Volume 166, Issue 3-4

Solid solutions of Me 3 (PO 4 ) 2 in Ni 3 (PO 4 ) 2 , with the olivine-related sarcopside structure ( P 2 1 / a ), have been prepared and equilibrated at 1070 K ( Me = Mg, Mn, Fe, Co, Cu, or Zn). Accurate unit cell dimensions have been obtained from Guinier-Hägg photographic X-ray diffraction data. The cell volumes of the (Ni l – z Me z )3(PO 4 ) 2 phases are correlated to the size and amount of Me 2+ . Rietveld full-profile refinements based on neutron powder diffraction data have been utilized to determine the distribution of cations among the two distinct octahedral sites M1 and M2. The preference for M1 over M2 is Ni 2+ > Co 2+ > Mg 2+ , Zn 2+ > Mn 2+ > > Fe 2+ . The cation distribution results are compared with corresponding results for olivines, orthopyroxenes, and some other oxosalt structures with metal-oxygen octahedra similar in size and shape to those in olivine. It is concluded that the Ni 2+ / Me 2+ distributions in these structure types are mainly controlled by crystal field energies, while the size effects are small.

The crystal structure of C.I. Pigment Yellow 1, α -(1-hydroxyethylidene) acetanilide- α -azo-(4′-methyl-2′-nitrobenzene), C 17 H 16 N 4 O 4 , has been determined by single crystal X-ray diffraction techniques. It crystallises in the monoclinic system with cell parameters a = 7.587 ± 0.042 Å, b = 20.362 ± 0.053 Å, c = 12.033 ± 0.046 Å, β = 120.68 ± 0.29°. The space group is P2 1 / c and there are four molecules per unit cell. The structure was solved from that of C.I. Pigment Yellow 6 by isomorphous replacement, and least-squares refinement has been completed on three-dimensional data, 1696 reflections (Cu Kα radiation). The hydrogen atoms have been found and included but only those associated with the methyl groups have been refined. The final residual is 8.0%. The molecule exists as the hydrazone tautomer and intramolecular hydrogen bonds keep the molecule approximately planar. The molecules are packed in layers parallel to the (100) plane and in columns parallel to the a axis. Alternate molecules within the columns are in antiparallel position. The molecules are linked by van der Waals forces. Although the structure was solved from that C.I. Pigment Yellow 6, it is concluded that the two structures are not strictly isomorphous.

The crystal structure of ZnBr 2 is tetragonal, space group I 4 1 / acd , a = 11.389(4), c = 21.773(9) Å, V = 2826(3) A 3 , μ = 308.2 cm −1 . D m = 4.208, Z = 32, D x = 4.233 Mg m −3 . The structure was determined from 146 independent observed [ F > 2 σ ( F )] reflections to an R value of 0.074. The bromide ions are arranged in an fcc array with Zn atoms filling in 1/4 of the tetrahedral sites. This results in the formation of ‘super-tetrahedral’ groups of Zn 4 Br 6 Br 4/2 , which again interconnect to give a three-dimensional network. These groups are similar to those of P 4 O 10 , hexamethylenetetramine, [N 4 (CH 2 ) 6 ], and the large ‘cage’, Zn 4 S 6/2 S 4/4 , present in the zinc blende structure. However, the cage groups in ZnBr 2 have point group [unk] in this space group and they are only slightly deviated from [unk]3 m , the point group for idealized cages. The mean Zn – Br distance is 2.42(1) Å, and the mean Br – Zn – Br angle is 109(3)°. All the Br atoms are 2-coordinated, with Zn – Br – Zn angles ranging from a mean value of 105.3(3) for intracage bonds to 107.9(5)° for intercage connections. The ZnBr 2 structure is related to those of HgI 2 , Be 3 P 2 and Cd 3 As 2 in a very interesting way.

The morphological lattice of monoclinic potassium feldspars is a P -lattice with a /2 and b /2 and co-ordinates 1/41/41/4. The reciprocal crystal has 8 faces and symmetry 2/ m . The morphological units (KT 4 O 8 , T = A1, Si) are connected over T – O bonds along [100], [010] and [102] and over K – O bonds along [001]. The arrangements of the polyhedra parallel to the crystal faces show that (001), (010), (100), ([unk]01), (110) and ([unk]11) are F-faces and ([unk]01), (130) and (021) S-faces according to Hartman and Perdok. Considering the morphological extinction rules (110) has to be regarded as an S-face and ([unk]11) as a K-face. The areas of the net meshes divided by the number of the morphological units per growth layer correspond to the attachment energies, the quotients are proportional to the central distances of the reciprocal morphological lattice. The thickness of the growth layer is determined by the extinction rules. By a Wulff-plot a growth form is obtained which shows all the important faces.

