Band 223, Heft 7

Structural changes within the isotypic series ABiO 2 (A = Na, K, Rb, Cs) and ASbO 2 (A = K, Rb, Cs) and between corresponding members of the two series are analyzed after re-determination of the structure of NaBiO 2 . Despite the low valence of A—O bonds as compared to E—O bonds (E = Sb, Bi), the A atoms of different sizes are largely able to satisfy their individual spatial requirements. Small deviations between expected and experimentally determined Na/K size differences in the ABiO 2 series are explained by a change in the bonding scheme in the transition from NaBiO 2 to KBiO 2 . The results of DFT calculations show that the unexpected increase of the lattice parameters b in the three transitions ABiO 2 → ASbO 2 is not caused – as assumed before – by the different stereochemical activities of the Sb and Bi lone electron pairs. Instead, this increase is caused by cation-cation repulsions owing to the observed de crease in c .

Powder FTIR spectra of the solid solution series |(Ca 2 – x Eu x ) 4 (OH) 8 |[(Al 2 + x Si 1 – x ) 4 O 24 ]- SOD , 0 ≤ x ≤ 1, were taken at room temperature. All members, including the mineral bicchulite, |Ca 8 (OH) 8 |[Al 8 Si 4 O 24 ]- SOD , have a sodalite-type structure. Spectra taken in the hydroxyl region (4000 − 3000 cm −1 ) yield information related to the local structural states of the pseudo-cubane-like (Ca 2 + x Eu 2 – x )(OH) 4 -clusters, 0 ≤ x ≤ 2. Three different patterns of short range order could be identified. Depending on x , different concentrations of Ca 4 (OH) 4 , EuCa 3 (OH) 4 , and Eu 2 Ca 2 (OH) 4 clusters are found, whereas Eu 3 Ca(OH) 4 or Eu 4 (OH) 4 clusters are not observed. Hence, short range order is maintained such that each SOD cage of an all-alumina framework contains two Ca and two Eu per cluster. The positions of the framework stretching and bending modes shift linearly towards lower wavenumbers with increasing Al content. The shifts are correlated with changes of the framework geometry. Furthermore, Alrich samples show splitting of the stretching and bending modes. This is interpreted as the change of the local environment of Al due to the substitution of Eu 3+ for Ca 2+ . With the use of deuteration experiments a more detailed assignment could be achieved, especially for the M—OH absorption bands. Finally, changes in the line shape, resulting from cation ordering, are studied by autocorrelation analysis. In particular, samples of intermediate composition show large broadening parameters, Δ corr , suggesting high degrees of local structural heterogeneity.

Crystals of thallium dihydrogendiphosphate Tl 2 Me (H 2 P 2 O 7 ) 2 · 2 H 2 O ( Me = Mg (1) , Mn (2), Co (3) , Ni (4) and Zn (5) ), have been synthesized and analyzed by powder X-ray diffractometry (Mg phase) and single crystal X-ray diffractometry (other phases). They resulted to be isostructural within triclinic group P -1, with the following unit-cell parameters: a = 6.9620(1), b = 7.3635(1), c = 7.7713(1) Å, α = 81.8014(5), β = 70.8597(6), γ = 86.1373(7)°, V = 372.44(8) Å 3 (1) ; a = 6.9577(6), b = 7.4745(6), c = 7.8248(7) Å, α = 80.723(2), β = 71.912(1), γ = 85.661(1)°, V = 381.62(6) Å 3 (2) ; a = 6.9767(7), b = 7.3634(7), c = 7.7690(7) Å, α = 81.421(2), β = 71.114(2), γ = 86.424(2)°, V = 373.36(6) Å 3 (3) ; a = 6.9658(7), b = 7.3079(7), c = 7.7016(7) Å, α = 81.801(2), β = 71.185(2), γ = 86.528(2)°, V = 367.27(6) Å 3 (4) and a = 6.9628(7), b = 7.3625(7), c = 7.7401(8) Å, α = 81.590(2), β = 71.441(2), γ = 86.323(2)°, V = 372.04(6) Å 3 (5) . Me is octahedrally coordinated by two water molecules and four oxygen atoms belonging to two different diphos phate groups. Thallium cations make up interactions with oxygen atoms within Van der Waals coordination sphere, making up irregular coordination polyhedra. The framework of the present compounds can be described as a three-dimensional framework made from vertex-sharing polyhedra. The basic unit is the [ Me (H 2 P 2 O 7 ) 2 · 2 H 2 O] moiety, which displays a crystallographic Ci symmetry, with the Me cation on the inversion centre. Such units are held together by an intricate scheme of Tl…O interactions; hydrogen bonds complete the network.

