Myrtil L. Kahn

Analytical Determination of the {Ln–Aminoxyl Radical} Exchange Interaction Taking into Account Both the Ligand‐Field Effect and the Spin–Orbit Coupling of the Lanthanide Ion (Ln=DyIII and HoIII)

Numerous compounds in which a paramagnetic LnIII ion is in an exchange interaction with a second spin carrier, such as a transition metal ion or an organic radical, have been described. However, except for GdIII, very little has been reported about the magnitude of the interactions. Indeed, for these ions both the ligand-field effects and the exchange interactions between the magnetic centers become relevant in the same temperature range; this makes the analysis of the magnetic behavior of such compounds more difficult. In this study, quantitative analyses of the thermal variations of the static isothermal initial magnetic susceptibility measured on powdered samples of the [Ln(NO3)3-[organic radical]2] (Ln = DyIII and HoIII) compounds were performed. The ligand-field effects on the Ln ions were taken into account, and the exchange interactions within a molecule were treated exactly within an appropriate Racah formalism. Values of the intramolecular [Ln-aminoxyl radical] exchange parameter have thus been rigorously deduced for both the Dy Kramers and Ho non-Kramers ion-based compounds. Ferromagnetic [Ln-radical] interactions are found for both the Dy and Ho derivatives with J = 8 cm(-1) and J = 4.5 cm(-1), respectively.

Synthesis and Magnetic Behavior of Rare-Earth Complexes with N,O-Chelating Nitronyl Nitroxide Triazole Ligands: Example of a [GdIII{Organic Radical}2] Compound with anS=9/2 Ground State

A ferromagnetically coupled gadolinium–radical compound is described. A series of three lanthanide complexes of general formula [Ln(organic radical)2(NO3)3] (Ln =Y3+, La3+, and Gd3+, shown on the right) have been synthesized. With the paramagnetic GdIII a ferromagnetic interaction with the ligands was found, which gives rise to a S = 9/2 ground-state spin.

Organometallic chemistry: an alternative approach towards metal oxide nanoparticles

The synthesis of nanoparticles of controlled size, shape, size distribution and surface state is nowadays recognized to be of prime importance both from a fundamental point of view and for applications. Among all nanomaterials, nanoparticles of metal oxides are very attractive as their unique characteristics make them the most diverse class of materials with properties covering almost all aspect of solid-state physics, materials science and catalysis. In this feature article, we present our efforts toward the synthesis of metal oxide nanoparticles of controlled size and shape using organometallic chemistry. We show that this approach is versatile and can be generalized to several metal oxides from semiconducting to magnetic materials as well as from monometallic to mixed-metal-oxide nanomaterials. We point out that the control over the size, the shape, and the surface state of such materials is of prime importance for understanding and controlling their physical properties. We also report the use of such semiconducting nanoparticles for two different applications, highlighting the importance of the implementation of the nanoparticles in the fabrication of devices.

Liquid crystalline thermotropic and lyotropic nanohybrids

This review is meant to give the reader an insight into hybrids incorporating different types of nanoparticles, e.g. metallic or metal oxides, within different types of lyotropic and thermotropic liquid crystals, from relatively small calamitic molecules to the larger discotics and polymers. In particular, this review highlights the importance of nanoparticle-liquid crystal interactions in accessing hybrid materials that exhibit synergetic properties.

Organometallic approach for the synthesis of nanostructures

Nanostructures are considered as chemical systems of high potential owing to their unusual properties at the interface of those of molecular species and bulk metals. Consequently, they are promising candidates for application in different domains such as catalysis, magnetism, medicine, opto-electronics or sensors. The control of the characteristics of nanostructures is a fundamental prerequisite if one envisages exploring their physical or chemical properties since they vary dramatically with size, shape and surface state. Thus, the development of efficient methods leading to reproducible nanostructures is presently one of the main objectives in the nanochemistry community. Although organometallic chemistry has been early involved, it arises only marginally in the field. Nevertheless, the concepts and techniques of organometallic chemistry appear to be well-adapted for the growth of well-controlled nanostructures. This will be discussed through recent advances in the synthesis of metal and metal oxide nanoparticles in terms of size dispersion, chemical composition, surface state, shape or organization, pointing out the role of ligands. Moreover their characterization at a molecular level and the development of their chemical/physical properties towards applications will be described. This review reflects more than 20 years of efforts of our team to achieve these goals.

