Roberto Salcedo

Universidad Nacional Autónoma de México, Ciudad de México, Mexico City, Mexico

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Publications (116)246.64 Total impact

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    ABSTRACT: Large fullerenes such as C180 and C116 can be used as hosts for other molecules of the same family. Based on this idea, two complexes were designed, one in which C180 accepts a C60 molecule as a guest and the other in which C20 was placed inside C116. The behavior of these new assemblies was closer to that of a large endohedral complex rather than onion-like. There were marked differences between the systems. In the first system, there was minor interaction between the two cages but the association resulted in a more stable thermodynamic state. In the second system, there was strong electronic interchange between the cages, and the thermodynamic results suggest that such a combination might be useful for forming stable C20.
    Journal of Molecular Modeling 04/2015; 21(4):2646. DOI:10.1007/s00894-015-2646-9 · 1.87 Impact Factor
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    ABSTRACT: Colloidal solutions at room temperature were used to obtain various polymorphic forms of a [PcCoCN]n and double potassium salt from 1,8 dihydroxyanthraquinone derivative. Nanocrystals in the form α and β were characterized using IR and UV–Vis spectroscopy techniques. Likewise in this context, an energy doublet in the absorption spectra of the monoclinic form at 1.8 and 2 eV was observed. The complex structure inherent to the spectra of the CoPc derivative is attributed to the simultaneous presence of both crystalline and molecular phases in the samples. The optical absorption of the compound was also investigated in order to evaluate changes in the electronic structure of these metal organic nanostructures. The absorption spectra of the CoPc derivative recorded in the UV–Vis region manifested two absorption bands, namely the Q- and B- bands. DFT calculations of this structure help to establish the source of the spectroscopic behavior and also lead to a particular phenomenon not known previously in this kind of complex, because the optimized structure of the cobalt complex manifests a very strange deformation of the bond between the anthraquinone derivative and the cobalt atom; the origin of this deformation is also discussed.
    Journal of Molecular Structure 03/2015; 1084. DOI:10.1016/j.molstruc.2014.11.071 · 1.60 Impact Factor
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    ABSTRACT: The [2+2] cycloaddition reaction between a double bond from a fullerene and an oestrogen or similar organic derivative has been studied in the scheme of the ab initio atom-centred density matrix propagation molecular dynamics model. The reaction was simulated considering vacuum, a little polar medium (butyric acid) and a strong polar medium (water). The results are completely different with the change of environments; some leading to an unidentified broken species without identification, whereas others produced a defined organic complex. The reaction stages have been analysed here and possible applications for medicine are achieved.
    Molecular Simulation 12/2014; 41(15). DOI:10.1080/08927022.2014.983100 · 1.12 Impact Factor
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    ABSTRACT: The electronic structure of hyperbranched polymers obtained from para-diaminodiphenyldiacetylenes as AB(2) type monomers by one-step polymerization is studied using DFT calculations. Five generations are modelled with optimization at each step. As the molecule grows it shows a helical shape conserving the C2 symmetry with wing like fragments covering the backbone. There is accidental degeneracy of the HOMO with the HOMO-1 and of the HOMO-2 with the HOMO-3. The LUMO is always located at the backbone and the HOMO set at the dianyline-pyrrole fragment. The HOMO-LUMO gap decreases as the molecule grows. Conductivity measurements as well as microscopy studies of para-hyperbranched polymer were carried out. Conductivity measurements as a function of temperature show semiconductor behavior. Optical microscopy reveals a macroscopic crystalline structure of this hyperbranched polymer. (c) 2014 Elsevier B.V. All rights reserved.
    Journal of Molecular Structure 09/2014; 1074:534-541. DOI:10.1016/j.molstruc.2014.06.031 · 1.60 Impact Factor
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    ABSTRACT: Simulated compounds have been proposed for organometallic clusters of nanodiamond with iron; the complexes take advantage of carboxylic ending in order to form a comprehensive bond with the metal ion. The performance is notorious; it seems that the control of electronic behavior is localized on both, the metallic atom and the carboxylic fragments, but not on the intrinsic nanodiamond unities, however, the presence of these nanodiamond ligands is fundamental to establish a sort of electronic confinement, which is responsible of the peculiar electronic behavior. The nature of the frontier molecular orbitals is also studied. (c) 2014 Elsevier B.V. All rights reserved.
    Computational and Theoretical Chemistry 05/2014; 1035. DOI:10.1016/j.comptc.2014.02.017 · 1.37 Impact Factor
  • Citlalli Rios · Roberto Salcedo
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    ABSTRACT: A number of hexaarylbenzene compounds were studied theoretically, in order to compare energy changes as a result of the toroidal delocalization effect that is characteristic of all these species. The energy was studied taking advantage of locally designed isodesmic reactions. Results indicate that the amount of aromaticity manifested by each substituent is a factor that should be considered when assessing the quantity of energy dissipated from each aromatic center. The influence of different substituents on electronic delocalization is also analyzed, as well as the role played by their frontier molecular orbitals.
