J. V. Silverton

Nickel (II) complexes of a thiosemicarbazone prepared from 2-acetylpyridine

SummaryThe ligand 3-azabicyclo[3.2.2]nonane-3-thiocarboxylic acid 2-[1-(2-pyridinyl)ethylidene]hydrazide (HL), which is observed in an unusual tautomeric form in the solid state, and its selenium analogue (HLSe) have been used to prepare a series of nickel(II) complexes. Compounds of the general formula [NiLX] (X=Cl, Br, NCS, N3, NO2 or NCSe) as well as [Ni(LSe)Cl] have been found to be diamagnetic, planar complexes. A single crystal study of [NiL(NCS)] shows the deprotonated ligand bound in a tridentate mannervia its pyridyl nitrogen, imine nitrogen and the thione sulphur atom with the nitrogen atom of the thiocyanato-ligand occupying the fourth coordination position. The solids prepared from the nickel(II) salts having tetrafluoroborate, nitrate and iodide ions approximate to octahedral symmetry and have neutral HL ligands coordinated in a bidentate fashionvia the pyridine and imine nitrogens with the remaining coordination sites being occupied by the anions or water molecules. The [NiL2] solid is also octahedral with the two deprotonated ligands bonding as tridentate groupsvia the same atoms as in the [NiLX] complexes.

Characterization and crystal structure of two polymorphic forms of racemic thalidomide

There are two polymorphic forms of racemic thalidomide. The α-polymorph was formed by crystallization from 2-ethoxyethanol, methanol or dichloromethane, while the β-polymorph was formed by crystallization from a supersaturated solution in refluxing 2-ethoxyethanol. The two polymorphs were characterized by IR spectra, differential scanning calorimetry (DSC), melting points, powder X-ray diffraction patterns, and X-ray crystallography. They were easily differentiated by IR (KBr) in which the α polymorph absorbed at 3196, 3098 and 859 cm–1 and the β at 3276 and 755 cm–1. DSC scans of the α and β forms showed endothermic peaks at 272.3 and 275.7 °C, respectively. During this measurement the α form was partially or fully converted into the β form if the rate of temperature change was slow or if the α form contained some β which provided seed crystals for the interconversion. Upon remelting both forms gave one peak corresponding to the β polymorph. The powder X-ray diffraction patterns for the two forms differ significantly. The crystal structures of the two polymorphs differ primarily in their mode of hydrogen bonding. In the α polymorph the molecules form dimers, while in the β the dimers form infinite linear strings linked by bifurcated hydrogen bonds along the b-axis.

Anomalous magnetic properties of tetraphenylporphinato Co(II) complex in the solid state

Abstract The α,β,γ,δ-tetraphenylporphinatocobalt(II) complex is found to exist in two distinct, but interconvertible, polycrystalline forms. The one with a tetragonal crystal symmetry (species B) gives the EPR spectrum which has been attributed to the low-spin electronic configuration of Co(II) ion in an axial crystal field. The other form (species A) having a triclinic crystal symmetry shows no easily detectable EPR signal even at liquid helium temperature. Magnetic susceptibility and magnetization meaurements demonstrated that the complex is paramagnetic in both forms, but the species (A) is characterized by ferromagnetic exchange coupling, while the species (B) behaves as a normal paramagnet. The experimental susceptibility versus 1/ T curve can be reproduced quite well by using the Ising method. The g values thus obtained ( g | = 5.2, g ⊥ = 0) can not be explained by a low-spin electronic configuration, but are consistent with a high-spin ground state. Assigning a high-spin state to the species (A), the first such case in Co(II) porphine complexes, can not only explain the absence of EPR signal, but is also supported by the results of X-ray structural analyses.

Optical resolution of the α-tocopherol spiro dimer and demonstration of its fluxional nature

A model compound (1b) for the oxidative dimer of α-tocopherol (vitamin E)(1a) has been shown to undergo fluxion by NMR spectroscopy through a magnetization transfer experiment. This compound has also been resolved at low temperature using an optically active HPLC column. Its rate of racemization parallels the fluxion process suggesting a biradical intermediate and free radicals are shown to be present in non-degassed solutions of (1b). Its crystalline form has been examined with solid-state NMR spectroscopy and X-ray crystallography.

Synthesis of pyrrolizidine oximes 222 and 236: Novel alkaloids of a dendrobatid poison frog

Abstract The structures of two novel spiropentanopyrrolizidine oxime alkaloids, namely 2′,3′,5′,6′,7′,7a′-hexahydro-2,2-dimethylspiro[cyclopentane-1

Stereochemistry and mechanisms of thermal cycloaddition reactions of conjugated enynes. The stereospecific formation of six tetrahedral centers in a single reaction

Abstract Thermal condensations of penta-1,5-dien-3-ynes with two molecules of olefinic dienophiles proceed stereospecifically with retention of the configurations of the dienophiles, and with both molecules of the dienophile in each reaction adding to the same face of the dienyne.

X-Ray structure of viridicatumtoxin: a new class of mycotoxin from Penicillium viridicatum Westling

The structure of viridicatumtoxin, the main toxin of strains of Penicillium viridicatum Westling has been established as (1a) by X-ray methods; the toxin is structurally related to the tetracyclines.

X-Ray structure determination of gardmultine. A bis-indole alkaloid isolated from Gardneria multiflora Makino

The structure of gardmultine, C45H54N4O10, isolated from Gardneria multiflora Makino, has been determined by single crystal X-ray analysis. The orthorhombic crystals belong to the space group P212121 with a= 8.625(1), b= 20.791 (2), c= 24.494(3)A and Z= 4. The phase problem was solved by direct methods making use of the technique of negative quartet frequencies to determine the starting set of MULTAN, and refined to a final R value of 0.053 for 3 238 observed diffractometer data taken with Cu-Kα radiation. Gardmultine is a novel bis-indole alkaloid, comprising gardneramine and chitosenine linked by a spiro-five-membered ring.

Crystal and molecular structure of cis-2-isopropyl-3-(4-nitrophenyl)-oxaziridine

The crystal structure of the title compound (monoclinic, a= 11·206, b= 6·516, c= 14·757 A, β= 98·50°. Z= 4, space group P21/n) has been established by direct methods using three-dimensional X-ray counter data. The structure was solved by direct methods and refined by least-squares techniques to R 0·005 for 993 observed reflections. σ For bond lengths is ca. 0·005 A. The geometry of the nitrophenyl part of the molecule is as expected, and the oxaziridine ring contains a long N–O bond (1·500 A) a fairly short C–N bond (1·434 A), and a C–O bond (1·405 A) of fairly normal length.