Zinc(II) as a versatile template for the design of dipolar and octupolar NLO-phores

Thermally stable dipolar and octupolar (D2d, D3) NLO-phores are readily accessible by combining one, two, or three 4,4'-bis(dialkylaminostyryl)-[2,2']-bipyridyl ligands with zinc(II) salts. The off-resonant beta0 values point out the superiority of octupoles versus dipoles in terms of nonlinearity/transparency tradeoff. The octahedral tris(bipyridyl)zinc(II) complex exhibits a very large beta0 value (241 x 10-30 esu), which is the largest ever reported for octupolar molecules.     

A route to heat resistant solid membranes with performances of liquid electrolytes

The confinement of ionic liquids within a porous silica matrix was performed by a one-step non-hydrolytic sol-gel route, leading to hybrid materials (called "ionogels") featuring both the mechanical and transparency properties of silica gels and the high ionic conductivity and thermal stability of ionic liquids.     

Comparison of Omega and PPP techniques for reactivity calculations in methyl-substituted naphthalenes

The dependence of electron density, superdelocalizability and localization energy on the value of the parameter for the inductive effect of the methyl group in 1,4-dimethyl naphthalene is exactly the same when calculated by the Omega or by the Pople-Pariser-Parr techniques.

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Zusammenfassung Die Abhängigkeit der Elektronendichte, der Superdelokalisierbarkeit und der Lokalisierungsenergie vom Wert des Parameters für den induktiven Effekt der Methylgruppe in 1,4-Dimethylnaphthalin ist genau dieselbe, wenn man diese Größen mit der Omegatechnik oder der PPP-Methode berechnet.

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Résumé La densité électronique, la super délocalisabilité et l'énergie de localisation du 1,4 diméthyl naphtalène dépendent de la même manière de la valeur du paramètre de l'effet inductif du groupe méthyle selon que les calculs sont effectués par la méthode oméga ou par la méthode de Pople-Pariser-Parr.

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This work was done with financial assistance from the National Research Council of Canada. L.-K. H. wishes to acknowledge the award of a Colombo Plan scholarship.     

Comparison of whole blood, plasma and nails as monitors for the dietary intake of selenium

Haem peroxidases are globular proteins with an iron-porphyrin complex as prosthetic group. They catalyze the oxidation of substrate by peroxides, frequently via free-radical intermediates. The catalytic cycle involves changes in the redox states of the prosthetic group, that can be monitored by changes in the intense absorption spectra. During the past decades, considerable scientific effort has been put into the elucidation of the mechanisms of reactions catalyzed by these enzymes. Radiation-chemical techniques have made an important contribution by providing information on the redox states of the enzymes and their interconversions, as well as on the properties of the free-radical intermediates involved.     

pH-controlled change of the metal coordination in a dicopper(II) complex of the ligand H-BPMP: crystal structures, magnetic properties, and catecholase activity

The dinucleating ligand 2,6-bis[(bis(2-pyridylmethyl)amino)methyl]-4-methylphenol (H-BPMP) has been used to synthesize the three dinuclear Cu(II) complexes [Cu2(BPMP)(OH)][ClO4](2).0.5C4H8O (1), [Cu2(BPMP)(H2O)2](ClO4)(3).4H2O (2), and [Cu2(H-BPMP)][(ClO4)4].2CH3CN (3). X-ray diffraction studies reveal that 1 is a mu-hydroxo, mu-phenoxo complex, 2 a diaqua, mu-phenoxo complex, and 3 a binuclear complex with Cu-Cu distances of 2.96, 4.32, and 6.92 A, respectively. Magnetization measurements reveal that 1 is moderately antiferromagnetically coupled while 2 and 3 are essentially uncoupled. The electronic spectra in acetonitrile or in water solutions give results in accordance with the solid-state structures. 1 is EPR-silent, in agreement with the antiferromagnetic coupling between the two copper atoms. The X-band spectrum of powdered 2 is consistent with a tetragonally elongated square pyramid geometry around the Cu(II) ions, in accordance with the solid-state structure, while the spectrum in frozen solution suggests a change in the coordination geometry. The EPR spectra of 3 corroborate the solid-state and UV-visible studies. The 1H NMR spectra also lead to observations in accordance with the conclusions from other spectroscopies. The electrochemical behavior of 1 and 2 in acetonitrile or in water solutions shows that the first reduction (Cu(II)Cu(II)-Cu(II)Cu(I) redox couple) is reversible and the second (formation of Cu(I)Cu(I) irreversible. In water, 1 and 2 are reversibly interconverted upon acid/base titration (pK 4.95). In basic medium a new species, 4, is reversibly formed (pK 12.0), identified as the bishydroxo complex. Only 1 exhibits catecholase activity (oxidation of 3,5-di-tert-butylcatechol to the corresponding quinone, vmax = 1.1 x 10(-6) M-1 s-1 and KM = 1.49 mM). The results indicate that the pH dependence of the catalytic abilities of the complexes is related to changes in the coordination sphere of the metal centers.     

Magic numbers in the mass distribution of the benzene+-argonn ions: evaporation dynamics and cluster structure

The intensity distribution of benzene⁺-Ar_n cluster ions formed by laser ionization of neutral clusters has been investigated: two main intensity anomalies (magic numbers atn=20 and 45) have been observed in the 15–60 size range. The evaporation dynamics of these species in the 2–50 microsecond time window following ionization has been studied using the electrostatic mirror of a reflectron time-of-flight mass spectrometer as a kinetic energy analyser capable to distinguish parent and daughter ions. The magic numbers are interpreted in terms of size dependent evaporation behaviors: beyondn=20, a sudden decrease of the evaporation energy is observed; in then=45–47 size range, the magic number is accounted for by the specific dynamics of then=46 and 47 clusters, in particular the possible loss of two argon atoms forn=47 within the experimental time window. These results and their implications on the cluster structure are discussed in the light of the evaporative ensemble model and compared to the evaporation characteristics of similar species, in particular the neat rare gas clusters.     

Stabilization of the unhybridized Sn2+ stannous ion in the BaClF structure and its characterization by119Sn Mössbauer spectroscopy

In divalent tin halides, when the halogen is small and highly electronegative (F, Cl), the tin valence orbitals are hybridized, the tin(II) non-bonded electron pair is located on one of the hybrid orbitals, and the resulting large electric field gradient gives a large quadrupole splitting. The reaction of barium chloride and tin difluoride in aqueous solutions, for large BaCl₂.2H₂O/SnF₂ ratios (>10) results in the precipitation of a white powdered material, which is identified by X-ray diffraction to be BaCIF. However, Tin-119 Mossbauer spectroscopy shows the material contains a fairly large amount of divalent tin in the Sn²⁺ ionic form, with unhybridized orbitals, like in SnCl₂. Using X-ray diffraction, we have established that Sn²⁺ ions substitute 15% of the Ba²⁺ ions at random, and chemical analysis shows the material has the formula Ba_5.66SnCl_7.30F_6.04 and thus is enriched in chlorine.     

Easy synthesis of heterocyclic carbene complexes by activation of chalcogenopyrones and benzopyrones to pyrylium salts and subsequent addition of carbanion of methoxy(methyl)pentacarbonyltungsten carbene complex

Methylenechalcogenopyran and benzopyran Fischer carbene complexes are easily obtained from commercially available chalcogenopyrones or benzopyrones and carbanion of methoxy(methyl)carbene tungsten complex. The key of the heterocyclic carbene formation is the activation of the carbonyl group by alkylation with alkyl trifluoromethanesulfonate reagent.