Volume 188, Issue 3-4

Synthetic solid solutions of n-paraffins C 23 H 48 and C 21 H 44 have been studied by the thermoroentgenographic method. It is shown that the limits of isomorphous substitutions of molecules in these paraffins with molecular ratios C 23 :C 21 = 1:2, 1:1 and 2:1 are temperature dependent. At rising temperatures all solid solutions first break down to form two phases which coexist in a narrow temperature range (3 – 5°C) and then become homogeneous at further elevation of temperature. Isomorphism in the system is established to be violated in the course of intensive structural rearrangements; it gets restored shortly (7 – 9°C) before the orthorhombichexagonal polymorphic transformation. A decrease in the limits of isomorphous substitutions which occurs at rising temperatures is explained by differences in energy states of paraffin chains having different lengths: relatively long chains oscillate about their own axes whereas shorter chains perform complete rotations and get “separated” from solid solutions.

Careful experimental techniques, especially with synchrotron radiation, give well-resolved diffraction patterns. Remaining overlapping peaks can be separated by profile analysis and profile fitting. The mathematical formalism is given. The derived parameters are: peak positions for lattice constants, integrated intensities for crystal structure work and half-width for line broadening analysis. Crystal structure refinements with the powder least-squares program POWLS yield R factors routinely around R = 1.5% and as low as R = 0.6%. For actual structure analysis Fourier maps have been calculated in the case of the orthorhombic olivine analogue Mg 2 GeO 4 . Another non-trivial example concerns CeO 2 , where chemical bonding features are derived. From an analysis of anomalous dispersion in Yb 2 O 3 the correction terms f ′ have been derived as a function of energy for four wavelengths measured close to the L-absorption edge of Yb.

It is shown that the mean expected X-ray intensities of main and superstructure reflexions can be described by different functions of sin 2 π | h | · | δ |/(2 π | h | · | δ | when the intensities are obtained from a crystal structure in which all atoms fullfil one or more pseudotranslations approximately. In these formulas | δ | is a measure of the mean deviations of the atoms from their ideal positions. If the pseudotranslations are not taken into account in the normalising procedure, similar functions for the expected mean E 2 -values can be derived, from which the mean values of E 2 depending on | δ | are obtained by integration. The relations to formulas published earlier are discussed. It can furthermore be demonstrated that real structures exist in which the pseudotranslations can not be recognized by the different mean intensities of main and superstructure reflexions but by their variation along | h |.

The crystal structure of Luvangetin (C 15 H 14 O 4 ) has been determined from three-dimensional X-ray diffraction data. The compound crystallizes in the triclinic space group P [unk] with unit cell parameters a = 8.391(1) Å, b = 11.617(10) Å, c = 7.461(10) Å, α = 99.014°, β = 116.476°, γ = 75.886°, cell volume = 630.23 Å 3 , d c = 1.36 g/ml, d m = 1.32 g/ml, μ (Cu Kα ) = 8.27/cm, Z = 2. The gross structure was determined from 835 observed reflections by direct methods which on refinement yielded R = 0.052. The hydrogen atoms were located from difference syntheses. There are no hydrogen bonds in the crystal. The structural relationships between the rings are discussed.

Tris-glycine zinc chloride, a complex of glycine with ZnCl 2 , crystallises in an orthorhombic unit cell of dimensions a = 11.230(2) Å b = 15.251(3) Å c = 15.564(4) Å in the space group Pbn 2 1 with Z = 8. The structure has been determined using diffractometer data (2345 Mo Kα reflections) to a final R value of 0.034. All the six glycine molecules in an asymmetric unit exist as zwitterions, NH 3 + CH 2 COO − and are held together by a network of N – H…O and N – H…Cl type of hydrogen bonds. Each of the two zinc atoms is coordinated to two oxygen atoms and two chlorine atoms, forming a distorted tetrahedron.

The deconvolution of (multiple wavelength) Patterson maps by minimum function was replaced by ratio image seeking ( β synthesis). The resulting map shows less spurious peaks and more details in two heavyatom structures (hemimorphite, barium nitrite monohydrate). The transformation of Bijvoet differences in a Sinus-Patterson synthesis enabled the estimation of hydrogen positions which could not be derived by usual X-ray methods.

The crystal structure of anthophyllite Na 0.01 Ca 0.02 Mg 5.71 -Fe 1.24 Mn 0.02 (Si 7.95 Al 0.05 )O 22 (OH) 2 has been refined by single crystal X-ray methods using 1316 independent reflections. The space group is Pnma with the unit cell dimensions a = 18.544(2) Å, b = 18.026(2) Å, c = 5.282(1) Å and V = 1765.6(4) Å 3 , Z = 4. Chemical and optical data are given. The refinement of the atomic parameters and of the cation distribution gives final values of R = 0.034 and R w = 0.035. The M sites show a high degree of Mg and Fe cation ordering. M2 is only occupied by Mg and M1, M3 also contain very little iron. M4 is greatly enriched in iron: 0.62 Fe and 0.38 Mg. The coordination of M4 is highly irregular with five next oxygens and two longer M4 – O distances. The A site is found to be empty.

A method for the precise determination of the X-ray scale factor measuring absolute intensities from powder specimens has been tested. It proved to be applicable to electron density determinations of high accuracy with a relative standard deviation of 1 – 2% of the observed relative structure amplitudes. The necessary sample quality showed to be the most serious possible handicap.

The X-ray analysis proved that the configuration at C8 of the hydroperoxide of atractyligenin is 8 α -OOH and not 8 β -OOH.

