Laure Catala

Spin-crossover coordination nanoparticles.

Spin-crossover coordination nanoparticles of the cyanide-bridged three-dimensional network Fe(pyrazine){Pt(CN) 4} were prepared at three different sizes using a microemulsion. The 14 nm particles present a transition centered around 265 K with a hysteresis of 6 K.

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.

Core–Multishell Magnetic Coordination Nanoparticles: Toward Multifunctionality on the Nanoscale

Three-dimensional Prussian Blue analogues (PBAs) and related cyano-bridged coordination networks have been at the forefront of the field of molecular magnetism for more than a decade because of the extraordinary variety of their physical properties (electrochromism, ferromagnetism, photomagnetism, piezomagnetism, spin crossover), which opens up prospects for original functional materials. The large metal–metal distance ( 5 ) across the cyano bridge leads to relatively large porosity, which may play a role in hydrogen storage, ion selection, catalysis, and sensors. 14] One important issue is the effect of size reduction on the physical and chemical behavior of cyano-bridged coordination networks and their possible application as molecule-based components in devices. 16] A unique way to take advantage of the physical behavior of PBAs stemming from their rich electronic properties and porosity is to synthesize multishell nanoparticles such that a single particle consists of a core of a given network surrounded by shells of networks that may contain other functionalities. We report here the design of core–multishell nanocrystals thanks to the stabilization of surfactant-free particles in water. Epitaxial growth of different shells on various charged cores is demonstrated, and the thickness of the shells can be fine-tuned. The synergy between the different components is illustrated with one selected magnetic core–shell system. During the last few years, several groups have attempted to establish chemical routes that allow the stabilization of coordination (or metal–organic) nanoparticles of various face-centered-cubic PBAs of the general formula AxM [M’(CN)6](2+x)/3, where A is an alkali-metal cation and M II and M’ are transition-metal ions (see the Supporting Information). Generally, a chemical agent (organic or inorganic) is used during the synthetic process to control the growth of the particles, preclude their aggregation, and ensure their dispersion in different solvents. However, the presence of such protective agents weakens, in most cases, the surface reactivity of the particles and their electronic coupling with other objects, consequently decreasing their multifunctional potential. This can be avoided by the stabilization in solution of surfactant-free nanoparticles. We have recently shown that such electrostatic stabilization can be achieved in the case of the Cs[NiCr(CN)6] network leading to quasi-monodisperse particles with a size of 6.5 nm in diameter. The stabilization of surfactant-free nanoparticles makes it possible to perform coordination chemistry on the particles surface and opens the possibility of the epitaxial growth of one or several shells on the preexisting cores in solution. Thus, the key requirement for the preparation of pure core–shell nanoparticles is 1) stabilization in solution of well-defined crystalline surfactant-free charged nanoparticles and 2) prevention of the side nucleation of the shell by controlling the addition rate and the concentration of the components. Inorganic multishell particles have been prepared on oxides, sulfides, and metallic cores; some interesting examples of shape control have been reported by epitaxial growth seed-mediated procedures involving surfactants. 34] However, this is the first example of coremultishell particles based on coordination networks. The general procedure for the simple growth process on the charged cores present in solution is straightforward and thus feasible on a large scale: a dilute solution containing the divalent metal salt (M(H2O)6Cl2) and CsCl, and another containing the hexacyanometalate(III) salt are added dropwise (1 mL s ) to a stirred solution containing the core particles. The thickness of the growing shell is finely controlled by adjusting the amount of material added in solution (see the Supporting Information). As the growth process occurs, the solution is diluted in order to avoid aggregation that may occur because of the increase of the ionic force. To show the versatility and the efficiency of this approach, we report the preparation and the characterization of surfactant-free Cs[FeCr(CN)6] and Cs [CoCr(CN)6] nanoparticles as well as the design of core–(multi)shell particles of three different systems: 1) bicomponent particles made of a shell of CoII[CrIII(CN)6]2=3 on top of the Cs[FeCr(CN)6] core (denoted CsFeCr@CoCr), 2) tricomponent particles made of two different shells of Cs[FeCr(CN)6] and then Cs [NiCr(CN)6] grown on [*] Dr. L. Catala, Dr. D. Brinzei, Y. Prado, Prof. T. Mallah Institut de Chimie Mol culaire et des Mat riaux d’Orsay Universit Paris-Sud 11, 91405 Orsay (France) Fax: (+ 33)1-6915-4754 E-mail: laurecatala@icmo.u-psud.fr mallah@icmo.u-psud.fr

Photomagnetic nanorods of the Mo(CN)8Cu2 coordination network

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.

