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Prussian blue analogue nanocrystals of the CsINiII[CrIII(CN)6] cubic network with 6 nm size were assembled as a single monolayer on highly organized pyrolytic graphite (HOPG). X-ray magnetic circular dichroism (XMCD) studies, at the Ni and Cr L2,3 edges, reveal the presence of an easy plane of magnetization evidenced by an opening of the magnetic hysteresis loop (coercive field of ≈200 Oe) when the magnetic field, B, is at 60° relative to the normal to the substrate. The angular dependence of the X-ray natural linear dichroism (XNLD) reveals both an orientation of the nanocrystals on the substrate and an anisotropy of the electronic cloud of the NiII and CrIII coordination sphere species belonging to the nanocrystals' surface. Ligand field multiplet (LFM) calculations that reproduce the experimental data are consistent with an elongated tetragonal distortion of surface NiII coordination sphere responsible for the magnetic behavior of monolayer.

International audience; Photoswitchable 11 nm nanocrystals with the coordination network Cs{Co[Fe(CN)6]} were obtained using a template-free method. The nanocrystals were recovered from the colloidal solutions as solid materials surrounded by cetyltrimethylammonium (CTA) cations or embedded in the organic polymer polyvinylpyrrolidone (PVP). Complementary magnetic, spectroscopic, and structural techniques, including EPR spectroscopy, reveal a majority (∼70%) of the low-spin and photoactive diamagnetic CoIIIFeII pairs located in the core of the nanocrystals and a mixture of CoIIFeII and CoIIFeIII species present mainly within the shell of the objects. While bulk compounds with similar vacancy concentration do not exhibit noticeable photoinduced charge transfer, the observed photoactivity of the nanocrystals is ascribed to their nanometric size. The relaxation temperature of the photoinduced state shifts upward by ∼55 K when PVP is replaced by CTA. This is ascribed to the larger rigidity of the dense CsCoFe_CTA material, whose metastable state is lower than that for CsCoFe_PVP, leading to a larger relaxation energy barrier and, therefore, to a higher relaxation temperature.

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International audience; Responsive materials that can answer to chemical or physical external stimuli offer numerous prospects in material science. Here, we have elaborated a two-step synthetic approach that allows incorporating molecular cubic switches into a polymeric material. Firstly, a preformed half-capped, Cs+-templated {Fe4Co4} cyanido-polymetallic cubic unit (“pro-cube”) is obtained and proven to be stable in solution, as demonstrated by paramagnetic NMR. Secondly, the reaction of the pro-cube with a ditopic scorpionate ligand enables the precipitation of a polymeric network containing the cubic unit. Furthermore, the adequately chosen ditopic ligand that coordinates the Co ions of the pro-cube allows us to preserve the switchable properties of the cubic unit. Indeed, the magnetic properties of the polymeric material compare well with those of the molecular cubic model that is obtained by reacting a non-bridging scorpionate ligand, and that was prepared as a reference. Both the polymeric material and the molecular model cube show a thermally-induced metal–metal electron transfer near room temperature. Interestingly, the magnetic state of the polymeric material is shown to depend on its hydration state, indicating its capability to act as a chemo-sensor.

Photoinduced charge-transfer is an important process in nature and technology and is responsible for the emergence of exotic functionalities, such as magnetic order for cyanide-bridged bimetallic coordination networks. Despite its broad interest and intensive developments in chemistry and material sciences, the atomic-scale description of the initial photoinduced process, which couples intermetallic charge-transfer and spin transition, has been debated for decades; it has been beyond reach due to its extreme speed. Here we study this process in a prototype cyanide-bridged CoFe system by femtosecond X-ray and optical absorption spectroscopies, enabling the disentanglement of ultrafast electronic and structural dynamics. Our results demonstrate that it is the spin transition that occurs first on the Co site within ~50 fs, and it is this that drives the subsequent Fe-to-Co charge-transfer within ~200 fs. This study represents a step towards understanding and controlling charge-transfer-based functions using light. Cyanide-bridged CoFe coordination networks exhibit photomagnetism because of coupled charge-transfer and spin transition. Now, femtosecond X-ray and optical absorption spectroscopies have enabled the electronic and structural dynamics of this light-induced process to be disentangled and show that it is the spin transition on the cobalt atom, occurring within ~50 fs, that induces the Fe-to-Co charge-transfer within ~200 fs.