The crystal structure of the aluminosilicate, MCM-71, was determined by a match of the powder X-ray diffraction pattern to one calculated from a theoretically predicted framework model. The unit cell contains 48 T -sites and 96 framework oxygens, where T = 41.1 Si, 6.9 Al. It crystallizes in space group Cmca , a = 7.4422(2), b = 18.5324(5), c = 19.1877(5) Å. The framework contains an elliptical 10-membered ring channel (4.3 × 6.5 Å) and an orthogonal undulating 8-membered ring channel (3.6 × 4.7 Å) to constitute a two-dimensional network of channels. Considering the aluminosilicate framework as a silicate, the crystal density is 1.77 g/cm 3 and the T -site framework density is 17.8 T /1000 A 3 . The structure was refined against Debye-Scherrer and Bragg-Brentano powder synchrotron data by the Rietveld procedure. While non-framework oxygen atoms, consistent with water content, could be justified by TGA measurements, it was not possible to derive an accurate extra-framework model using synchrotron data from hydrated specimens. Refinement against powder data from an anhydrous specimen subsequently detected the presence of extra-framework aluminum, identified also by solid state NMR measurements.

A high-pressure quasi-single crystal X-ray diffraction study of a synthetic iron oxide Fe 0.95 O sample was performed up to 80 GPa using the diamond anvil cell technique. At a pressure of about 75 GPa after laser annealing we observed a new high-pressure monoclinic modification of FeO with P 2 1 / m space group. The structure is closely related to that of cubic sodium chloride as a distortion of the lattice. The sequence of transitions cubic-trigonal-monoclinic for FeO follows group-subgroup relations.

[(CH 3 ) 3 Sn] 2 S 2 (C 2 N 2 S) is monoclinic, space group P 2 1 /c , a = 10.492(5), b = 12.257(6), c = 12.691(6) Å, β = 95.86(1)°. The zigzag chain structure of the coordination polymer can be derived by the structure correlation method. The starting point is a monomolecular symmetric bis(trimethyltin)-1,3,4-thiadiazole-2,5-dithiolate (Me 3 SnS) 2 (C 2 N 2 S): The first of the Me 3 SnS moieties, bound to the atom C 5 of the heterocyclus, remains tetrahedral, whereas the other, bound to C 2 , is transformed through the N 3 atom of the neighbouring ring to a trigonal bipyramid S···(Me 3 Sn)···N. The three C atoms and the Sn atom of this Me 3 Sn group are nearly coplanar and form the equatorial plane. With the N 3 atom of the starting molecule, an equivalent linking to the other neighbour takes place. The resultant plane ribbons run parallel to the crystallographic b -axis. The analysis of the bond distances and angles reveals that the regular trigonal bipyramid almost exactly represents the transition state along a chemical reaction pathway for a nucleophilic S N 2 displacement at tetrahedrally coordinated tin.

The conformational features of three 2-substituted 4-methyloxan-4-ol (tetrahydropyran) derivatives were investigated by single crystal X-ray crystallographic studies and the geometries were optimized using semi-empirical PM6 methods. The tetrahydropyran ring in each of ( I )–( III ) adopts a chair conformation with their hydroxyl groups occupying equatorial, axial and axial positions, respectively. The strongest hydrogen bonding interactions apparent in each of the respective crystal structures, as judged from distance and angle considerations, involve the ring-bound O2-hydroxyl group and tetrahydropyran ring oxygen atom. These hydrogen bonds lead to a supramolecular chain with a linear topology in each case but generated by glide symmetry in ( I ) and ( II ), and 2 1 -screw symmetry in ( III ). In the latter, a two dimensional array constructed by O—H…O bonding is found leading to undulating layers. Despite the absence of additional O—H…O hydrogen bonding sites, two dimensional arrays are also generated in each of ( I ) and ( II ), but this time mediated by C—H…O contacts that lead to flat layers. The theoretical structures for each of ( I ) and ( III ) differ from their respective experimental structures in terms of the relative orientation of the aromatic substituent. By contrast, for ( II ), there is close agreement between the experimental and theoretical structures. ( I ) C 12 H 16 O 2 , monoclinic, Cc , a = 18.7887(8), b = 6.0634(2), c = 10.4178(4) Å, β = 116.945(7)°, V = 1057.99(10) Å 3 , Z = 4, R 1 = 0.029; ( II ) C 13 H 18 O 3 , orthorhombic Pc 2 1 n, a = 9.3664(17), b = 10.0472(18), c = 12.240(2) Å, V = 1151.9(3) Å 3 , Z = 4, R 1 = 0.037; ( III ) C 13 H 18 O 4 , orthorhombic P 2 1 2 1 2 1 , a = 9.814(3), b = 9.966(2), c = 11.845(2) Å; V = 1158.5(5) Å 3 , Z = 4, R 1 = 0.079.

The dicyanamido diethelenetriamine copper (II) compound, C 8 H 13 CuN 9 (I), has been synthesized, and structurally characterized independently using X-ray powder- and single-crystal diffraction data. The direct methods program package EXPO-2004 has been used for structure solution from laboratory powder diffraction data. Intermolecular N—H···N hydrogen bonds in (I) generate R 2 2 (16) rings, which are fused forming molecular columns propagating along the [100] direction. Further linking of parallel columns through N—H···N hydrogen bonds results into a three-dimensional supramolecular network.