Examinando por Autor "Arratia-Pérez, Ramiro"

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    4-: Coinage Metal Tetrahedral Superatoms as Useful Building Blocks Related to Pyramidal Au20 Clusters (M = Cu, Ag, Au). Electronic and Bonding Properties from Relativistic DFT Calculations
    (American Chemical Society, 2018-03) Gam, Franck; Arratia-Pérez, Ramiro; Kahlal, Samia; Saillard, Jean-Yves; Muñoz-Castro, Álvaro
    Characterization of the tetrahedral Au20 structure in the gas phase remains a major landmark in gold cluster chemistry, where further efforts to stabilize this bare 20-electron superatom in solution to extend and understand its chemistry have failed so far. Here, we account for the structural, electronic, and bonding properties of [M16Ni24(CO)40]4- (M = Cu, Ag, Au) observed in solution for gold and silver. Our results show a direct electronic relationship with Au20, owing that such species share a common tetrahedral [M16]4- central core with a 1S21P61D102S2 jellium configuration. In the case of Au20, the [Au16]4- core is capped by four Au+ ions, whereas in [M16Ni24(CO)40]4- it is capped by four Ni6(CO)10 units. In both cases, the capping entities are a full part of the superatom entity, where it appears that the free (uncapped) [M16]4- species must be capped for further stabilization. It follows that the Ni6(CO)10 units in [M16Ni24(CO)40]4- should not be considered as external ligands as their bonding with the [M16]4- core is mainly associated with a delocalization of the 20 jellium electrons onto the Ni atoms. Thus, the [M16Ni24(CO)40]4- species can be seen as the solution version of tetrahedral M20 clusters, encouraging experimental efforts to further develop the chemistry of such complexes as M(111) finite surface section structures, with M = Ag and Au and, particularly promising, with M = Cu. Furthermore, optical properties were simulated to assist future experimental characterization. © 2018 American Chemical Society.
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    Electronic Structure and Properties of Berkelium Iodates
    (Journal, 2017-09) Silver, Mark A.; Cary, Samantha K.; Garza, Alejandro J.; Baumbach, Ryan E.; Arico, Alexandra A.; Galmin, Gregory A.; Chen, Kuan-Wen; Johnson, Jason A.; Wang, Jamie C.; Clark, Ronald J.; Chemey, Alexander; Eaton, Teresa M.; Marsh, Matthew L.; Seidler, Kevin; Galley, Shane S.; Van De Burgt, Lambertus; Gray, Ashley L.; Hobart, David E.; Hanson, Kenneth; Van Cleve, Shelley M.; Gendron, Frédéric; Autschbach, Jochen; Scuseria, Gustavo E.; Maron, Laurent; Speldrich, Manfred; Kögerler, Paul; Celis-Barros, Cristian; Páez-Hernández, Dayán; Arratia-Pérez, Ramiro; Ruf, Michael; Albrecht-Schmitt, Thomas E.
    The reaction of 249Bk(OH)4 with iodate under hydrothermal conditions results in the formation of Bk(IO3)3 as the major product with trace amounts of Bk(IO3)4 also crystallizing from the reaction mixture. The structure of Bk(IO3)3 consists of nine-coordinate BkIII cations that are bridged by iodate anions to yield layers that are isomorphous with those found for AmIII, CfIII, and with lanthanides that possess similar ionic radii. Bk(IO3)4 was expected to adopt the same structure as M(IO3)4 (M = Ce, Np, Pu), but instead parallels the structural chemistry of the smaller ZrIV cation. BkIII-O and BkIV-O bond lengths are shorter than anticipated and provide further support for a postcurium break in the actinide series. Photoluminescence and absorption spectra collected from single crystals of Bk(IO3)4 show evidence for doping with BkIII in these crystals. In addition to luminescence from BkIII in the Bk(IO3)4 crystals, a broad-band absorption feature is initially present that is similar to features observed in systems with intervalence charge transfer. However, the high-specific activity of 249Bk (t1/2 = 320 d) causes oxidation of BkIII and only BkIV is present after a few days with concomitant loss of both the BkIII luminescence and the broadband feature. The electronic structure of Bk(IO3)3 and Bk(IO3)4 were examined using a range of computational methods that include density functional theory both on clusters and on periodic structures, relativistic ab initio wave function calculations that incorporate spin-orbit coupling (CASSCF), and by a full-model Hamiltonian with spin-orbit coupling and Slater-Condon parameters (CONDON). Some of these methods provide evidence for an asymmetric ground state present in BkIV that does not strictly adhere to Russel-Saunders coupling and Hund's Rule even though it possesses a half-filled 5f 7 shell. Multiple factors contribute to the asymmetry that include 5f electrons being present in microstates that are not solely spin up, spin-orbit coupling induced mixing of low-lying excited states with the ground state, and covalency in the BkIV-O bonds that distributes the 5f electrons onto the ligands. These factors are absent or diminished in other f7 ions such as GdIII or CmIII. © 2017 American Chemical Society.