Photoinduced charge-transfer is an important process in nature and technology and is responsible for the emergence of exotic functionalities, such as magnetic order for cyanide-bridged bimetallic coordination networks. Despite its broad interest and intensive developments in chemistry and material sciences, the atomic-scale description of the initial photoinduced process, which couples intermetallic charge-transfer and spin transition, has been debated for decades; it has been beyond reach due to its extreme speed. Here we study this process in a prototype cyanide-bridged CoFe system by femtosecond X-ray and optical absorption spectroscopies, enabling the disentanglement of ultrafast electronic and structural dynamics. Our results demonstrate that it is the spin transition that occurs first on the Co site within ~50 fs, and it is this that drives the subsequent Fe-to-Co charge-transfer within ~200 fs. This study represents a step towards understanding and controlling charge-transfer-based functions using light.

This review is dedicated to the synthesis, properties and potential applications of Prussian blue analogs and other cyanide-bridged coordination polymers that have been recently investigated at the nanoscale. A wide range of nanostructures including core-shells, hollow particles and other architectures were designed with the objective of creating new and original functionalities targeting a wide range of fields such as information storage, waste water treatment, catalysis, gas storage and biomedical applications. Cyanide-bridged coordination nanoparticles have also chemical functionality and serve as precursors for the controlled design of other nanomaterials (alloys, oxides…).

Ultrasmall sub-10 nm nanoparticles of Prussian blue analogues incorporating GdIII ions at their periphery revealed longitudinal relaxivities above 40 mM-1 s-1 per GdIII regardless of the nature of the core and the polymer coating. Large T1-weighted contrast enhancements were achieved in addition to a highly efficient photothermal effect and in vivo photoacoustic imaging in tumors.

International audience; Gemini Observatory plans to revitalize its AO facility at Gemini North for the benefit of the US and international user community, including a funded MCAO system now in development. Our Strategic Plan calls for the development of a GLAO system enabled by an Adaptive Secondary Mirror. We discuss our plans, progress, and funding outlook.

International audience; Gemini Observatory has been awarded from the National Science Foundation a major fund to build a new state-of-the-art Multi Conjugate Adaptive Optics facility for Gemini North on Maunakea called GNAO. The current Telephone: 1+56 51 2205 642 baseline system will use two lasers each split in two to create an artificial constellation of four laser guide star to measure the distortions caused by the atmosphere. At least two deformable mirror conjugated to 0km and the main altitude layer above Maunakea will be used to correct these distortions. The facility will be designed to feed future instrumentation, initially a near infrared imager and potentially a visiting 4-arm multi object adaptive optics IFU spectrograph. 1 In this paper I will present the main characteristics of this exciting facility, its promises and its challenges. I will also present its conceptual design and results of trade studies conducted within the team and the Gemini Adaptive Optics Working Group. The expected first light is for October 2024.

Recent advances in structural control during the synthesis of SWCNTs have in common the use of bimetallic nanoparticles as catalysts, despite the fact that their exact role is not fully understood. We therefore analyze the effect of the catalyst' s chemical composition on the structure of the resulting SWCNTs by comparing three bimetallic catalysts (FeRu, CoRu and NiRu). A specific synthesis protocol is designed to impede the catalyst nanoparticle coalescence mechanisms and stabilize their diameter distributions throughout the growth. Owing to the ruthenium component which has a limited carbon solubility, tubes grow in tangential mode and their diameter is close to that of their seeding nanoparticle. By using as-synthesized SWCNTs as a channel material in field effect transistors, we show how the chemical composition of the catalysts and temperature can be used as parameters to tune the diameter distribution and semiconducting-to-metallic ratio of SWCNT samples. Finally, a phenomenological model, based on the dependence of the carbon solubility as a function of catalyst nanoparticle size and nature of the alloying elements, is proposed to interpret the results., 10 pages, 6 figures

International audience; This contribution reports on the state of the art of the elaboration and the application of nanoparticles (NPs) and nanohybrid/nanocomposite materials based on spin-crossover (SCO) complexes. The first part of this review concerns the syntheses and the characterizations of the physical properties of SCO NPs. All of the methods including homogeneous and heterogeneous media syntheses developed for the elaboration of such NPs and the associated methods used for their morphological characterization are presented. A particular attention is paid on the effects of the size reduction and the influence of the environment on the SCO properties and to specific and recent remarkable advanced physical measurements realized on a batch of NPs or on an isolated object. The second part presents the elaboration of various nanocomposite or nanohybrid materials for which SCO NPs have been associated with magnetic entities, noble metals, different fluorescent dyes, and different active polymers with the objectives to go toward specific applications based on synergistic effects between the two components.

