Volume 171, Issue 1-2

The crystal structure of KLiO was determined by X-ray diffraction techniques. The compound crystallizes orthorhombically in the space group = Cmca ( Z = 8) with the cell parameters a = 861.8(4), b = 640.3(2), c = 641.7(2) pm. The structure was solved from 1307 counter reflections (414 symmetry independent reflections) by direct methods and refined to a weighted least-squares residue of 0.05. The structure is characterized by condensed LiO − -anions in which Lithium is surrounded by three oxygen atoms.

The crystal structure of C.I. Pigment Yellow 4, α -(1-hydroxyethylidene) acetanilide- α -azo-(4′nitrobenzene), C 16 H 14 O 4 N 4 , has been determined by single crystal X-ray diffraction techniques. It crystallises in the triclinic system with cell parameters a = 7.691(2) Å, b = 10.247(2) Å, c = 11.195(2) Å, α = 109.00(2)°, β = 73.80(2)°, γ = 112.21(2)°. The space group is P [unk] and there are two molecules per unit cell. The structure was solved by direct methods and least-squares refinement has been completed on three-dimensional data, 2716 reflections (Cu K α radiation). The hydrogen atoms have been found and included in the refinement but only those associated with the methyl group have been independently refined. The final residual is 5.4%. The molecule exists as the hydrazone tautomer. It is approximately planar due partly to intramolecular hydrogen bonds and partly due to steric hinderence. The molecules are packed in layers parallel to the ([unk]11) plane with the length parallel to [011] and in columns approximately parallel to a *. Alternate molecules within the columns are in antiparallel. The molecules are linked by van der Waals forces.

The crystal structure of a polymorph ( α ) of C.I. Pigment Yellow 5, α -(1-hydroxyethylidene) acetanilide- α -azo-(2′-nitrobenzene), C 16 H 14 O 4 -N 4 , has been determined by single crystal X-ray diffraction techniques. It crystallises in the monoclinic system with cell parameters a = 7.593 ∓ 0.001 Å, b = 20.029 ∓ 0.004 Å, c = 10.217 ∓ 0.002 Å, β = 101.87 ∓ 0.02°. The space group is P 2 1 / n and there are four molecules per unit cell. The structure was solved from the coordinates of Hansa Yellow 5G and least-squares refinement has been completed on three-dimensional data, 2547 reflections (Cu K α radiation). The hydrogen atoms have been found and included in the refinement but only those associated with the methyl group have been independently refined. The final residual is 6.6%. The molecule exists as the hydrazone tautomer and intramolecular hydrogen bonds keep the molecule approximately planar. The molecules are packed in layers approximately parallel to the ([unk]01) plane and in columns parallel to the a axis. Alternate molecules within the columns are in antiparallel. The molecules are linked by van der Waals forces. It is concluded that the present structure is isomorphous with Hansa Yellow 5G and C.I. Pigment Yellow 1.

It is observed that neither inspection of z values, consideration of near-neighbour coordination, nor chemical considerations show in all cases which atom occupies site 2 ( c I ) and which site 2 ( c II ) of the Cu 2 Sb tP 6 structure. Calculation of the Wirkungsbereiche by the Dirichlet construction shows indisputably which site is which. Assignments are made for all phases whose z values have been determined. Separation of phases with the Cu 2 Sb structure into two groups is effected on chemical considerations and observed physical properties. Wirkungsbereiche , near-neighbour coordination, and framework descriptions of the structure are discussed, as well as related derived structure types. Stability and availability of the structure is discussed in relation to the number of valency electrons provided by the component atoms.

The well known tetragonal NbTe 4 structure was refined ( R = 0.047; 186 independent reflections). In this average structure the Nb atoms in the centers of tetragonal Te 8 -antiprisms as well as the Te-atoms show strong anisotropic behaviour. This basic structure is modulated along the c -axis with an incommensurate modulation period of about μ = 3.20. The determination of the modulated structure is presented. At first, the determination was based on a commensurate threefold superstructure ( μ′ = 3.00), yielding four types of atomic shifts which belong to different but not independent periodic modulations of the atomic positions: a longitudinal deformation mode (1) of the Nb position along the c -axis; a transversal breathing mode (2) of the Te squares accompanied by both, a libration mode (3) and a weak longitudinal mode (4) of the squares ( R = 0.049; 1227 independent reflections including 904 satellite reflections). The Nb mode results in the formation of Nb 3 groups and the breathing mode forms larger Te 4 squares around short Nb – Nb distances and smaller ones between adjacent Nb 3 groups. In a second step model calculations on chains of Nb atoms with a tenfold superstructure ( μ′ = 3.33) were performed, which show that most of the Nb positions remain virtually unchanged but substantiate the origin of the incommensurateness: Nb 2 pairs, which are introduced into a chain of Nb 3 groups as discommensurations. The result is discussed and a brief chemical interpretation of the modulation is given. The formation of Nb 3 groups indicates a lower mean oxidation state z(Nb) < + 4 and the modulation can be described as a redox wave.

