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D Ruiz-Molina

Publications and source records attributed to D Ruiz-Molina.

5 recordsLinked to original sources
PubMed2005

Long-range ferromagnetism of Mn12 acetate single-molecule magnets under a transverse magnetic field.

We use neutron diffraction to probe the magnetization components of a crystal of Mn12 single-molecule magnets. Each of these molecules behaves, at low temperatures, as a nanomagnet with spin S = 10 and strong anisotropy along the crystallographic c axis. The application of a magnetic field H(perpendicular) perpendicular to c induces quantum tunneling between opposite spin orientations, enabling the spins to attain thermal equilibrium. For T approximately < 0.9(1) K, this equilibrium state shows spontaneous magnetization, indicating the onset of ferromagnetism. These long-range magnetic correlations nearly disappear for mu0H(perpendicular) approximately > 5.5 T, possibly suggesting the existence of a quantum critical point.

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PubMed2004

Synthesis, structural and magnetic properties of a series of copper(II) complexes containing a monocarboxylated perchlorotriphenylmethyl radical as a coordinating open-shell ligand.

A series of complexes of copper(II)-containing a perchlorotriphenylmethyl radical functionalized with a carboxylic group as a new ligand is reported. The compounds [Cu(PTMMC)(2)(L)(3)](PTMMC = (tetradecachloro-4-carboxytriphenyl)methyl radical; L =(1) H(2)O, (2) pyrimidine and ethanol or (3) pyridine), [Cu(2)(PTMMC)(2)(MeCOO)(2)(H(2)O)(2)](4) and [Cu(HPTMMC)(2)(L)(3)](HPTMMC =alpha-H-(tetradecachlorotriphenyl)methane-4-carboxylic acid; L = pyridine)(5) were structurally characterized. In complexes 1, 2, 3, and 5, the copper(II) ion is coordinated to two PTMMC (or HPTMMC) units in a slightly distorted square planar surrounding, while 4 shows a paddle-wheel copper(II) dimer structure, where each Cu metal ion has four O atoms of different carboxylate groups, two of them belonging to two PTMMC radicals. The copper(II)-radical exchange couplings are antiferromagnetic for complexes 1, 2 and 3. A linear three-spin model was applied to complexes 1, 2 and 3 to give J/k(B)=-24.9, -15.0 and -20.7 K, respectively. Magnetic properties of 4 show that it is one of the scarce examples of a spin-frustrated system composed of organic radicals and metal ions. In this case, experimental data were fitted to a magnetic model based on a symmetrical butterfly arrangement to give a copper(II)-copper(II) exchange coupling of J/k(B)=-350.0 K and a copper(II)-radical exchange coupling of J/k(B)=-21.3 K, similar to that observed for the copper(II)-radical interactions in complexes, and.

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PubMed2001

Influence of topology on the long-range electron-transfer phenomenon.

Intramolecular electron-transfer phenomena in the radical anions derived from the partial reduction of diradicals (E,E)-p-divinylbenzene-beta,beta'-ylene bis(4-tetradecachlorotriphenylmethyl) diradical (1) and (E,E)-m-divinylbenzene-beta,beta'-ylene bis(4-tetradecachlorotriphenylmethyl) diradical (2) have been studied by optical and ESR spectroscopy. The synthetic methodology used allows for complete control of the geometry of diradicals 1 and 2, which have para and meta topologies, respectively, as well as of their E/Z isomerism. This fact is used to show the influence of the different topologies on the ease of electron transfer, which is larger for the para than for the meta isomer, in which a small or negligible electronic coupling is observed. A related monoradical compound (E)-bis(pentachlorophenyl)[4-(4-bromophenyl-beta-styryl)-2,3,5,6-tetrachlorophenyl]-methyl radical (3), which has only one such redox site, has also been obtained and studied for comparison purposes.

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PubMed2000

Spin Frustration in a Dimeric Mn(II) Complex with a Metallocene-Substituted alpha-Nitronyl Nitroxide Radical This work was supported by grants from DGES (project PB96-0802-C02-01), CIRIT (project SGR 96-00106), Fonds zur Förderung der Wissenschaftlichen Forschung, Vienna (Project P 13128), Austrian Federal Ministry of Science (BMWV), Acción Integrada Hispano-Austríaca (HU-1999-0015), and the 3MD Network of the TMR program of the E.U. (contract ERBFMRX CT980181). C.S. thanks the Austrian Federal Ministry of Science for the award of a research scholarship. D.R.-M. thanks the Generalitat de Catalunya for a postdoctoral grant. The authors acknowledge the suggestions given by one of the referees.

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