A number of tools exist to guide the monitoring and evaluation of science, technology, engineering and mathematics (STEM) education and outreach programmes. Fewer tools exist for evaluating astronomy outreach programmes. In this paper we try to overcome this limitation by presenting a monitoring and evaluation framework developed for the International Astronomical Union’s Office of Astronomy for Development (OAD). The mandate of the OAD is to stimulate sustainable development at an international level and to expand astronomy education and outreach globally. The broad assumptions of this programme are that astronomy has the potential to contribute to human development by means of the transferable nature of its science discoveries, as well as its potential to activate feelings of wonderment, inspiration and awareness of the universe. As a result, the programme potentially embodies a far broader mix of outcomes than conventionally considered in STEM evaluation approaches. Towards this aim, we operationalise our monitoring and evaluation approach by first outlining programme theories for three key OAD programmes: a programme for universities and research, another one for schools, and one for public outreach. We then identify outcomes, indicators and measures for each one of these programmes. We conclude with suggestions for evaluating the global impact of astronomy for development.

International audience; We study the transient electron transfer process in CsCoFe and RbMnFe Prussian Blue Analogues (PBA), by time-resolved X-ray Absorption Near Edge Structure (XANES) and by time-resolved optical spectroscopy. We performed time-resolved studies on CsCoFe nanocrystals dispersed in solution. The XANES results obtained at room temperature clearly evidence the Co III (LS)Fe II →Co II (HS)Fe III electron transfer between the metal centers, through the opposite spectral shifts at the Fe and Co edges. We also studied the Mn III (LS)Fe II →Mn II (HS)Fe III process in RbMnFe powder sample, at thermal equilibrium as well and under laser excitation. Optical spectroscopy reveals that the process occurs on the picosecond timescale, as already reported by Raman spectroscopy and that the lifetime of the photoinduced charge-transfer states is in the 1-10 µs range, depending on the sample and on temperature.

In the race towards miniaturization in nanoelectronics, magnetic nanoparticles (MNPs) have emerged as potential candidates for their integration in ultrahigh-density recording media. Molecular-based materials open the possibility to design new tailor-made MNPs with variable composition and sizes, which benefit from the intrinsic properties of these materials. Before their implementation in real devices is reached, a precise organization on surfaces and a reliable characterization and manipulation of their individual magnetic behavior are required. In this paper, it is demonstrated how molecular-based MNPs are accurately organized on surfaces and how the magnetic properties of the individual MNPs are detected and tuned by means of low-temperature magnetic force microscopy (LT-MFM) with variable magnetic field. The magnetization reversal on isolated and organized MNPs is investigated; in addition, the temperature dependence of their magnetic response is evaluated.

Prussian blue analogues (PBA) ferromagnetic nanoparticles Cs I x Ni II [Cr III (CN)6 ] z ·3(H2O) embedded in CTA+ (cetyltrimethylammonium) matrix have been investigated by magnetometry and magnetic small-angle neutron scattering (SANS). Choosing particle sizes (diameter D = 4.8 and 8.6 nm) well below the single-domain radius and comparable volume fraction of particle, we show that the expected superparamagnetic regime for weakly anisotropic isolated magnetic particles is drastically affected due to the interplay of surface/volume anisotropies and dipolar interactions. For the smallest particles (D = 4.8 nm), magnetocrystalline anisotropy is enhanced by surface spins and drives the system into a regime of ferromagnetically correlated clusters characterized by a temperature-dependent magnetic correlation length L mag which is experimentally accessible using magnetic SANS. For D = 8.6 nm particles, a superparamagnetic regime is recovered in a wide temperature range. We propose a model of interacting single-domain particles with axial anisotropy that accounts quantitatively for the observed behaviors in both magnetic regimes.

CsNiCr(CN)6 coordination nanoparticles with sizes ranging from 6 to 30 nm are highly diluted in an organic polymer matrix. Their static and dynamic magnetic behaviour allows unravelling of surface anisotropy and interparticle dipolar interaction effects. The single magnetic domain critical size is thus evaluated to be around 22 nm with a blocking temperature of 21 K (at ν = 1 Hz) and an effective energy barrier for the reversal of the magnetization of 426 K.

Large longitudinal relaxivities were observed in Mn(II)-containing Prussian blue analogue nanoparticles. At low concentrations and high field (7 T), a remarkable positive contrast enhancement was seen which exceeded that of clinical contrast agents and was attributed to the very large proportion of surface atoms of these coordination nanoparticles.

