Formation of negative oxidation states of platinum and gold in redox ionic liquid: Electrochemical evidence

The electrochemical reduction of noble metal electrodes in the presence of redox ionic liquid, 1-ferrocenylethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [FcEMIM][TFSI], was investigated by cyclic voltammetry. Our experiments suggest the formation of metal with negative oxidation states, in the cases of platinum and gold electrodes [M_n⁻, FcEMIM⁺]. By analogy with the previous work, the formation of these phases is concomitant with the insertion of the supporting electrolyte; which correspond in our experimental condition to the redox cation of the ionic liquid. As an exciting result, the electrochemical investigations of the reduced electrode in electrolytic solution, containing solvent and supporting electrolyte, evidence the presence of the ferrocene groups at the electrode surface. Moreover, the reduced electrode exhibits the presence of the ferrocene even after, contact with air, after ultrasound, and after physical polishing, highlighting the large stability of this organo-metallic phases formed in this media. The AFM investigations demonstrate the morphological change of the platinum surface after the reduction process. Finally, our works bring a formal electrochemical proof of the presence of the ionic liquid cation inside the electrode material after the cathodic treatment in this media.     

Gadolinium chelate coated gold nanoparticles as contrast agents for both X-ray computed tomography and magnetic resonance imaging

Functionalized gold nanoparticles were applied as contrast agents for both in vivo X-ray and magnetic resonance imaging. These particles were obtained by encapsulating gold cores within a multilayered organic shell which is composed of gadolinium chelates bound to each other through disulfide bonds. The contrast enhancement in MRI stems from the presence of gadolinium ions which are entrapped in the organic shell, whereas the gold core provides a strong X-ray absorption. This study revealed that these particles suited for dual modality imaging freely circulate in the blood vessels without undesirable accumulation in the lungs, spleen, and liver.     

Far-infrared spectroscopy of small polycyclic aromatic hydrocarbons

Both experimental and theoretical spectroscopic studies on small gas phase polycyclic aromatic hydrocarbons in the far-infrared spectral region are reported. The experimental set-up based on thermal emission and Fourier transform far infrared analysis led to the detection of relatively broad vibrational bands, unresolved in rotation, representative of each molecule. Detailed theoretical investigations were performed, including both ab initio calculations and spectral simulations. For the majority of the samples, this study provides the first detection of the vibrational modes associated with the skeleton motions.     

Structural and luminescent properties of micro- and nanosized particles of lanthanide terephthalate coordination polymers

Reaction in water between rare earth ions (Ln = Y, La-Tm, except Pm) and the sodium salt of terephthalic acid leads to a family of lanthanide-based coordination polymers of general formula [Ln2(C8H4O4)3(H2O)4] n with Ln = La-Tm or Y. The isostructurality of the compounds with the previously reported Tb-containing polymer is ascertained on the basis of their X-ray powder diffraction diagrams. The coordination water molecules can be reversibly removed without destroying the crystal structure for compounds involving one of the lighter lanthanide ions (La-Eu). For compounds involving one of the heavier lanthanide ions (Tb-Tm) or yttrium, a structural change occurs during the drying process. X-ray diffraction data show this new anhydrous phase corresponding to the linking of pairs of Er(III) ions through mu-carboxylate bridges. Porosity profiles calculated for the anhydrous phases of Tb(III) and Er(III) show the presence of channels with very small sections. The luminescent properties of all the compounds have been recorded and the two most luminescent polymers, namely, the europium- and the terbium-containing ones, have been studied in more detail. Tb(III)-containing compounds display large quantum yields, up to 43%. Polyvinylpyrrolidone nanoparticles doped with [Ln2(C8H4O4)3(H2O)4] n (Ln = Eu, Tb, Er) have also been synthesized and characterized. The encapsulation of the coordination polymers results in somewhat reduced luminescence intensities and lifetime, but the nanoparticles can be dispersed in water and remain unchanged in this medium for more than 20 h.     

Preparation and structure of three solvatomorphs of the polymer [Co(dbm)2(4ptz)]n: spin canting depending on the supramolecular organization