The crystal structures of N-benzylcarbonyl- α -aminoisobutyric acid methyl ester (1) and N-benzylcarbonyl- α -aminoisobutyryl- α -aminoisobutyryl- α -aminoisobutyric acid methyl ester (2) have been determined by X-ray diffraction techniques. The compounds possess the following parameters: (1) orthorhombic, space group Pbca (No. 61), a = 20.124(3) Å, b = 9.497(1) Å, c = 13.825(2) Å, and Z = 8; (2) orthorhombic, Fdd 2 (No. 43), a = 31.454(3) Å, b = 34.132(3) Å, c = 8.448(1) Å, and Z = 16. The crystal structures were solved by direct methods. The least-squares refinements led to R values of 0.061 and 0.057 for 1112 and 1131 reflections with I ⩾ 3 σ ( I ) for (1) and (2), respectively. The conformation of the N- and C-blocking groups is similar in the two compounds. However, the conformation of the Aib residue in (1) is semi -extended, while those of the three Aib residues in (2) are helical.

The crystal structure of U 4 Ni 5 Al 18 has been refined from single crystal X-ray counter data; U 4 Ni 5 Al 18 crystallizes in a unique structure type with the noncentrosymmetric space group C m and lattice parameters: a = 1.5547(3) nm, b = 0.4061(1) nm, c = 1.6458(3) nm, β = 120.00(1)°, Z = 2. For 1471 reflections (| F o | > 3 σ ) the obtained reliability factor was R = Σ | ΔF |/ Σ | F o | = 0.046, wR = 0.035. The structure type of U 4 Ni 5 Al 18 shows complete order of all atoms. It is further characterized by a typical triangular prismatic coordination |U 2 A1 4 | or [Al 6 | around the nickel atoms and belongs to the so-called series of inhomogeneous structures.

The crystal structure of dicesium pentaazidoneodymiate(III), Cs 2 Nd(N 3 ) 5 , was determined by single crystal X-ray methods. The crystals are monoclinic, a = 2460.1(7) pm, b = 1256.8(3) pm, c = 1818.5(5) pm, β = 113.98(2)°, space group C 2/ c , Z = 16,2278 observed reflections, R = 0.083, R w = 0.072. Both neodymium atoms in one asymmetric unit are coordinated to eight azide groups, the coordination polyhedra are linked via nitrogen atoms and azide groups to a three-dimensional network. One cesium atom is surrounded by eight and the three other cesium atoms by six azide groups, respectively.

Single crystals of Tl 5 Te 3 have been synthesized from stoichiometric mixtures of the elements in a two step reaction. Tl 5 Te 3 crystallizes in the tetragonal space group I 4/ mcm (No. 140) with a = 8.930(2) Å and c = 12.589(4) Å. The structure is isopointal to the Cr 5 B 3 structure type but differs in some details. The interatomic distances clearly show a separation into Tl 2 Te molecular-like fragments (Tl – Te = 3.16 Å; [unk] Tl – Te – Tl = 78.5°) and one-dimensional infinite linear TlTe chains (Tl – Te = 3.15 Å). The axial ratio c / a and the positional parameters indicate unambiguously that Tl 5 Te 3 and Cr 5 B 3 belong to definitively separated branches of the Cr 5 B 3 structure type.

The crystal structure of the title compound (FQTP hereafter) was determined from three-dimensional data of 2733 independent reflections. The cell constants, are a = 10.148(2) Å, b = 11.049(2) Å, c = 13.352(2) Å, α = 76.07(2)°, β = 82.98(2)°, γ = 78.18(2)°, V = 1418.05 Å 3 , Z = 2, space group P [unk], μ = 1 cm −1 . The structure was solved by direct methods and the positional and thermal parameters were refined by full-matrix least-squares calculations. The final R value was 0.064. The furazanoquinoxalinyl group is planar with bonds and angles falling within the expected ranges. The carbanion atom has an sp 2 hybridization and the bond length P = C sp 2 (1.75 Å) indicates a major contribution of the resonance form Ph 3 [unk] – [unk] [unk] to the structure of this ylide. The triphenylphosphorane group has a distorted tetrahedral conformation around the P atom.

The title compound, 2-thiophenecarboxylic acid, crystallizes in the monoclinic space group P 2 1 / c with unit cell parameters a = 5.698(1) Å, b = 5.043(1) Å, c = 19.712(2) Å, β = 98.49(1)°, Z = 4; D x = 1.519 Mg m −3 . The structure was solved by direct-methods and refined by a full-matrix least-squares procedure on 958 reflections to final R = 0.034. The S(1) – C(2) and S(1) – C(5) bond distances are 1.707(2) Å and 1.695(2) Å respectively. In the crystal lattice the molecules associate via the carboxylic acid groups to form centrosymmetric dimers.

Large single crystals of optical quality of the following betaine adducts have been grown from aqueous solutions (b = betaine): b · H 2 O, b · HCl, b · HBr, b · HI, b · HNO 3 , b · H 2 SO 4 · H 2 O, b 2 · H 2 SO 4 , b · H 3 PO 3 , b · H 3 PO 4 , b · 1,4-CH 3 (C 6 H 4 )SO 3 H, b 3 · 2MnCl 2 , b · KBr · 2H 2 O. The crystals were characterized by their metric data, space group symmetry, density and thermal expansion. Complete elastic and thermoelastic tensors were determined by the aid of ultrasonic resonance methods. All betaine adducts investigated so far display common structural features and similar physical properties expressing the dominant role of the betaine molecule in the crystalline bond system. In addition to the already known phase transitions a ferroelastic phase transition in b · 1,4-toluene sulfonic acid at about 140 K, which is accompanied by a softening of c 66 , and a first-order transition in b · KBr · 2H 2 O at about 335 K were observed.