International audience; Catalyst engineering is a key point for selective growth of single-walled carbon nanotubes (SWCNT) with chemical vapor deposition (CVD). Here, we develop a new general synthesis method able to produce a wide range of homogenous bimetallic catalyst nanoparticles with controlled stoichiometry and sizes. The basics of this catalyst synthesis is to use preformed stoichiometric bimetallic Prussian blue analog (PBA) nanoparticles. Catalyst nanoparticles are then prepared in-situ in a hot filament CVD reactor with subsequent high temperature treatment in reducing atmosphere prior to SWCNT growth. The capabilities of the synthesis route are demonstrated by testing five PBA systems involving various transition metals. Transmission electron microscopy (TEM), scanning TEM and energy dispersive X-ray spectroscopy (STEM-EDX), and in-situ X-ray photoelectron spectroscopy (XPS) measurements are used to finely follow the size and composition of the catalyst at each step of the process. Each system yields small size catalysts with a narrow distribution, which act as efficient catalysts for SWCNT growth with a good yield and small diameter distribution. The versatility of the PBA family paves a new way for a fine tuning of the catalyst properties monitored by the metal involved in the PBA, and for opening routes to more selective SWCNT synthesis.

The differential Optical Transfer Function (dOTF) is a focal plane wavefront sensing method that uses a diversity in the pupil plane to generate two different focal plane images. The difference of their Fourier transforms recovers the complex amplitude of the pupil down to the spatial scale of the diversity. We produce two simultaneous PSF images with diversity using a polarizing filter at the edge of the telescope pupil, and a polarization camera to simultaneously record the two images. Here we present the first on-sky demonstration of polarization dOTF at the 1.0m South African Astronomical Observatory telescope in Sutherland, and our attempt to validate it with simultaneous Shack-Hartmann wavefront sensor images., 11 pages, 9 figures, Proc. SPIE Vol. 9912

At the last COST (European Cooperation in Science and Technology) EU–US meeting held in May 2011 in Prague, one of the main questions raised was how can molecular chemistry with an emphasis on the use of non noble metal complexes contribute to water photolysis for the production of solar fuels. In general molecular chemistry can help not only in the understanding of the sequential steps of water oxidation with the design of sophisticated metal complexes but also in the catalytic reaction involving the reduction of protons to hydrogen to make a fuel. The water oxidation reaction stands as the grand challenge for molecular chemists as water has been recognised as the source of protons and electrons to be used in the synthesis of solar fuels. Based on recent advances, it seems that the development of molecular metal complexes with abundant and cheap metals holds the promises for their putative integration in functional devices for the hydrogen production reaction. However, for the majority of these metal complexes, the electrocatalytic activity towards the reduction of protons has been reported in organic solvents and only rarely in aqueous medium. Furthermore, these molecular catalysts also suffer from degradative processes upon catalytical activity in solution. Hence there is still much room for the design and preparation of molecular based catalysts capable to perform the H 2 production in aqueous phase. In this review/article we give a brief overview on the state of the art on solid polymer exchange (SPE) membrane water electrolysers and their limitations regarding their widespread commercialisation, that is in part related to the expensive and rare noble metal catalysts used for both the hydrogen producing reaction and the water oxidation process. We focus herein on the recent advances made in preparing modified carbon electrodes with molecular based complexes and on their catalytic properties in heterogeneous medium. A challenging step in this research field is to couple the cathodic process to that of the water oxidation reaction. We report here on the implementation of fluroboryl dimethylglyoxime cobalt complexes supported on a carbonaceous material at the cathode of a proton exchange membrane (PEM) water electrolysers. electrocatalytic activity for the H 2 production was observed with current densities in the range of 500 mA cm −2 for a cell efficiency of 80% using iridium at the anode. The durability of these systems was tested for several days upon on and off polarisation without noticeable loss in activity. These results therefore lead us to think that it should be feasible to reduce the cost of actual PEM water electrolyser by replacing platinum at the cathode.

Prussian-blue analogues (PBA) are a family of molecule-based magnetic compounds of general formula A x M y [M’(CN) 6 ] z , whose magnetic properties can be tuned by an external stimulus. This tunability makes PBA good candidates for their integration into new electronic or spintronic devices. As a previous step to accomplish this integration, PBA need to be deposited onto surfaces in controllable ways and if possible into specifi c positions on the surface. Even though the study of PBA has traditionally been limited to bulk, lately they have also been processed as nanoparticles (NPs). Here an effi cient approach is presented for the accurate deposition and organization of PBA-NPs of different sizes (from ∼ 6 to ∼ 25 nm) over silicon surfaces. The approach used in this work, relies on a combination of surface functionalization with local oxidation nanolithography (LON) and uses electrostatic interactions between PBA-NPs and a charged self-assembled monolayer patterned on specifi c parts of the silicon surface. By using atomic force microscopy (AFM), magnetometry, infrared spectroscopy (IR) and auger electron spectroscopy (AES) we show that the deposition process does not affect NPs properties. In addition, we present a study on the evolution of AFM nanolithographed SiO 2 patterns under sonication.