Full Characterization of Colloidal Solutions of Long‐Alkyl‐Chain‐Amine‐Stabilized ZnO Nanoparticles by NMR Spectroscopy: Surface State, Equilibria, and Affinity

Full NMR characterization of ZnO nanoparticles (NPs) stabilized by various amines (hexadecylamine, dodecylamine, and octylamine) in C(7)D(8) demonstrated that the surface of this apparently simple system was very complex. Using different NMR spectroscopic techniques ((1)H, PGSE-NMR, diffusion-filtered (1)H NMR, NOESY, ROESY), we observed at least three different modes of interaction of the amines at the surface of the NPs, in thermodynamic equilibrium with the free amines, the relative populations of which varied with their concentration. The first mode corresponded to a strong interaction between a small amount of amine and the ZnO NPs (k(desorp)≈13 s(-1)). The second mode corresponded to a weak interaction between the amines and the surface of the ZnO NPs (k(off(2))≈50-60 s(-1)). The third, and weakest, mode of interaction corresponded to the formation of a second ligand shell by the amine around the NPs that was held together through van der Waals interactions (k(off(1))≈25×10(5) s(-1)). The second and third modes were in fast exchange on the NMR timescales with the free amines. The strongly interacting amines at the NPs surface (first mode) were in slow exchange with the other modes. A complex hydrogen-bonding network at the NPs surface was also observed, which did not only involve the coordinated amine but also THF and water molecules that remained from the synthesis.

Experimental study of LO phonons and excitons in ZnO nanoparticles produced by room-temperature organometallic synthesis

We report here the study by optical microspectroscopy of crystalline ZnO nanoparticles produced by room-temperature organometallic synthesis. We present resonant Raman scattering spectrum obtained from different sized nanostructures from which the longitudinal-optical (LO) phonon frequency has been found to be very weakly dependent on their size. Low-temperature photoluminescence measurements reveal that (i) the band-edge PL of ZnO nanoparticles is dominated by weakly bound localized exciton, and that (ii) its energy does not exhibit any spatial confinement effect. These results enlighten the need for surface passivation of the nanoparticles to improve their UV emission potential.

Raman study of E2 and surface phonon in zinc oxide nanoparticles surrounded by organic molecules

Using Raman spectrometry, we obtained results showing the influence of organic ligands on the vibrational properties of small zinc oxide nanocrystals (2.1–6.8nm). It is shown that it is possible to distinguish both mechanical and dielectric effects from the E2 nonpolar phonon mode and from a surface mode, theoretically predicted but rarely observed. It has been found that E2 phonon is not dependent on the nanocrystal size, but its frequency decreases with increasing ligand length, characteristic of a tensile stress on the nanocrystal. We report also the observation of a surface optical mode, the experimental frequency of which is in reasonable agreement with available calculations.

A new honeycomb-like molecular compound: Gd[C6H3(COO)3](H2O)3·1.5H2O

The reaction in gel of Gd(lII) ions with TMA 3- , where TMA 3- stands for [C 6 H 3 (COO) 3 ] 3- has afforded single crystals of a bidimensional molecular compound formulated as Gd[TMA(H 2 O) 3 ].1.5H 2 O whose crystal structure is reported here: C2/c, a=20.454(2) A, b=9.973(1) A, c=15.251(2) A, β=125.68(1)° and Z=8. The structure consists of parallel double-sheet networks based on honeycomb-like motifs based on Gd(III) ions and TMA 3- groups. This compound exhibits a paramagnetic behaviour in the whole temperature range (2-300K).

Liquid crystal based on hybrid zinc oxide nanoparticles

Here we report the synthesis of a novel liquid crystal based on zinc oxide nanoparticles. Due to the presence of fluxional ligands, the hybridized material presents mesomorphic behavior even for a high content of inorganic material. In combination with promising luminescent properties, it may well be exploited for electro-optical applications.