Biomedical subjects

Miquel Llunell

Publications and source records attributed to Miquel Llunell.

7 recordsLinked to original sources

PubMed2006

Concerning the different roles of cations in metallic Zintl phases: Ba7Ga4Sb9 as a test case.

The question of the different roles of cations in metallic Zintl phases has been examined by taking Ba7Ga4Sb9, an electron-rich phase, as a test case. The electronic structure of this solid has been studied by means of a first-principles density functional theory approach and, indeed, the different Ba atoms are found to play very different roles in determining the structural and transport properties of this phase. It is also found that Ba7Ga4Sb9 should be an anisotropic metal with both one- and three-dimensional contributions to the Fermi surface so that the system could exhibit a potentially very interesting physical behavior while keeping the metallic properties down to very low temperatures. Suggestions in order to modify the band filling and the physical properties are examined. Although isostructural electron-precise phases may be envisioned, it is predicted that they would be essentially three-dimensional metals.

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PubMed2006

Theoretical determination of multiple exchange couplings and magnetic susceptibility data in inorganic solids: the prototypical case of Cu2(OH)3NO3.

Density functional theory based on hybrid functionals and localized atomic type basis sets is employed to calculate the exchange couplings in the layered three-dimensional compound Cu2(OH)3NO3. We assign accurate values to the six different in-plane exchange couplings. Interlayer exchange interactions through hydrogen bonds are also quantified. The calculated exchange coupling constants are then employed to perform quantum Monte Carlo simulations to yield magnetic susceptibility data, which compare successfully with experiments. Our approach sets the foundations of a viable methodology to extract reliable magnetic susceptibilities from density functional data.

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PubMed2005

Magnetic properties of cyano-bridged Ln3+-M3+ complexes. Part I: trinuclear complexes (Ln3+ = La, Ce, Pr, Nd, Sm; M3+ = FeLS, Co) with bpy as blocking ligand.

The reaction of Ln(NO3)3(aq) with K3[Fe(CN)6] or K3[Co(CN)6] and 2,2'-bipyridine in water/ethanol led to eight trinuclear complexes: trans-[M(CN)4(mu-CN)2{Ln(H2O)4(bpy)2}2][M(CN)6].8H2O (M = Fe3+ or Co3+, Ln = La3+, Ce3+, Pr3+, Nd3+, and Sm3+). The structures for the eight complexes [La2Fe] (1), [Ce2Fe] (2), [Pr2Fe] (3), [Nd2Fe] (4), [Ce2Co] (5), [Pr2Co] (6), [Nd2Co] (7), and [Sm2Co] (8) have been solved; they crystallize in the triclinic space group P and are isomorphous. They exhibit a supramolecular 3D architecture through hydrogen bonding and pi-pi stacking interactions. A stereochemical study of the nine-vertex polyhedra of the lanthanide ions, based on continuous shape measures, is presented. No significant magnetic interaction was found between the lanthanide(III) and the iron(III) ions.

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PubMed2005

Electronic structure of the K3Bi2 metallic phase.

The electronic structure of K3Bi2 is discussed on the basis of first-principles DFT calculations. It is shown that the dimers are formally (Bi2)3-, even though this might seem to be in contradiction with the metallic character of the salt. The apparent puzzle is explained by the sizable participation of the K levels in the bonding.

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PubMed2005

The rich stereochemistry of eight-vertex polyhedra: a continuous shape measures study.

A stereochemical study of polyhedral eight-vertex structures is presented, based on continuous shape measures (CShM). Reference polyhedra, shape maps, and minimal-distortion interconversion paths are presented for eight-vertex polyhedral and polygonal structures within the CShM framework. The application of these stereochemical tools is analyzed for several families of experimental structures: 1) coordination polyhedra of molecular transition-metal coordination compounds, classified by electron configuration and ligands; 2) edge-bonded polyhedra, including cubane structures, realgar, and metal clusters; 3) octanuclear transition-metal supramolecular architectures; and 4) coordination polyhedra in extended structures in inorganic solids. Structural classification is shown to be greatly facilitated by these tools, and the detection of less common structures, such as the gyrobifastigium, is straightforward.

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PubMed2005

Electronic structure of Li2Ga and Li9Al4, two solids containing infinite and uniform zigzag chains.

The electronic structure of inorganic solids such as Li(2)Ga and Li(9)Al(4) containing infinite zigzag homoatomic chains is discussed. It is shown that Li(2)Ga, a solid for which a Zintl-type electron-counting approach would suggest that a half-filled pi-type band occurs as in trans-polyacetylene, is really a three-dimensional solid with strong covalent interchain connections and small effective charge transfer. The zigzag chains do not play a dominant role as far as the electronic structure near the Fermi level is concerned, and there is no reason for the occurrence of a Peierls distortion despite the possible analogy with trans-polyacetylene. It is suggested that even assuming that a Zintl-type approach is appropriate for electron counting purposes, the infinite zigzag chains in this compound and those in trans-polyacetylene are not isolobal. The bonding in Li(9)Al(4) and Li(2)Ga is very similar, and both phases are predicted to be stable three-dimensional metals.

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PubMed2004

Minimal distortion pathways in polyhedral rearrangements.

A definition of minimum distortion paths between two polyhedra in terms of continuous shape measures (CShM) is presented. A general analytical expression deduced for such pathways makes use of one parameter, the minimum distortion constant, that can be easily obtained through the CShM methodology and is herein tabulated for pairs of polyhedra having four to eight vertexes. The work presented here also allows us to obtain representative model molecular structures along the interconversion pathways. Several commonly used polytopal rearrangement pathways are shown to be in fact minimum distortion pathways: the spread path leading from the tetrahedron to the square, the Berry pseudorotation that interconverts a square pyramid and a trigonal bipyramid, and the Bailar twist for the interconversion of the octahedron and the trigonal prism. Examples of applications to the analysis of the stereochemistries of several families of metal complexes are presented.

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