Javier González-Platas

EosFit7c and a Fortran module (library) for equation of state calculations

Abstract The relationship between linear elasticity theory of solids and their equations of state (EoS) is reviewed, along with the commonly-used types of isothermal EoS, thermal expansion models, and P-V-T EoS. A new console program, EosFit7c, is presented. It performs EoS calculations and fitting for both volume and linear isothermal data, isobaric data and P-T data. Linear data is handled by cubing the quantities and treating them as volumes in all EoS formulations. Least-squares fitting of EoS to data incorporates the option to weight the fit with the measurement uncertainties in P, V and T simultaneously. The EosFit7c program is built with a new library of subroutines for EoS calculations and manipulation, written in Fortran. The library has been incorporated as a module, cfml_eos, in the publicly-available CrysFML library. The module handles Murnaghan, Tait, Birch-Murnaghan, Vinet, and Natural Strain EoS. For P-V-T calculations any of these isothermal EoS can be combined with a variety of published thermal expansion models, including a model of thermal pressure. The entire library has been revalidated against other software and against an ab-initio re-derivation of the EoS, which identified a number of small errors in published formulae for some EoS.

Endohedral and exohedral adsorption in C60: An analytical model

A simple description of the interaction potential between a small molecule and a fullerene 60 cage is discussed on the basis of the continuum approximation. General conditions are obtained for the validity of this continuum approximation and for the confinement mechanism of the molecule inside (or outside) the cage. Application to the insertion of alkali metal ions and rare gas atoms shows that these conditions can adequately interpret the equilibrium positions of inside (outside) adducts, the adsorption energy and the collision experiments between the ions and atoms and the C60 cage.

Stimulated and upconverted emissions of Nd3+ in a transparent oxyfluoride glass-ceramic

Abstract The stimulated emission properties of Nd3+ ions in an oxyfluoride glass-ceramic have been studied. Ultraviolet and visible emissions generated by upconversion processes inside the laser cavity under lasing and non-lasing conditions have been also characterized. The expected losses produced by these processes have been estimated.

Comment on “High-pressure x-ray diffraction study of YBO3/Eu3+, GdBO3, and EuBO3: Pressure-induced amorphization in GdBO3” [J. Appl. Phys. 115, 043507 (2014)]

High-pressure x-ray diffraction studies on vaterite-type borates were reported on the above paper and their room-temperature P-V equation of state (EOS) determined. YBO3/Eu3+ and GdBO3 were found to have bulk moduli around 320 GPa, 90% larger than the bulk modulus obtained for EuBO3. Consequently, it was stated that vaterite-type borates are as incompressible as cubic BN. Such a different compressional behavior of isomorphic borates contradicts the known systematic of related borates. Here, we show that the conclusions reported on the above article could be hindered by experimental errors and artifacts. Ab initio calculations support our criticism giving similar bulk moduli (130–141 GPa) in the three compounds. Based upon these arguments, we conclude that the high-pressure behavior of vaterite-type borates should be revised using accurate experimental techniques. Finally, a methodological critic on EOS fits and to structural refinements is also presented.

Synthesis, Reactivity, and Kinetics of Substitution in W3PdSe4 Cuboidal Clusters. A Reexamination of the Kinetics of Substitution of the Related W3S4 Cluster with Thiocyanate

The reaction of Pd(dba)(2) (dba = dibenzylideneacetone) with [W(3)Se(4)(H(2)O)(9)](4+) in 2 M HCl gives the cuboidal cluster [W(3)(PdCl)Se(4)(H(2)O)(9)](3+), which undergoes edge-to-edge condensation and crystallizes from Hpts solutions as edge-linked double-cubane cluster [{W(3)PdSe(4)(H(2)O)(9)}(2)](pts)(8) x 18 H(2)O (pts(-) = p-toluenesulfonate). The substitution of Cl(-) by different ligands, including phenylsulfinate PhSO(2)(-), was explored. The phenylsulfinate complex was crystallized as a 2:1 adduct with cucurbit[6]uril (C(36)H(36)N(24)O(12)), [W(3)(Pd(PhSO(2))Se(4)(H(2)O)(8.58)Cl(0.42)](2)(C(36)H(36)N(24)O(12))Cl(5.16) x 16.83 H(2)O, and its structure was determined by X-ray diffraction. Solution studies indicate that the Pd atom is able to stabilize the pyramidal tautomer of hypophosphorous and phosphorous acid: HP(OH)(2) and P(OH)(3). Kinetic studies were carried out on the reactions with H(3)PO(2) and thiocyanate, which were found to proceed in two and three kinetically resolvable steps, respectively. The kinetic results are discussed in terms of the mechanistic proposals put forward in the literature for related complexes. To gain insight into the details of the substitution kinetics in these kinds of clusters, the reaction of the related [W(3)S(4)(H(2)O)(9)](4+) complex with NCS(-) has been reexamined, and the results obtained provide for the first time information about the rates of substitution of the whole set of nine-coordinated water molecules.

