Search

Herein, we report the successful characterization of sulfur vacancies in ZnS nanoplatelets by in-depth high-field and DNP-enhanced solid-state NMR of 33S and 67Zn nuclei and DFT modeling. This two-dimensional 1 nm-thick nanomaterial was obtained by reacting a dicyclohexyl zinc complex, ZnCy2, with (TMS)2S as the S source under mild conditions (45 °C) in dodecylamine. The joint experimental and theoretical studies on these nanoplatelets evidenced that a large fraction of the Zn and S atoms are located near the surface covered by dodecylamine and that the deviation from stoichiometry (agreeing with energy gap and photoluminescence properties of non-stoichiometric material) is due to sulfur vacancies. Additionally, this work reports the first 33S DNP-NMR spectrum reported in the literature alongside several ultra-high-field 33S and 67Zn solid-state NMR spectra.

Hydrogen technology, as a future breakthrough for the energy industry, has been defined as an environmentally friendly, renewable, and high-power energy carrier. The green production of hydrogen, which mainly relies on electrocatalysts, is limited by the high cost and/or the performance of the catalytic system. Recently, studies have been conducted in search of bifunctional electrocatalysts accelerating both the hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR). Herein, we report the investigation of the high efficiency bifunctional electrocatalyst TaS2for both the HER and the HOR along with the asymmetric effect of inhibition by organic intercalation. The linear organic agent, to boost the electron donor property and to ease the process of intercalation, provides a higher interlayer gap in the tandem structure of utilized nanosheets. XRD and XPS data reveal an increase in the interlayer distance of 22%. The HER and the HOR were characterized in a Pt group metal-free electrochemical system. The pristine sample shows a low overpotential of −0.016 V at the onset. The intercalated sample demonstrates a large shift in its performance for the HER. It is revealed that the intercalation is a potential key strategy for tuning the performance of this family of catalysts. The inhibition of the HER by intercalation is considered as the increase in the operational window of a water-based electrolyte on a negative electrode, which is relevant to technologies of electrochemical energy storage.

Ultrasmall gold nanoparticles (NPs) stabilized in networks by polymantane ligands (diamondoids) were successfully used as precatalysts for highly selective heterogeneous gold-catalyzed dimethyl allyl(propargyl)malonate cyclization to 5-membered conjugated diene. Such reaction usually suffers from selectivity issues with homogeneous catalysts. This control over selectivity further opened the way to one-pot cascade reaction, as illustrated by the 1,6-enyne cycloisomerization–Diels–Alder reaction of dimethyl allyl propargyl malonate with maleic anhydride. The ability to assemble nanoparticles with controllable sizes and shapes within networks concerns research in sensors, medical diagnostics, information storage, and catalysis applications. Herein, the control of the synthesis of sub-2-nm gold NPs is achieved by the formation of dense networks, which are assembled in a single step reaction by employing ditopic polymantanethiols. By using 1,1'-bisadamantane-3,3'-dithiol (BAd-SH) and diamantane-4,9-dithiol (DAd-SH), serving both as bulky surface stabilizers and short-sized linkers, we provide a simple method to form uniformly small gold NPs (1.3 ± 0.2 nm to 1.6 ± 0.3 nm) embedded in rigid frameworks. These NP arrays are organized alongside short interparticular distances ranging from 1.9 to 2.7 nm. The analysis of gold NP surfaces and their modification were achieved in joint experimental and theoretical studies, using notably XPS, NMR, and DFT modeling. Our experimental studies and DFT analyses highlighted the necessary oxidative surface reorganization of individual nanoparticles for an effective enyne cycloisomerization. The modifications at bulky stabilizing ligands allow surface steric decongestion for the alkyne moiety activation but also result in network alteration by overoxidation of sulfurs. Thus, sub-2-nm nanoparticles originating from networks building create convenient conditions for generating reactive Au(I) surface single-sites—in the absence of silver additives—useful for heterogeneous gold-catalyzed enyne cyclization. These nanocatalysts, which as such ease organic products separation, also provide a convenient access for building further polycyclic complexity, owing to their high reactivity and selectivity.

