Volume 209, Issue 1

The F forms, as defined by the Periodic Bond Chain Theory, of K 2 S 4 O 6 with space group Cc have been derived from the crystal structure. When each F form is characterized by the indices { nh , nk , nl } of its slice thickness d nh, nk, nl and when polarity is disregarded, the F forms are in decreasing order of d nh, nk, nl : {200}, {110}, {[unk]11}, {111}, {400}, {310}, {[unk]11}, {002}, {[unk]02}, {311}, {202}, {[unk]02}, {[unk]12}, {312} and {402}. The description as given by Groth (Chemische Krystallographie, Vol. II, p. 717) contains several errors. A new description is given. The observed forms are all F forms. To explain the polar habit the hypothesis is made that the dehydration of the cations determines the growth rate of a face. This hypothesis leads to the prediction that {[unk]02} should be present at the positive end of the c axis and {[unk]} at the negative end. This agrees with the observations.

Powders and X-ray size single crystals of the rare earth disilicates RE 2 Si 2 O 7 (RE = La to Nd and Gd to Lu and Y) were synthesized from the melts in a fast crucible-free process. The purity and unit cell parameters of the disilicates were determined from Guinier photographs. Previously reported structure types of the high temperature phases of RE 2 Si 2 O 7 (RE = La, Ce, Ho, Er, Yb, and Y) were confirmed by profile refinement of neutron powder diffraction data. The high temperature modifications of La 2 Si 2 O 7 and Ce 2 Si 2 O 7 have the type G -structure. They are monoclinic, P 2 1 / c with Z = 4 and a = 5.4109(6), b = 8.796(8), c = 14.287(1) Å, β = 112.74(1)° for La 2 Si 2 O 7 , and a = 5.401(1), b = 8.723(1), c = 14.169(2) Å, β = 112.61(2)° for Ce 2 Si 2 O 7 , respectively. The high temperature modifications of Ho 2 Si 2 O 7 and Y 2 Si 2 O 7 have the type E -structure. They are orthorhombic, Pna 2 1 with Z = 4 and a = 13.681(4), b = 4.997(3), c = 8.187(2) Å for Ho 2 Si 2 O 7 , and a = 13.6650(1), b = 5.0166(1), c = 8.1494(1) Å for Y 2 Si 2 O 7 , respectively. Er 2 Si 2 O 7 and Yb 2 Si 2 O 7 have the type C -structure at high as well as at low temperatures. They are monoclinic, C 2/ m with Z = 4 and a = 6.8491(9), b = 8.9395(10), c = 4.7222(5) Å, β = 108.810(9)° for Er 2 Si 2 O 7 , and a = 6.7988(3), b = 8.8759(4), c = 4.7101(3) Å, β = 101.982(4) for Yb 2 Si 2 O 7 , respectively.

KZnSbTN is an example from the large acentric double salt-like family of tartrato-antimonates. Its crystal structure was determined from single-crystal X-ray diffraction data (orthorhombic, P 2 1 2 1 2 1 , a = 8.112(2) Å, b = 15.507(4) Å, c = 16.090(5) Å, Z = 4, D x = 2.600 Mgm −3 , μ (Mo K α ) = 2.855 mm −1 , T = 293 K, R = 0.046 for 5320 unique reflections ( I > 3 σ ( I )). The main structural feature is the (4-)-bridged binuclear tartrato-antimonate(III) complex [Sb 2 {(+)-C 4 H 2 O 6 } 2 ] 2− . Single crystals of the title compound of up to 4×4×6 cm 3 were grown from aqueous solutions at 35°C. The electrostrictive tensor [ d ijk ] and the unclamped electro-optic tensor [ r ijk σ were determined at room temperature and λ = 633 nm. The maximum value of the electro-optic effect is two orders smaller than that of KH 2 PO 4 (KDP). The maximum electrostrictive constant is 1.3-times greater than that of α -quartz.

