Volume 210, Issue 4

The available tables of irreducible representations of space groups differ considerably in completeness, kind of listing, and nomenclature. Although published more than 50 years ago, Wintgen's approach making use of the isomorphism between the reciprocal-space groups and the symmorphic space groups has not yet been applied in any of the published listings of irreducible representations of the space groups. In this paper the implications of such a classification scheme are discussed. Use of the International Tables for Crystallography, Vol. A makes such a classification simpler, more transparent, and facilitates some applications. Moreover, the International Tables may serve as a basis for the standardization of the types and symbols of representations.

The unknown quantities of crystal structure analysis are defined by the optimisation principle of the method of least squares. This is, because of its relative complex mathematical form, in general only used for parameter refinement in the final step of structure determination. It will be shown, that the optimisation principle becomes considerably simpler, if the condition of non-interpenetrating atoms is introduced for constraints.

The temperature dependence of the Zn 2+ /Mg 2+ cation ordering among five- and six-coordinated metal sites in γ -(Zn 1− x Mg x ) 3 (PO 4 ) 2 solid solutions has been studied by X-ray powder diffraction methods. The structures of polycrystalline samples ( P 2 1 / n ; Z = 2) prepared at and quenched from different temperatures have been refined with the Rietveld technique. The structure factor R -values are in the range 0.04–0.05. It is shown that ordering with zinc preferably at the five-coordinated site is enhanced with temperature. Approximate thermodynamic data for the exchange reaction have been derived.

The reaction of Se, I 2 and WCl 6 in the molar ratio 12:1:2 in a sealed evacuated ampoule at 423 K yields (Se 6 I + ) n · n (WCl 6 − ) in quantitative yield as black, moisture sensitive crystals with a bronze luster. The compound crystallizes triclinic (space group P [unk]) with the lattice constants a = 670.1(3) pm, b = 741.7(5) pm, c = 803.5(5)pm, α = 92.18(5)°, β = 97.71(4)°, γ = 95.48(4)°. The structure was refined to R W ( F 2 ) = 9.2% based on 2248 unique reflections and r (| F |) = 3.7% based on 1912 reflections with | F | > 4 σ ( F ). The one-dimensional polymeric cation (Se 6 I + ) n is built of Se 6 rings in the chair conformation which are connected by iodine atoms bound to the Se 6 rings in the 1,4 positions and forming linear bridges. The WCl 6 − anions form slightly distorted octahedra. The structure is compared with that of (Se 6 I)MF 6 (M = As, Sb) with a nearly isostructural polycation.

Single crystals having optical quality and dimensions up to 50 mm of sulfamic acid (H[NH 2 SO 3 ]), of the monosulfamates of Li, Na, K, Rb, Cs, Tl, NH 4 , C(NH 2 ) 3 , (CH 3 ) 3 NCH 2 COOH, of CsH[NH 2 SO 3 ] 2 and NH 4 [NH 2 SO 3 ] * NH 4 [HSO 4 ] have been grown from aqueous solutions by standard methods (controlled lowering of temperature and evaporation between 330 K and 285 K). All species possess orthorhombic symmetry, except those having larger cations (Cs,C(NH 2 ) 3 , (CH 3 ) 3 NCH 2 COOH) which show monoclinic symmetry. No hydrates are formed above 300 K. The elastic constants c ij and the thermoelastic constants T ij = d log c ij / d T , T temperature, were determined from ultrasonic resonance frequencies of thick plates and their temperature dependence, respectively. The tensor of thermal expansion has also been measured. The elastic and thermoelastic behavior of the sulfamates resembles those of alkali Perchlorates and other chemically related families, despite their different structures. The elastic anisotropy is weak. The general rules concerning the relation between the mean elastic stiffness and molecular volume, the deviation from Cauchy relations and the Grüneisen relation are confirmed. Cs[NH 2 SO 3 ] and (CH 3 ) 3 NCH 2 COOH[NH 2 SO 3 ] undergo a first- order phase transition on heating above 350 K. An anomalous thermal expansion was found in NH 4 [NH 2 SO 3 ] at temperatures below 260 K.

DL-aspartic acid nitrate monohydrate, (C 4 H 8 NO 4 ) + (NO 3 ) − · H 2 O, M = 214.128, triclinic, P [unk], a = 5.680(1) Å, b = 7.331(2) Å, c = 10.812(1) Å, α = 76.74(1)°, β = 105.33(1)°, γ = 96.41(1)°, V = 422.0 Å 3 , D m = 1.66 g cm −3 (flotation), D c = 1.685 g cm −3 Z = 2, μ = 1.561 cm −1 , λ (Mo K α = 0.70926 Å. The crystal structure was solved by direct, Fourier and difference-Fourier methods and refined by full-matrix least-squares technique to an R = 0.041 and wR = 0.049 for 1249 unique reflections. The aspartic acid molecule exists in cationic form by the protonation of the α -carboxylic group. All the hydrogen atoms were located by difference-Fourier-syntheses.