We report a novel method to prepare patterns of nanoparticles over large areas of the substrate. This method is based on the adsorption of the negatively charged nanoparticles dispersed in an aqueous subphase onto a monolayer of the phospholipid dipalmitoyl-l-α-phosphatidylcholine (DPPC) at the air-water interface. It has been used to prepare patterns of nanoparticles of Prussian blue analogues (PBA) of different size (K(0.25)Ni[Fe(CN)(6)](0.75) (NiFe), K(0.25)Ni[Cr(CN)(6)](0.75) (NiCr), K(0.25)Ni[Co(CN)(6)](0.75) (NiCo), Cs(0.4)Co[Cr(CN)(6)](0.8) (CsCoCr), and Cs(0.4)Co[Fe(CN)(6)](0.9) (CsCoFe)). The behavior of DPPC monolayer at the air-water interface in the presence of the subphase of PBA nanoparticles has been studied by the compression isotherms and Brewster angle microscopy (BAM) images. Atomic force microscopy (AFM) of the transferred films on mica substrates shows that patterns of the nanoparticles are observed for a 10(-4) M concentration of the subphase, based on the nanoparticle precursors, at surface pressures between 1 and 6 mN/m and transfer velocities from 10 to 80 mm/min. Vertical, horizontal, or tilted fringes of the nanoparticles with respect to the transfer direction can be obtained depending on the transfer velocity and surface pressure.

Designing new objects in the perspective of creating useful functionalities at the nanoscale has been the subject of intense research efforts during the last 20 years. Coordination nanoparticles (CNPs) emerged less than 10 years ago, opening new possibilities for the design of bistable molecule-based objects where magnetism may be controlled or tuned by an external perturbation (light irradiation, temperature change, magnetic field, etc.). Magnetic cyanide-bridged networks have been shown to possess the potential to be shaped as nanoparticles, leading to new functionalities. Light- and temperature-induced bistable nanoparticles were thus discovered. Luminescent CNPs were also prepared, demonstrating the large potential of these objects.

Negatively charged 4 nm bimetallic Ni II –Fe III cyanide-bridged nanoparticles were obtained and isolated by different coating agents. The magnetic properties of the particles were studied in the powder form and in diluted samples. A spin-glass like behaviour occurs in the concentrated sample, while the magnetic behaviour of the diluted ones strongly depends on the method used to isolate the nanoparticles. Only high dilution in a polymer matrix leads to a single-domain superparamagnetic behaviour, with a blocking temperature of 3.5 K.

Magnetic Langmuir−Blodgett (LB) films of bimetallic coordination nanoparticles of the Prussian blue analogue Cs0.4Ni[Cr(CN)6]0.9 were prepared by using the adsorption properties of a monolayer of dioctadecyldimethylammonium bromide (DODA). The molecular organization of the DODA monolayer is strongly affected by the presence of the water-dispersable Cs0.4Ni[Cr(CN)6]0.9 nanoparticles in the subphase as has been shown by π−A isotherms and Brewster angle microscopy (BAM) images at the air−water interface. BAM images suggest that a layer of inorganic nanoparticles is adsorbed under the monolayer of DODA, for high surface pressure and medium concentration of nanoparticles in the subphase and for all surface pressures at high concentrations of nanoparticles. Transfer of the monolayer onto different substrates allowed the preparation of multilayers containing Cs0.4Ni[Cr(CN)6]0.9 nanoparticles. Magnetic properties of these LB films show a spin-glass-like behavior that can be explained by the strong magnetic dipola...

The spontaneous stabilization of 6.5 nm bimetallic Ni–Cr cyanide bridged nanoparticles was achieved in water. Dispersible particles were recovered from solution using two different coating agents. The magnetic studies of the particles in the powder form show either a superparamagnetic or a spin glass like behaviour depending on the isolation technique used.