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    Rare-Earth Metal(II) Aryloxides: Structure, Synthesis, and EPR Spectroscopy of [K(2.2.2-cryptand)][Sc(OC6H2tBu2-2,6-Me-4)3]
    (Wiley-VCH Verlag, 2018-12) Moehring, Samuel A.; Páez-Hernández, Dayánb; Arratia-Pérez, Ramiro; Ziller, Joseph W.; Evans, William J.; Beltrán-Leiva, María J.
    The suitability of aryloxide ligands for stabilizing +2 oxidation states of Sc and Y has been examined and EPR evidence indicating the first O-donor complexes of ScII and YII has been obtained, as well as an X-ray crystal structure of a ScII aryloxide complex. The trivalent rare-earth metal aryloxide precursors, Ln(OAr′)3, 1-Ln (Ln=Sc, Y, Gd, Dy, Ho, Er; OAr′=OC6H2tBu2-2,6-Me-4), were synthesized from the corresponding rare-earth metal trichlorides and LiOAr′⋅OEt2. Reduction of THF solutions of 1-Ln with potassium graphite in the presence of 2.2.2-cryptand (crypt) yielded dark-colored solutions, 2-Ln, whose EPR spectra at 77 K are characteristic of the LnII ions: a two-line spectrum (g∥=1.99, g□=1.97, Aave=154 G) for 2-Y and an eight-line spectrum (gave=2.01 and Aave=291 G) for 2-Sc. Solutions of 2-Y decompose within one minute at room temperature, wheras 2-Sc persists up to 40 min at room temperature. 2-Sc was identified by X-ray crystallography as [K(crypt)][Sc(OAr′)3], which has a trigonal-planar arrangement of oxygen-donor atoms around ScII. Analogous reductions of 1-Ln for Ln=Gd, Dy, Ho, and Er also gave dark solutions of limited stability. Theoretical analysis using time-dependent density functional theory (TD-DFT) along with complete active space self-consistent field (CASSCF) methods, and structural analysis with the Guzei ligand solid angle G-parameter method are presented. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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    RELATIVISTIC ELECTRONIC STRUCTURE OF MOLECULARPRECURSORS: THE CASE OF THE [RE6Q8(CN)64- /RE6Q8(CN)63- ] (Q = S, Se) REDOX COUPLES.
    (SOC CHILENA QUIMICA, 2003-12) Hernández-Acevedoa, Lucía; Arratia-Pérez, Ramiro
    The understanding of the electronic structure, optical, magnetic, photophysical, electrochemical, and, structural properties of metal clusters, may lead to the development of nanoscale inorganic materials of technological interest[1-7]. Nowadays, there are many reasons to consider the increasing diversity of octahedral metal clusters of the type M6X8X6, and M6Q8(L,X)6 [4-7,15-34] that could became part of nanoscale devices due to their unusual optical and magnetic properties. In these clusters, M could be Mo, W, or Re; Q = S, Se, Te, are the face-capped chalcogenide ligands, and X is an halide or L could be an cyanide or pyr or N-heterocycle or triethylphospine, etc., acting as terminal ligands. [3-35] For example, it has been observed that the M6X8X6 (M = Mo, W; X = halide), and more recently, rhenium-chalcogenide Re6Q8L6 clusters, display long emissive lifetimes, significant quantum yields, and, undergo facile ground-and-excited state multielectron transfer reactions, thus representing a novel class of metal cluster photoreceptors for chemical reactions induced by light.[3,5-15,24,25,32,34,35] Moreover, the synthetic versatility of the [Re6Q8(CN)6]q+ (Q = S, Se) clusters has allowed the synthesis of extended new porous materials that can be used as molecular sieves, or used as starting material for designing versatile chemical sensors for the detection of a large variety of volatile pollutants; or it has also been used as building blocks for constructing extended multicluster aggregates, new solid phases and exotic metallo-dendrimers.[26-31,33]
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    Spin-orbit and solvent effects in the luminescent [re6q8(ncs)6]4-, q=s, se, te clusters: molecular sensors and molecular devices
    (Sociedad Chilena de Química, 2010) Ramírez-Tagle, Rodrigo; Alvarado-Soto, Leonor; Hernández-Acevedo, Lucia; Arratia-Pérez, Ramiro
    Relativistic time-dependent density functional (TDDFT) calculations including spin orbit interactions via the zero order regular approximation (ZORA) and solvent effects using the COSMO model were carried out on the [Re6Q8(NCS)6]4- , (Q = S, Se, Te) clusters. These calculations indicate that the lowest energy allowed electronic transitions are characterized by being of LMCT type. The calculated absorption maximum tends to shift to longer wavelengths as the face-capping chalcogenide ligand becomes heavier. Thus our calculations predict that the [Re6Te8(NCS)6]4- cluster might be also luminescent. Due to the unusual properties exhibited by these and other isoelectronic and isostructural hexarhenium (III) chalcogenide clusters, hexamolybdenum halide clusters and hexatungsten halide clusters, we propose here the design of nanodevices, such as, molecular sensors and molecular nanocells for molecular electronics.
