Roberto Salcedo

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

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Publications (124)249.51 Total impact

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    ABSTRACT: Several octahedral iron complexes that contain two lateral diamondoid (formerly called nanodiamond) units (joined by terminal COO1- groups) have been proposed. All newly proposed coordination species reach a stable configuration. The nature of the apical substituents (H2O, NH3, CO, CN1-, NO) accounts for the change in properties of the resultant compounds, therefore those compounds containing H2O or NH3 ligands manifest a scheme of chemical properties similar to their analogues as coordination compounds. Furthermore the complexes containing CO or CN1- ligands fulfill the typical description of organometallic species, whereas the complexes with the NO ligand, in their three manifestations, range between both behaviors and are studied as a special case. However, in all cases, the diamondoid ligands work as insulator walls restricting electronic movements to the regions which accommodate the metallic center, the apical ligands and the terminal COO1- groups. The nature of the molecular orbitals scheme shows wide variation that ranges between insulator and conductor behavior.
    No preview · Article · Dec 2015
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    ABSTRACT: TTF derivative of substituted pyrrole was obtained by means electrochemical synthesis, the resultant colored mix was characterized by Mass spectrometry, NMR and EPR studies, its intrinsic electronic behavior was measured by a four point probe method, besides theoretical calculations were carried out on the possible structures of the resultant molecular adduct. All the results show that there is a net transfer of an electron between both organic moieties in solution giving place to a semiconductor species.
    No preview · Article · Dec 2015
  • Estrella Ramos · Ana Martinez · Citlali Rios · Roberto Salcedo
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    ABSTRACT: The electronic properties of nine different hexaarylbenzene molecules substituted by sandwich compounds have been studied by applying density functional theory. Different structures and the particular electron donor power of these systems have been considered in order to analyse their oxidant capacity, using bis(ciclopentadienyl) scandium, ferrocene and bis(benzene)chromium as sandwich compounds. Both monometallic and bimetallic combinations are investigated. According to the Ionization Energies and Electron Affinities, compounds with Cr are nucleophiles and represent the best electron donors, whereas compounds with Sc are electrophiles and represent the best electron acceptors. The worse electron donor or acceptor is hexakis(4-ferrocenyl phenyl) benzene. This is very significant, as it implies that the very well-known electronic properties of hexakis(4-ferrocenyl phenyl) benzene can be improved by substituting with other metals, such as Sc and Cr. This suggests several possible applications for these compounds.
    No preview · Article · Nov 2015 · The Journal of Physical Chemistry A
  • Roberto Salcedo
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    ABSTRACT: The possibility of having a metallocene species, in which metal atoms as well as the corresponding aromatic rings appear within a fullerene sphere, is analyzed from a theoretical point of view. The complexes were simulated by joining a Cr(C6H6) fragment to the inner wall of a C116 (Th) fullerene. The large cage of this fullerene makes it possible to place two of these fragments within the sphere, so that several possibilities for isomers can be contemplated, and the mono-endo, di-endo, mono-endo-mono-exo and di-exo geometries can be modeled and compared.
    No preview · Article · Jul 2015 · Polyhedron
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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.
    No preview · Article · Apr 2015 · Journal of Molecular Modeling
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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.
    No preview · Article · Mar 2015 · Journal of Molecular Structure
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    ABSTRACT: Hyperbranched structures containing pyrrole units were obtained from ortho- , meta- and para -diaminodiphenyldiacetylenes as AB 2 type monomers by one-step polymerization. The para-hyperbranched compound was observed by optical microscopy and scanning electron microscopy. Microscopy studies identify two phases. The first is the insoluble one which gives origin to flake type structures. The second is acetone soluble phase, which generated crystalline structure manifesting in optic anisotropy and rhomboids and triangles dendrimeric structures.
    No preview · Article · Jan 2015 · MRS Online Proceeding Library
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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.
    Full-text · Article · Dec 2014 · Molecular Simulation
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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.
    No preview · Article · Sep 2014 · Journal of Molecular Structure
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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.
    No preview · Article · May 2014 · Computational and Theoretical Chemistry
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    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.
    Preview · Article · Mar 2014 · Molecules
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    ABSTRACT: Novel hyperbranched molecules containing pyrrole units were obtained from ortho-, meta- and para-diaminodiphenyldiacetylenes, as AB2 type monomers by one-step polymerization. Diacetylenic fragments reacted with terminal amino groups in the presence of copper chloride to give pyrrole units. Diaminodiphenyldiacetylene monomers have been synthesized from ethynilanilines in three steps. The novel monomers and hyperbranched molecules were characterized by NMR, IR and thermal analysis. Some conductivity proofs were also carried out and this behavior was assessed. The electronic behavior of some of these molecules was studied by means of theoretical methods. DFT optimization processes were carried out for three structures derived from the generation growing. There are at least two conformational isomers of the structure (meta- and para-) which show conductivity properties, the meta-isomer shows semiconductor nature but this species is hard to modeling because the steric hindrances cause optimization problems and indeed the third generation species was not achieved. In other context, the para-isomer allows the calculation of three generations and shows clearly a tendency to narrow the energy gap between the frontier orbitals but besides the behavior of the HOMO-1 seems reinforce the conductivity phenomenon.
    No preview · Article · Jan 2014
  • 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.
    No preview · Article · Jul 2013 · Computational and Theoretical Chemistry
  • 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.
    No preview · Article · Jul 2013 · Polyhedron
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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.
    No preview · Article · Jul 2013 · Molecular Simulation
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    Full-text · Dataset · Jun 2013
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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.
    Full-text · Article · Mar 2013 · Chemistry - A European Journal
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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.
    Full-text · Article · Dec 2012 · Molecules
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    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.
    Preview · Article · Dec 2012 · Molecules
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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.
    Full-text · Article · Oct 2012 · Journal of Molecular Modeling

Publication Stats

960 Citations
249.51 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