Orthorhombic crystals of nearly 1 cm lengths have been obtained from a solution of cadmiumbenzohydroxamate in ethylenediamine. The space group is Fdd 2, the cell constants are a = 41.004, b = 30.272, c = 8.840 Å. The final. R -value was 0.023. In the asymmetric unit there are one tris(ethylenediamine)-cadmium(II) chelatcomplex-ion, two benzohydroxamate-anions and one water molecule. Hydrogen bonds are formed between the hydroxamic acids and the water molecule. In the crystal the complex-ion is surrounded by five hydroxamic acids, three of them are in planes parallel and two of them perpendicular to the crystallographic c -axis.

4-Dimethylaminopyridine, C 7 H 10 N 2 , crystallizes in the monoclinic space group P 2 1 /n with a = 14.813(3), b = 7.604(2), c = 6.103(2) Å, β = 93.2(2)° and Z = 4. The structure was solved from automated diffractometer data by direct methods and refined by least-squares techniques to R = 0.072 ( R Fw = 0.092) for 1137 observed reflections. Only small deviations from the aromatic pyridine system are found in this molecule. Between the dimethylamino group and the plane of the pyridine ring the torsion angle is 7(1)°. The results are compared with those obtained for other derivatives.

Scolecite, CaAl 2 Si 3 O 10 · 3 H 2 O, monoclinic (space group Cc ), but described here in the pseudo-orthorhombic setting of Fd , with a = 18.508(5), b = 18.981(5), c = 6.527(2) Å, β = 90.64(1)° in analogy to natrolite. 225 parameters, including hydrogen atoms, were refined anisotropically from 1319 neutron diffraction reflections, the final conventional R value being 2.0%. Tetrahedral Si 4+ and Al 3+ are well-ordered as well as the three water molecules. Hydrogen bonding is discussed.

The crystal and molecular structure of [4]peristylanedione, C 12 H 12 O 2 , has been determined by X-ray diffraction techniques. The substance crystallizes in the monoclinic space group P 2 1 / c having cell parameters a = 7.352(5), b = 11.349(6), c = 12.556(8) Å, β = 122.5(1)° and Z = 4. The calculated density for four molecules per unit cell is 1.42gcm −3 . The crystal structure was determined by direct methods. The least-squares refinement led to a R value of 0.047 for 1607 observed reflections. The molecule shows almost perfect C 2 v -symmetry. The four-membered ring and both five-membered rings bearing the ketone groups are almost planar, the other two five-membered rings show half-chair conformation. The molecules are held together by van der Waals forces mainly.

C 12 N 6 , M r = 228.2, Pa 3, a = 10.781(6) Å, V = 1253.1(1) Å 3 , Z = 4, D c = 1.21 g cm −3 , λ (MoK α ) = 0.71069 Å, F (000) = 456, μ = 0.49 cm −1 . Three different refinements (high-angle data, charge-cloud model and a multipolemodel) gave the R -values 0.046, 0.035 and 0.039 respectively. The resulting peak heights of the deformation density lie within the range 0.25 – 0.46 eÅ −3 in the ring, 0.26 – 0.48 eÅ −3 in the C – C single bond, 0.33 – 0.74 eÅ −3 in the C – N triple bond and 0.00 – 0.12 eÅ −3 in the lone pair region, whereas the integrated charges in the deformation peaks show a good correspondence (0.12 – 0.15 e, 0.10 – 0.13 e, 0.18 – 0.29 e,0.00 e). These charge contents of the bond peaks are in good agreement with theoretical values (C = C: 0.15 e, C – C: 0.09 e, C ≡ N: 0.26 e) computated for p-dicyanobenzene. The difference between the experimental and theoretic (0.19 e) values for the lone pair together with the high melting point (370°C) of hexacyanobenzene(HCB) suggest a probability of an intermolecular charge compensation in the crystal.

Na 4 CaSi 3 O 9 crystallizes in space group Pa 3 with a = 15.087(2) Å and Z = 16 formula units per unit cell. The refinement of the atomic parameters gave a final R -value of R = 0.063 ( R w = 0.054) for 1227 observed reflections. The compound is isostructural with K 4 SrGe 3 O 9 , the crystal structure contains rings of 12 corner-sharing SiO 4 tetrahedra normal to the three-fold axes. A close structural relationship also exists to tricalciumaluminate Ca 3 Al 2 O 6 which contains Al 6 O 18 -rings of corner-sharing A1O 4 tetrahedra.

