Microheterogeneity in aqueous-organic solutions: Heat capacities,volumes and expansibilities of some alcohols,aminoalcohol and tertiary amines in water

The heat capacities per unit volume and the densities of aqueous solutions of 2-propanol, neopentanol, tert-amylalcohol, 2-amino-2-methylpropanol, triethylamine and diethylmethylamine were measured, in many cases as a function of temperature, over the whole mole fraction or solubility range. Apparent and partial molal heat capacities, volumes and expansibilities were derived. The concentration dependence of these functions suggest the existence of transitions in some of these systems, in the water-rich region, qualitatively similar to micellization. The large relaxation contribution observed with some of the thermodynamic functions of hydrophobic alcohols and amines suggests a reinforcement of hydrophobic hydration due to strong hydrogen-bonding interactions of the polar groups with water.     

New example of a non-heme mononuclear iron(IV) oxo complex. Spectroscopic data and oxidation activity

The green complex S=1 [(TPEN)FeO]2+ [TPEN=N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine] has been obtained by treating the [(TPEN)Fe]2+ precursor with meta-chloroperoxybenzoic acid (m-CPBA). This high-valent complex belongs to the emerging family of synthetic models of Fe(IV)=O intermediates invoked during the catalytic cycle of biological systems. This complex exhibits spectroscopic characteristics that are similar to those of other models reported recently with a similar amine/pyridine environment. Thanks to its relative stability, vibrational data in solution have been obtained by Fourier transform infrared. A comparison of the Fe=O and Fe=(18)O wavenumbers reveals that the Fe-oxo vibration is not a pure one. The ability of the green complex to oxidize small organic molecules has been studied. Mixtures of oxygenated products derived from two- or four-electron oxidations are obtained. The reactivity of this [FeO]2+ complex is then not straightforward, and different mechanisms may be involved.     

Combined charge and spin density experimental study of the yttrium(III) semiquinonato complex Y(HBPz3)2(DTBSQ) and DFT calculations

High-resolution X-ray diffraction and polarized neutron diffraction experiments have been performed on the Y-semiquinonate complex, Y(HBPz3)2(DTBSQ), in order to determine the charge and spin densities in the paramagnetic ground state, S = (1/2). The aim of these combined studies is to bring new insights to the antiferromagnetic coupling mechanism between the semiquinonate radical and the rare earth ion in the isomorphous Gd(HBPz3)2(DTBSQ) complex. The experimental charge density at 106 K yields detailed information about the bonding between the Y3+ ion and the semiquinonate ligand; the topological charge of the yttrium atom indicates a transfer of about 1.5 electrons from the radical toward the Y3+ ion in the complex, in agreement with DFT calculations. The electron density deformation map reveals well-resolved oxygen lone pairs with one lobe polarized toward the yttrium atom. The determination of the induced spin density at 1.9 K under an applied magnetic field of 9.5 T permits the visualization of the delocalized magnetic orbital of the radical throughout the entire molecule. The spin is mainly distributed on the oxygen atoms [O1 (0.12(1) mu B), O2(0.11(1) mu B)] and the carbon atoms [C21 (0.24(1) mu B), C22(0.20(1) mu B), C24(0.16(1) mu B), C25(0.12(1) mu B)] of the carbonyl ring. A significant spin delocalization on the yttrium site of 0.08(2) mu B is observed, proving that a direct overlap with the radical magnetic orbital can occur at the rare earth site and lead to antiferromagnetic coupling. The DFT calculations are in good quantitative agreement with the experimental charge density results, but they underestimate the spin delocalization of the oxygen toward the yttrium and the carbon atoms of the carbonyl ring.     

Siloxane-Based Nanobuilding Blocks by Reaction Between Silanediol and Trifunctional Silicon Alkoxides

The preparation of nanostructured organic-inorganic materials by assembling of nanobuilding blocks allows controlling the extent of phase interaction, which in its turn governs structure-properties relationships. We present here the synthesis of siloxane-based nanobuilding blocks prepared by reacting diphenylsilanediol with vinyltriethoxysilane and triethoxysilane. The reaction products were obtained by non-hydrolytic condensation between silanediol and ethoxide groups in inert atmosphere, in the presence of pyridine, triethylamine or butyl lithium. Different synthetic conditions were examined by means of ATR-FTIR and NMR spectroscopies, showing the formation of siloxane bonds. In the case of triethoxysilane the reaction carried out in the presence of pyridine leads to Si–H bond preservation in the final product. Air stable products with improved Si–O–Si hydrolytic stability can be obtained by removal of the base after the reaction completion. The condensation products can be described as a mixture of siloxane rings involving difunctional and trifunctional silicon units.     