The interdependence of hydrogen – oxygen distances in inorganic compounds can be described by a close correlation if sufficiently high coordination numbers for hydrogen are taken into account. For this purpose, the coordination is favourably defined as chemical coordination number K which is derived from the geometrical coordination or Niggli's Wirkungsbereich. Distances R i [pm] from one hydrogen to the surrounding oxygen atoms are connected by the rule that the sum of bond valences, s ( R i ) equals the valence of hydrogen: [unk]

A systematic analysis of a family of triply periodic minimal surfaces of genus seven and trigonal symmetry is given. The family is found to contain five such surfaces free from self-intersections, three of which are previously unknown. Exact parametrisations of all surfaces are provided using the Weierstrass representation.

Large single crystals of optical quality of monoclinic ethylenediammonium bis(hydrogensuccinate) were grown from aqueous solutions. An X-ray structure analysis yielded space group P 2 1 / c , a 1 = 5.358(1), a 2 = 12.947(3), a 3 = 9.608(2) Å, α 2 = 95.26(2)°, Z = 2, ϱ calc = 1.483(1); ϱ obs = 1.481 (2) g cm −3 . This acid succinate salt can be classified as type B 2 salt. The structure contains short hydrogen bonds between adjacent succinate ions which form periodic bond chains along [20[unk]]. The length of the short hydrogen bond is 2.581(1) Å. The chains are interconnected by hydrogen bonds via the ethylenediammonium cations forming a three-dimensional network. The thermal expansion was studied between 230 and 350 K. The tensor of thermal expansion exhibits a very large anisotropy ( α max − α min = 459 · 10 −6 K −1 ). Further, the dielectric constants between 10 KHz and 10 MHz and the indices of refraction in the visible spectrum were determined.

In 3 SnI 5 prepared from the binary iodides transforms at 247.3(8)°C from a low to a high temperature modification. Single crystal studies reveal, that the low temperature product consists of three different polymorphs, the structures of which are described in detail. Common feature of all these forms is the arrangement of the cation coordination polyhedra in layers of two different kinds and the stacking sequence of the layers. They differ in the relative orientation of successive layers of one type. An estimation of relative thermodynamic stabilities via Effective Coordination Numbers ECoN and Madelung Parts of Lattice Energies MAPLE revealed an approximately equal stability of all polymorphs.

The crystal structure of (Na 1/3 , (H 2 O) 2/3 ) 12 · [NaFe 3 3+ O(SO 4 ) 6 (H 2 O) 3 ] was solved using 1143 single crystal X-ray reflections (sin θ / λ ≤ 0.70 Å −1 , λ = 0.7107 Å) and was refined to R (unweighed) = 0.064. Salient crystal data are: a = 15.015(4), b = 11.154(3), c = 18.385(4) Å, space group Cmcm , V = 3079(1) Å 3 , Z = 4, D m = 2.30 (by flotation), D x = 2.31 g cm −3 , μ (MoK α = 30.30 cm −1 . The structure contains the three-nuclear iron complex [Fe 3 3+ O(SO 4 ) 6 (H 2 O) 3 ] 5− already found in other similar compounds. Such structural units are linked together by Na atoms to form [NaFe 3 3+ O(SO 4 ) 6 (H 2 O) 3 ] 4− bond chains running along the c axis. The experienced disorder concerning some cations and water molecules of a related group of trigonal iron(III) sulphates, affects also the title compound. Moreover, like its hexagonal potassium analogue, this salt is unstable under the atmospheric conditions even if the chemical behaviour is different both in respect to the time of reaction and to the product obtained.

The structure of the (Al, Cu) 13 Co 4 phase was determined by powder X-ray diffractometry and Rietveld refinement for 2,4,5 and 6 at.% Cu. The increase in the copper content is realized by the permanent replacement of the Al atoms by Cu in the ( x 0 z ) plane of the binary Al 13 Co 4 structure. For up to 2 at.% of Cu this occurs at the (0.5, 0, 0.5) position. For the higher Cu content its atoms occupy completely or partially two other positions, whose coordinates for the 6 at.% Cu phase are (0.890, 0, 0.200) and (0.075, 0, 0.777). No partial occupancies of pure Al-sites are suggested for the 2–6 at.% Cu.

