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Daniel Ruiz-Molina

Publications and source records attributed to Daniel Ruiz-Molina.

At least 19 recordsLinked to original sources
PubMed2006

A new hexaferrocene complex with a [M3(mu3-O)]7+ core.

The new hexaferrocene complex 1 has been synthesized and characterized by X-ray diffraction. Its magnetization data were fitted to a detailed theoretical model that considers nonequivalent exchange parameters between Fe ions to yield the magnetic exchange coupling values of J1/kB = -31.5 K and J2/kB = -25.8 K. Moreover, the cyclic voltammogram of complex 1 confirmed its redox activity associated with the presence of ferrocene units, with very small or negligible electronic interactions between them.

Journal Article↗
PubMed2006

Three-dimensional six-connecting organic building blocks based on polychlorotriphenylmethyl units--synthesis, self-assembly, and magnetic properties.

The synthesis of a three-dimensional, six-connecting, organic building block based on a robust, rigid, and open-shell polychlorotriphenylmethyl (PTM) unit (radical 1) is reported, and its self-assembly properties are described in detail. The tendencies of this highly polar molecule and its hydrogenated precursor, compound 4, to form hydrogen bonds with oxygenated solvents ([1THF(6)] and [4THF(6)]) were reduced by replacing THF with diethyl ether in the crystallization process to yield two-dimensional (2D) hydrogen-bonded structures ([1(Et(2)O)(3)] and [4(Et(2)O)(3)]). The presence of direct hydrogen bonds between the radicals in the latter phase of 1 gives rise to very weak ferromagnetic intermolecular interactions at low temperatures, whereas when the radicals are isolated by THF molecules these interactions are antiferromagnetic and very weak. The role played by the carboxylic groups not only in the self-assembly properties but also in the transmission of the magnetic interactions has been illustrated by determination of the crystal structure and measurement of the magnetic properties of the corresponding hexaester radical 6, in which the close packing of molecular units gives rise to weak antiferromagnetic intermolecular interactions. Attempts to avoid solvation of the molecules in the solid state and to increase the structural and magnetic dimensionality were pursued by recrystallization of both compounds 1 and 4 from concentrated nitric acid, affording two three-dimensional (3D) robust hydrogen-bonded structures. While the structure obtained with compound 4 is characterized by the presence of polar channels and boxes containing water guest molecules along the c axis, radical 1 was oxidized to the corresponding fuchsone 10, which presented a completely different close-packed, guest-free structure.

Journal Article↗
PubMed2006

Ordered patterning of nanometric rings of single molecule magnets on polymers by lithographic control of demixing.

We report a new patterning process which takes place as a result of demixing of a binary polymer/solute mixture. An efficient, sustainable approach for ordering nanosized rings of so-called single molecule magnets (SMMs) is thus provided. It exploits the self-organization process in which SMM patterned film evolves to a spatially correlated pattern of nanosized rings. At long time, the anisotropic patterning of the film drives the ring to coalesce, into parallel lines of nanometric width.

Letter↗
PubMed2006

Influence of bridge topology and torsion on the intramolecular electron transfer.

To study molecules able to act as good "molecular wires", intramolecular electron transfer between two triphenylmethyl redox centers connected by bridges with different topologies and substituents have been studied in solution, both by UV-Vis-NIR and EPR spectroscopies. The synthetic methodology used allows a complete control of the geometry of polychlorotriphenylmethyl 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 in the ease of electron transfer, which is larger for the para than for the meta isomer where a small or negligible electronic coupling is observed. The related diradical 3 that have the same topology as the para isomer 1 but bearing two substituents on the central phenyl ring shows similar ease of electron transfer, that the para isomer 1.

Journal Article↗
PubMed2004

Magneto-structural characterization of metallocene-bridged nitronyl nitroxide diradicals by X-Ray, magnetic measurements, solid-state NMR spectroscopy, and ab initio calculations.

Crystallization of ferrocene and ruthenocene substituted in the 1- and 1'-positions by two nitronyl nitroxide radicals gave the new crystal phases beta-1 (besides the known phase alpha-1), alpha-2, and beta-2 whose structures were determined by X-ray analysis. In beta-1 the radical moieties adopt transoid positions, whereas two different cisoid conformations are adopted by alpha-2 and beta-2. These conformations result from inter- and intramolecular hydrogen bonds, respectively. All compounds experience antiferromagnetic interactions, and J/k(B) values up to -7 K have been found by fitting the experimental magnetic susceptibilities to a modified Bleaney-Bowers equation. The solid diradicals alpha-1, beta-1, alpha-2, and beta-2 as well as the ferrocene 3, which was substituted by a unique nitronyl nitroxide, were investigated by (13)C and (1)H NMR spectroscopy with magic angle spinning. The carbon signals cover a range of 2000 ppm, and are well resolved such that the structure could be confirmed. Conversion of the signal shifts into spin densities disclosed the mechanisms by which spin delocalization from the nitronyl nitroxide substituents to the metallocene core occurs. The spin density distribution in alpha-1, beta-1, and 3 was also predicted by DFT calculations. There is good agreement between the experimental and theoretical trends of the spin delocalization. The magnetic interactions were discussed in the light of intramolecular spin transfer and its dependence on geometric constraints, demonstrating that the 1,1'-metallocenylene bridge is not a robust magnetic coupler.

Crystallography, X-Ray↗
PubMed2004

Supramolecular photomagnetic materials: photoinduced dimerization of ferrocene-based polychlorotriphenylmethyl radicals.

New ferrocenyl Schiff-base polychlorotriphenylmethyl radicals have been synthesized and characterized. The imino group of one such radical undergoes an irreversible trans to cis structural isomerization induced by light. Such photoinduced isomerization has been monitored by UV/Vis and ESR spectroscopy and also monitored by HPLC. ESR frozen solution experiments at low temperature revealed that the cis isomer dimerizes, showing a strong antiferromagnetic interaction. Although numerous photochromic supramolecular systems have been described, such a photoinduced self-assembly process represents the first 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 dimerization process driven by the formation of hydrogen bonds. DFT calculations on the minimized structure and on the rotational barriers have been performed to establish the origin of such behavior. The effect of the substituents and the media polarity on the photoisomerization of this imine chromophore have also been studied. It has been observed that the efficiency of the process is markedly dependent on the presence and characteristics of electron-donor and electron-acceptor substituents of the ferrocenyl Schiff-base polychlorotriphenylmethyl radicals as well as on the polarity of the solvent.

Journal Article↗
PubMed2003

A nanoporous molecular magnet with reversible solvent-induced mechanical and magnetic properties.

Interest in metal-organic open-framework structures has increased enormously in the past few years because of the potential benefits of using crystal engineering techniques to yield nanoporous materials with predictable structures and interesting properties. Here we report a new efficient methodology for the preparation of metal-organic open-framework magnetic structures based on the use of a persistent organic free radical (PTMTC), functionalized with three carboxylic groups. Using this approach, we create an open-framework structure Cu3(PTMTC)2(py)6(CH3CH2OH)2(H2O), which we call MOROF-1, combining very large pores (2.8-3.1 nm) with bulk magnetic ordering. MOROF-1 shows a reversible and highly selective solvent-induced 'shrinking-breathing' process involving large volume changes (25-35%) that strongly influence the magnetic properties of the material. This magnetic sponge-like behaviour could be the first stage of a new route towards magnetic solvent sensors.

Copper↗