An additional 3 D net (no. 82a) was obtained by combining double-crankshaft chains with a 4.6.12 net. Removal of one of the mirror lines from the 4.6.12 2 D net yields a new 3-connected net with cmm symmetry and (4.6.10) 4 (6.6.10) 1 connectivity. Fifteen 4-connected 3 D nets are selected from the infinite number obtainable by addition of an up or a down linkage to each 3-connected node. The most elegant one (no. 263) has strict alternation of up and down linkages, and represents the probable framework of the eleventh member of a new series of aluminophosphate molecular sieves.

Radial distribution analysis of X-ray intensities diffracted by sepiolite samples untreated and treated at different temperatures up to 1000°C have been carried out. Interatomic distances, coordination numbers, mean square displacements and the interatomic coupling constants for different atom pairs have been calculated from the radial distribution curves. The results show that the disorder takes place in the octahedral layer which finally collapses above 600°C with the elimination of hydroxyl groups leading finally to the formation of the amorphous phase at 800°C, characterized by coordination number four of Mg. The variation of lattice parameters including volume reveals that the dehydration is accompanied by contraction of the cell dimensions at each stage of dehydration till the amorphous phase is fully developed around 800°C. It is also seen that there is a similarity between the starting material and the new crystalline product formed at 1000°C. The entire dehydration process and thermal transformation have been interpreted in terms of these data.

Madelung numbers α were computed for CaMg(CO 3 ) 2 (dolomite), Na 2 Mg(CO 3 ) 2 (eitelite), K 2 Mg(CO 3 ) 2 , K 2 Ca(CO 3 ) 2 (buetschliite), CaCO 3 (aragonite) and Na 3 Mg(CO 3 ) 2 Cl (northupite) which all have slightly aplanar carbonate groups according to careful structure determinations. Heptapole models for the CO 3 2− -complexion were used, and the distance d of the C-atom from the plane of the three O-atoms was set at d = 0.02 Å in all six compounds. Both geometrically possible orientations were taken into account. The results of our computations show that the electrostatic crystal field does not in all six cases favour the orientation of the aplanarity as determined experimentally. It is, therefore, concluded that the polarizibilities of the carbonate group and of its oxygen atoms play an important role in giving rise to this effect.

N-Phenyl-2-(2-methyl-phenylhydrazono)-3-oxobutyramide crystallizes in the monoclinic space group C 2/ c with 2 quite different molecules in the asymmetric unit. In one case the methylphenyl-group is twisted against the hydrazono-group by an angle of 1.7°, whereas in the other case this angle is 11.4°. The two NH-groups are involved in intramolecular hydrogen bonding with the two oxygens of the molecule. Like many other “azopigments” the molecule is the hydrazone tautomer, at least in the crystalline state. In the crystal lattice the molecules lie in layers with distances between 3.27 and 3.44 Å. Above every molecule in the layer there is a column of other molecules. The surroundings of the two different molecules in the crystal are the same. Therefore, it has to be concluded, that their differences are not a consequence of crystal forces.

The crystal structure of metachloro-nitrobenzene, C 6 H 4 C1 (1) (NO 2 ) (3) was redetermined at T = 298 K: Space group Pna 2 1 , Z = 4, a = 2114.90(40) pm, b = 593.20(10) pm, c = 529.00(10) pm, R w ( F ) = 0.038. The molecule is almost planar, with a small out of plane bending of the NO 2 group. Measurements of Zeeman-split 35 Cl NQR spectra give a nuclear quadrupole coupling constant e 2 ϕ zz Qh −1 = (69.745 ± 0.002) MHz at T = 298 K and (70.608 ± 0.002) MHz at T = 129 K. The asymmetry parameter is 0.1091 ± 0.0015 at 298 K (0.1066 ± 0.0040 at 129 K). ϕ zz is within 0.45° parallel to the bond direction C (1) – Cl (1) ; ϕ yy and ϕ xx are almost in the C (1 … 6) -plane and perpendicular to it, respectively. The temperature dependence v ( 35 Cl) = f ( T ) was studied from 77 K up to the melting point. Structure and electric field gradient orientation are discussed.