Dibarium-nickel-hexaazido-trihydrate crystallizes monoclinic in space group Cc , a = 10.624(4), b = 9.359(3), c = 16.275(5) Å, β = 110.72(8)°, Z = 4. The crystal structure was determined by direct methods (Mo Kα , 1150 observed reflections) and refined to R = 0.077. Nickel is octahedrally coordinated by six azide groups. Each of the two barium ions is surrounded by eight azide groups and two water molecules.

Diffraction intensity data of well ordered protoenstatite, MgSiO 3 , inverted from orthoenstatite, were collected at 1260°C and 1360°C by means of four-circle diffractometry using a gas flame heater. The effect of temperature on the structure of protoenstatite was studied based on these data and those at 1080°C (Murakami, Takeuchi and Yamanaka, 1982). The results revealed the following notable features of the structure of protoenstatite at high temperatures up to near the incongruent melting point: (1) The variations of the b axis and the unit cell volume as a function of temperature were approximately linear. (2) The expansion of the c axis terminated at around 1300°C, whereas that of a markedly enhanced at temperatures above 1300°C. (3) The structure underwent a minor sudden change at around 1300°C; the O1 atoms were displaced approximately towards the Si atoms along the a axis perpendicular to the oxygen layers, and the O2 atoms, towards the Mg atoms along the same direction. The Si – O(1) and Si – O(2) bond distances uncorrected for thermal motion are 1.55(2) Å and 1.64(1) Å, respectively, at 1360°C.

Crystals of molybdenum hexacarbonyl are orthorhombic, with a = 12.019(2), b = 11.415(2), c = 6.488(1) Å, space group Pnma , and Z = 4. The structure has been refined to R F = 0.025 for 1316 observed Mo Kα . data. The Mo(CO) 6 octahedron conforms closely to idealized m 3 m symmetry, and the averages of chemically equivalent bond lengths are: Mo – C = 2.059(3) Å and C – O = 1.125(5) Å.

The crystal structures of the ternary selenogallates Cs 6 Ga 2 Se 6 , Cs 8 Ga 4 Se 10 , Cs 10 Ga 6 Se 14 and CsGaSe 2 -I are characterized by the existence of linear oligimeric and polymeric anions [Ga n Se 2 n + 2 ]( n + 4)− ( n = 2,4,6, ∞). These anions consist of edge sharing GaSe 4 -tetrahedra and show systematic geometrical variations of distances and angles which correlate with the degree of oligomerisation. In connection with the geometrical variations remarkable space filling changes are observed. Preliminary transmission measurements with small single crystals of the air sensitive compounds show an optical band gap of about 3 eV. A significant shift of the optical band gap to higher energies is observed and can be correlated with the length of the oligomeric anions and qualitative arguments about the chemical bonding in them.

The hexagonal rare earth aluminates REAl 11 O 18 , REMgAl 11 O 19 , and RELi 0.5 Al 11.5 O 19 were prepared by solid state reaction. The phases REA1 11 O 18 were found to exist only for RE = La, Ce, REMgAl 11 O 19 for RE = La – Gd, and RELi 0.5 Al 11.5 O 19 for RE = La – Eu. The values of c/a indicate REMgAl 11 O 19 and RELi 0.5 Al 11.5 O 19 to belong to the magnetoplumbite type. This may also be true for REA1 11 O 18 which was formerly assumed as a β -alumina phase.

The crystal structure of Cs 0.35 Al 0.35 Si 2.65 O 6 has been determined with direct methods from X-ray four-circle single-crystal diffractometer data at 293 K. The space group is monoclinic, B 2 1 with Z = 4; a = 7.3585(4) Å; b = 5.0334(3) Å; c = 15.950(1) Å; β = 90.778(9) 0 ; V = 590.7 Å 3 ; D c = 2.55g cm −3 , D m = 2.56g cm −3 . The refinement converged to R = 0.044. The aluminosilicate framework is isotypical with the framework of bikitaite. The Cs atom is located in the large channel coordinated by ten oxygens in the range 3.24 Å to 3.58 Å.

The crystal structure of a new poly type 14H 9 of cadmium iodide has been determined. In Zhdanov notation the structure is 2211(211) 2 . The space group is P 3 m l.