Homoleptic tris(dithiolene) and tetrakis(dithiolene) complexes of uranium(IV)

Reaction of UCl4 with 3 or 4 mol equiv of Na2dddt (dddt = 5,6-dihydro-1,4-dithiine-2,3-dithiolate) in THF afforded the first example of a tetrakis(dithiolene) metal compound, [Na4(THF)8U(dddt)4](infinity) (1). The red crystals of 1 are composed of infinite zigzag chains in which Na2(micro-THF)3 fragments ensure the linking of Na2(THF)5U(dddt)4 moieties; the uranium atom is in a dodecahedral environment of eight sulfur atoms. Treatment of UCl4 with 3 mol equiv of Na2dddt in pyridine gave a mixture of tris- and tetrakis(dithiolene) compounds. After addition of 18c6 (18-crown-6), only the tris(dithiolene) complex was obtained and crystallized as orange crystals of [Na(18c6)(py)2]2[U(dddt)3].2py (2.2py) in which the isolated [U(dddt)3]2- anion adopts a slightly distorted trigonal prismatic configuration. A few red crystals of the unsolvated complex 2 and the trinuclear anionic compound [Na(18c6)(py)2]3[Na{U(dddt)3}2] (3) were also obtained along with orange crystals of 2.2py. All the tris(dithiolene) compounds exhibit large folding of the dddt ligand and significant interaction between the C=C double bond and the metal center.     

Polychloroprene. I. Etude de la microstructure par RMN 1H

The microstructure of polychloroprenes was studied by ¹H-NMR at high field (350 MHz). An examination with two solvents, CDCl₃ and C₆D₆, was necessary to show all the addition modes. The complementary information obtained made possible the quantitative determination of head-to-tail, head-to-head, tail-to-tail, trans-1–4, and cis-1–4, 1–2, and 3–4 additions.     

Hyperelectronic polarization in macromolecular solids

Hyperelectronic polarization may be viewed as the electrical polarization in external fields due to the pliant interaction with the charge pairs of excitons, in which the charges are molecularly separated and range over molecularly limited domains. It is particularly pronounced in molecular solids composed of long polymeric molecules having extensive regions of electronic orbital delocalization. Hyperelectronic polarization is regarded as the principal contributor to the high polarizabilities of the following five macromolecular solids: four polyacene quinone radical polymers formed by condensation of aromatic hydrocarbon derivatives with aromatic acids and poly(Cu(II)-N,N′- dimethyl rebeanate). The first four polymers at 100 hz had dielectric constants of 1800–2400, decreasing to about 58–100 at 100,000 hz, with relaxation times of 10^?3 to 10^?4 sec. A sixth polymer, a Schiff-base condensate of 1,4-napthaquinone and p-toluene diisocyanate, however, showed little hyperelectronic polarization, displaying a dielectric constant of 10, constant over 100–100,000 hz. By simple arguments it is shown that the relaxation times and the frequency response of conduction are consonant with the proposed model of charges roaming over long molecular domains (up to 4000 A.) but restricted by molecular boundaries.     

Acidity of secondary hydroxyls in ATP and adenosine analogues and the question of a 2',3'-hydrogen bond in ribonucleosides

As sugar-modified nucleosides, nucleotides, and oligonucleotides are much used in pharmacology and enzymatic studies, knowledge on the relative pKa values of the secondary hydroxyls can be of great help in design and interpretations. To obtain this, we have determined the acidity constants for ATP, dATP, 2'-F-dATP, 2'-NH2-ATP, and 2'-O-methyl ATP in aqueous solution. The influence of the relative acidities seem to be mainly from inductive effects since a good correlation between pKa values and group electronegativity is found. There is no clear energetic contribution from a much suggested H-bond between the 2'-OH and 3'-oxyanion in adenosine. To clarify if this kind of H-bond would make a more-prominent energetic contribution in less-polar solvents, we also determined the acidity of secondary hydroxyls in adenosine, 2'-O-methyladenosine, and 3'-O-methyladenosine in water, methanol, and DMSO. The relative differences in pKa values were, however, quite similar in all solvents, suggesting that no major energetic contribution is made by an intramolecular H-bond in adenosine.     

C60F14OFPh3, a fluoroxy derivative of C60F15Ph3; evidence for the presence of ‘missing’ fluorine through restricted rotation of a phenyl group

From the reaction of C₆₀F₁₈ with benzene in the presence of SbCl₅ we have isolated a compound of 1252 amu indicated to be C₆₀F₁₄OFPh₃, a fluoroxyfullerene. Temperature-variable ¹H NMR shows that one phenyl group suffers restricted rotation on cooling to 218 K, attributed to the presence of the OF group which, as in the case of the recently characterised C₆₀F₁₇OF, fails to give a signal for this group in the ¹⁹F NMR. We have isolated also, C₆₀F₁₄O₂FPh₃ (1268 amu) a mixture of oxahomo derivatives of C₆₀F₁₄OFPh₃ arising from oxygen insertion into FCCF bonds. Theoretical calculations for C₆₀F₁₄OFPh₃ indicate that the phenyl group nearest to the OF group is twisted out of the plane containing the other two.     

