Oriol Vallcorba

Solid-state transformation of the MOF [Ni2(bipy)1.5(PDC)2(H2O)2]·3.5H2O

The combination of non-centrosymmetric ligands and dipyridyl spacers produces a MOF that potentially can be porous with formula [Ni2(bipy)1.5(PDC)2(H2O)2]·3.5H2O (bipy = 4,4′-bipyridine and PDC = pyridine-2,5-dicarboxylate). Dehydration of this compound results in a new MOF in which the formation of additional bonds between the carboxylate groups of PDC and the metal ion has occurred. This solid-state transformation takes place with no significant changes in the coordination sphere of the metal ion, which is unusual for coordination polymers. Both compounds exhibit the same unprecedented topology where the connectivity between nodes is remarkably high.

DAJUST: a suite of computer programs for pattern matching, space-group determination and intensity extraction from powder diffraction data

DAJUST is the generic name of a software package for powder diffraction formed by the core programs AJUST and SGAID (both written in Fortran) controlled by an easy-to-use Java user interface (DAJUST_UI). While AJUST performs whole-pattern matching (cell-parameter refinement, profile fitting and intensity extraction), SGAID provides a list of the most probable space groups. For the extraction of the integrated intensities, AJUST uses the Le Bail procedure but with a different formula for refining the integrated intensities. Laboratory, synchrotron X-ray and neutron sources, and both reflection and transmission experimental geometries, are supported. Other program options include automated background estimation, asymmetry correction, and corrections for absorption, variable divergence and/or illumination. The extracted intensity data are written in text format and can be directly processed by the direct methods program XLENS [Rius (2011). Acta Cryst. A67, 63–67] and the multisolution direct-space structure determination program TALP [Vallcorba, Rius, Frontera & Miravitlles (2011). Acta Cryst. A67, C272].

Charge Transfer States in Stable Neutral and Oxidized Radical Adducts from Carbazole Derivatives

In this paper we report the spectral properties of the stable radical adducts 1(•)-3(•), which are formed by an electron donor moiety, the carbazole ring, and an electron acceptor moiety, the polychlorotriphenylmethyl radical. The molecular structure of radical adduct 1(•) in the crystalline state shows a torsion angle of approximately 90° between the phenyl and the carbazole rings due to steric interactions. They exhibit a charge transfer band in the visible range of the electronic spectrum. All of them are chemically oxidized with copper(II) perchlorate to the respective cation species, which show a strong charge transfer band into the near-infrared region of the spectrum. Radical adducts 1(•)-3(•) and the corresponding stable oxidized species 1(+)-3(+) are real organic mixed-valence compounds due to the open-shell nature of their electronic structure. Charge transfer bands of the cation species are stronger and are bathochromically shifted with respect to those of the neutral species due to the greater acceptor ability of the positively charged central carbon atom of the triphenylmethyl moiety. The cationic species 1(+)-3(+) are diamagnetic, as shown by the absence of a signal in the EPR spectrum in acetonitrile solution at room temperature, but they show an intense and unique band in frozen solutions (183 K).

Variable behaviour of flexible N,O-mixed pyrazole ligand towards Zn(II), Cd(II) and Hg(II) ions. Synthesis, crystal structure and fluorescent properties

The variable coordination behaviour of the mixed ligand 1-(2-hydroxyethyl)-3,5-dimethylpyrazole (L) towards Zn(II), Cd(II) and Hg(II) ions has been investigated. Three new complexes, [ZnCl2(L)] (1), [CdCl2(L)]2 (2), and [HgCl2(L)]n (3), with different structures and topologies have been fully characterized by analytical and spectroscopic techniques including heteronuclear 113Cd and 199Hg NMR analyses. Complexes 1–3 were also characterized by single crystal and powder X-ray diffraction techniques. The L ligand exhibits high versatility and provides different environments to the metal centre as a function of its diverse coordination mode. The weak π–π stacking interactions and intermolecular hydrogen bonds resulted in the two-dimensional network structures. All these results point out the structural diversity of the hybrid pyrazole ligand on its coordination. Finally, we determined the fluorescent properties of complexes 1–3. Surprisingly, L displays a high selectivity for Hg(II) ion. The findings indicate that the variable behaviour of the hydroxyl group substituent exerts an important effect on the spectroscopic properties. Moreover, the fluorescence of these complexes has been rationalized through theoretical calculations. The primary results suggest that the use of L is a promising strategy to synthesize novel materials with unique photoluminescent properties and further applications for the detection of heavy metals in real environmental samples.

