On the Stereochemistry of the Lone-Pair Electrons in AX6E-Systems: Dynamically Distorted Anion in (NH4)2SeBr6, Statically Distorted Anion in l, 3-Propanediammonium-Hexabromoselenate(IV) (C3N2H12)SeBr6

Using 293 K diffractometer intensity data, the crystal structures of (NH4)2SeBr6 (1) and [H3N(CH2)3NH3]SeBr6 (2) have been determined by single crystal X-ray technique and refined to a final Rw of 0.049 and 0.040, respectively. The dark red crystals of 1 are cubic (space group Fm3m) with a = 10.478(2) Å and Z = 4. This structure contains SeBe62- octahedra (point symmetry m3̄m, distance Se-Br: 2.577(2) Å in an antifluorite type arrangement of cations and anions. In contrast, the SeBr fi 2-ion in 2 is statically distorted (approximate point symmetry 3m, distance Se-Br min. 2,547(2), max. 2.595(2) Å. The dark red crystals are orthorhombic (space group Pnma) with a = 17.795(3), b = 7.5037(6), c = 10.476(1) Å and Z = 4. The results agree with the rules for the appearance of a static/dynamic stereochemical effect of the lone pair electrons given for TeX62- (X = Cl, Br, I) species (W. Abriel, Acta Crystallogr. B 42, 449 (1986)). Consequently these rules can be extended considering SeX62- as well. Basic structural data for all compounds containing AX62- ions (A = Se, Te; X = Cl, Br, I) known to date are given including the ⊿-values (R. D. Shannon, Acta Crystallogr. A 32, 751 (1976)) as a measure for the distortion of the octahedral anion

Vibronische Kopplung und dynamisch verzerrte Strukturen in Hexahalogenotelluraten(IV): Ergebnisse aus Tieftemperatur-Röntgenbeugungsuntersuchungen (300—160 K) und aus FTIR-spektroskopischen Experimenten (300—5 K) [1]

From theoretical considerations a dynamically distorted octahedron as a result of vibronic coupling between the ground state and the first excited state should exist for 14 electron AX6E systems like TeX62- . A high symmetry crystal field yielding at least a center of symmetry for the Te position stabilizes this fluctuating structure, otherwise statical distortion will be observed. From X-ray diffraction experiments on antifluorite type compounds A2TeX6 (A = Rb. Cs: X = Cl, Br) the averaged structure (m3̅m symmetry) of the anions was found even at very low temperatures. The thermal parameters are not significantly different from those of similar SnX62 compounds. Distortions therefore are very small and are evident from FTIR spectroscopic meas­urements only. Here very broad T1u-deformation vibration bands are observed down to tempera­tures <10 K without splitting: Astatically distorted species could not be frozen out. In contrast to XeF6 for TeX62- the energy gap between the threefold, fourfold or sixfold minima of the potential surface (according to the symmetry of one component of the T1u-vibration) is very small and shifted to temperatures lower than reached with the devices used for these experiments

Zur Stereochemie des freien Elektronenpaares in AX6E-Systemen, VIII Statisch verzerrte Anionen in [H3N(CH2)3NH3]3(BiX6)2(H2O)2 mit X = Cl, Br

Using 293 K diffractometer intensity data, the crystal structures of [H3N(CH2)3NH3]3(BiX6)2(H2O)2 with X - Cl, Br have been determined by single crystal X-ray technique and refined to a final Rw of 0.027 and 0.043, respectively. The structures are isotypic, space group P21/c, Z = 2 with a = 14.415(1). b = 9.7401(7), c = 12.4609(9)Å, β = 105.997(8)°for X - Cl and a = 14.794(2), b = 10.127(2), c = 12.853(2)Å, β = 105.68(2)° for X - Br. Statically distorted BiX63- octahedra confirm the symmetry rules for the stereochemistry of the lone pair electrons in AX6E-systems. Basic structural data for all compounds containing BiX63- and SbXh3 ions (X = Cl, Br, I) known to date are given including the ⊿-values as a measure for the distortion of the octahedral coordination polyhedron

Darstellung und Kristallstruktur von [H3N(CH2)3NH3]SbCl5

Using 293 K diffractometer intensity data, the structure of [H3N(CH2)3NH3]SbCl5 has been determined by single crystal X-ray technique and refined to a final Rw of 0.026. The colorless crystals are monoclinic (space group P21/c) with a = 10.1338(5), b = 11.4623(7), c = 11.3668(6) Å, β = 113.52(5)° and Ζ = 4. The structure contains ψ-octahedral SbCl52- anions. A center of symmetry connects two anions forming a (Sb2Cl10)4- unit with rather long Sb—Cl distances for the bridging Cl-atoms (2.92 and 3.68 A, respectively)