A series of silver amidinate complexes has been studied both experimentally and theoretically, in order to investigate the role of the precursor complex in the control of the synthesis of silver nanoparticles via an organometallic route. The replacement of the methyl substituent of the central carbon atom of the amidinate anion by a n-butyl group allows for the crystallization of the tetranuclear silver amidinate complex 3instead of a mixture of di- and trinuclear silver amidinate complexes 1and 2, as obtained with a methyl substituent. The relative stabilities and dissociation schemes of various isomeric arrangements of silver atoms in 3are investigated at the computational DFT level of calculation, depending on the substituents of the amidinate ligand. The tetranuclear silver amidinate complex 4, exhibiting a diamondlike arrangement of the four silver atoms, is also considered. Ag–N bonds and argentophilic Ag–Ag interactions are finely characterized using ELF and QTAIM topological analyses and compared over the series of the related di-, tri-, and tetranuclear silver amidinate complexes 1–4. In contrast to the Ag–N dative bonds very similar over the series, argentophilic Ag–Ag interactions of various strengths and covalence degree are characterized for complexes 1–4. This gives insight into the role of the amidinate substituents on the nuclearity and intramolecular chemical bonding of the silver amidinate precursors, required for the synthesis of dedicated AgNPs with chemically well defined surfaces.

The technological interest in developing novel functional nano-objects that exhibit new properties arising from their nanoscopic nature is undoubtful. Although bulk ZnO is considered to be non-ferroelectric, herein, the ferroelectric behavior of undoped and self-standing ZnO nanoparticles is reported for the first time. The nanoparticles (NPs) under study are synthesized by an organometallic approach. When dispersed in a PMMA dielectric matrix, clear polarization loops and antisymmetric switching currents are recorded for the NPs with the larger volume, in coherence with the significant polar response of these NPs in solution, measured by polarization-resolved second harmonic scattering experiments. Structural characterizations reveal that ferroelectricity is related to the appearance of a new hexagonal crystalline phase, its unit cell being swelled with respect to the well-known wurtzite ZnO cell. The volume fraction of this new phase, the polar SHS response, and the amount of ferroelectric polarization response are all linearly linked, underlining the consistency between these complementary physical characterizations.

Herein, we achieved spontaneous emulsification of organometallic precursors to elaborate subμm metal nanocapsules after interfacial reduction. Depending on the proportion of the three components, water, solvent, and the metal precursor, either thermodynamically stable “surfactant-free microemulsions” (SFME) or metastable Ouzo emulsions are formed. We investigated the catalytic transition metals Au, Pd, and Pt, individually or combined, and stabilized by various ligands. Upon reduction of the precursors, either shells of discrete nanoparticles (NPs) or continuous shells were obtained, for the SFME and Ouzo emulsions, respectively. The Au/Pd mixed emulsions lead to a unique structural morphology, in which the Au–Pd nanoparticles are embedded in a continuous submicronic metal shell. The AuNPs are available to grow larger particles within the NP shell using a seeded growth approach. The water-stable and surfactant-free nanocapsules are appealing as catalysts, and, as such, were evaluated for the hydrolysis of ammonia-borane as a promising catalytic strategy for H2release from an H-high-content storage material. This work establishes for the first time a genuine activity of water-compatible gold colloids for this reaction.

Access to removable nanocomposite electrodes for electrosensing of pollutants is of great importance. However, the preparation of reproducible and reliable carbon electrodes decorated with metallic nanoparticles, a prerequisite for trustworthy devices, remains a challenge. Here we describe an innovative and easy method to prepare such electrodes. These latter are silicon-coated with a thin carbon film on which controlled silver nanostructures are grafted. Different silver nanostructures and surface coverage of the carbon electrode (16, 36, 51, and 67%) can be obtained through a careful control of the time of the hydrogenolysis of the N–N′ isopropyl butylamidinate silver organometallic precursor (t= 1, 5, 15, and 60 min, respectively). Importantly, all nanocomposite surfaces are efficient for the electrodetection of 4-nitrophenol with a remarkable decrease of the overpotential of the reduction of such molecule up to 330 mV. The surfaces are characterized by atomic force microscopy, grazing incidence X-ray diffraction, scanning electronic microscopy, and Raman spectroscopy. Furthermore, surface-enhanced Raman scattering effect is also observed. The exaltation of the Raman intensity is proportional to the surface coverage of the electrode; the number of hot spots increases with the surface coverage.