TALP: a multisolution direct-space strategy for solving molecular crystals from powder diffraction data based on restrained least squares

TALP is a new direct-space strategy for ab initio crystal structure determination of molecular crystals from powder diffraction data. The strategy is based on a preliminary exploration stage, which considers atomic overlap, followed by a subsequent stage of local incremental scans, both coupled to fast restrained least-squares minimizations with the atomic coordinates as refined parameters. The observed intensities are extracted from the powder pattern by a three-step procedure [Vallcorba, Rius, Frontera, Peral & Miravitlles (2012). J. Appl. Cryst. 45, 844–848], and the molecular model and distance restraints are derived from molecular mechanics calculations or from similar reported structures. The solution process consists of several independent trials, each one resulting in a crystal structure proposal with an associated figure of merit. TALP has been tested on laboratory X-ray powder diffraction data of 14 molecular compounds of known crystal structure and of variable complexity. In most cases, the crystal structure is solved in a short time (less than an hour), even for calculated models. For the most complex structures (e.g. 13 torsion angles), the general scan is assisted by a rotation function, which provides a ranked list of most probable model orientations. In this way only the positional and conformation parameters need to be explored.

A Magnetic Ionic Liquid Based on Tetrachloroferrate Exhibits Three‐Dimensional Magnetic Ordering: A Combined Experimental and Theoretical Study of the Magnetic Interaction Mechanism

A new magnetic ionic liquid (MIL) with 3D antiferromagnetic ordering has been synthetized and characterized. The information obtained from magnetic characterization was supplemented by analysis of DFT calculations and the magneto-structural correlations. The result gives no evidence for direct iron-iron interactions, corroborating that the 3D magnetic ordering in MILs takes place via super-exchange coupling containing two diamagnetic atoms intermediaries.

Anion−π and Halide–Halide Nonbonding Interactions in a New Ionic Liquid Based on Imidazolium Cation with Three-Dimensional Magnetic Ordering in the Solid State

We present the first magnetic phase of an ionic liquid with anion-π interactions, which displays a three-dimensional (3D) magnetic ordering below the Néel temperature, TN = 7.7 K. In this material, called Dimim[FeBr4], an exhaustive and systematic study involving structural and physical characterization (synchrotron X-ray, neutron powder diffraction, direct current and alternating current magnetic susceptibility, magnetization, heat capacity, Raman and Mössbauer measurements) as well as first-principles analysis (density functional theory (DFT) simulation) was performed. The crystal structure, solved by Patterson-function direct methods, reveals a monoclinic phase (P21 symmetry) at room temperature with a = 6.745(3) Å, b = 14.364(3) Å, c = 6.759(3) Å, and β = 90.80(2)°. Its framework, projected along the b direction, is characterized by layers of cations [Dimim](+) and anions [FeBr4](-) that change the orientation from layer to layer, with Fe···Fe distances larger than 6.7 Å. Magnetization measurements show the presence of 3D antiferromagnetic ordering below TN with the existence of a noticeable magneto-crystalline anisotropy. From low-temperature neutron diffraction data, it can be observed that the existence of antiferromagnetic order is originated by the antiparallel ordering of ferromagnetic layers of [FeBr4](-) metal complex along the b direction. The magnetic unit cell is the same as the chemical one, and the magnetic moments are aligned along the c direction. The DFT calculations reflect the fact that the spin density of the iron ions spreads over the bromine atoms. In addition, the projected density of states (PDOS) of the imidazolium with the bromines of a [FeBr4](-) metal complex confirms the existence of the anion-π interaction. Magneto-structural correlations give no evidence for direct iron-iron interactions, corroborating that the 3D magnetic ordering takes place via superexchange coupling, the Fe-Br···Br-Fe interplane interaction being defined as the main exchange pathway.

