Volume 213, Issue 10

We present here the first investigation of coulomb lattice potentials within and between two epitactically contacted crystals as a new application of lattice potential calculations. The necessary formulas are derived from the Parry-Heyes formulas for the calculation of lattice potentials in crystal surfaces. A program has been developed for the calculation of potentials at atom positions and at interstitial sites in bicrystals, where the distance and the orientation of the two crystal parts can be varied. These potentials, which we call “xeno-potentials”, are used to define the Madelung Part of Contact Energy (MAPCE) as a new parameter to characterize the stability and the reactivity of surfaces and interfaces of ionic crystals.

The title compounds were reinvestigated by single crystal X-ray diffraction. They crystallize with the ordered NdPtSb type structure (space group P 6 3 mc ) rather than with the disordered CaIn 2 type structure (space group P 6 3 / mmc ) as reported previously. Cell parameters for NdCuSn: a = 4.5705(10) Å, c = 7.662(4) Å, c / a = 1.68; SmCuSn: a = 4.5515(9) Å, c = 7.461 (4) Å, c / a = 1.64; and GdCuSn: a = 4.5341(11) Å, c = 7.363(3) Å, c / a = 1.62. The Cu–Sn distances between the [CuSn] polyanions (3.42 Å (Nd), 3.19 Å (Sm), 3.11 Å (Gd)), scale with the size of Ln atoms, while those within the anions remain nearly unchanged (2.67 Å (Nd), 2.68 Å (Sm), 2.68 Å (Gd)).

The various modular approaches to the structure type of sapphirine are presented and discussed. Like biopyriboles sapphirine is built up by TOT rod modules (where T stands for tetrahedral chains and O for octahedral ribbons) which are connected as the corresponding modules in biopyriboles. Two distinct orientations ( S , Z ) of the modules are possible; their structures and stacking ways are constrained by the condition of cubic close packing of oxygen atoms. The various possible stacking ways are presented and the homogeneous sequences are indicated. The order-disorder (OD) character of sapphirine is discussed in terms of one kind of OD layers, with presentation of the OD groupoid family and indication of the structures with maximum degree of order (MDO structures), as well as in terms of two kinds of layers, namely as a regular alternation of slices 〈P〉 and 〈S〉 cut from the structures of pyroxene and spinel, respectively. Finally, the diffraction features of sapphirine are discussed in relation to the different modular approaches.

The Ca-rich part of the cation substitution series of aluminate sodalites (Ca 1− x Sr x ) 8 [Al 12 O 24 ](WO 4 ) 2 has been studied as a function of temperature and composition. The intermediate β -phase of pure calcium tungstate aluminate sodalite was found to have a (3 + 2)-dimensional commensurately modulated structure with an isometric unit cell. The probable superspace group is Abm 2( α 0 γ ) 0 s 0, 000 with α = ¼, γ = ¼, a = b = [unk] · 9.301(1) Å, c = 9.301(1) Å at 636 K. Its average structure was found to be similar to that of the room-temperature γ -phase. In crystals with 0 < x ≤ 0.18 the existence of a new intermediate phase could be confirmed. At variance with the otherwise very similar room-temperature phase with x = 0, this γ ′-phase has an incommensurate modulation vector. Its proposed superspace group is Abm 2(½ 0 γ ) 0 ss with γ = 0.05(1). Within the precision of our TEM-experiments γ does not change with temperature or composition. The average structure of the γ ′-phase could be refined and was found closely related with the average structure of γ -CAW.

SrV 12 O 27 · 3 H 2 O, synthesized hydrothermally. Monoclinic P 2 1 / m ; a = 11.684(2) Å, b = 11.126(2) Å, c = 9.052(2) Å, β = 110.94(2)°; Z = 2. R ( F ) = 0.049, R W ( F ) = 0.039 for 3756 observed reflections. The structure includes a new vanadate framework V 4 O 9 , similar to the V 2 O 5 in vanadium bronzes β -A x V 2 O 5 . The V 4 O 9 framework, forming a substructure with b ′ = b /3, consists of 2 × 3 columns of edge-sharing VO 6 octahedra and chains of edge-sharing VO 5 trigonal bipyramids. The columns and the chains run parallel to [010] and are connected through common corners of VO 6 and VO 5 . The columns neighbouring in [001] direction share two corners of octahedra per b ′ period. The Sr atoms and H 2 O molecules are accommodated in the wide [010] tunnels characteristic of the V 4 O 9 framework.