Le present travail complete et etend nos travaux precedents portant sur la determination des couplages d'echange magnetique intramoleculaires de series de biradicaux, [ 1 , 2 ] et partant de cette connaissance, de l'analyse des correlations magnetostructurales dans l'etat cristallin. Nous presentons ici l'etude de series de triradicaux comprenant des radicaux α-nitronyl nitroxydes (NN) ou α-imino nitroxydes (IN) substitues en meta d'un groupement phenylene d'une part, et en para d'un groupement phenylene ethynylene d'autre part. Des derives tetraradicalaires ont aussi ete synthetises et etudies. Les interactions d'echange magnetique a travers les liaisons sont estimees d'apres l'etude de ces molecules isolees par RPE en solution ainsi que par des calculs effectues dans l'approximation de la fonctionnelle densite (DFT). Alors que l'ensemble des derives triradicalaires presente un etat fondamental magnetique quartet de spin, un etat singulet est propose pour les tetraradicaux. Ce dernier resultat confirme nos travaux precedents [ 1 ] ayant conclu a un etat fondamental singulet pour des biradicaux bases sur le meme coupleur. De plus, le couplage d'echange magnetique au travers du coupleur phenylene ethynylene pour des biradicaux substitues dans une topologie ortho-meta est ferromagnetique, confirmant ainsi les hypotheses anterieures. [ 1 ] Suivant une methodologie precedemment decrite,121 les proprietes magnetiques des triradicaux a l'etat cristallin ont pu etre analysees dans le detail et permettent de proposer des chemins d'interaction magnetique et des geometries de contacts intermoleculaires precises pour l'etablissement d'interactions magnetiques bien identifiees.

An extensive investigation of the magnetic properties of three series of biradicals (bis-nitronyl nitroxides diNN-R, bis-imino nitroxides diIN-R and mixed INNN-R, where R is either hydrogen, a triple bond or trimethylsilylacetylenic group) has been carried out to give clear values of the intramolecular interactions through the m-phenylene coupling unit with alpha-nitronyl nitroxides (NN) or alpha-imino nitroxides (IN). An EPR study of the molecules in the isolated state is validated by ab initio calculations, which show the respective influence of spin polarisation and molecular conformation on the singlet-triplet gaps. All these results indicate that the triplet state is the ground state for such biradicals, except when the imidazolyl cycles are orthogonal to the phenyl ring. The magnetic properties of the biradicals in the solid state can be rationalised by examination of the short contacts produced between the ONCNO and ONCN groups. EPR studies on single crystals of the H-substituted series have confirmed the presence of a structural distortion for diNN-H whereas diIN-H and INNN-H do not exhibit such a peculiarity. The magnetic behaviour of diIN-H is described well by a four-spins model, with a strong intermolecular antiferromagnetic interaction of -90 K, whereas in the case of the two other compounds, a supplementary contact involves more complex interactions between the dimers. The compound diNN-tmsa exhibits a ferromagnetic intermolecular interaction of +11 K within the dimers, and this could be attributed to the relative disposition of the imidazolyl rings. Compound diNN-tr reveals a chain-like behaviour, whereas diIN-tr shows a predominant antiferromagnetic interaction within the dimers. The values for the intramolecular interactions in the solid state are in good agreement with those found for the isolated molecules.

The magnetic properties of a series of stable diradicals based on imino nitroxide (IN) and nitronyl nitroxide (NN) are investigated. Both radical fragments are coupled through various diamagnetic conjugated organic spacers made of aromatic rings ( 4 ) alternating with either a triple ( 1 x , 3 ) or a double bond ( 2 x ), where x indicates the length of the molecules with respect to the repeating unit. The optimised geometry and the corresponding electronic structure of the whole series ( x =0,…,10) have been determined by means of semiempirical calculations based on the NDDO approximation within the AM1 parametrisation scheme. The singlet–triplet splitting has then been studied using configuration interaction within different active spaces. It turns out that the most important parameters are: (a) of geometrical nature (e.g. twist angles between the radical moieties and the planar conjugated spacer); and (b) of topological nature (e.g. the radical substitution at ortho , meta , and para positions of phenyl cycles). The results of the calculations enable us to predict some rules in relation to the experimental observations: (a) for a given value of x , the hierarchy of the exchange coupling within series of derivatives is such as J (R 1 =R 2 =NN)> J (R 1 =IN, R 2 =NN)> J (R 1 =R 2 =IN); (b) whatever the nature of the radical substituent, the singlet is the ground state and the exchange coupling decreases nearly exponentially with the length of the spacer, i.e. as x increases. The exchange coupling is still efficient up to x =8 for R 1 =R 2 =IN (experimentally it has been previously found efficient up to x =5 in the para position).

The synthesis, solution studies, X-ray structures and magnetic properties of two new radical derived pyrazole ligands, based on α-nitronyl and imino nitroxides are reported. The spin distribution on the radicals has been studied in solution using EPR spectroscopy on dilute solutions. In concentrated solutions the radicals form aggregates in solution in which the magnetic interactions have been studied using low-temperature EPR spectroscopy.

