Volume 210, Issue 1

The Al subnet in corundum is related to the diamond-like structure of Si. Each Al atom is four-fold coordinated, forming an inverted tetrahedron (umbrella-like). Three Al–Al distances (2.79 Å) are close to those of the parent fcc -Al (2.85 Å), and one has a shorter value of 2.66 Å. Unexpectedly, this cation subnet is similar, in topology and distances, to the 2D diamond-like layers formed by the [Al 2 ] 3− polyanions in the Zintl phase Li 3 Al 2 and is also topologically related to the [Al 2 Si 2 ] 2− subnet in CaAl 2 Si 2 .

The so-called exponential scale analytical functions are used to describe the shape of crystals. The Platonic solids and also irregular polyhedra such as the pyritohedron have been calculated.

Plate-shaped untwinned and twinned single crystals of the perovskite BiFeO 3 show different etch figures and etch figure arrangements on the surface when attacked with dilute nitric acid. These etch figures can be correlated with the orientation of the spontaneous polarization vector. With a view to correlating the direction of the polarization vector with the atomic positions in the crystal, the absolute configuration was determined from X-ray diffraction patterns at room temperature on a dendritic ferroelastic/ferroelectric asgrown single domain crystal. The typical etch figure arrangement close to the crystal edges was used as a reference system. The absolute structure shows that the part of the crystal corresponding to the positive end of the spontaneous polarization vector etches faster than the negative one. The structure refinement of a single crystal switched by uniaxial stress along the polar axis showed a complete reorientation of the (super)structure with rearrangement to an angle of 70.5° compared with the former polarization direction. As already suggested by the analysis of new etch figures close to 45°-inclined domain walls, no merohedral twinning occurs during this rearrangement. Despite atom displacements from 0.4 Å (for Fe) and 0.9 Å (for O) the crystal does not break during switching.

The crystal structure of SrTi 6 Co 6 O 19 has been refined in space group P 6 3 / mmc to an R -value of 0.045 ( R w = 0.038). The distribution of the cobalt and titanium ions has been determined by refining the site occupancy factors and by bond lengths considerations. Co 2+ occupies the tetrahedral sites and Ti 4+ is enriched on the octahedral sites in the spinel S-blocks and in the face-sharing octahedra in the R-blocks of the magnetoplumbite type structure, while Co 2+ and Ti 4+ are distributed at random over the trigonal bipyramid of the R-blocks and the octahedra between the R- and spinel S-blocks. The cation distribution is discussed in terms of the Madelung part of lattice energy.

The superstructure of tetrataenite, FeNi from the Saint Severin meteorite was determined using X-ray diffraction data from a conventional X-ray source and synchrotron radiation. Lattice constants of tetrataenite show clearly tetragonal symmetry; a = 3.581(2) Å, b = 3.582(2) Å, c = 3.587(2) Å, α = 90.03(3)°, β = 90.04(3)° and γ = 90.00(3)°. The structure, however, is monoclinic. The space group may be Pm . The atomic coordinates and the temperature were determined by data from conventional X-ray diffraction. The ordering of Fe/Ni was determined by refinement of site occupancies of the atoms applying the difference of anomalous scattering factors of Fe and Ni with synchrotron radiation λ = 1.746 Å. The tetrataenite from the Saint Severin meteorite does not show perfect ordering of Fe and Ni. It still contains 15% disorder of Fe/Ni on average.

Single crystals of the compound Na 2 (Mg 3.6 · Fe 2.4 )[(Ge 5.6 Fe 0.4 )O 18 ]O 2 have been grown from a Na 2 O–MoO 3 –V 2 O 5 flux. The compound crystallizes in the triclinic P [unk] space group with a = 8.994 Å, b = 9.924 Å, c = 10.495 Å, α = 64.30°, β = 84.07°, γ = 65.87° and Z = 2. The refinement of its structure using single-crystal X-ray data shows that it is isostructural with the silicate minerals aenigmatite, Na 2 (Fe 5 Ti)(Si 6 O 18 )O 2 , and krinovite, Na 2 (Mg 4 Cr 2 )(Si 6 O 18 )O 2 .

