E. J. Gabe

Application of a segment description of the unique set of reflections to data collection and data reduction

The relationships h1 = h0 + Δhn and n = Δh−1(h1 − h0) [Gabe (1969). In Crystallographic Computing, edited by F. R. Ahmed. Copenhagen: Munksgaard], establishing the correspondence between the crystal indices h1 and the segment indices n of a given reflection, can be used to generate the reflections in the unique set, decide whether a reflection belongs to the unique set, find the unique indices of a given reflection and check the correctness of the segment data Δh and h0. These relationships have been used as the basis of the index generation scheme of the NRC diffractometer program to collect intensity data as a sequence of symmetry-related sets and as the principle of the ordering algorithm of a data reduction program which can treat all symmetries including the trigonal symmetries in rhombohedral cells without the requirement of any special logic.

Structure of naproxen, C14H14O3

An effective inhibitor of cyclo-oxygenase. Mr=230.25 , monoclinic, P21, a= 13.3150(10), b = 5.7765 (4), c= 7.8732 (4)A, fl= 93.88 (1) °, V= 604.2 (1)A 3, Z= 2, Din= 1.25 (2) (flotation), D~= 1.265 Mg m -3, 2(Mo Ka 1) = 0.70926/~, #(Mo Ka) = 0.095 mm -1, F(000) = 244, T= 296 K, final R(F) = 0.061 for 1037 observed reflections. The rotation of the carboxyl group with respect to the benezene ring, which seems to be connected with anti-inflammatory potential, is similar to the other two substituted propionic acids already reported. The benzene rings in the naphthyl group are inclined at an angle of 5.2 (2) °. Introduction. The title compound, an effective inhibitor of the cyclo-oxygenase responsible for biosynthesis of prostaglandins, was obtained from Dr Natarajan, Institute of Basic Medical Sciences, Madras. It exhibits anti-inflammatory, analgesic and antipyretic activity in man (Goodman & Gilman, 1980). The analysis of its structure was undertaken to help to establish the structure-activity relationship in propionic acid derivatives.

Inhomogeneous mosaicity in extinction correction

Extinction effects in ground spherical samples can differ between the surface and the interior. The formula: |Finhom| = |Fcalc|[1 + x(d2 −1)]1/2/d, with d = (1 + 2gβ|Fcalc|2)1/4, where x is the non-extinct volume fraction of the crystal, g a parameter describing the mosaic and βa geometrical expression calculable at data reduction time, has been applied in the least-squares refinement of two low-quartz samples and one corundum sample. The effect is considerable for one quartz sample where the mosaic block size is 5.2 μm, small for the other quartz sample where the mosaic block size is 1.4 μm and unimportant in corundum where the block size is 0.4 μm and where extinction is larger than in the previous sample. This observation is compatible with the expectancy that the effect should essentially depend on the mosaic block size.

Binuclear nickel(II) and cobalt(II) complexes of the novel binucleating ligand 3,6-bis(1′-pyrazolyl)pyridazine. Crystal and molecular structure and magnetism of bis[µ-3,6-bis(1′-pyrazolyl)pyridazine-N1(Ni1)N2′(Ni1)N2(Ni2)N2″(Ni2)]bis[diaquanickel(II)] tetrachloride dihydrate

Reaction of the ligand 3,6-bis(1′-pyrazolyl)pyridazine (ppd) with nickel(II) and cobalt(II) salts produces binuclear derivatives in which the two pseudo-octahedral metal centres are bound simultaneously between two adjacent ligands in a doubly bridged structure. The complex [Ni2(ppd)2(H2O)4]Cl4·2H2O (1) crystallizes in the triclinic space group P with a= 7.133 9(7), b= 10.331 0(6), c= 10.820 9(5)A, α= 85.503(4), β= 89.939(6), γ= 75.479(6)°, and Z= 1. Refinement based on 4 505 unique reflections gave R= 0.0353. The binuclear cation [Ni2(ppd)2(H2O)4]4+ is essentially planar with in-plane Ni–N distances of 2.1 30(2), 2.035(2), 2.059(2), and 2.1 21(2)A, axial Ni–O distances of 2.044(2) and 2.048(2)A, and N–Ni–N angles of 98.6(1), 77.8(1), 77.9(1), and 105.8(1)°. Variable-temperature magnetic susceptibility measurements on (1) indicate significant antiferromagnetic exchange between the nickel(II) centres with –J= 14.8 cm–1. Analogous cobalt(II) compounds are also produced and in one case, [Co2(ppd)2(OH)(H2O)2][ClO4]3·1.5H2O, a triply bridged structure is proposed involving an additional hydroxide bridge.

A robust alternative to η refinement for assessing the hand of chiral compounds

Assessment of the hand of chiral molecular compounds by least-squares refinement of a chirality parameter with all reflections is not statistically robust and can lead to incorrect answers due to a single, unnoticed, gross intensity-measurement error. An alternative is described in which the most easily observable Bijvoet differences are derived from the solved structure and remeasured at slow speed and possibly longer wavelength. Errors due to absorption, multiple reflections and anisotropic extinction can be cancelled out in the measurement for the sense of Bijvoet pairs with the proper experimental technique. An estimate of the probability of having derived the wrong hand, based exclusively on the number of remeasurements and the number of contradictions, and therefore insensitive to individual measurement errors, is developed. With this estimate, determination of the hand of compounds with oxygen as the heaviest scatterer is statistically unambiguous with Cu Ktr intensity data, and feasible even with Mo Ka data. Consequently, the method can be applied to Cu Ka data for molecules with carbon as the heaviest scatterer. This approach has been been automated as the utility BIVOET in the NRCVAX system of programs.