    Molecules 03/2014; 19(3):3274-3296. DOI:10.3390/molecules19033274 · 2.42 Impact Factor
  • Anabel Ruiz-Espinoza · Estrella Ramos · Roberto Salcedo
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    ABSTRACT: The ubiquitous benzene derivative of fullerene has been analyzed from a theoretical point of view. The pronounced difficulties involved in its preparation relate to the structure of the frontier orbitals of the primitive fragments (i.e. benzene and fullerene C60) and their corresponding interactions. The nature of the inductive effect is studied on the basis of the nitro and amino derivatives (functional groups substituted on benzene ring). The electrophilic activation/deactivation patterns induced by substituent groups added to phenyl-fullerene molecule are studied applying the criteria of reactivity indexes in conjunction with the molecular electrostatic potential and the dipole moment of the molecules. The capacity of the resultant molecule to generate organometallic derivatives similar to the dibenzene-chromium is also studied. All structures were calculated using DFT methods.
    Computational and Theoretical Chemistry 07/2013; 1016:36–41. DOI:10.1016/j.comptc.2013.04.011 · 1.37 Impact Factor
  • Citlalli Rios · Roberto Salcedo
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    ABSTRACT: Lanthanum is able to join in eta(5) and eta(6) fashion to cyclopentadienyl and phenyl rings, yielding known organometallic complexes, where the metal manifests oxidation number 2. A theoretical comparison between these types of molecules and the known cyclopentadienyl derivatives with oxidation number 3 indicates that some kind of extra stabilization takes place in the case of the first compounds and this study attempts to find an explanation for this phenomenon. Besides this, we also present an electronic description of both kinds of organolanthanum complexes.
    Polyhedron 07/2013; 57:47-51. DOI:10.1016/j.poly.2013.04.018 · 2.05 Impact Factor
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    ABSTRACT: In this article, the antioxidant activity of fullerene is theoretically studied by applying the density functional theory (DFT) method in terms of its protective effects against the derivatives of estrone that constitute species known to exhibit carcinogenic activity. Several reactions involving fullerene C60 in different possible reactive centres of estradiol and epoxidised estradiol were studied. Surprisingly, the ring that supports the epoxide group is able to react with fullerene by means of a 2+2 cycloaddition, forming a very stable compound. This new compound has the potential to avoid known reactions between the epoxidised molecule and DNA fragments causing the mutagenic process of breast cancer. Therefore, fullerene C60 represents the possibility of a new agent for combating this disease.
    Molecular Simulation 07/2013; 39(8). DOI:10.1080/08927022.2012.758845 · 1.12 Impact Factor
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    ABSTRACT: We describe herein the first synthesis of a new class of anti-aromatic planar cyclooctatetraenes: the azatrioxa[8]circulenes. This was achieved by treating a suitably functionalised 3,6-dihydroxycarbazole with 1,4-benzoquinones or a 1,4-naphthoquinone. We fully characterised the azatrioxa[8]circulenes by using optical, electrochemical and computational techniques as well as by single-crystal X-ray crystallography. The results of a computational study (NICS) suggest that the central planar cyclooctatetraene is anti-aromatic when the molecules are in neutral or oxidised states (2+), and that the corresponding dianions are aromatic. We discuss the aromatic/anti-aromatic nature of the planar cyclooctatetraenes and compare them with the isoelectronic tetraoxa[8]circulenes.
    Chemistry - A European Journal 03/2013; 19(12):3898-904. DOI:10.1002/chem.201203113 · 5.70 Impact Factor
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    Delia Soto · Roberto Salcedo
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    ABSTRACT: The different coordination modes in fullerene organometallic complexes are reviewed. The main modes are η2 and η5, but there are some interesting studies about the other four, all of them are revised in order to show which is the state of art of this kind of compounds with the respect of the hapticity.
    Molecules 12/2012; 17(6):7151-68. DOI:10.3390/molecules17067151 · 2.42 Impact Factor
  • Citlalli Rios · Roberto Salcedo
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    ABSTRACT: C(80) is a fullerene species which appears in different isomeric configurations. A general homodesmotic reaction previously designed to study the energy of fullerenes was implemented, in order to analyze the energy of this family of isomers. These results concur with some of the experimental data, but energy differences referring to all the configurations yield novel propositions about their particular behavior. The corresponding lanthanum complexes are also analyzed here and a new isodesmic reaction was designed for this particular case.
    Molecules 12/2012; 17(12):14588-14601. DOI:10.3390/molecules171214588 · 2.42 Impact Factor
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    ABSTRACT: Recently synthesized π-extended symmetrical tetraoxa[8]circulenes that exhibit electroluminescent properties were calculated at the density functional theory (DFT) level using the quantum theory of atoms in molecules (QTAIM) approach to electron density distribution analysis. Nucleus-independent chemical shift (NICS) indices were used to characterize the aromaticity of the studied molecules. The tetraoxa[8]circulene molecules were found to consist of two antiaromatic perimeters (according to the Hückel "4n" antiaromaticity rule) that include 8 and 24 π-electrons. Conversely, NICS calculations demonstrated the existence of a common π-extended system (distributed like a flat ribbon) in the studied tetraoxa[8]circulene molecules. Thus, these symmetrical tetraoxa[8]circulene molecules provide examples of diatropic systems characterized by the presence of induced diatropic ring currents.