Chemical preparations and crystal data are reported for two new diphosphates: Zn 3 Rb 2 (P 2 O 7 ) and Co 3 Rb 2 (P 2 O 7 ) 2 . These two salts are isotypic, space group P 2 1 Z = 2 and the following unit cell dimensions a = 13.22(1), b = 7.224(6), c = 7.196(5) Å, β = 92.08(2)° for the zinc salt and a = 13.25(1), b = 7.248(7), c = 7.213(6) Å, β = 92.00(5)° for the cobalt salt. The crystal structure of this new type of diphosphates has been solved using the zinc salt ( R = 0.043, 2023 hkl ). The main feature of the atomic arrangement is a three dimensional network of ZnO 4 and PO 4 tetrahedra crossed by channels. The rubidium atoms are located inside these channels. The zinc salt is piezoelectric.

l -C 5 H 9 NO 4 · HI, P 2 1 2 1 2 1 , a = 5.982(1), b = 11.461(4), c = 13.405(4) Å, V = 919.0(5) Å 3 , Z = 4, MW = 274.55 g, D x = 1.986, D exp = 1.994 g/cm 3 . Single crystal X-ray structure analysis shows l -glutamic acid hydroiodide ( l -GA · HI) to be isostructural to l -glutamic acid hydrochloride and l -glutamic acid hydrobromide. However, the compound is not a halogen acid salt, but a 1:1 complex of l -GA and undissociated HI connected by hydrogen bonds. The different bonding explains anomalous lattice constants and physical properties compared to l -glutamic acid hydrochloride and hydrobromide.

The crystal structure of the so-called iodide of Wells “K 3 Pb 2 I 8 · 4H 2 O” (single crystal X-ray methods; P 4/ mmm , a = 1318.3 pm, c = 453.9 pm; R F = 0.025 with 463 unique reflections) is devided in an ordered part K 2 PbI 4 · 2H 2 O and a disordered part 0.237 KI 3 · 0.37 H 2 O. The former is an unexpected simple arrangement of linear chains along [001] of edge-bridged octahedrally coordinated anionic complexes ∞ [PbI 4/2 I 2 ] 2− , cations K + and water molecules leaving two different channels parallel to the chains. This is caused by filling up one channel entirely with a onedimensional triiodide chain ∞ (I 3 − ), which is incommensurate with the translation of the former part. The other is partially filled with cations K + and water molecules.

A neutron diffraction study at 20 K of a single crystal of scolecite (CaAl 2 Si 3 O 10 · 3H 2 O, a = 6.516(2), b = 18.948(3), c = 9.761(1) Å, β = 108.98(1)°; Cc , Z = 4, D c = 2.28 g/cm 3 ) utilized 2109 diffraction intensities from the Brookhaven National Laboratory High Flux Beam Reactor ( λ = 1.0505(1) Å, R (F) = 0.016). There is no indication of substitutional disorder in the structure. The Ca atoms coordinate four framework oxygens and three water oxygens in a distorted pentagonal bipyramid. The hydrogen bonds to the framework oxygens vary in length [O … H: 1.746(1) – 2.119(1) Å] and linearity [O – H … O:130.9(1)° – 177.1(1)°]. The O – H distances in water fall in the range 0.979 – 0.993 Å, and the water angles H – O – H are 106.7(1)°, 107.3(2)° and 111.1(1)°. A neutron scattering length for Ca of 0.465(3) × 10 −14 m is suggested.

The crystal structure of Gysinite has been determined at the composition La 0.16 Nd 1.18 Pb 0.66 (CO 3 ) 2 (OH) 1.34 · 0.66 H 2 O, M r = 483.85. Orthorhombic space group Pmcn , a = 5.0028(8), b = 8.555(1) and c = 7.2392(8) Å, V = 309.83 Å 3 , Z = 2, D x = 5.18 g · cm −3 . Single crystal X-ray refinement, Mo Kα , λ = 0.7107 Å, μ = 34.8 mm −1 , F (000) = 425.4, room temperature, R = 0.065 for 368 independent contributing reflections. The Pb-containing Gysinite is isostructural to the Ca and Sr analog Ancylite and to synthetic hydroxy-carbonates of lanthanides elements.