Gas-phase ion/molecule reactions between dimethoxyphosphonium ions and aromatic hydrocarbons

Ion/molecule reactions between O=P(OCH(3))(2)(+) phosphonium ions and six aromatic hydrocarbons (benzene, toluene, 1,2,4-trimethylbenzene, naphthalene, acenaphthylene and fluorene) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH(3))(2)(+) phosphonium ions, formed by electron impact from neutral trimethyl phosphite, were found to react with aromatic hydrocarbons (ArHs) to give (i) an adduct [ArH, O=P(OCH(3))(2)](+) and (ii) for ArHs which have an ionization energy below or equal to 8.14 eV, a radical cation ArH(+ *) by charge transfer reaction. Collision-induced dissociation experiments, which produce fragment ions other than the O=P(OCH(3))(2)(+) ions, indicate that the adduct ions are covalent species. Isotope-labeled ArHs were used to elucidate fragmentation mechanisms. The charge transfer reactions were investigated using density functional theory at the B3LYP/6-311 + G(3df,2p)//B3LYP/6-31G(d,p) level of theory. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH(3))(2)(+) and benzene is described.     

Synthesis of Molecular Wires of Linear and Branched Bis(terpyridine)‐Complex Oligomers and Electrochemical Observation of Through‐Bond Redox Conduction

Films of linear and branched oligomer wires of Fe(tpy)₂ (tpy=2,2′:6′,2′′‐terpyridine) were constructed on a gold‐electrode surface by the interfacial stepwise coordination method, in which a surface‐anchoring ligand, (tpy? C₆H₄N?NC₆H₄? S)₂ ( 1 ), two bridging ligands, 1,4‐(tpy)₂C₆H₄ ( 3 ) and 1,3,5‐(C?C? tpy)₃C₆H₃ ( 4 ), and metal ions were used. The quantitative complexation of the ligands and Fe^II ions was monitored by electrochemical measurements in up to eight complexation cycles for linear oligomers of 3 and in up to four cycles for branched oligomers of 4 . STM observation of branched oligomers at low surface coverage showed an even distribution of nanodots of uniform size and shape, which suggests the quantitative formation of dendritic structures. The electron‐transport mechanism and kinetics for the redox reaction of the films of linear and branched oligomer wires were analyzed by potential‐step chronoamperometry (PSCA). The unique current‐versus‐time behavior observed under all conditions indicates that electron conduction occurs not by diffusional motion but by successive electron hopping between neighboring redox sites within a molecular wire. Redox conduction in a single molecular wire in a redox‐polymer film has not been reported previously. The analysis provided the rate constant for electron transfer between the electrode and the nearest redox‐complex moiety, k₁ (s^?1), as well as that for intrawire electron transfer between neighboring redox‐complex moieties, k₂ (cm² mol^?1 s^?1). The strong effect of the electrolyte concentration on both k₁ and k₂ indicates that the counterion motion limits the electron‐hopping rate at lower electrolyte concentrations. Analysis of the dependence of k₁ and k₂ on the potential gave intrinsic kinetic parameters without overpotential effects: k₁⁰=110 s^?1, k₂⁰=2.6×10¹² cm² mol^?1 s^?1 for [n Fe 3 ], and k₁⁰=100 s^?1, k₂⁰=4.1×10¹¹ cm² mol^?1 s^?1 for [n Fe 4 ] (n=number of complexation cycles).     

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Pressure broadening study at low temperature: application to methane

We studied the R(0) line profile in the CH4 v4 band from room temperature to 188 K with N2 as a perturber, to 100 K with O2 as perturber, and from room temperature to 15 K using He as a perturber. The N2 and O2 measurements were performed over a total pressure range of 15-110 mbar, and for the He measurements the maximum sample pressure at 15 K was 1.10 mbar. Broadening parameters were determined, taking into account the confinement narrowing (Dicke effect), and narrowing parameters, deduced from the soft or hard collision model, are compared with the dynamic friction coefficient calculated values. We also obtained preliminary values for the temperature dependence of the N2, O2 and He line broadening parameters for this transition.