DL-alanine nitrate (C 3 H 8 NO 2 ) + (NO 3 ) − , M = 152.11, monoclinic, P 2 1 / c , a = 7.648(1) Å, b = 5.631(1) Å, c = 16.335(3) Å, β = 94.42(1)°, V = 701(1) Å 3 , D m = 1.45 (flotation), D c = 1.44, Z = 4, μ (Mo K α ) = 1.3 cm −1 , λ (Mo K α ) = 0.70926 Å. The crystal structure was solved by direct methods and refined to an R value of 0.062 and wR of 0.063 for 680 unique reflections with I > 3 σ ( I ). The intensity data seem to have suffered from secondary extinction effects. Alanine molecules exist in cationic form with protonation of the carboxylic group. The hydrogen-bonded chains run along the c -direction at x = ¼ and ¾ planes.

Compound (1), 2-hydroxyiminomethyl-1-benzylimidazole, C 11 H 11 N 3 O, M r = 201.23, space group orthorhombic P 2 1 2 1 2 1 , a = 9.496(3) Å, b = 9.850(4) Å, c = 11.024(8) Å, V = 1031.1(9) Å −3 , Z = 4, D x = 1.296 Mgm −3 , λ (Mo K α ) = 0.7107 Å, μ = 0.81 cm −1 , F (000) = 424, T = 293 K, final R = 0.0364 for 625 independent observed reflections. An intermolecular hydrogen bond O–H … N of 2.700(4) Å stabilizes the structure. Compound (2), 2-hydroxyiminomethyl-1-benzyl-3-methylimidazolium-iodide, C 12 H 14 IN 3 O, M r = 343.17, space group orthorhombic Pbca , a = 12.484(5) Å, b = 17.339(5) Å, c = 12.616(5) Å, V = 2731(2) Å 3 , Z = 8, D x = 1.669 Mgm −3 , λ (Mo K α ) = 0.7107 Å, μ = 23.08 cm −1 , F (000) = 1344, T = 293 K, final R = 0.0287 for 2104 independent observed reflections. The iodide anion is linked to the oxime-oxygen by hydrogen bond of 3.397(4) Å. Quaternization of the imidazolium ring causes the rotation of the oxime group about C–C bond connecting the imidazolium ring and oxime group. Compound (3), 4-[(hydroxyimino)methyl]-1-[[[2-[(hydroxyimino)methyl]-3-phenyl-1 H -imidazolium-1-yl]methoxy]methyl]pyridinium diiodide, C 18 H 19 I 2 N 5 O 3 , M r = 607.19, monoclinic, P 2 1 / c , a = 13.547(3) Å, b = 14.501 (3) Å, c = 11.781(2) Å, β = 102.75(2)°, V = 2257.3(8) Å 3 , Z = 4, D x = 1.787 Mgm −3 , λ (Mo K α ) = 0.7107 Å, μ = 27.82 cm −1 , F (000) = 1168, T = 293 K, final R = 0.0480 for 2835 independent observed reflections. The iodide anions are linked to oxime-oxygens of the cation by hydrogen bonds of 3.336(6) and 3.388(5) Å, respectively. It has been found that the geometry of the oxime group of the imidazolium ring in the investigated structure can be compared with that of the oxime group of compound (2).

In N , N -dimethyldithiocarbamylacetonethiosemicarbazone, C 7 H 14 N 4 S 3 (triclinic, P [unk], a = 6.226(1) Å, b = 8.111(1) Å, c = 12.387(1) Å, α = 85.19(2)°, β = 84.81(1)°, γ = 74.21(2)°), the sulfur atom of the = N–NH–C(=S)–NH 2 unit is hydrogen bonded to the amino nitrogen atom of an adjacent molecule to form a centrosymmetric dimer. Tris(hydroxymethyl)-methylammonium N , N -dimethyldithiocarbamylacetate, C 9 H 20 N 2 O 5 S 2 (monoclinic, P 2 1 / c , a = 10.773(2) Å, b = 10.2615(8) Å, c = 13.116(3) Å, β = 109.253(9)°) adopts a 3- d network structure in which the cation is linked to the sulfur and carboxyl atoms of adjacent anions by hydrogen bonds.

The title compound was detected in a crystalline form under the stem bark of Ancistrocladus robertsoniorum when wounded by insects. These “biogenic crystals” belong to the orthorhombic system, space group Pbca , with a = 805.0(3) pm, b = 1606.5(6) pm, c = 1410.2(6) pm.

The title compound was prepared by Pd II -catalyzed intermolecular aryl aryl coupling from 1-tri- n -butylstannylnaphthalene and 4-bromo-1,3-dimethoxy-5-methyl-benzene. It crystallizes in the monoclinic system, space group P 2 1 / n , with a = 2221.2(8) pm, b = 822.0(2) pm, c = 831.5(2) pm and β = 90.42(2)°.