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Eugenio Coronado

Publications and source records attributed to Eugenio Coronado.

11 recordsLinked to original sources
PubMed2003

A molecular metal ferromagnet from the organic donor bis(ethylenedithio)tetraselenafulvalene and bimetallic oxalate complexes.

A new dual-function hybrid molecular material has been obtained from the organic donor bis(ethylenedithio)tetraselenafulvalene and the honeycomb oxalate-based bimetallic network [MnCr(ox)3]-. This multilayer material consists of layers of the inorganic anionic 2D network, responsible for the appearance of ferromagnetic ordering below 5.3 K, alternating with segregated layers of the organic cation radical responsible for the transport properties: metal-like conductivity is observed from room temperature down to 150 K.

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PubMed2003

Microscopic approach to the pseudo-spin-1/2 Hamiltonian for Kramers doublets in exchange coupled Co(II) pairs.

The microscopic theory of the magnetically anisotropic effective pseudo-spin-(1)/(2) Hamiltonian for a pair of Co(2+) ions is reported. In the framework of the second-order perturbation approach, the analytical expressions are found for the components of the tensor of the exchange interaction, g-tensor, and the factor in the temperature independent paramagnetic contribution. The parameters of the Hamiltonian are expressed in terms of the basic intra- and intercenter parameters of the pair, namely, the spin-orbit coupling constant, orbital reduction factor, exchange integral, and low symmetry crystal field parameters including axial and rhombic terms.

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PubMed2002

Electron delocalization in mixed-valence Keggin polyoxometalates. Ab initio calculation of the local effective transfer integrals and its consequences on the spin coupling.

We present a quantitative evaluation of the influence of the electron transfer on the magnetic properties of mixed-valence polyoxometalates reduced by two electrons. For that purpose, we extract from valence-spectroscopy ab initio calculations on embedded fragments the value of the transfer integrals between W nearest-neighbor atoms in a mixed-valence alphaPW(12)O(40) polyoxowolframate Keggin anion. In contradiction with what is usually assumed, we show that the electron transfer between edge-sharing and corner-sharing WO(6) octahedra have very close values. Considering fragments of various ranges, we analyze the accuracy of calculations on fragments based on only two WO(5) pyramids which should allow a low cost general study of transfer parameters in polyoxometalates. Finally, these parameters are introduced in an extended Hubbard Hamiltonian that models the whole anion. It permits to prove that electron transfers induce a large energy gap between the singlet ground state and the lowest triplet states providing a clear explanation of the diamagnetic properties of the mixed-valence Keggin ions reduced by two electrons.

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PubMed2002

Magnetism in polyoxometalates: anisotropic exchange interactions in the Co3II moiety of [Co3W(D2O)2(ZnW9O34)2](12-)--A magnetic and inelastic neutron scattering study.

The ground-state properties of a Co3II moiety encapsulated in a polyoxometalate anion were investigated by combining measurements of specific heat, magnetic susceptibility, and low-temperature magnetization with a detailed inelastic neutron scattering (INS) study on a fully deuterated polycrystalline sample of Na12[Co3W(D2O)2(ZnW9O34)2].40D2O (Co3). The ferromagnetic Co3O14 cluster core consists of three octahedrally oxo-coordinated CoII ions. According to the single-ion anisotropy and spin-orbit coupling of the octahedral CoII ions, the appropriate exchange Hamiltonian to describe the ground-state properties of the Co3 spin cluster is anisotropic and is expressed as H = -2 sigma a = x,y,z (Ja12 S1a S2a + Ja23 S2a S3a), where Ja are the components of the exchange interactions between the CoII ions. To reproduce the INS data, different orientations of the two anisotropic J tensors must be considered, and the following conditions had to be introduced: Jx12 = Jy23, Jy12 = Jx23, Jz12 = Jz23. This result was correlated with the molecular symmetry of the complex. The following set of parameters was obtained: Jx12 = Jy23 = 1.37, Jy12 = Jx23 = 0.218, and Jz12 = Jz23 = 1.24 meV. This set also reproduces in a satisfactory manner the specific heat, susceptibility, and magnetization properties of Co3.

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PubMed2002

Ferromagnetism and chirality in two-dimensional cyanide-bridged bimetallic compounds.

The combination of hexacyanoferrate(III) anions, [Fe(CN)(6)](3)(-), with nickel(II) complexes derived from the chiral ligand trans-cyclohexane-1,2-diamine (trans-chxn) affords the enantiopure layered compounds [Ni(trans-(1S,2S)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (1) and [Ni(trans-(1R,2R)-chxn)(2)](3)[Fe(CN)(6)](2).2H(2)O (2). These chiral systems behave as ferromagnets (T(c) = 13.8 K) with a relatively high coercive field (H(c) = 0.17 T) at 2 K. They also exhibit an unusual magnetic behavior at low temperatures that has been attributed to the dynamics of the magnetic domains in the ordered phase.

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PubMed1998

Charge Transfer Salts Based on Polyoxometalates and Seleno-Substituted Organic Donors. Synthesis, Structure, and Magnetic Properties of (BEST)(3)H[PMo(12)O(40)].CH(3)CN.CH(2)Cl(2) (BEST = Bis(ethylenediseleno)tetrathiafulvalene).

Electrochemical oxidation of the tetrathiafulvalene (TTF) type organic donor bis(ethylenediseleno)tetrathiafulvalene (BEST) in the presence of the Keggin polyoxometalate [PMo(12)O(40)](3)(-) affords the radical salt formulated as (BEST)(3)H[PMo(12)O(40)] (crystal data: triclinic, space group P&onemacr; with a = 13.056(1) Å, b = 13.957(1) Å, c = 22.302(3) Å, alpha = 97.019(9) degrees, beta = 94.17(1) degrees, gamma = 95.847(9) degrees, and Z = 2). This is the first salt of a selenium-containing donor with a polyoxometalate cluster. The structure of this organic/inorganic hybrid consists of layers of the organic donors that alternate with polyoxometalate layers in the c direction. The organic molecules, which are completely ionized, form two types of layers with unprecedented packing arrangements and many intra- and interlayer side-on short contacts which give rise to a marked 3D electronic character. The magnetic susceptibility measurements indicate that the BEST(+) radicals are strongly antiferromagnetically coupled and that the polyanion has been reduced by one electron to give the mixed-valence anion [PMo(12)O(40)](4)(-). The ESR spectra show the progressive localization of the additional electron which becomes fully trapped on one of the Mo sites of the Keggin unit at low temperatures (T < 7 K).

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