X-ray beam polarization measurements

A simple modification of the jig proposed by the IUCr Commission on Crystallographic Apparatus for the measurement of polarization ratios for X-rays allowing the full rotation of the detector arm permits cancellation of the first-order errors by averaging pairs of measurements differing by 180° around the rotation axis of the detector arm. The plot of Imeas as a function of cos2 Φ, where Φ is the angle between the detector arm and one of the principal directions of polarization in the beam gives a reliable value of the polarization ratio K. The experimental results are: Mo Kα 0.969 ± 3, 0.970 ± 3; Cu Kα 0.908 ± 5, 0.897 ± 5 for a 0.42° and a 0.60° FWHM graphite monochromator respectively.

Structure of 1,4-benzenedicyanamide dianion derivatives

The crystal structures of four tetraphenylarsonium salts of 1,4-dicyanamidebenzene derivatives, namely, bis(tetraphenylarsonium) 1,4-benzenedicyanamide(2-), bis(tetraphenylarsonium) 2,5-dimethyl-1,4-benzenedicyanamide(2-), bis(tetraphenylarsonium) 2,5-dichloro-1,4-benzenedicyanamide(2-) and bis(tetraphenylarsonium) 2,3,5,6-tetrachloro-1,4-benzenedicyanamide(2-), were determined. All of the derivatives are essentially planar with the cyanamide groups in an anti configuration, suggesting a significant degree of π coupling between the cyanamide groups and phenyl ring. No evidence was seen of π stacking for any of the 1,4-dicyanamidebenzene dianion derivatives

Baeyer–Villiger oxidation of 19-substituted steroidal ketones: structure of rearranged products involving participation of the 19-substituent

Baeyer–Villiger reactions of 19-hydroxy-4β,5-epoxy-5β-androstane-3,17-dione (2), 19-hydroxy-4α,5-epoxy-5α-androstane-3,17-dione (13), 17β,19-dihydroxy-5β-androstan-3-one (18), and 19-hydroxyandrost-4-ene-3,17-dione (1) are reported. When carbonyl functions are present at C-3 and C-17, Baeyer–Villiger rearrangement occurs preferentially at C-17. The rearrangement product obtained from the Δ4-3-ketone (1) was found to be 5β-formyl-5,19-dihydroxy-17-oxo-A-nor-3,5-seco-5β-androstane-3-carboxylic acid 5,19(R) lactol 3,5-lactone (27).

Correction of single-crystal intensities for average values of multiple reflection

For short wavelengths, Umweganregung cannot be experimentally eliminated. Its average unscaled intensity for a random orientation of the crystal is U(2θ1) = ∫θ, ϕ (sin 2 θ/sin 2θ1)P(θ1, θ, ϕ) exp [-2K(sin2 θ + sin2 θ12)] dθ dϕ, where (2θ, ϕ) are the spherical coordinates of a point on the Ewald sphere when the intensity measurement is made at (2θ1, 0), the angle between the two directions being 2θ12, while K is the slope of a plot of In (F(obs)) as a function of sin2 θ, and P(θ1, θ, ϕ) is the polarization correction appropriate to the double reflection. Diffraction intensities were measured for epidote and quartz. A plot of (|F(calc)|)/(F(obs)) as a function of F(obs) for epidote was considerably improved by the subtraction from each intensity measurement of a number of counts SU(2θ1), where S is an experimental scale factor while U(2θ1) was calculated for epidote by numerical integration over the Ewald sphere. The refinement residuals for both compounds improved after correction of the intensities and the weights.

Phenoxo-bridged dinickel(II) complexes of a macrocyclic ligand: synthesis, stereochemical equilibria and structure

Dinuclear nickel(II) complexes of a tetraaminediphenol macrocyclic ligand (H2L) of composition [Ni2L(B)2][ClO4]2(B = NH3, imidazole, pyridine, or pyrazine) have been synthesised and characterized. With pyrazole (Hpz)[Ni2L(pz)(H2O)2][ClO4] and [Ni2L(pz)(Hpz)(H2O)][ClO4] complexes have been obtained in which pz– appears to act as a bridging ligand. The equilibrium constants for the reaction [Ni2L(MeOH)4]2++ 2B ⇌[Ni2L(B)2]2++ 4MeOH [B = pyridine, 2-methylpyridine (2Me-py), 3Me-py, 4Me-py, imidazole, or pyrazine] in methanol solutions have been determined spectrophotometrically at room temperature. The X-ray structure of [Ni2L(py)2][ClO4]2 has been determined: monoclinic, space group P21/n, with a= 9.251(1), b= 11.457(2), c= 18.555(2)A, β= 100.21(1)°, and Z= 2. The structure was determined by direct methods and refined to R= 0.053 and R′= 0.039. In the complex cation the two nickel(II) centres are in square-pyramidal configuration with N2O2 in-plane donor sets, involving two phenoxide bridges and two trans-axially disposed pyridines. The distance between the two nickel centres is 3.206(5)A.