Volume 164, Issue 3-4

Electron diffraction can be performed on small single crystal domains of ordered transition metal hydrides. The qualitative spot patterns – neglecting the difficult intensity determination – can be related to the superlattice of H-ordering if the large number of possible structures is reduced to physical meaningful structures by a structure model. The consideration of equal numbers of H atoms nearby each metal atom gives rise to a larger number of structures with H at tetrahedral interstices of bcc metal matrix compared to structures with H at octahedral interstices of ccp metal matrix.

CuCl(C 2 N 2 S 2 H 4 ) 1.5 (H 2 O) 0.45 crystallizes in the orthorhombic system, space group Ccca. The cell parameters are: a = 14.528(3) Å, b = 22.686(4) Å, c = 13.503(3) Å. The crystal structure has been determined using X-ray single crystal techniques and refined by full-matrix least-squares calculations to R = 0.051. The structure is polymeric and consists in double helical chains … Cu SC(NH 2 )C(NH 2 )S Cu …, wrapped round the [0 1/4 z] axis. In these chains, the rubeanic acid acts as a bidentate ligand through the two S atoms. The connections between the chains are ensured by a third ligand, showing the same coordination scheme. The metal atom Cu(I) is surrounded by three S atoms and one Cl atom, achieving a near perfect tetrahedron.

The title compound CuCl(C 2 N 2 S 2 H 4 ) crystallizes in the orthorhombic system, space group Pbca with parameters a = 15.576(3), b = 6.923(3), c = 11.416(3) Å. The crystal structure reveals infinite ribbons … Cu[SC(NH 2 )C(NH 2 )S]Cu … running along the a axis; these ribbons are coupled by two interribbon interactions between copper and sulfur atoms; this weak bonding gives a distance Cu – S = 2.68(2) Å. Within the ribbon the copper I is bonded to two sulfur atoms pertaining to two different rubeanates and a chlorine atom: Cu – S = 2.24(1) and 2.25(1) Å and Cu – Cl = 2.31(1) Å. The coordination of copper(I) is described as being [3 + 1] the weak interribbon bonding pulling the copper out of the trigonal coordination plane by some 0.38 Å.

The relations between the structures within the CaO – SiO 2 – H 2 O system were studied. They are divided into two groups depending on whether the (SiO 4 ) 4− tetrahedra are isolated or infinitely connected. It is shown that most of the structures can be interrelated not only within the groups, but also between them. The members of the first group are Ca-rich and most of them decompose topotactically during heat treatment into γ -Ca 2 SiO 4 or β -Ca 2 SiO 4 . The Ca/Si ratio for the second group is, with the exception of hillebrandite, < 1.5 and all these phases decompose topotactically into one of the wollastonite forms. The relations are discussed and described by the corresponding transformation matrices.

Series of diffraction patterns were measured with dry powdered ammonium nitrate from 50 – 60°C on heating and from 50 – 40°C on cooling. The variation of lattice constants allows to observe the transition. On heating the phase transition IV/II occurs between 52 and 56°C. In this temperature interval both phases are existent. On cooling, simultaneous transitions II/IV and II/V occur with phase V slowly transforming into phase IV.

The electron-density distribution in monoclinic Fe 2 (SO 4 ) 3 at room temperature has been determined from precise single-crystal X-ray data. In order to study and reduce parameter bias, arising from bonding effects, separate least-squares refinements were performed on the high-order data ( R = 0.039) and the entire data set ( R = 0.027). Also a refinement based on a point charge model for the representation of positive residual charge accumulations was carried out ( R = 0.019). Difference density maps ( X – X HO ), based on the atomic parameters from the high-order refinement, were calculated in all interesting sections with special attention to the charge distribution within the [SO 4 ] 2− anions and around the Fe cations. Positive residual maxima of different heights, deviating in shape considerably from the rotational cylindrical symmetry of σ -bond charge accumulations, were observed on the S – O bond lines of the [SO 4 ] 2− anions, revealing strong polarization effects from the Fe cations. No residual electron density was observed on the Fe – O bond lines of the FeO 6 octahedra, indicating that these bonds are primarily of ionic type. On the other hand significant density peaks were observed around the Fe cations in directions bisecting the Fe – O bond lines and at distances of about 0.4 – 0.5 Å from the atomic centers, revealing a deviation from the spherical distribution of the 3 d electrons of the Fe ions.

Solid solutions of Mn(II), Fe(II), or Mg in nickel-hexahydroxoheptaoxo-hexaborate-ethanol-3.5 water, Ni x M 1 – x [B 6 O 7 (OH) 6 ] · C 2 H 5 OH · 3.5 H 2 O ( M = Mn: x = 0.8, 0.75, or 0.67; M = Fe: x = 0.75; M = Mg: x = 0.75), have been crystallized. The crystal structure of one of these compounds with Mn(II), Ni 0.8 Mn 0.2 (H 2 O) 3 [B 6 O 7 (OH) 6 ] · C 2 H 5 OH · 0,42 H 2 O, has been determined from single-crystal X-ray diffractometer data. The compound crystallizes in the monoclinic space group P2 1 /c. The lattice constants are a = 9.586(1) Å, b = 12.420(3) Å, and c = 14.645(3) Å; β = 106.62(5)°; V = 1673.01 Å 3 ; the unit cell contains four formula units; the measured density was D m = 1.74 and the calculated density was D c = 1.76 g · cm −3 . The crystal structure has been solved from 2093 observed reflections by means of the Patterson method and refined by least-squares calculations to an index of R conv. = 7.3% and R w = 6.2%. The structure contains the insular hexaborate ion [B 6 O 7 (OH) 6 ] 2− , found already in other magnesium, cobalt or nickel hexaborates. The cations are surrounded octahedrally by three hydroxyl groups and three water molecules. Connections between the hexaborate ions are provided by a hydrogen bonding system of the OH groups, the H 2 O molecules, and the ethanol molecule, thus forming a three-dimensional framework.

