Jaume Veciana

Magnetic nanoporous coordination polymers

The use of organic molecules as an alternative strategy for achieving new nanoporous metal–organic materials has become an attractive prospect. So far, the use of chemical coordination or crystal engineering techniques allows the systematic design of open-framework structures with a considerable range of modulatable pore sizes and functionalities using different organic ligands such as phosphane, cyano groups, N,N′-type ligands and polycarboxylic acids. Furthermore, the use of transition metal ions opens the possibility to obtain nanoporous materials with additional electrical, optical or magnetic properties. Among them, the search for magnetic open-framework structures has become a major challenge due to their potential applications in the development of low-density magnetic materials, magnetic sensors and intelligent or multifunctional materials.

Surface Supramolecular Organization of a Terbium(III) Double-Decker Complex on Graphite and its Single Molecule Magnet Behavior

The two-dimensional self-assembly of a terbium(III) double-decker phthalocyanine on highly oriented pyrolitic graphite (HOPG) was studied by atomic force microscopy (AFM), and it was shown that it forms highly regular rectangular two-dimensional nanocrystals on the surface, that are aligned with the graphite symmetry axes, in which the molecules are organized in a rectangular lattice as shown by scanning tunneling microscopy. Molecular dynamics simulations were run in order to model the behavior of a collection of the double-decker complexes on HOPG. The results were in excellent agreement with the experiment, showing that-after diffusion on the graphite surface-the molecules self-assemble into nanoscopic islands which align preferentially along the three main graphite axes. These low dimension assemblies of independent magnetic centers are only one molecule thick (as shown by AFM) and are therefore very interesting nanoscopic magnetic objects, in which all of the molecules are in interaction with the graphite substrate and might therefore be affected by it. The magnetic properties of these self-assembled bar-shaped islands on HOPG were studied by X-ray magnetic circular dichroism, confirming that the compounds maintain their properties as single-molecule magnets when they are in close interaction with the graphite surface.

A robust molecular platform for non-volatile memory devices with optical and magnetic responses

Bistable molecules that behave as switches in solution have long been known. Systems that can be reversibly converted between two stable states that differ in their physical properties are particularly attractive in the development of memory devices when immobilized in substrates. Here, we report a highly robust surface-confined switch based on an electroactive, persistent organic radical immobilized on indium tin oxide substrates that can be electrochemically and reversibly converted to the anion form. This molecular bistable system behaves as an extremely robust redox switch in which an electrical input is transduced into optical as well as magnetic outputs under ambient conditions. The fact that this molecular surface switch, operating at very low voltages, can be patterned and addressed locally, and also has exceptionally high long-term stability and excellent reversibility and reproducibility, makes it a very promising platform for non-volatile memory devices.

A Liquid‐Crystalline Single‐Molecule Magnet with Variable Magnetic Properties

This work was supported by the Marie Curie EST FuMaSSEC, EU NoE MAGMANet (515767-2), EMOCIONA (CTQ2006-06333/BQU), Grup de Recerca de Catalunya (2009 SGR-516) and Molecular Nanoscience (CSD2007-00010) and Molchip (MAT2009-13977-C03) projects.

Bacterial inclusion bodies: making gold from waste

Many protein species produced in recombinant bacteria aggregate as insoluble protein clusters named inclusion bodies (IBs). IBs are discarded from further processing or are eventually used as a pure protein source for in vitro refolding. Although usually considered as waste byproducts of protein production, recent insights into the physiology of recombinant bacteria and the molecular architecture of IBs have revealed that these protein particles are unexpected functional materials. In this Opinion article, we present the relevant mechanical properties of IBs and discuss the ways in which they can be explored as biocompatible nanostructured materials, mainly, but not exclusively, in biocatalysis and tissue engineering.

Single-crystal organic field-effect transistors based on dibenzo-tetrathiafulvalene

We report on the fabrication and characterization of field-effect transistors based on single crystals of the organic semiconductor dibenzo-tetrathiafulvalene (DB-TTF). We demonstrate that it is possible to prepare very-good-quality DB-TTF crystals from solution. These devices show high field-effect mobilities typically in the range 0.1–1?cm2/V?s. The temperature dependence was also studied revealing an initial increase of the mobility when lowering the temperature until it reached a maximum, after which the mobility decreased following a thermally activated behavior with activation energies between 50 and 60?meV. Calculations of the molecular reorganization energy and intermolecular transfer integrals for this material were also performed and are in agreement with the high mobility observed in this material.

Gold complexes with dithiothiophene ligands: a metal based on a neutral molecule.

The gold complexes n-Bu4N[Au(alpha-tpdt)2] (5), n-Bu4N[Au(dtpdt)2] (4) and n-Bu4N[Au(tpdt)2] (6) based on new dithiothiophene ligands (alpha-tpdt= 2,3-thiophenedithiolate, dtpdt=2,3-dihydro-5,6-thiophenedithiolate and tpdt = 3,4-thiophenedithiolate) have been prepared and characterised. These gold(III) complexes are diamagnetic, but they can be oxidised with iodine to the paramagnetic compounds [Au(alpha-tpdt)2] (8), [Au(dtpdt)2] (7) and n-Bu4N[[Au(tpdt)2]n-2] (9), which were isolated as fine powders and which exhibit paramagnetic susceptibilities that are almost temperature independent with room temperature values of 2.5 x 10(-4), 2.0 x 10(-4) and 5 x 10(-4) emu x mol(-1), respectively. Interestingly, the neutral complex [Au(alpha-tpdt)2] (8) as a polycrystalline sample displays the properties of a metallic system with a room temperature electrical conductivity of 6 S x cm(-1) and a thermoelectric power of 5.5 microVK(-1); this is the first time that this metallic property has been observed in a molecular system based on a neutral species.

High‐Performance Single Crystal Organic Field‐Effect Transistors Based on Two Dithiophene‐Tetrathiafulvalene (DT‐TTF) Polymorphs

Solution prepared single crystal organic field-effect transistors (OFETs) combine low-cost with high performance due to structural ordering of molecules. However, in organic crystals polymorphism is a known phenomenon, which can have a crucial influence on charge transport. Here, the performance of solution-prepared single crystal OFETs based on two different polymorphs of dithiophene-tetrathiafulvalene, which were investigated by confocal Raman spectroscopy and X-ray diffraction, are reported. OFET devices prepared using different configurations show that both polymorphs exhibited excellent device performance, although the -phase revealed charge carrier mobility between two and ten times higher in accordance to the closer stacking of the molecules.

Probing the Magnetic Properties of Three Interconvertible Redox States of a Single-Molecule Magnet with Magnetic Circular Dichroism Spectroscopy

The hysteresis of magnetization of the anionic, neutral, and cationic forms of a bis(phthalocyaninato)terbium-based complex ([Pc(2)Tb](-/0/+)) have been determined using magnetic circular dichroism (MCD) spectroscopy in frozen dilute solutions at low temperatures (1.5 K) showing that the three oxidation states of the complex exhibit single-molecule magnetic behaviors.

A simple and robust reversible redox–fluorescence molecular switch based on a 1,4-disubstituted azine with ferrocene and pyrene units

Taking advantage of the properties of the ferrocene as a redox and electron donor active unit and the pyrene as a fluorescent unit, dyad 2 shows a fast and reversible redox-switchable fluorescence emission.