Study of metallic components of historical organ pipes using synchrotron radiation X-ray microfluorescence imaging and grazing incidence X-ray diffraction.

A comparative study of the composition and microstructure of two different brass alloys from reed pipes, one from a Spanish baroque organ and the other from a modern one, was carried out. This study allowed us to determine the procedure followed to produce the brass used to make ancient reed pipes. Moreover the distribution and correlation of lead and other trace elements present into the main component of the brass, the copper and zinc phases, of the historical tongues and shallots were established. This chemical composition was compared with that of a tongue from a twentieth-century organ. The whole study was accomplished using a combination of laboratory and synchrotron radiation techniques. X-ray fluorescence was the technique used to obtain elemental and chemical imaging of the main phases and the trace elements at a sub-micrometer scale.

Po(IV) hydration: a quantum chemical study.

This work presents a theoretical study on the hydration of Po(IV) in solution. Three points have been addressed: (i) the level of calculation needed to properly describe the system under study, (ii) the hydration number of Po(IV), and (iii) the nature of the polonium-water bonding. The condensed medium effects have been included by means of a continuum solvation model, thus different [Po(H(2)O)(n)](4+) hydrates were embedded in a cavity surrounded by a polarizable dielectric medium. Among the quantum-mechanical calculation levels here considered, the MPW1PW91 functional was shown to be the most suitable, allowing a proper description of the Po-H(2)O interactions at affordable cost. The hydration number of Po(IV) was found to be between 8 and 9. This value is ruled by a dynamic equilibrium involving the octa- and ennea-hydrates, although the 7-fold coordination cannot be completely excluded. The hydration free energy of Po(IV) is estimated to be around -1480 kcal/mol. The Po-H(2)O bonding is dominated by strong electrostatic contributions although a small covalent contribution is responsible for the peculiar arrangement adopted by the smaller hydrates (n < or = 5). A natural bond order (NBO) analysis of the hydrate wave functions shows that the covalent bond involves the empty 6p orbitals of the polonium ion and one lone pair on the oxygen atom of the water molecule. A parallel investigation to the hydrate study, where the polonium ion was replaced by a tetravalent point charge plus a repulsion potential, was carried out. These results allowed a detailed examination of the electrostatic and nonelectrostatic contributions to the polonium hydrate formation.

Importance of multiple-scattering phenomena in XAS structural determinations of [Ni(CN)4]2- in condensed phases.

A quantitative analysis of the XAS spectra of the tetracyanonickelate complex [Ni(CN)4]2- has been carried out. The simultaneous study of the EXAFS and XANES regions yielded complementary information regarding the geometric and electronic structures of the complex. XANES spectra were modeled by applying recently developed self-consistent, full multiple-scattering algorithms in the FEFF8 code (version 8 x 34). XANES spectra for clusters of different sizes (from 9 to 125 atoms) were computed and compared with experimental spectra. This region of the spectra was proportional to a broadened Ni p-density of states diagram above the Fermi level. Although the main features of the XANES spectra were reasonably reproduced by computations, the weak dependence of the theoretical spectra on cluster size contrasts with the close similarity between the experimental spectra of the solid and solution systems. Because of the special geometry of the complex, calculations with polarized light parallel and perpendicular to the molecular plane were carried out, yielding a reasonable reproduction of the experimental data from another report for cluster sizes equal to or higher than 45 atoms. The highly symmetric square planar structure of the complex was found to be responsible for the unusual amplitude of the multiple-scattering (MS) contributions to the EXAFS spectra. Spectra in this region were fitted using the FEFFIT EXAFS analysis program, taking into account only the MS paths that simultaneously have both a high amplitude, as calculated with the ab initio code FEFF, and a small Debye-Waller factor, as estimated by the independent-vibration approximation model. Fitting results yielded very similar structures for the Ni2+ complex in the solid state and in solution, though the larger Debye-Waller factors found for the solid suggest higher static disorder in this state.