 S 3 )Cl and monoclinic m-Cu(Sb 2 S 3 )Cl have similar layers to the precursor and differ only in the stacking of the layers. These consist of uncharged Sb 2 S 3 strands, whose sulfide ions, together with chloride ions, coordinate the copper(I) cations. Only one chloride ion remained from the [AlCl 4 ] − group. DFT calculations confirm the structure solution for the orthorhombic form and suggest that the monoclinic structure is metastable against transformation to o-Cu(Sb 2 S 3 )Cl.
The clathrate Is uperconductor Sr 8 Si 46 is obtained under high-pressureh igh-temperature conditions, at 5GPa and temperatures in the range of 1273 to 1373 K. At ambient pressure, the compound decomposes upon heatinga t T = 796(5) Ki nto Si and SrSi 2 .T he crystal structure of the clathrate is isotypic to that of Na 8 Si 46 .C hemical bonding analysisr eveals conventionalc ovalent bondingw ithin the silicon network as well as additional multi-atomic interactions between Sr and Si within the framework cages. Physical measurements indicateabulk BCS type II superconducting state below T c = 3.8(3) K.
The metastable type-II clathrate Na 24-δ Ge 136 was obtained from Na 12 Ge 17 by applying a two-step procedure. At first, Na 12 Ge 17 was reacted at 70°C with a solution of benzophenone in the ionic liquid (IL) 1,3-dibutyl-2-methylimidazolium-bis(trifluoromethylsulfonyl) azanide. The IL was inert towards Na 12 Ge 17 , but capable of dissolving the sodium salts formed in the redox reaction. By annealing at 340°C under an argon atmosphere, the X-ray amorphous intermediate product was transformed to crystalline Na 24-δ Ge 136 (δ � 2) and α-Ge in an about 1 : 1 mass ratio. The product was characterized by X-ray powder diffraction, chemical analysis, and 23 Na solid-state NMR spectroscopy. Metallic properties of Na 24-δ Ge 136 were revealed by a significant Knight shift of the 23 Na NMR signals and by a Pauli-paramagnetic contribution to the magnetic susceptibility. At room temperature, Na 24-δ Ge 136 slowly ages, with a tendency to volume decrease and sodium loss.
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