The high yield synthesis of an isophthalic acid derivative bearing a nitronyl-nitroxide moiety at the 5-position was achieved. The structural analysis in the crystalline phase by X-ray diffraction on single crystals revealed the formation of a 3-D network through strong H-bonds between the acid groups and the nitronyl-nitroxide moieties. The spin label obtained was also analysed by EPR spectroscopy which showed a five line pattern with aN=7.51 G and a g-factor of 2.0066. Magnetic measurements revealed that at low temperature, the systeme showed a Curie-Weiss like behaviour with weak ferromagnetic intermolecular interactions.

2-(4-Carboxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-yloxyl ( p-IMBAH), 2-(3-carboxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-yloxyl (m-IMBAH) and 2-(2-carboxyphenyl)-4,4,5,5-tetramethyl-4,5-dihydro-3-oxido-1H-imidazol-3-ium-1-yloxyl (o-NITBAH) have been prepared. The m-IMBAH and p-IMBAH radicals crystallised in monoclinic space group P2 1 /n while the o-NITBAH radical occupied the monoclinic space group Cc. In p-IMBAH, a 12-membered ring is formed via strong hydrogen bonds between two water molecules and two radicals, this unit being propagated along the b axis via additional hydrogen bonds. In m-IMBAH, the radicals are arranged in dimers held together by strong hydrogen bonds between the acid and the imine functions, each dimer being connected with its neighbours via hydrogen bonds forming alternating chains along the c axis. No cyclic arrangements are evident in o-NITBAH, the radicals being organized into infinite chains. In each case, the product of paramagnetic susceptibility with T lies in the 0.362 to 0.374 emu K mol –1 range at room temperature while the reciprocal susceptibility follows a Curie-Weiss law above 20 K with θ=+1.38, +5.24 and –0.81 K, respectively, for p-IMBAH, m-IMBAH and o-NITBAH. The isotropic 14 N hyperfine coupling constants are found from solution experiments to be 9.20 (a N1 ) and 4.28 (a N2 ) G for the imino radicals and 7.59 G for the nitronyl nitroxide radical. The principal values of the g-tensor measured on single crystals afforded an average of 2.0066/7 while in solution g iso =2.0060 for p/m-IMBAH and 2.0065 for o-NITBAH.

The reaction of Cr(Bztacn)(CN)3 (Bztacn is 1,4,7-trisbenzyl-1,4,7-triazacyclononane) with Ni(iPrtacn)Cl2 (iPrtacn is 1,4,7-trisisopropyl-1,4,7-triazacyclononane) affords a CrNi3 tetranuclear complex. Variable temperature and magnetization versus field measurements show a S = 9/2 ground state and an appreciable magnetic anisotropy with a negative D(9/2) value equal to -0.54 cm(-1). Magnetization studies on one single crystal using a micro-SQUID show a fast tunneling process at zero field at very low temperature.

International audience; Nanorods of the photomagnetic coordination network Mo(CN)8Cu2 coated with polyvinylpyrrolidone were prepared and exhibit an enhanced effect upon irradiation when compared to the bulk...

International audience; Based on nickel hexacyanidochromate and cobalt hexacyanidoferrate Prussian blue analogues, two series of photomagnetic/ferromagnetic sub-50 nm core multishell coordination nanoparticles have been synthesized in a surfactant-free one-pot multistep procedure with good control over the dispersity (10% standard deviation) and good agreement with the targeted size at each step. The composition and the valence state of each shell have been probed by different techniques that have revealed the predominance of Co(II)-NC-Fe(III) pairs in a series synthesized without alkali while Co(III)-NC-Fe(II) photoswitchable pairs have been successfully obtained in the photoactive coordination nanoparticles by control of Cs(+) insertion. When compared, the photoinduced behavior of the latter compound is in good agreement with that of the model one. Exchange coupling favors a uniform reversal of the magnetization of the heterostructured nanoparticles, with a large magnetization brought by a soft ferromagnetic shell and a large coercivity due to a harder photomagnetic shell. Moreover, a persistent increase of the photoinduced magnetization is observed for the first time up to the ordering temperature (60 K) of the ferromagnetic component because of a unique synergy.