Spontaneous stabilization and isolation of dispersible bimetallic coordination nanoparticles of CsxNi[Cr(CN)6]y

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.

Synthesis of various crystalline gold nanostructures in water: The polyoxometalate β-[H4PMo12O40]3− as the reducing and stabilizing agent

This paper reports a facile, one-pot, room-temperature synthesis, in water, of various Au nanostructures using, as reducing agent, the mixed-valence polyoxometalate β-H3[H4P(MoV)4(MoVI)8O40]3−. By modifying the initial concentrations of the polyoxometalate and chloroauric acid, the morphology of the synthesized Au nanostructure can be tuned. The whole process is a “green-chemistry-type” synthesis of Au0 nanostructures.

Investigation of the photoinduced magnetization of copper octacyanomolybdates nanoparticles by X-ray magnetic circular dichroism

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.

Synergy in Photomagnetic/Ferromagnetic Sub-50 nm Core-Multishell Nanoparticles

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.

Patterning of Magnetic Bimetallic Coordination Nanoparticles of Prussian Blue Derivatives by the Langmuir−Blodgett Technique

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.

Magnetic anisotropy of two trinuclear and tetranuclear CrIIINiII cyanide-bridged complexes with spin ground states S = 4 and 5

The trinuclear and the tetranuclear complexes [[iPrtacnCr(CN)3]2[Ni(cyclam)]](NO3)2.5H2O 1 (cyclam = 1,4,8,11-tetraazacyclotetradecane, iPrtacn = 1,4,7-tris-isopropyl-1,4,7-triazacyclononane) and [[iPrtacnCr(CN)3Ni(Me2bpy)2]2](ClO4)4.2CH3CN 2 (Me2bpy = 4,4-dimethyl-2,2-bipyridine) were synthesized by reacting (iPrtacn)Cr(CN)3 with [Ni(cyclam)](NO3)2 and [Ni(Me2bpy)2(H2O)2](ClO4)2, respectively. The crystallographic structure of the two compounds was solved. The molecular structure of complex 1 consists of a linear Cr-Ni-Cr arrangement with a central Ni(cyclam) unit surrounded by two Cr(iPrtacn)(CN)3 molecules through bridging cyanides. Each peripheral chromium complex has two pending CN ligands. Complex 2 has a square planar arrangement with the metal ions occupying the vertices of the square. Each Cr(iPrtacn)(CN)3 molecule has two bridging and one non-bridging cyanide ligands. The magnetic properties of the two complexes were investigated by susceptibility vs. temperature and magnetization vs. field studies. As expected from the orthogonality of the magnetic orbitals between Cr(III) (t2g3) and Ni(II) (e(g)2) metal ions, a ferromagnetic exchange interaction occurs leading to a spin ground states S = 4 and 5 for 1 and 2, respectively. The magnetization vs. field studies at T = 2, 3 and 4 K showed the presence of a magnetic anisotropy within the ground spin states leading to zero-field splitting parameters obtained by fitting the data D4 = 0.36 cm(-1) and D5 = 0.19 cm(-1) (the indices 4 and 5 refer to the ground states of complexes 1 and 2, respectively). In order to quantify precisely the magnitude of the axial (D) and the rhombic (E) anisotropy parameters, High-field high frequency electron paramagnetic resonance (HF-HFEPR) experiments were carried out. The best simulation of the experimental spectra (at 190 and 285 GHz) gave the following parameters for 1: D4 = 0.312 cm(-1), E4/D4 = 0.01, g4x = 2.003, g4y = 2.017 and g4z = 2.015. For complex 2 two sets of parameters could be extracted from the EPR spectra because a doubling of the resonances were observed and assigned to the presence of complexes with slightly different structures at low temperature: D5 = 0.154 (0.13) cm(-1), E5/D5 = 0.31 (0.31) cm(-1), g4x = 2.04 (2.05), g4y = 2.05 (2.05) and g4z = 2.03 (2.02). The knowledge of the magnetic anisotropy parameters of the mononuclear Cr(iPrtacn)(CN)3, Ni(cyclam)(NCS)2 and Ni(bpy)2(NCS)2 complexes by combining HF-HFEPR studies and calculation using a software based on the angular overlap model (AOM) allowed to determine the orientation of the local D tensors of the metal ions forming the polynuclear complexes. We, subsequently, show that the anisotropy parameters of the polynuclear complexes computed from the projection of the local tensors are in excellent agreement with the experimental ones extracted from the EPR experiments.