Nathalie Daro

Nanoparticles of iron(II) spin-crossover

We report the synthesis of spin crossover 69 nm spherical nanoparticles of [Fe(NH2-trz)3](Br)2.3H2O.0.03(surfactant) (NH2trz = 4-amino-1,2,4-triazole, surfactant = Lauropal), prepared by the reverse micelle technique, which exhibit at room temperature a thermal hysteresis characterized by magnetic, diffuse reflectivity and Raman studies.

Nanoparticles of [Fe(NH2-trz)3]Br2.3H2O (NH2-trz=2-amino-1,2,4-triazole) prepared by the reverse micelle technique: influence of particle and coherent domain sizes on spin-crossover properties.

This paper describes the synthesis of iron(II) spin-crossover nanoparticles prepared by the reverse micelle technique by using the non-ionic surfactant Lauropal (Ifralan D0205) from the polyoxyethylenic family. By changing the surfactant/water ratio, the size of the particles of [Fe(NH2-trz)3]Br2.3H2O (with NH2trz=4-amino-1,2,4-triazole) can be controlled. On the macroscopic scale this complex exhibits cooperative thermal spin crossovers at 305 and 320 K. We find that when the size is reduced down to 50 nm, the spin transition becomes gradual and no hysteresis can be detected. For our data it seems that the critical size, for which the existence of a thermal hysteresis can be detected, is around 50 nm. Interestingly, the change of the particle size induces almost no change in the temperature of the thermal spin transition. A systematic determination of coherent domain size carried out on the nanoparticles by powder X-ray diffraction indicates that at approximately 30 nm individual particles consist of one coherent domain.

Synthesis, X-ray crystal structures and magnetic properties of Cu(II)(NITpPy)2[N(CN)2]2·solv (NITpPy=nitronyl nitroxide radical, solv=H2O or CH3CN). From discrete molecules to 2-D polymeric coordination compounds

Abstract The synthesis, X-ray crystal structures and magnetic properties of five new copper(II) complexes containing nitroxide radicals Cu(NITpPy)2(NO3)2 (1), Cu(NITpPy)2(CH3COO)2 (2), Cu(NITpPy)2[N(CN)2]2·(H2O)2 (3), Cu(NITpPy)2[N(CN)2]2·3CH3CN (4) and Cu(NITpPy)2[N(CN)2]2·2CH3CN (5) are reported. Compounds 1–3 consists of discrete molecules in the solid state, but in compounds 4 and 5 the Cu(NITpPy)22+ units are connected through N(CN)2− bridging ligands in μ2 coordination developing, respectively, into one-dimensional and two-dimensional polymeric networks. For all compounds, the magnetic properties have been investigated and antiferromagnetic interactions dominate at low temperature.

Ferromagnetic interactions in Mn(II) coordination complex containing nitronyl nitroxide radical and silver–dicyanide anion: structure and magnetic studies of MnII(NITpPy)2[Ag(CN)2]2

Abstract A new complex of formula, Mn(NITpPy)2[Ag(CN)2]2, where NITpPy stands for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, was synthesized and characterized structurally and magnetically. The Mn atom is in a distorted octahedral geometry. It is coordinated to two organic radicals and [Ag(CN)2]− anions. Each [Ag(CN)2]− unit is μ2 bridging between two adjacent Mn ions yielding infinite 1D chains. Intramolecular ferromagnetic interactions are observed but antiferromagnetic interactions dominate at very low temperature.

Mechanism for optical switching of the spin crossover [Fe(NH2-trz)3](Br)2·3H2O compound at room temperature

This paper reports on phase transition photo-induced by a nanosecond laser pulse in the molecular spin crossover material [Fe(NH(2)-trz)(3)] (Br)(2).3H(2)O (with NH(2)trz = 4-amino-1,2,4-triazole) around room temperature and in the close vicinity of the thermal hysteresis loop. The measurements are carried out using a time-resolved pump-probe experiment and by recording the reflectivity change at various temperatures and laser intensities. The dynamics of the optically induced reflectivity changes are presented and discussed. We propose a simple model that describes well the recorded phenomena. It takes into account the physical and optical properties of the sample that directly impact the amplitude and the dynamics of the laser-induced heating of the compound.

Synthesis, X-ray crystal structures and magnetic properties of CuII and MnII complexes containing imino nitroxide radicals and a dicyanamide anion

Two new complexes having the formula cis-Cu(imi-pPy)2[N(CN)2]2 (1) and Mn(imi-pPy)2[N(CN)2]2(H2O)2 (2), where imi-pPy stands for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl, were synthesized and structurally and magnetically characterized. The two compounds 1 and 2 crystallize in the space groups C2/c (no. 15) and P (no. 2), respectively. The metal atoms are in a distorted octahedral geometry. 1 presents a 1D infinite chain structure and 2 has a finite structure. Antiferromagnetic interactions are observed in the Cu containing salt while ferromagnetic interactions are observed in the Mn compound but antiferromagnetic interactions dominate at very low temperature.

A New Photomagnetic Molecular System Based on Photoinduced Self‐Assembly of Radicals

An irreversible trans→cis isomerization of the imino group occurs during the irradiation of the new ferrocenyl Schiff-base polychlorotriphenylmethyl radical 1 by light. Low-temperature ESR investigations of frozen solutions revealed that the cis isomer exists as the (cis-1)2 dimer with strong antiferromagnetic interactions. The radical 1 constitutes an example of a one-way photoswitchable magnetic system in which a conversion between a doublet and a singlet ground-state species is promoted by a photoinduced self-assembly process driven by the formation of hydrogen bonds.

H2O as a chemical link for ferromagnetic interactions between aminoxyl units

A bis(radical) derivative based on a triphenylphosphane core substituted by two nitronyl nitroxide units is reported. This compound was isolated in two forms. One consists of an H2O adduct where H2O is hydrogen-bonded to the radical units, whereas the second lacks this bridging unit. Magnetic studies revealed that the presence of the H2O bridge induces ferromagnetic exchange interaction between the spin carriers. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

One-dimensional tunable photonic crystals with spin crossover material for the terahertz range

The authors use a spin crossover material as a defect inserted into a periodic structure of alternating layers of glass and air. A single defect mode of this Bragg filter designed for the submillimeter wavelength can be tuned over 15GHz by inducing the spin transition of the defect. This shows potential applications of spin crossover materials at terahertz frequencies.

Dielectric characterization of [Fe(NH2−trz)3]Br2•H2O thermal spin crossover compound by terahertz time domain spectroscopy

The complex optical index refraction of an iron (II) spin-crossover coordination polymer is measured in the Terahertz frequency range by Terahertz time-domain spectroscopy (THz-TDS). By scanning the temperature from 288 to 333 K, we have recorded the evolution of the THz spectrum within the low spin - high spin thermal hysteresis loop. We were able to simultaneously infer the refractive index and absorption variations. The low spin-high spin transition has a marked spectral signature in the millimeter wavelength. In the 0.1–0.6 THz frequency range, the variation of real and imaginary part of the index of refraction is 6% and 20%, respectively. A marked absorption is observed above 500 GHz. The THz-TDS provides a clear direct fingerprint of this class of materials, which are interestingly potential candidates for optical data storage and processing devices.