S. García-Blanco

Conformational and molecular study of the 4-(2-carboxyethyl)-1,2,3,4-tetrahydrocyclopent[b]indole

Abstract A conformational study of the title compound has been carried out in solution and solid states. The molecules are packed in the crystal forming a charge-transfer complex, where two different molecular pairs are found. Visible spectra data show two weak absorption bands.

The crystal structure of calcium orthoborate: a redetermination

reflexions to the data sets, as in the case of K3[Co(CN)6], is not possible. The implication of these results is that the partial symmetry operations of the OD groupoid symbol are to be regarded as approximate rather than exact and that the degree to which they are obeyed varies from structure to structure, f)urovi6 (1974) has suggested that the more ordered the crystal, the less it complies with the ideal OD model. Although this is consistent with K3[Cr(CN)6], which exhibited well-defined maxima on exceedingly weak streaks, it is by no means consistent with Ka[VO(CN)s] for which the streaks were more or less continuous and without well-defined maxima. Similarly, it would seem somewhat difficult to reconcile this suggestion with preliminary results from the refinement of diaquobis(salicylato)copper(II) (Jagner, Hazell & Larsen, 1975) which indicate that the partial symmetry operations are preserved more exactly in the monoclinic MDO2 structure than in the orthorhombic MDO1 structure, both structures having been solved from the same crystal. Obviously, more evidence is needed before the extent to which the partial symmetry operations relax can be classified and suitably interpreted. From a practical point of view, since it is usually necessary to impose some sort of constraint, at least during the initial stages of refinement, in order to obtain convergence, it would seem more appropriate to preserve the partial symmetry operations of the OD groupoid symbol, even if these constraints are later released, than to more or less arbitrarily select one or more parameters to be fixed. In those cases where there is little difference between the constrained and unconstrained models, constrained refinement does, of course, yield bond distances and angles with smaller standard deviations.

Crystal structure of 3Bi2O3:5B2O3. A new type of polyborate anion (B5O11)7−

Single crystals of 3Bi2O3:5B2O3 have been obtained from the melt and subsequent devitrification of the glassy compound, at 450°C during 90 hr. The compound is orthorhombic, space group Pnma with two formula units in the cell. The lattice parameters are a = 6.532 A, b = 7.733 A, c = 18.566 A. The structure was solved from a complete set of three-dimensional MoKα diffractometer data, the final R being 0.097. The structure is made up of Bi3+ cations and O2− and (B5O11)7− anions. The pentaborate anion is formed by two BO4 tetrahedra and three BO3 triangles, sharing edges and corners. An oxygen that is not bonded to any boron is in the center of a three-bismuth triangle. Two independent bismuth atoms are present in the structure. Bi(1) has six first-neighbor oxygens with an average BiO distance of 2.44 A and Bi(2) has either six or seven oxygens in the first coordination sphere with an average BiO distance of 2.43 or 2.80 A, respectively.

A model for describing the conformations of flexible 6-membered rings—I : The non-chair conformations

Abstract An empirical model for calculating the torsional angles for flexible 6-membered rings is presented in terms of three independent parameters, two geometrical and one pseudorotation angle. The rings are classified according to four estimators, the fit of the model depending upon their values. Equations are given for defining any conformation by a point in a 2-dimensional pathway. Some examples have been examined in the light of this model.

Crystal structures of analogues of D-galactose. I. 2,3-Di-O-acetyl-1,6-anhydro-β-D-galactopyranose (DAG)

The structure of DAG has been determined from three-dimensional diffractometer data by direct methods with the tangent formula. The space group is P21 with a = 11.3328 (17), b=6.1197 (4), c-8-2568 (11)/~, fl= 103.44 (1) °. The molecule has an anhydro bridge across the galactose moiety forming a five-membered ring which has an envelope conformation while the pyranose ring has a strained chair conformation. An intermolecular hydrogen bond (2.864 A) occurs between the hydroxyl group and the O atom of the bridge.

The crystal structure of 7-amino-4H-furazo[3,4-d]-1,2,6-thiadiazine 1,1-dioxide

The single-crystal structure of CaHaNsO3S was determined by a three-dimensional X-ray study. It crystallizes in the space group P21/c with cell dimensions a=9.901 (1), b=4-992 (1), c= 13.852 (1) .~ and fl= 108.53 (1) °. The structure was solved with the Patterson function. Full-matrix least-squares treatment gave a final unweighted R value of 0.035. The thiadiazine ring conformation in the molecule was found in the expected envelope form at the sulphur atom. An interpretation of experimental results is given in terms of molecular diagrams. The molecules are linked by van der Waals forces and N-H. • • O and N H . . . N weak hydrogen interactions.

Crystal structure and magnetic properties of linear chain potassium aquotetrafluoromanganate(III)

Abstract The crystal structure and single-crystal ac magnetic susceptibilities of KMnF 4 ·H 2 O are reported. The structure, which is isomorphous to that of RbMnF 4 ·H 2 O, consists of chains of alternating trans-[ MnF 4 F 2 2 ] 2− and trans-[ MnF 2 F 2 2 ( H 2 O ) 2 ] tetragonally elongated octahedra connected to each other by shared apical fluorine atoms. Crystal data: Space group C2 c , a = 13.907(1) A, b = 6.2136(2) A, c = 10.492(1)A, β = 104.69(1)°, V = 877.0(2) A 3 , D c = 2.85 g cm −3 , Z = 8, R = 0.044. Magnetic susceptibility measurements show a broad maximum around 52 K indicative of lower dimensionality behavior. The data may be fit to a Heisenberg S = 2 linear chain model with J k B = −6.5 K and g = 2.05. At 8.45 K a sharp peak in the susceptibility data parallel to the chains indicates weak ferromagnetic behavior.

1H,4H-1,4-Diphenylpyridazino[1,2-α]pyridazine-6, 9-dione

Crystals of C20H16N2O2 are orthorombic:P212121,a = 28.1364(21),b = 7.6474(2),c = 7.5376(2) Å,Z = 4, μ = 6.4 cm−1 (CuKα radiation), andM = 316.36. The structure has been solved by direct methods and refined by two-block least-squares toR = Rw = 0.042. The conformation of ringB is a distorted envelope at N(10), and the phenyl rings have acis configuration with respect to the pyridazine ring. Thermal motion of the molecule has been analyzed in terms of the rigid-body TLS model.

Crystal structure of 1,3 diphenyl-5-carbethoxymethylene-1H-4,5-dihydro-1,2,4-benzotriazepine

C24H21N3O2 is orthorhombic,P212121,a = 15.1342(3),b = 14.1692(3),c = 9.6533(3) Å,Z = 4,Dm = 1.23 g cm−3. The structure was solved by direct methods, and refined to anR of 0.048 (Rw = 0.068) for 1831 observed reflections. An intramolecular hydrogen bond is present. The conformation of the seven membered ring is boatlike with a quasi-mirror plane through N(1).

Crystal and molecular structure of 2,2′-diphenyl-4,4′-di(2-phenyl-2-propenyl)-4, 4′-bi-5(4H)thiazolone

Molecules of C36H28N2O2S2 crystallize in the monoclinic space groupP21/c with cell dimensionsa = 8.9326(3),b = 20.0197(11),c = 17.0349(8) Å, and β = 92.20(1) °,Z = 4,Dx = 1.276 g cm−3, μ (CuKα) = 18.16 cm−1. The structure was solved by Patterson methods and refined by least-squares calculations to anR of 0.057 andRw = 0.066 for all reflections. The main differences in the two halves of the dimer are due to the different torsion angles in the propenyl chain.