From Conjugated Tertiary Skipped Diynes to Chain-Functionalized Tetrasubstituted Pyrroles

Authors thank the Spanish Ministerio de Educacion y Ciencia and the European Regional Development Fund (CTQ2005-09074-C02-02), the Spanish MSC ISCIII (RETICS RD06/0020/1046), CSIC (Proyecto Intramural Especial 200719) and Fundacion Instituto Canario de Investigacion del Cancer (FICI-G.I. No. 08/2007) for financial support. S.L.-T. Thanks MEC for a FPU grant.

ABSORB-7 and ABSORB-GUI for single-crystal absorption corrections

ABSORB is a program to calculate and apply absorption corrections to single-crystal X-ray intensity data from any source, any detector type and any instrument configuration. A new version, ABSORB-7, contains several significant new features. ABSORB-GUI has been developed to allow much easier specification of standard experiments and to enable experimental information to be imported from diffractometer software. The program that calculates the absorption calculations has been reconfigured to allow it to be called directly from other commercial and non-commercial software packages. In addition, a number of new features have been introduced to allow more flexibility in the way the experimental configuration is described and to correct synchrotron diffraction data collected with beams smaller than the sample crystal.

Endohedral adsorption in graphitic nanotubules

Calculations based on simple interaction potentials are performed to define the adsorption characteristics of molecules encapsulated in carbon nanotubules. The continuum approximation used to describe the cylindrical sheets is shown to work fairly well within a large range of tubule diameters. Criteria for molecule confinement are given which include the influence of the number of graphitic shells describing the whole tubule and they are compared to similar results obtained for carbon Buckyballs. Application to the most common encaged species, i.e., rare gas atoms and alkali‐metal ions, confirms these general rules.

Structural study of the Eu3+ environments in fluorozirconate glasses: role of the temperature-induced and the pressure-induced phase transition processes in the development of a rare earth's local structure model.

The correlation between the optical properties of the Eu(3+) ions and their local structures in fluorozirconate glasses and glass-ceramics have been analyzed by means of steady-state and time-resolved site-selective laser spectroscopies. Changes in the crystal-field interaction, ranging from weak to medium strength values, are observed monitoring the luminescence and the lifetime of the Eu(3+) ions in different local environments in the glass. As key roles in this study, the Eu(3+) luminescence in the thermally-induced crystallization of the glass and the pressure-induced amorphization of the crystalline phase of the glass-ceramic experimentally states the existence of a parent local structure for the Eu(3+) ions in the glass, identified as the EuZrF(7) crystalline phase. Starting from the ab initio single overlap model, crystal-field calculations have been performed in the glass and the glass-ceramic. From the site-selective measurements, the crystal-field parameters sets are obtained, giving a suitable simulation of the (7)F(J) (J=0-6) Stark energy level diagram for the Eu(3+) ions in the different environments present in the fluorozirconate glass. A simple geometrical model based on a continuous distortion of the parent structure is proposed for the distribution of local environments of the Eu(3+) ions in the fluorozirconate glass.

Synthesis and conformational analysis of cyclic homooligomers from pyranoid ε-sugar amino acids.

New pyranoid ε-sugar amino acids were designed as building blocks, in which the carboxylic acid and the amine groups were placed in positions C2 and C3 with respect to the tetrahydropyran oxygen atom. By using standard solution-phase coupling procedures, cyclic homooligomers containing pyranoid ε-sugar amino acids were synthesized. Conformation analysis was performed by using NMR spectroscopic experiments, FTIR spectroscopic studies, X-ray analysis, and a theoretical conformation search. These studies reveal that the presence of a methoxy group in the position C4 of the pyran ring produces an important structural change in the cyclodipeptides. When the methoxy groups are present, the structure collapses through interresidue hydrogen bonds between the oxygen atoms of the pyran ring and the amide protons. However, when the cyclodipeptide lacks the methoxy groups, a U-shape structure is adopted, in which there is a hydrophilic concave face with four oxygen atoms and two amide protons directed toward the center of the cavity. Additionally, we found important evidence of the key role played by weak electrostatic interactions, such as the five-membered hydrogen-bonded pseudocycles (C5) between the amide protons and the ether oxygen atoms, in the conformation equilibrium of the macrocycles and in the cyclization step of the cyclic tetrapeptides.