The two structures are built of ∞ 2 [MT Urea ], M = Pb, Ba, layers with cornerlinked ReO 4 tetrahedra (T) and O-coordinated urea bridges between the cations. The layers are decorated on both sides by half of the ReO 4 groups and water or urea molecules. An extensive network of hydrogen bonds and one long coordinative M–O bond in Pb(ReO 4 ) 2 · Urea · H 2 O holds the layers together. The cations have 4-capped square antiprismatic MO 9 coordination and the polyhedra form centrosymmetric dimers by sharing an edge of urea O atoms.

The title compound, [Ni(acac) ( Φ en Φ )(O 2 NO)] C 19 H 23 N 3 NiO 5 , is monoclinic, space group P 2 1 / a , Z = 4. Cell dimensions are a = 13.659(7) Å, b = 12.746(6) Å, c = 13.707(7) Å and β = 117.71(3)°. A total of 3498 reflections were measured with a PC-computer controlled PHILIPS PW1100 automatic diffractometer using Mo K α radiation. The structure was refined by full-matrix least squares to a conventional R = 0.038 for 2623 observed reflections with I > 2 σ ( I ). The coordination around the central nickel atom is a distorted octahedron with the apices of the octahedron occupied by the oxygen atoms of the acetylacetonato (2,4-pentanedionato) moiety, the nitrogen atoms of the N,N′-diphenyl-1,2-diaminoethane ( Φ en Φ ) ligand, and two of the oxygens on the nitrato group, [NO 3 ] − . As a result of this coordination a resonance-stabilised six-membered β -dionato chelate ring, a five-membered chelate ring with the 1,2-diamine ligand in the gauche conformation, and a four-membered chelate ring are formed, with the NO 3 − acting as an O,O′ chelating ligand. As expected, the bite angle becomes more acute as the ring size diminishes, the actual values being 95.43°, 81.83°, and 59.63° respectively.

The title compound is a synthetic precursor to important cyanine dyes. It crystallizes from isopropanol in the monoclinic system, space group P 2 1 / c , with a = 784.7(1)pm, b = 2240.1(2)pm, c = 734.2(1)pm, β = 90.69(1)°, Z = 4.

HgBr 2 (C 12 H 24 S 6 ), M r = 721.12, monoclinic, P 2 1 , a = 8.264(2) Å, b = 15.580(5) Å, c = 8.305(4) Å, β = 95.33(2)°, V = 1064.7(7) Å 3 , Z = 2, D x = 2.249(2)g cm −3 , μ = 11,50mm −1 , λ (Mo K α ) = 0.71073 Å, F (000) = 684, room temperature, R = 0.035, wR = 0.043 for 1736 unique reflections [ I > 2 σ ( I )]. The compound crystallizes as a homopolymer with chains running along the a axis. The 1,4,7,10,13,16-hexathiacyclooctadecane ring acts as a doubly bidentate bridging ligand, coordinating to two translationally related Hg(II) centers via two opposite pairs of thia donors [Hg–S = 2.906(4) Å, 2.866(5) Å, 2.894(4) Å, 2.848(5) Å] and two S atoms remain uncoordinated. The octahedron around Hg(II) is completed by two terminal bromo ligands [Hg–Br = 2.618(2) Å, 2.593(2) Å with the angle Br1–Hg–Br2 of 179.42(6)°]. The conformation of the 18S6 ring shows no symmetry.