Absolute rate constants for the reaction of O(3P) aroms with n-butane and NO(M  Ar) over the temperature range 298–439 K

Absolute rate constants for the reaction of O(³P) atoms with n-butane (k₂) and NO(M  Ar)(k₃) have been determined over the temperature range 298–439 K using a flash photolysis-NO₂ chemiluminescence technique. The Arrhenius expressions obtained were k₂ = 2.5 × 10^?11exp[-(4170 ± 300)/RT] cm³ molecule^?1 s^?1, k₃ = 1.46 × 10^?32 exp[940 ± 200)/ RT] cm⁶ molecule^?2 s^?1, with rate constants at room temperature of k₂ = (2.2 ± 0.4) × 10^?14 cm³ molecule^?1 s^?1 and k₃ = (7.04 ± 0.70)×10^?32 cm⁶ molecule^?2 s^?1. These rate constants are compared and discussed with literature values.     

Etude cristallochimique de LiPN2: Une structure derivée de la cristobalite

LiPN₂ has been prepared by reaction between Li₃N and P₃N₅ nitrides. The unit cell is tetragonal with a = 4.567(1) and c = 7.140(4) Å. The space group is $\text{I}\text{4}\text{2d}$. The structure is related to the β cristobalite type and is isostructural with CaGeN₂. It is built up from a PN₄ tetrahedra framework in the holes of which the lithium atoms are localized. The values of the rotation angle ф of tetrahedra, $\text{c}\text{a}$ ratio and θ (NPN) angle have been discussed in relation to the parameter x of the nitrogen atoms.     

Determination of chlorinated toluenes in raw and treated water samples from the Llobregat river by closed loop stripping analysis and gas chromatography-mass spectrometry detection

A study of the occurrence of chlorinated toluenes in Llobregat river (NE Spain) has been carried out. These compounds are currently being used in local textile industries as dye carriers and have replaced the common trichlorobenzene mixtures. Closed loop stripping analysis (CLSA), routinely used to monitor the quality of river water for a broad range of volatile compounds, has been employed as an analytical tool to determine them at ng/L levels in wastewater and textile industry effluents and also in raw and treated water from two drinking water treatment plants situated in the river course. The CLSA extracts were analyzed by HRGC/MS. Ring halogenated dichloro- and, to a lesser extent, mono- and trichlorotoluenes have been identified. These compounds have not been reported to our knowledge as common water pollutants.     

Novel unsymmetrical P/O substituted ferrocene ligands and the first structurally characterised hydroxyferrocene derivative

Two new unsymmetrical 1'-substituted hydroxyferrocene ligands featuring either phosphine or phosphine oxide substituents have been synthesised and the phosphine oxide derivative has been structurally characterised. A nickel complex of the hydroxyl/phosphine ligand has been formed, along with preliminary evaluation of the complex for catalysis of ethylene polymerisation.     

Determination of sulfonamide residues in the tissues of food animals using automated precolumn derivatization and liquid chromatography with fluorescence detection

A liquid chromatographic method for the determination of sulfachloropyridazine, sulfadiazine, sulfadimethoxine, sulfadoxine, sulfaethoxypyridazine, sulfamethazine, sulfaquinoxaline, and sulfathiazole residues in the muscle, liver, and kidney of food animals using sulfapyridine as internal standard is reported. Tissues are extracted using a modified version of AOAC Official Method 983.31 (Sulfonamide Residues in Animal Tissues). The sample extract is reconstituted in pH 3.0 buffer-acetonitrile (60 + 40) and filtered into an autosampler vial. Using a programmable autosampler of a liquid chromatograph, a portion of the sample is derivatized precolumn with fluorescamine. The sulfonamide derivatives are separated by liquid chromatography using a C18 column with a mobile phase of 0.02M phosphoric acid-acetonitrile (60.5 + 39.5) and detected by fluorescence (excitation, 405 nm; emission, 495 nm). The method was applied to swine and cattle muscle, liver, and kidney; sheep and horse muscle and kidney; and chicken muscle and liver. The mean values for samples fortified with sulfonamides at levels between 0.05 and 0.2 microg/g agreed within 96-99% of spiked levels, with coefficients of variation ranging from 4-10%. The limit of detection (LOD) for all sulfonamides was 0.01 microg/g, with the exception of sulfaquinoxaline, for which the LOD was 0.015 microg/g.