The syntheses and X-ray structures of three isomeric 1D coordination polymers are reported. The complex [Co(dbm)2(MeOH)2] (1) was used as a precursor in these reactions. The preparation and structure of 1 is also presented; this mononuclear complex is in the cis configuration because this allows the formation of a network of intermolecular hydrogen bonds in the solid state. Reaction of 1 with 2,4,6-tris-(4-pyridyl)-1,3,5-triazine (4ptz) yields the polymers [Co(dbm)2(4ptz)]n.nTHF (2a), [Co(dbm)2(4ptz)]n.0.75nTHF.0.5nEt2O (2b), and [Co(dbm)2(4ptz)]n.3nDMF (2c) in the form of zigzag chains, instead of the expected honeycomb architectures. This is because of the establishment of extended pi-pi stacking throughout these solids, which could not have occurred otherwise. Compounds 2a, 2b, and 2c are solvatomorphs, and formation of either one of them depends on the exact conditions of crystallization, which lead to significant differences in the supramolecular organization of the chains. Bulk magnetic measurements on 2a reveal weak antiferromagnetic exchange within the chains and small ordering throughout the solid that results in the manifestation of the phenomenon of spin canting, whereas for 2c the different supramolecular organization causes the antiferromagnetic exchange not to result in spin canting.     

Redox Multifunctionality in a Series of PtII Dithiolene Complexes of a Tetrathiafulvalene‐Based Diphosphine Ligand

The redox‐active and chelating diphosphine, 3,4‐dimethyl‐3′,4′‐bis(diphenylphosphino)‐tetrathiafulvalene, denoted as P2 , is engaged in a series of platinum complexes, [(P2)Pt(dithiolene)], with different dithiolate ligands, such as 1,2‐benzenedithiolate (bdt), 1,3‐dithiole‐2‐thione‐4,5‐dithiolate (dmit), and 5,6‐dihydro‐1,4‐dithiin‐2,3‐dithiolate (dddt). The complexes are structurally characterized by X‐ray diffraction, together with a model compound derived from bis(diphenylphosphino)ethane, namely, [(dppe)Pt(dddt)] . Four successive reversible electron‐transfer processes are found for the [(P2)Pt(dddt)] complex, associated with the two covalently linked but electronically uncoupled electrophores, that is, the TTF core and the platinum dithiolene moiety. The assignments of the different redox processes to either one or the other electrophore is made thanks to the electrochemical properties of the model compound [(dppe)Pt(dddt)] lacking the TTF redox core, and with the help of theoretical calculations (DFT) to understand the nature and energy of the frontier orbitals of the [(P2)Pt(dithiolene)] complexes in their different oxidation states. The first oxidation of the highly electron‐rich [(P2)Pt(dddt)] complex can be unambiguously assigned to the redox process affecting the Pt(dddt) moiety rather than the TTF core, a rare example in the coordination chemistry of tetrathiafulvalenes acting as ligands.     

Control of ionic transport through gated single conical nanopores

Control of ionic transport through nanoporous systems is a topic of scientific interest for the ability to create new devices that are applicable for ions and molecules in water solutions. We show the preparation of an ionic transistor based on single conical nanopores in polymer films with an insulated gold thin film “gate.” By changing the electric potential applied to the “gate,” the current through the device can be changed from the rectifying behavior of a typical conical nanopore to the almost linear behavior seen in cylindrical nanopores. The mechanism for this change in transport behavior is thought to be the enhancement of concentration polarization induced by the gate. Figure   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis of tricyclic nitrogen heterocycles by a sequence of palladium-catalyzed N-H and C(sp3)-H arylations

A range of tricyclic nitrogen heterocycles were synthesized in a straightforward and efficient manner via a sequence involving palladium-catalyzed N-arylation and C(sp(3))-H arylation as the key steps. Whereas the C(sp(3))-H arylation furnished fused 6,5,6-membered ring systems efficiently, the formation of the more strained 6,5,5-membered systems proved to be more challenging and required a subtle adjustment of the reaction conditions.     

Foam films in the presence of functionalized gold nanoparticles

Dry aqueous foams made of anionic surfactant (SDS) and spherical gold nanoparticles are studied by small angle X-ray scattering and by optical techniques. To obtain stable foams, the surfactant concentration is well above the critical micelle concentration. The specular reflectivity signal obtained on a very thin film (thickness 20 nm) shows that functionalized nanoparticles (17 nm typical size) are trapped within the film in the form of a single monolayer. In order to isolate the film behavior, investigations are made on a single film confined in a tube. The film thinning according to the ratio of functionalized nanoparticle and SDS micelles (1:1, 1:10, 1:100) is mainly governed by the structural arrangement of SDS micelles. In thick films, nanoparticles tend to form aggregates that disappear during drainage. In particular self-organization of nanoparticles (with different surface charge) inside the film is not detected.     

Ultrafast fluorescence studies of dye sensitized solar cells

Time-resolved fluorescence spectra from the RuN719 dye exhibit very short lifetimes (<30 fs) in solutions, on non-injecting substrates and on injecting ones. This reveals <10 fs intramolecular energy redistribution competing with the injection. We conclude that injection proceeds on a sub-10 fs time scale from non-thermalized levels of the dye.