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    Theoretical calculations of an osmium molecular switch
    (2014 Sociedad Chilena de Química, 2013) Miranda-Barrientos, Fernando; Muñoz-Castro, Alvaro; Arratia-Pérez, Ramiro
    ABSTRACT We have investigated the molecular, electronic and optical properties of the [Os(tpy-py)2]2+ complex (tpy-py = 4'-(4-pyridyl)-2,2':6',2"-terpyridine) and its protonated derivative [Os(tpy-pyH)2]4+ through Density Functional Relativistic calculations including Scalar and Spin Orbit corrections. The molecular geometry of the parent complex is not strongly modified by the protonation at the basic nitrogen atoms of the pyridine moieties of the terpyridine ligands in the complex. On the other hand, the optical properties of these complexes can be controlled by a change in the chemical acid-base environment, converting them into suitable materials to act as molecular switches or pH sensor devices.
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    Two new fluorinated phenol derivatives pyridine schiff bases: Synthesis, spectral, theoretical characterization, inclusion in epichlorohydrin-β-cyclodextrin polymer, and antifungal effect
    (Frontiers Media S.A., 2018-07) Carreño, Alexander; Rodríguez, Leonardo; Páez-Hernández, Dayán; Martin-Trasanco, Rudy; Zúñiga, César; Oyarzún, Diego P.; Gacitúa, Manuel; Schott, Eduardo; Arratia-Pérez, Ramiro; Fuentes, Juan A.
    It has been reported that the structure of the Schiff bases is fundamental for their function in biomedical applications. Pyridine Schiff bases are characterized by the presence of a pyridine and a phenolic ring, connected by an azomethine group. In this case, the nitrogen present in the pyridine is responsible for antifungal effects, where the phenolic ring may be also participating in this bioactivity. In this study, we synthesized two new pyridine Schiff Bases: (E)-2-[(3-Amino-pyridin-4-ylimino)-methyl]-4,6-difluoro-phenol (F1) and (E)- 2-[(3-Amino-pyridin-4-ylimino)-methyl]-6-fluoro-phenol (F2), which only differ in the fluorine substitutions in the phenolic ring. We fully characterized both F1 and F2 by FTIR, UV-vis, 1H; 13C; 19F-NMR, DEPT, HHCOSY, TOCSY, and cyclic voltammetry, as well as by computational studies (DFT), and NBO analysis. In addition, we assessed the antifungal activity of both F1 (two fluorine substitution at positions 4 and 6 in the phenolic ring) and F2 (one fluorine substitution at position 6 in the phenolic ring) against yeasts. We found that only F1 exerted a clear antifungal activity, showing that, for these kind of Schiff bases, the phenolic ring substitutions can modulate biological properties. In addition, we included F1 and F2 into in epichlorohydrin-β-cyclodextrin polymer (βCD), where the Schiff bases remained inside the βCD as determined by the ki, TGA, DSC, and SBET. We found that the inclusion in βCD improved the solubility in aqueous media and the antifungal activity of both F1 and F2, revealing antimicrobial effects normally hidden by the presence of common solvents (e.g., DMSO) with some cellular inhibitory activity. The study of structural prerequisites for antimicrobial activity, and the inclusion in polymers to improve solubility, is important for the design of new drugs. © 2018 Carreño, Rodríguez, Páez-Hernández, Martin-Trasanco, Zúñiga, Oyarzún, Gacitúa, Schott, Arratia-Pérez and Fuentes.