The structures of hexagonal μ -MgZnRE phases of Mg 28.3 Zn 65.2 Sm 6.5 and Mg 28.6 Zn 63.8 Gd 7.7 , were determined by single crystal X-ray structural analysis: μ MgZnSm, P 6 3 / mmc (No. 194), a = 14.619(1) Å, c = 8.708(1) Å, atoms/cell = 92, F (000) = 2484, μ = 27.44 mm −1 , D calc = 5.621 Mg m −3 , R = 0.0201 for the observed 1110 reflections with F obs > 4.0 σ ( F obs ) and μ -MgZnGd, P 6 3 / mmc (No. 194), a = 14.633(2) Å, c = 8.761(2) Å, atoms/cell = 92, F (000) = 2527, μ = 28.51 mm −1 , D calc = 5.707 Mg m −3 , R = 0.0210 for the observed 1084 reflections with F obs > 4.0 σ ( F obs ). The structure of μ -MgZnRE is closely related to that of the MgZn 2 Laves phase ( P 6 3 / mmc , a = 5.223 Å, c = 8.566 Å). The introduction of large RE elements increases the distortion of the icosahedral atomic arrangement around Zn and this produces a variety of icosahedral linkages in the μ -MgZnRE structure.

In the course of our search for new anti-inflammatory glucocorticosteroids with improved therapeutic index, the 6 α ,9 α -difluoro-11 β ,21-dihydroxy-16 α ,17 α -propylmethylenedioxypregn-4-ene-3,20-dione was synthesised, and the conformation, configuration and crystallisation behaviour of one of its C(22) epimers, rofleponide, was studied by X-ray single-crystal diffraction. The crystals, grown from a 2-propanol solution, had a body-centred tetragonal ( I 4, No. 79) unit cell with a = b = 27.952(2) Å, c = 6.3299(3) Å, V c = 4945.6(6) Å 3 , D c = 1.2989(2) g cm −3 and F (000) = 2064, containing eight steroid and two solvent molecules. The alcoholic guest molecules were found to be disordered, each one occupying two partly overlapping disorder positions with equal probability. The structure model was refined to R = 0.045 for 1199 observations with I > 2 σ ( I ). The basic cyclopentanoperhydrophenanthrene steroid skeleton, containing four ( A , B , C and D ) rings, has a flat shape with the trans- anti -trans- anti -trans stereochemistry, like the naturally occurring steroid hormones. The dioxolane ( E ) ring is fused to the cyclopentane ( D ) ring (at the 16 α , 17 α -positions) in a cis manner, with the angular hydroxyacetyl substituent at C(17) approximately equatorially oriented to the D and axially to the E rings, and with the C(22)-propyl chain equatorially attached to the dioxolane ring. Hence, the stereogenic centre at C(22), created during the formation of the cyclic 16 α ,17 α -acetal, has the absolute R configuration. The rofleponide molecules in the crystal are linked via hydrogen bonds [O(21) ⋯ HO(3)] into infinite helical chains winding around the four-fold screw axes. The helices are tied to each other by additional hydrogen bonds [O(11) ⋯ HO(20)], thus forming a three-dimensional H-bonded framework. This packing arrangement is stabilised by inclusion of the 2-propanol solvent, yielding a singular type of ‘tubulato clathrate’, where the alcoholic guests reside in channel-like cavities not inside but between the host helices without any noticeable interaction with the steroid molecules.

The crystal structure of syn -2-hydroxy, 2-carboxyl[4.4.1]propellane-6-ene has been determined at 293 K and 150 K, with the latter results preferred because disorder in the molecule is less pronounced than at 293 K. The two molecules (A, B) in the asymmetric unit (space group C 2/ c , Z = 16) are conformers with differences in the location of the carboxyl groups and hydroxyl hydrogens and the conformations of the cyclohexene rings. Chains of A and B molecules are linked by hydrogen bonds in hydroxyl 4-rings, and in two independent A–A and B–B carboxylic acid dimers. The 4-rings are centrosymmetric and homodromic, while the carboxyl dimers, appreciably distorted from planarity in somewhat different ways, have crystallographic two fold axes normal to their mean planes.