The title compound (C 25 H 31 N 3 O 5 Cu) is monoclinic, with space group P 2 1 / c , Z = 4 and cell dimensions a = 9.5077(10), b = 9.8105(14), c = 27.123(4) Å and β = 91.315(13). A total of 7833 reflections were measured on a Philips PW1100 automatic diffractometer using Mo Kα radiation. The structure was refined by full-matrix least-squares to a conventional R = 0.0496 for the 3648 unique reflections. The co-ordination around the central copper atom is square pyramidal with the copper atom 0.177(2) Å above the base plane of three oxygen and one nitrogen atoms. The Cu–O bond lengths have a mean value of 1.956 Å, whereas the Cu–N bond length is 2.030 Å. The apex of the pyramid is occupied by the second nitrogen atom of neocuproine at a distance of Cu–N = 2.266 Å.

Crystal structure of title compounds dafone (4,5-diazafluoren-9-one) and its tetrachlorocobaltate salt have been determined at room temperature by X-ray diffraction and refined to residuals R = 0.032 and 0.048 for 710 and 1173 observed reflections, respectively. In both the structures the dafone ring system is almost planar. There is a possible C–H … N interaction in the crystal structure of dafone. In the dafone-tetrachlorocobaltate structure no direct bonding is observed between the metal and the dafone ring. The protonated nitrogen in dafone ring participates in hydrogen bonding. The water molecule links the dafone with the tetrachlorocobaltate anions.

C 4 H 10 O 2 S 2 , M r = 154.25, monoclinic, T = 87(1) K. ( α ) P 2 1 / n , a = 10.520(2), b = 5.818(1), c = 12.029(2) Å, β = 92.86(1)°, V = 735.3(2) Å 3 , Z = 4, D x = 1.3934(4) Mgm −3 , λ (Mo Kᾱ ) = 0.71073 Å, μ = 0.617 mm −1 , F (000) = 328, R = 0.023 for 2080 reflections. ( β ) P 2 1 / c , a = 10.413(1), b = 6.706(1), c = 10.229(1) Å, β = 94.32(2)°, V = 712.3(2) Å 3 , Z = 4, D x = 1.4384(8) Mgm −3 , λ (Mo K ᾱ) = 0.71073 Å, μ = 0.637 mm −1 , F (000) = 328, R = 0.021 for 2007 reflections. The main conformational distinction between the two forms is the − synclinal and + synclinal orientation of the C(Me)–S–C–C in the thio end of the α and β forms, respectively. The bond lengths and angles are very similar in the two forms, and in good agreement with some related sulfone and sulfide structures.

The crystal structure of the title compound O -ethyl- N -phenylthiocarbamate, [EtOC(=S)N(H)Ph], has been determined at room temperature. The colorless crystals are triclinic, space group P [unk] with unit cell dimensions a = 11.972(4), b = 12.114(1), c = 9.607(2) Å, α = 95.52(1), β = 94,80(3), γ = 89.34(2)°, Z = 6 and D x = 1.307 Mg m −3 . The structure was solved by direct-methods and refined by a full-matrix least-squares procedure to final R = 0.054 using 3499 reflections. There are three molecules in the crystallographic asymmetric unit which differ by minor variations in the orientations of the terminal ethyl and phenyl groups. The –OC(=S)N(H) chromophore is essentially planar in each molecule and the average C=S, C–O and C–N bond distances of 1.650(3), 1.302(4) and 1.323(4) Å, respectively indicate substantial delocalization of π -electron density over this moiety.

The dication crystallises with imposed two-fold symmetry. Both cations show P–C bonds appreciably shortened with respect to the parent compound 1,6-diphosphatriptycene. The cage C–C bonds are longer than the opposite bonds in the phenyl rings. The C(Ar)–P–C(Ar) angles widen by 6–7° compared with the parent compound.

Faraday rotation and magnetic circular dichroism have been determined as a function of temperature in chromium-doped potassium alum. Measurements show strong anomalies at T O = 59 K which are caused by birefringent domains. Below the phase transition birefringence decreases the Faraday rotation. In contrast to direct birefringence measurements this decrease does not depend on the sign of domains. Thus changes of the Faraday rotation are a more reliable measure of the temperature dependence of the order parameter. The occurrence of birefringence below T O reveals apparative limits in the measurement of magnetic circular dichroism which is three orders of magnitude smaller than the Faraday rotation.