The simple polymethine dye 1,7-bis-(dimethylamino)-heptamethinium perchlorate (C 11 H 19 ClN 2 O 4 ) forms in crystals J-aggregates. The crystal structure was determined from single crystal X-ray diffraction data (monoclinic, C 2/ c , a = 1160.3(5)pm, b = 880.3(4)pm, c = 1524.8(7)pm, β = 109.7(6)°, Z = 4, D x = 1.263 g/cm 3 , T = 293 K, R = 0.103 for 1460 unique reflections I > 1 σ ( I )). The polymethine cations as well as the perchlorate anions are disordered. The molecular structure of the dye depends on the crystalline environment. The main structural feature is the arrangement of dye molecules in one-dimensional staircase aggregates. The dye forms crystals with different habit and color but same crystal structure depending on crystallisation process.

A series of silver(I) complexes with the unsaturated isomeric dicarboxylic acids, maleic and fumaric, has been prepared and the structures of three of these, silver(I) hydrogen maleate, (1), silver(I) maleate, (2) and silver(I) fumarate, (3), were determined by X-ray diffraction. All three structures are polymeric, with (1) and (2) based on bis(carboxylato- O , O ′) dimers. With (1), a strong intramolecular hydrogen bond is found [O … O, 2.494(2) Å], involving the acidic proton and the cis -related carboxylate group. In this respect it is similar to maleic acid and other hydrogen maleates. With (2), a unique feature is the presence of an ethylene-Ag π -bond to one of the independent silver ions [Ag–C, 2.448(5) Å] giving angle distortion about the dimer unit. The polymeric structure of (3) is based on an unusual cyclic, open figure-eight Ag 4 complex unit involving four different carboxylato-( O , O ′) interactions. This results in three separate Ag … Ag contacts [2.924(1) Å, 2.925(1) Å, 3.090(1) Å].

The title compound was prepared by intramolecular aryl coupling of the corresponding phenyl bromonaphthoate. It crystallizes from CH 2 Cl 2 /petroleum ether in the orthorhombic system, space group P 2 1 2 1 2 1 , with a = 1021.3(1) pm, b = 1616.3(2) pm, c = 968.9(1)pm.

The crystal structures of the title compounds o -tol 3 PAu(S 2 CO i Pr), C 25 H 28 AuOPS 2 , and o -tol 3 PAu(S 2 COCH 2 CH 2 OMe), C 25 H 28 AuO 2 PS 2 , have been determined at room temperature. The colorless crystals of o -tol 3 PAu(S 2 CO i Pr) are monoclinic, space group P 2 1 / c , with unit cell dimensions a = 14.277(5) Å, b = 12.716(5) Å, c = 14.829(2) Å, β = 115.23(1)°, Z = 4 and D x = 1.736 Mg m −3 and the pale-yellow crystals of o -tol 3 PAu(S 2 COCH 2 CH 2 OMe) are triclinic, space group P [unk], with dimensions a = 11.209(4) Å, b = 13.195(5) Å, c = 9.046(3) Å, α = 107.05(3)°, β = 91.78(3)° and γ = 74.40(3)°, Z = 2 and D x = 1.761 Mg m −3 . The structures were solved by direct-methods and each refined by a full-matrix least-squares procedure to final R = 0.041 (0.041) using 2887 (3841) reflections, respectively. The gold atom in each of the structures exists in a linear geometry defined by the S atom, derived from a monodentate xanthate ligand, and the phosphine P atom. The major difference between the two molecules is found in the orientation of the xanthate ligand. In the structure of o -tol 3 PAu(S 2 CO i Pr) the O atom is directed towards the Au atom, i.e. a ′S, O′ conformation, such that the Au … O separation is 2.892(7) Å, by contrast, in the structure of o -tol 3 PAu(S 2 COCH 2 CH 2 OMe) a close intramolecular Au … S contact of 3.347(3) Å is found; the ′S, S′ conformation. A variable-temperature multinuclear magnetic resonance ( 1 H and 31 P) study did not show the presence of both S, O and S, S conformations co-existing in solution for either of the compounds.

A method for crystal growth, which allows a simultaneous crystallization of several substances at different rates, in a chamber furnace is described.