Since the advent of nanoscience, the grail of chemists is to perfectly and reproducibly elaborate nanoparticles (NPs) of fully defined size, shape, polydispersity, and surface state. It implies a total control of the experimental parameters affecting the synthesis. In the preparation of metal oxide nanoparticles using an organometallic approach, we evidenced that the mixing time between the precursor and the ligand is surprisingly a parameter of tremendous importance. Using NMR spectroscopy, wide angle X-ray scattering, and computational DFT studies, the formation of Zn-amido oligomers through an acid–base reaction between the organometallic zinc precursor and the amine ligand is demonstrated. Over time, this polymerization process plays a major role on the control of the size and shape of the ZnO nanoparticles formed through the hydrolysis reaction. Hence, nanorods are obtained for short mixing times before hydrolysis while isotropic NPs are obtained for longer times. Furthermore, mixing induces the formation of a gel with adjustable rheological properties, thus opening new opportunities for the design of processable hybrid materials.

Sustainable production of hydrogen gas, a green energy carrier of high density, is possible only by electrolysis of water based on the hydrogen evolution reaction (HER). Here, we report the effect of oxygen poisoning on the efficiency of hydrogen production and the consumption by the HER and the hydrogen oxidation reaction (HOR), respectively, on the interface of platinum group metal-free electrocatalyst TaS2in pristine form and intercalated by the organic Lewis base hexylamine. The state of the surface probed by photoelectron spectroscopy was significantly altered by both Lewis base doping and oxygen poisoning. This alteration dramatically affects the hydrogen production efficiency in the HER, while the back process by the HOR was less sensitive to the changes in the surface states of the electrocatalysts. The oxygenated and intercalated electrocatalyst shows more than 2 × 105times lower exchange current density of the HER compared to pristine oxygenated materials.

The role of ligands (i.e. hexadecylamine, dodecylamine, or octylamine associated with oleic acid) on the formation of ZnO nanoparticle superlattice structures (NSSs) was investigated by NMR spectroscopy in C7D8. This full study demonstrates that ion‐paired ammonium carboxylates play a crucial role in NSS formation. Using different NMR spectroscopic experiments, such as 1H NMR, pulsed field gradient spin‐echo (PGSE) NMR, and NOESY, we evidenced that the introduction of long‐alkyl‐chain carboxylic acid molecules into a colloidal solution of ZnO nanoparticles (NPs) stabilized by amine ligands leads to rearrangement of the amines on the surface of the NPs with the formation of ammonium carboxylate. This NMR spectroscopic study evidences the dependence of the nature of the ligands adsorbed on the NP surface on the colloid concentration. At high concentration, several ligand shells with a lot of ion‐paired ammonium carboxylate and inclusion of amine are observed. At low concentration, the ion‐paired ammonium carboxylate shells are replaced by amine shells. This NMR spectroscopic study suggests that the driving force of NSS formation is the presence of ion‐paired ammonium carboxylate shells around the nanoparticle.

Full NMR characterization of ZnO nanoparticles (NPs) stabilized by various amines (hexadecylamine, dodecylamine, and octylamine) in C7D8demonstrated that the surface of this apparently simple system was very complex. Using different NMR spectroscopic techniques (1H, PGSE‐NMR, diffusion‐filtered 1H 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 (kdesorp≈13 s−1). The second mode corresponded to a weak interaction between the amines and the surface of the ZnO NPs (koff(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 (koff(1)≈25×105s−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.

In control: The organization of a thermotropic liquid crystal can be used to control the growth of inorganic nano‐objects (like ZnO). When the systems are in their nematic phase state, anisotropic nanoparticles are formed, while in isotropic conditions, isotropic nanoparticles are obtained. Playing with the exact nature of the liquid crystal enables control of the size and the aspect ratio of the nanoparticles (see picture).

Unter Kontrolle: Die Organisation eines thermotropen Flüssigkristalls kann zur Kontrolle des Wachstums anorganischer Nano‐Objekte (wie ZnO) genutzt werden. Liegen die Systeme in ihrer nematischen Phase vor, so bilden sich anisotrope Nanopartikel, während unter isotropen Bedingungen isotrope Nanopartikel entstehen. Das Spiel mit der exakten Natur der Flüssigkristalle ermöglicht die Kontrolle der Größe und des Längenverhältnisses der Nanopartikel (siehe Bild).