Accuracy in Rietveld quantitative phase analysis: a comparative study of strictly monochromatic Mo and Cu radiations

This work focuses on the comparison of Mo Kα1 and Cu Kα1 radiations for the Rietveld quantitative phase analysis of challenging crystalline mixtures including amorphous content determination. The quantifications have been carried out by using calibration curves with increasing amounts of a given phase. Mo Kα1 patterns were found to yield slightly more accurate analyses than those derived from Cu Kα1 radiation.

1-Ethyl-2,3-dimethylimidazolium paramagnetic ionic liquids with 3D magnetic ordering in its solid state: synthesis, structure and magneto-structural correlations

Two novel paramagnetic ionic liquids, comprised of a 1-ethyl-2,3-dimethylimidazolium (Edimim) cation and a tetrahaloferrate(III) (FeX4) (X = Cl and Br) anion were synthetized and characterized by thermal, structural, Raman spectroscopy and magnetic studies. The crystal structures, determined by synchrotron X-ray powder diffraction and single crystal X-ray diffraction at 100 K for Edimim[FeCl4] and Edimim[FeBr4] respectively, are characterized by layers of cations (in non-planar configuration) and anions stacked upon one another in a three-dimensional (3D) manner with several non-covalent interactions: halide–halide, hydrogen bond and anion–π. Magnetization measurements show the presence of three-dimensional antiferromagnetic ordering below the Neel temperature (TN) with the existence of a noticeable magneto-crystalline anisotropy in the bromide compound. The corresponding magneto-structural correlations evidence that the 3D magnetic ordering mainly takes place via Fe–X⋯X–Fe (X = Cl and Br) interactions, displaying a higher superexchange magnetic interaction between the planes. Comparison with the Emim[FeX4] (X = Cl and Br) phases (Emim: 1-ethyl-3-methylimidazolium) reveals that the methylation at the C(2) position onto the imidazolium cation ring causes an increase of the melting point and a decrease of the TN. In contrast, the comparative study with Dimim[FeX4] (X = Cl and Br) compounds (Dimim: 1,3-dimethylimidazolium) shows a lower TN in the chloride compound, Edimim[FeCl4], whereas it is higher for the bromide, Edimim[FeBr4]. This fact is attributed to the spin delocalization of iron atoms in [FeBr4]− and discards the hypothesis that a bigger imidazolium ion size causes a weaker magnetic coupling in paramagnetic ionic liquids based on tetrahaloferrate anions and imidazolium cations with 3D magnetic ordering in its solid state.

Capabilities of through-the-substrate microdiffraction: application of Patterson-function direct methods to synchrotron data from polished thin sections

Some theoretical and practical aspects of the application of transmission microdiffraction (µXRD) to thin sections (≤30 µm thickness) of samples fixed or deposited on substrates are discussed. The principal characteristic of this technique is that the analysed micro-sized region of the thin section is illuminated through the substrate (tts-µXRD). Fields that can benefit from this are mineralogy, petrology and materials sciences since they often require in situ lateral studies to follow the evolution of crystalline phases or to determine new crystal structures in the case of phase transitions. The capability of tts-µXRD for performing structural studies with synchrotron radiation is shown by two examples. The first example is a test case in which tts-µXRD intensity data of pure aerinite are processed using Patterson-function direct methods to directly solve the crystal structure. In the second example, tts-µXRD is used to study the transformation of laumonite into a new aluminosilicate for which a crystal structure model is proposed.