    Journal of Molecular Modeling 10/2012; 19(2). DOI:10.1007/s00894-012-1617-7 · 1.87 Impact Factor
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    ABSTRACT: Density functional theory calculations and theoretical representations of the density of states (DOS) were undertaken in order to understand the electronic properties of silicon nanocrystals (Si-nc), when partially passivated with Cl and F. Effects relating to cluster size (Si29, Si35, and Si87), type, and percentages of halogen surface passivant, concerning both the cluster gap and electron-donor–acceptor capabilities, were analyzed. These calculations indicate that as the percentage of Cl and F substitution increases, the energy of the LUMO decreases, and consequently, the HOMO–LUMO gap decreases. Correspondingly, we found that the high-electronegativity substituent Cl and F atoms produce the appearance of shoulders in the DOS band edges, thus reducing the band gap. These results explain the photoluminescent experimental data reported for Si-nc. The evaluation of the electrodonating and electroaccepting powers of Si-nc partially passivated with Cl and F indicates that Si-nc have potential applications for bulk heterojunction solar cells and electroluminescent devices.
    The Journal of Physical Chemistry 02/2012; 116(6):3988-3994. DOI:10.1021/jp212013a · 2.78 Impact Factor
  • Roberto Salcedo
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    ABSTRACT: A brief summary about the research lines of our group is presented. The common factor in all the propositions is the fullerene in a chemical reactive role. The chemistry proposed is novel and can yield interesting results.
    MRS Online Proceeding Library 01/2012; 1483. DOI:10.1557/opl.2012.1618
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    ABSTRACT: The phenomenon of formation of two isomers, yellow and orange, of the cyclometalated Ru(II) complex, [Ru(o-C₆H₄-py)(MeCN)₄]⁺, was investigated by EELS spectroscopy and theoretical calculations. Both forms show very similar structures and spectroscopic properties, but slight differences in X-ray data and absorption between them were noted. No double minimum on the potential energy surface was found and thus these two forms cannot be considered as bond stretching isomers. However, the DFT study revealed the change in the hybridization of the carbon in trans-position of one of acetonitrile ligands. This effect can be responsible for the difference in colour. The results of the theoretical modelling coincide well with the experimental EELS data.
    Molecules 01/2012; 17(1):34-47. DOI:10.3390/molecules17010034 · 2.42 Impact Factor
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    ABSTRACT: Theoretical calculations were performed on 2, 5-aromatic substituted pyrroles which have a nitro-benzene or a cyano-benzene link to the nitrogen atom of the pyrrol fragment. The molecules manifested interesting semiconductor behavior that was confirmed when thin films were prepared and their corresponding electrical characterization undertaken. The reason for this behavior is discussed, with reference to the electron withdrawing feature of the substituents in the benzene chain.
    MRS Online Proceeding Library 01/2012; 1483. DOI:10.1557/opl.2012.1619
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    Bertha Molina · Liliana Pérez-Manriquez · Roberto Salcedo
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    ABSTRACT: Novel organometallic complexes of fullerene C₈₀ and aryl ligands were simulated. The nature and characteristics of this family of complexes involving π coordination between the fullerene and a metal centre have been studied from a theoretical point of view. We are particularly interested in complexes where η⁶ coordination is present, this being the strangest manifestation of known coordinations, and thus we have studied several known and simulated compounds of this kind in order to understand the lack of examples. The presence of other η⁶ or η⁵ ligands on the opposite side seems to be an important element aiding the stabilization of these complexes, also inducing the conductive and semiconductive behaviour of the studied species.
    Molecules 12/2011; 16(6):4652-9. DOI:10.3390/molecules16064652 · 2.42 Impact Factor
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    Roberto Salcedo · Lioudmila Fomina
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    ABSTRACT: Astronomical observations have revealed diffuse interstellar bands ranging from blue in the visible spectrum to the near IR. It has been suggested that these bands exist, owing to the presence of polyaromatic hydrocarbons or fullerene in the vicinity of certain stars, and constitute residual material from stellar explosions. The intention here is to study the relative stability of these species, when exposed to extreme conditions. The aromaticity of polycarbon molecules is an important aspect of this explanation.
    Structural Chemistry 10/2011; 22(5). DOI:10.1007/s11224-011-9780-5 · 1.90 Impact Factor

Publication Stats

631 Citations
246.64 Total Impact Points

Institutions

  • 1989–2015
    • Universidad Nacional Autónoma de México
      • • Materials Research Institute (IIM-UNAM)
      • • Department of Polymers
      Ciudad de México, Mexico City, Mexico
  • 1990–2006
    • Corporación Mexicana de Investigación en Materiales
      Saltillo, Coahuila, Mexico
  • 2001–2005
    • Instituto Mexicano del Petroleo
      Villa Gustavo A. Madero, The Federal District, Mexico