Die Kristallstrukturen von Verbindungen des Typs A2TeX6 (A = K, NH4, Rb, Cs; X = Cl, Br, I)

With the determination of the crystal structure of (NH4)2TeI6 the list of the descriptions of A2TeX6 structures is further completed. At 293 K three structure types are observed with an antifluorite packing of cations and anions: The cubic K2PtCl6 type structure (space group Fm 3̄ m, Z = 4), the tetragonal Rb2TeI6 type structure (space group P4/mnc, Z = 2), and the monoclinic K2TeBr6 type structure (space group P21/n, Z = 2). The latter type was found for (NH4)2TeI6 with a = 8.0694(7), b = 8.0926(9), c = 11.7498(8) Å and β = 89.605(8)° and refined to a final Rw of 0.065. From ionic radii ratios the symmetry of the A2MX6 type structures can be predicted including a prediction of low temperature instability (soft mode condensation). Group-subgroup relationships connect the corresponding space groups and the space groups of the high/low temperature polymorphs

Die Kristallstruktur von [(CH3)4N]2TeCl6 und über die Einschlußverbindung [(CH3)4N]2(CH3CN)TeCl6

Both title compounds show an antifluorite-like arrangement of (CH3)4N+ cations and TeCl6 2- anions. The remaining octahedral holes in this array can be filled with CH3CN molecules forming the inclusion compound by crystallization from CH3CN solution. [(CH3)4N]2TeCl6 (space group Fd3c with a = 25.791(3) Å at 265(5) K and Z = 32) contains almost regular TeCl6 2- octahedra. In contrast, in [(CH3)4N]2(CH3CN)TeCl6 (space group Cmcm with a = 12.765(6), b = 14.349(7), c = 12.716(3) Å and Z = 4) the anion is statically distorted with the approximate point symmetry 4 mm. At temperatures above 320 K the solvent molecules can be removed yielding the Fd3c phase. Finally, structural relationships between antifluorite-like phases A2BX6 and elpasolites A2B'BX6 considering halogenides and cyanides are discussed

Über hexakoordinierte gemischte Halogeno-Anionen des Te(IV): Kristallographische und Raman-spektroskopische Untersuchungen an Rb2TeBr3, 5Cl2, 5

The title compound contains the anions [TeBr3Cl3]2- and [TeBr4Cl2]2- in a 1:1 ratio. The corresponding point symmetries, detected by Raman spectroscopic methods, are 3 m and 4/mmm, respectively. The crystal structure analysis exhibits a random distribution of these anions: K2PtCl6- type, space group Fm3̅m with a = 10.4602(5) Å and Z = 4, final R = 0.036 from 178 F0 (MoKα)

On the Stereochemistry of Lone Pair Electrons in Compounds with Tetravalent Tellurium: Distorted TeCl62-Octahedron in [H3N(CH2)3NH3]TeCl6, Regular Octahedral Anion in [H3N(CH2)3NH3]SnCl6

Using 293 K diffractometer intensity data, the structures of [H3N(CH2)3NH3]TeCl6 and [H3N(CH2)3NH3]SnCl6 have been determined by single crystal X-ray technique and refined to a final of 0.027 and 0,029, respectively. The yellow crystals of the tellurate are orthorhombic (space group Pnma) with a = 22.952(2), b = 7.5414(4), c - 7.801(1) Å and Z = 4. This structure contains distorted TeCl62- octahedra (distances Te - Cl min. 2.426(1), max. 2.672(1) Å ) with approximate 2mm point symmetry. In contrast, the SnCl62- ion in the second title com pound is octahedral with only small deviations from m 3m symmetry (distances Sn -Cl mean: 2.438(3) Ä ). The colourless crystals of this tin com pound are orthorhombic (space group Pnma) with a - 17.6082(9), b = 7.1809(3), c = 10.190(1) Å and Z = 4. Considering the TeX62- (X = Cl, Br, I) salts known to date, a distorted species is an exception, although a distortion is predicted by the VSEPR theory. The results agree with the rules for the appearance of a static stereochemical effect of the lone pair electrons in the TeX62- species