The high temperature form of melanophlogite, 46 SiO 2 · 6M 14 · 2M 12 (M 12 = CH 4 , N 2 ; M 14 = CO 2 , N 2 ), is cubic with space group Pm 3 n and a = 13.436(3) Å at 200°C. The mineral is isostructural with the cubic gas hydrates of type I. Structure refinement with 667 independent reflections led to a weighted R w = 0.040. Corner-sharing [SiO 4 ] tetrahedra form a 3-dimensional framework which contains two types of cages: 2 pentagondodecahedra (V∼97 Å 3 ) and 6 tetrakaidecahedra (V∼136 Å 3 ) per unit cell. From difference Fourier syntheses it is concluded that the guest molecules M 12 and M 14 within the dodecahedral and tetrakaidecahedral cages are oriented in such a way that the van der Waals contacts between the guest molecules and the SiO 2 framework are optimized. The mean value of the Si – O – Si angles (168.8°) is considerably higher and that of the Si – O distances (1.576 Å) is considerably lower than corresponding angles and distances in the known silica polymorphs.

The crystal structures have been determined of (CH 3 ) 3 NHHgCl 3 , {(CH 3 ) 3 NH} 2 HgCl 4 and (CH 3 ) 3 NHHg 2 Cl 5 . In {(CH 3 ) 3 NH} 2 HgCl 4 a heavily distorted HgCl 4 2− tetrahedron is found with HgCl bonds ranging from 2.427(2) to 2.574(2) Å. (CH 3 ) 3 NHHgCl 3 has two independent Hg atoms. One has two short HgCl bonds and four long ones, the other one two short and two long HgCl bonds. Of the two independent Hg atoms in (CH 3 ) 3 NHHg 2 Cl 5 one has two short HgCl bonds and four long HgCl bonds. The other one has a trigonal bipyramidal coordination. The great variety of Hg – Cl bonds is discussed in terms of correlation diagrams. Each of the cations is involved in one N – H … Cl hydrogen bond, with N … Cl distances ranging from 3.236(6) to 3.325(6) Å.

Three-fold superlattice structures are observed at the composition Li 0.33 TiX 2 during the lithium intercalation of TiX 2 (X = S,Se). A model with a tripled c -axis is proposed for these complexes, and provides a satisfactory match between observed and calculated intensities on X-ray powder diffraction patterns.

The linear electrooptical tensor [ r ijk ] and the tensor of the adiabatic linear electrostriction [ d ijk S ] of lead tetraborate (PbB 4 O 7 , point group mm 2) have been determined: r 113 = +2.35(8), r 223 = +2.40(8), r 333 = +2.83(9), r 131 = +2.39(7), r 232 = +0.95(7); d 311 S = +2.8(2), d 322 S = +2.6(2), d 333 S = ±0.0(1), d 113 S = +2.1(1), d 223 S = +1.7(2) (Unit: 10 −12 m/V, T = 295 K, λ = 633 nm).

The phase diagram of the binary system sodium chromate-sodium carbonate has been studied using X-ray and thermal methods. The system shows a large miscibility gap at low as well as at high temperatures. The sodium carbonate rich part yields zone information. Sodium chromate rich crystals show dendritic and radial growth. The hexagonal high-temperature phase of mixed crystals with composition 85 × Na 2 CrO 4 + 15 × Na 2 CO 3 exhibit a vanishing volume expansion.

The crystal structure of Rb 2 [(+)-C 4 H 4 O 6 ] has been determined at room temperature by X-ray diffraction. The compound crystalizes in the space group P 3 2 21 with a = 7.158(4) Å, c = 13.087(2) Å, V = 580.7 Å 3 , D c = 2.737 Mgm −3 , Z = 3. The structure has been solved by Patterson and Fourier methods and refined by least-squares calculations to a final R value of 0.040 for 386 reflexions [| F 0 | ≥ 4 σ ( F 0)].

The crystal structure of the title compound has been determined with 971 independent reflections, measured on a computer-controlled Philips PW 1100 single-crystal diffractometer. The cell constants, obtained by least-squares calculations from ϑ-value measurements on the diffractometer, are: α = 7.4265(4), b = 19.6690(13), c = 14.6397(8) Å, β = 101.82°(1), Z = 4; space group P 2 1 / c . The positional and thermal parameters, with anisotropic temperature factors, were refined by full-matrix, least-squares calculations to a final R = 0.056. The molecule is made up of two almost planar p -chlorophenylazo-ligands attached to the two central C atoms of the decaline in cis-form. The interatomic distances are normal.

Lead tetrasodium trimetaphosphate PbNa 4 (P 3 O 9 ) 2 is triclinic, P [unk] with a = 7.268(4), b = 8.151(5), c = 7.851(5) Å, α = 121.52(5), β = 102.06(5), γ = 73.00(5)°, Z = 1, V = 378.3 Å 3 and d x = 3.393 g/cm 3 . Its crystal structure has been solved using 1507 reflexions, with a final R value 0.049 for 1268 reflexions. The atomic arrangement is characterized by a disorder between Pb and Na on one crystallographic site. Chemical preparation and crystal data are given for the isotypic barium salt: BaNa 4 (P 3 O 9 ) 2 .