Conditions for the elaboration of nanostructured varistors by spark plasma sintering (SPS) are investigated, using 8‐nm zinc oxide nanoparticles synthesized following an organometallic approach. A binary system constituted of zinc oxide and bismuth oxide nanoparticles is used for this purpose. It is synthesized at room temperature in an organic solution through the hydrolysis of dicyclohexylzinc and bismuth acetate precursors. Sintering of this material is performed by SPS at various temperatures and dwell times. The determination of the microstructure and the chemical composition of the as‐prepared ceramics are based on scanning electron microscopy and X‐ray diffraction analysis. The nonlinear electrical characteristics are evidenced by current–voltage measurements. The breakdown voltage of these nanostructured varistors strongly depends on grain sizes. The results show that nanostructured varistors are obtained by SPS at sintering temperatures ranging from 550 to 600 °C.

Amine ligands are expected to drive the organization of metallic centers as well as the chemical reactivity of silver clusters early growing during the very first steps of the synthesis of silver nanoparticles viaan organometallic route. Density functional theory (DFT) computational studies have been performed to characterize the structure, the atomic charge distribution, and the planar two-dimensional (2D)/three-dimensional (3D) relative stability of small-size silver clusters (Agn, 2 ≤ n≤ 7), with or without an ethylamine (EA) ligand coordinated to the Ag clusters. The transition from 2D to 3D structures is shifted from n= 7 to 6 in the presence of one EA coordinating ligand, and it is explained from the analysis of the Ag–N and Ag–Ag bond energies. For fully EA saturated silver clusters (Agn–EAn), the effect on the 2D/3D transition is even more pronounced with a shift between n= 4 and 5. Subsequent electron localization function (ELF) and quantum theory of atoms in molecules (QTAIM) topological analyses allow for the fine characterization of the dative Ag–N and metallic Ag–Ag bonds, both in nature and in strength. Electron transfer from ethylamine to the coordinated silver atoms induces an increase of the polarization of the metallic core.

No Abstract

No Abstract

Numerous compounds in which a paramagnetic Ln^III 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 Gd^III, 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=Dy^III and Ho^III) 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.

Numerous compounds in which a paramagnetic LnIIIion 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=DyIIIand 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−1and J=4.5 cm−1, respectively.

The exchange interactions between a lanthanide ion and its aminoxyl ligands in a series of {Ln(NitTRZ)2(NO3)3} compounds (where NitTRZ is a nitronyl nitroxide substituted triazole) have been investigated by qualitative and quantitative approaches. The analytical study of the exchange interactions has taken into account both the ligand field effects and the spin–orbit coupling of the Ln(III) ions.

The compounds of formula Ln2[M(opba)]3·xH2O·yDMSO containing 4f Ln^III and 3d M^II ions have been synthesized; opba stands for ortho-phenylenebis(oxamato). These compounds crystallize poorly, and hence structural information has been obtained from the wide angle X-ray scattering (WAXS) technique. It has been shown that the compounds present the same ladder-like motif as that previously described for Tm2[Cu(opba)]3·4H2O·10DMF. Changing the Ln^III and/or M^II ions results in more or less pronounced distortions of the ladders. For a given M^II ion, changing the Ln^III ion from La^III to Lu^III results in a decrease of the Ln–M distance parallel to the lanthanide contraction. In the same way, for a given rare earth, changing the M^II ion from Cu^II to Ni^II and Zn^II ions also results in the decrease of the Ln–M distance in accord with the decreasing radii of the M^II ions. The structural details have been analyzed and discussed.

A ferromagnetically coupled gadolinium–radical compoundis 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 GdIIIa ferromagnetic interaction with the ligands was found, which gives rise to a S= 9/2 ground‐state spin.

A sugar-substituted ligand allowed for the synthesis of chiral Cu(ii) tetranuclear aggregates which assemble via H-bonding in a 3D-network containing hydrophobic helical channels.

For Abstract see ChemInform Abstract in Full Text.