We present results from the first year of a campaign to characterize and monitor the optical turbulence profile at the SAAO Sutherland observing station in South Africa. A MASS-DIMM (MultiAperture Scintillation Sensor - Differential Image Motion Monitor) was commissioned in March 2010 to provide continuous monitoring of the seeing conditions. Over the first month of the campaign, a SLODAR (SLOpe Detection And Ranging) from Durham University was also installed allowing an independent verification of the performance of the MASS-DIMM device. After the first year of data collection, the overall median seeing value is found to be 1.32" as measured at ground level. The ground layer which includes all layers below 1 km accounts for 84% of the turbulence, while the free atmosphere above 1 km accounts for 16% with a median value of 0.41". The median isoplanatic angle value is 1.92", which is similar to other major astronomical sites. The median coherence time, calculated from corrected MASS measurements, is 2.85 ms. The seeing conditions at the site do show a strong correlation with wind direction with bad seeing conditions being associated with winds from the South-East., 15 pages, 10 figures, 6 tables

The local symmetry and local magnetic properties of 6 nm-sized, bi- metallic, cyanide-bridged CsNiCr(CN)6 coordination nanoparticles 1 and 8 nm- sized, trimetallic, CsNiCr(CN)6@CsCoCr(CN)6 core- shell nanoparticles 2 were studied by X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD). The measurements were per- formed at the Ni II ,C o II , and Cr III L2,3 edges. This study revealed the presence of distorted Ni II sites located on the particle surface of 1 that account for the uniaxial magnetic anisotropy ob- served by SQUID measurements. For the core-shell particles, a combination of the exchange anisotropy between the core and the shell and the pro- nounced anisotropy of the Co II ions is the origin of the large increase in coer- cive field from 120 to 890 Oe on going from 1 to 2. In addition, XMCD allows the relative orientation of the magnetic moments throughout the core-shell particles to be determined. While for the bimetallic particles of 1, alignment of the magnetic moments of Cr III ions with those of Ni II ions leads to uniform magnetization, in the core-shell parti- cles 2 the magnetic moments of the iso- tropic Cr III follow those of Co II ions in the shell and those of Ni II ions in the core, and this leads to nonuniform magnetization in the whole nanoobject, mainly due to the large difference in local anisotropy between the Co II ions belonging to the surface and the Ni II ions in the core.

The Southern African Large Telescope (SALT), located at the South African Astronomical Observatory (SAAO) site near Sutherland, South Africa, is an 11-metre fixed-elevation telescope currently operating at UV-visible wavelengths (320-950 nm) with a near-infrared extension (850-1700 nm) due in the near future. SALT does not currently have an adaptive optics (AO) system and a feasibility study for adding one is under way. Using results from an on-going site monitoring campaign at the SAAO we have begun carrying out simulations to investigate how different AO systems might perform and could be optimized for SALT. We will present the parameters of an optimization study and performance results for a single on-axis natural guide star (NGS) AO system on SALT for operation at both visible (R) and near-IR (J and H) wavelengths.

Core–shell magnetic coordination nanoparticles made of a soft core and a hard magnetic shell, containing anisotropic Co(II) ions, display a dramatic increase in their average blocking temperature with a coercive field value 25 times larger than that of the soft core, due to a large enhancement of the magnetic anisotropy.

International audience; Through an extensive set of SQUID magnetic measurements, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism, we have determined the nature of the metastable photomagnetic phase in the cyano-bridged 3D network Cs(2)Cu(7)[Mo(CN)(8)](4). The photomagnetic effect is induced by the photoconversion of Mo(IV) ions in low spin (LS) configuration (S = 0) into Mo(IV) ions in high spin (HS) configuration (S = 1). The magnetic and spectroscopic measurements fully support the LS to HS conversion, whereas the previously invoked charge transfer mechanism Mo(IV) + Cu(II) ⇒ Mo(V) + Cu(I) can be completely ruled out.

Negatively charged nanocrystals of the magnetic coordination network CsNiCr(CN)(6) were prepared in water through a seed-mediated growth with a few atomic layers accuracy and final sizes tailored from 6 to 30 nm. A lower limit of the magnetic single-domain critical size was determined to be around 15 nm possessing a blocking temperature above 20 K.

International audience; Anisotropic coordination nanoparticles of the photomagnetic network Cs(I)(2)Cu(II)(7)[Mo(IV)(CN)(8)](4) are obtained through a surfactant-free high-yield synthetic procedure in water. These particles are organised as Langmuir-Blodgett films with a preferential orientation of the nano-objects within the film that exhibit a magnetic bistability below 20 K with a very large coercivity due to an efficient photo-transformation.

International audience; The oriented grafting of the Mn12-carboxylate molecular nanomagnets has been achieved on semi-conducting flat Si(100) functionalized surfaces due to the bonding selectivity between axial and equatorial carboxylate groups present in the coordination sphere of the Mn12 complexes.