Valence change of europium in the Eu(Ir1−x Pd x )2Si2 silicides

Eu(Ir_1–x Pd _x )₂Si₂ solid solutions which exist only for 0x0.125 and 0.75x1 crystallize in the tetragonal ThCr₂Si₂-type structure. X-ray diffraction data, magnetic susceptibility and¹⁵¹Eu Mössbauer measurements suggest that these compounds can be characterized as homogeneous mixed valence systems. At room temperature and for 0x0.125, the europium valence decreases asx increases. For 0.75x1, a sharp continuous valence transition from Eu²⁺ to Eu³⁺ occurs near 48 K, 54 K and 78 K forx=0.75, 0.81 and 0.94 respectively. These valence changes are discussed in relation with the Eu–(Ir, Pd) interatomic distance.     

Phase transfer of metal cations by induced dynamic carrier agents: biphasic extraction based on dynamic covalent chemistry

In contrast to the classical method where a single molecule is designed to extract metal cations under specific conditions, dynamic covalent chemistry provides an approach based on the implementation of an adaptive dynamic covalent library for inducing the generation of the extractant species. This approach has been applied to the liquid–liquid extraction of copper(ii) nitrate based on a dynamic library of acylhydrazones constituents that self-build and distribute through the interface of a biphasic system. The addition of copper(ii) cations to this library triggers a modification of its composition and the up-regulation of the ligand molecules driven by coordination to the metal cations. Among these, one species has proven to be sufficiently lipophilic to play the role of carrier agent and its formation by component exchange enables the partial extraction of the copper(ii). The study of different pathways to generate the dynamic covalent library demonstrates the complete reversibility and the adaptability of the system. The detailed analytical investigation of the system provides a means to assess the mechanism of the dynamic extraction process.

Phase transfer of Cu(ii) cations is achieved by component exchange in a dynamic covalent library of acylhydrazone ligands. B1/B2 component exchange leads to the generation of a lipophilic carrier agent that extracts Cu(ii) into chloroform.     

Grafting of phosphonate groups on the silica surface for the elaboration of ion-sensitive field-effect transistors

Ion-sensitive field-effect transistors (ISFETs) sensitive to Ca(2+) ions could be elaborated by means of a new grafting process of the phosphonate group at the surface of the silica gate of FETs. A grafting process involving only one chemical reaction step at the surface afforded a significant improvement of the ISFET properties. The sensitivity of the ISFET towards Ca(2+) ions at pH 10 was quasi-linear in the concentration range from 10(-1) to 10(-3) M, and the slope was 10 mV pCa(-1). The site-binding model works well in predicting the experimental data, giving the complexation constant of 10(2.7) and a low value of the grafting density. The origin of the poor response of ISFETs sensitized by means of a multistep grafting process was investigated on silica powders of high specific area: the cleavage of the organic grafts at the SiOSi bonds occurring at each step could be disclosed by means of elemental analyses, infrared, and cross-polarization and magic angle spinning nuclear magnetic resonance of the grafts.     

μSR study of UTr2Si2, Tr=Co,Rh OR Pt

We have studied bySR spectroscopy the intermetallicsUTr ₂Si₂ where Tr=Co, Rh or Pt. Whereas for the Co compound we only get information on the muon localisation site, from the other two materials we obtain information on their electronic properties. We compare the characteristics of theirSR response.     

Micellar properties of zwitterionic phosphobetaine amphiphiles in aqueous solution: Influence of the intercharge distance

Zwitterionic amphiphiles of the general formula H(CH₂)_y ⁺ N(CH₃)₂(CH₂)_n PO₂C₆H ₅ ^– , where the number of intercharge methylenesn is varied, were studied in dilute aqueous solution. Their critical micellar concentrations show a peculiar variation withn, first increasing asn varies from 1 to 4 and then slowly decreasing as methylenes are added up to 10. This behavior is interpreted as being the consequence of two opposite contributions. The first is the classical CMC lowering due to the increase of hydrophobic character with the total number of methylene groups in the surfactant molecule. The second contribution is the increase in the dipole moment of the zwitterionic headgroup withn, leading to stronger dipole-dipole repulsions between headgroups at the micellar surface. Experimental results suggest that the dipole moment does not increase linearly withn because of the polymethylene chain flexibility. This is supported by¹³C NMR relaxation experiments.