17 results on '"Tiznado, William"'
Search Results
2. Searching for Systems with Planar Hexacoordinate Carbons.
- Author
-
Inostroza, Diego, Leyva-Parra, Luis, Yañez, Osvaldo, Solar-Encinas, José, Vásquez-Espinal, Alejandro, Valenzuela, Maria Luisa, and Tiznado, William
- Subjects
POTENTIAL energy surfaces ,ELECTROSTATIC interaction ,CARBON ,BERYLLIUM - Abstract
Here, we present evidence that the D
2h M2 C5 0/2+ (M = Li-K, Be-Ca, Al-In, and Zn) species comprises planar hexacoordinate carbon (phC) structures that exhibit four covalent and two electrostatic interactions. These findings have been made possible using evolutionary methods for exploring the potential energy surface (AUTOMATON program) and the Interacting Quantum Atoms (IQA) methodology, which support the observed bonding interactions. It is worth noting, however, that these structures are not the global minimum. Nonetheless, incorporating two cyclopentadienyl anion ligands (Cp) into the CaC5 2+ system has enhanced the relative stability of the phC isomer. Moreover, cycloparaphenylene ([8]CPP) provides system protection and kinetic stability. These results indicate that using appropriate ligands presents a promising approach for expanding the chemistry of phC species. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
3. Si6C18: A bispentalene derivative with two planar tetracoordinate carbons.
- Author
-
Inostroza, Diego, Leyva‐Parra, Luis, Yañez, Osvaldo, Cruz, J. César, Garza, Jorge, García, Víctor, Thimmakondu, Venkatesan S., Ceron, Maria L., and Tiznado, William
- Subjects
POTENTIAL energy surfaces ,ANALYTICAL chemistry ,CHEMICAL bonds ,MOLECULAR dynamics ,CARBON - Abstract
Here we show that substituting the ten protons in the dianion of a bispentalene derivative (C18H102−) by six Si2+ dications produces a minimum energy structure with two planar tetracoordinate carbons (ptC). In Si6C18, the ptCs are embedded in the terminal C5 pentagonal rings and participate in a three‐center, two‐electron (3c‐2e) Si‐ptC‐Si σ‐bond. Our exploration of the potential energy surface identifies a triphenylene derivative as the putative global minimum. Nevertheless, robustness to Born–Oppenheimer molecular dynamics (BOMD) simulations at 900 and 1500 K supports bispentalene derivative kinetic stability. Chemical bonding analysis reveals ten delocalized π‐bonds, which, according to Hückel's 4n + 2 π‐electron rule, would classify it as an aromatic system. Magnetically induced current density analysis reveals the presence of intense local paratropic currents and a weakly global diatropic current, the latter agreeing with the possible global aromatic character of this specie. [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
4. Planar Elongated B 12 Structure in M 3 B 12 Clusters (M = Cu-Au).
- Author
-
Solar-Encinas, José, Vásquez-Espinal, Alejandro, Leyva-Parra, Luis, Yañez, Osvaldo, Inostroza, Diego, Valenzuela, Maria Luisa, Orellana, Walter, and Tiznado, William
- Subjects
POTENTIAL energy surfaces ,CHEMICAL bonds ,DENSITY functional theory ,ANALYTICAL chemistry ,GENETIC algorithms - Abstract
Here, it is shown that the M
3 B12 (M = Cu-Au) clusters' global minima consist of an elongated planar B12 fragment connected by an in-plane linear M3 fragment. This result is striking since this B12 planar structure is not favored in the bare cluster, nor when one or two metals are added. The minimum energy structures were revealed by screening the potential energy surface using genetic algorithms and density functional theory calculations. Chemical bonding analysis shows that the strong electrostatic interactions with the metal compensate for the high energy spent in the M3 and B12 fragment distortion. Furthermore, metals participate in the delocalized π-bonds, which infers an aromatic character to these species. [ABSTRACT FROM AUTHOR]- Published
- 2023
- Full Text
- View/download PDF
5. E6C15 (E = Si–Pb): polycyclic aromatic compounds with three planar tetracoordinate carbons.
- Author
-
Inostroza, Diego, Leyva-Parra, Luis, Vásquez-Espinal, Alejandro, Contreras-García, Julia, Cui, Zhong-Hua, Pan, Sudip, Thimmakondu, Venkatesan S., and Tiznado, William
- Subjects
POLYCYCLIC aromatic compounds ,POTENTIAL energy surfaces ,AROMATIC compounds ,CARBON - Abstract
A systematic exploration of the potential energy surface reveals two global minima with three planar tetra coordinate carbons (ptCs) and two global minima with three quasi-ptCs for E
6 C15 (E = Si–Pb) combinations. These consist of aromatic polycyclic templates suitable for further design of different materials without hindering the ptC texture. [ABSTRACT FROM AUTHOR]- Published
- 2022
- Full Text
- View/download PDF
6. Insights on the structural and electronic properties of ScCn+, YCn+, LaCn+ (n = 3–6) systems
- Author
-
Osorio, Edison, Ferraro, Franklin, Hadad, C. Z., Rabanal-León, Walter A., and Tiznado, William
- Published
- 2016
- Full Text
- View/download PDF
7. Planar Hypercoordinate Carbons in Alkali Metal Decorated CE32− and CE22− Dianions.
- Author
-
Leyva‐Parra, Luis, Diego, Luz, Inostroza, Diego, Yañez, Osvaldo, Pumachagua‐Huertas, Rodolfo, Barroso, Jorge, Vásquez‐Espinal, Alejandro, Merino, Gabriel, and Tiznado, William
- Subjects
POTENTIAL energy surfaces ,ALKALI metals ,CHALCOGENS ,CHEMICAL bonds ,ANALYTICAL chemistry ,AB-initio calculations ,CARBON - Abstract
After exploring the potential energy surfaces of MmCE2p (E=S−Te, M=Li−Cs, m=2, 3 and p=m‐2) and MnCE3q (E=S−Te, M=Li−Cs, n=1, 2, q=n‐2) combinations, we introduce 38 new global minima containing a planar hypercoordinate carbon atom (24 with a planar tetracoordinate carbon and 14 with a planar pentacoordinate carbon). These exotic clusters result from the decoration of V‐shaped CE22− and Y‐shaped CE32− dianions, respectively, with alkali counterions. All these 38 systems fulfill the geometrical and electronic criteria to be considered as true planar hypercoordinate carbon systems. Chemical bonding analyses indicate that carbon is covalently bonded to chalcogens and ionically connected to alkali metals. [ABSTRACT FROM AUTHOR]
- Published
- 2021
- Full Text
- View/download PDF
8. Evaluation of restricted probabilistic cellular automata on the exploration of the potential energy surface of Be6B11−.
- Author
-
Yañez, Osvaldo, Inostroza, Diego, Usuga-Acevedo, Brandon, Vásquez-Espinal, Alejandro, Pino-Rios, Ricardo, Tabilo-Sepulveda, Mauricio, Garza, Jorge, Barroso, Jorge, Merino, Gabriel, and Tiznado, William
- Subjects
PROBABILISTIC automata ,POTENTIAL energy surfaces ,CELLULAR automata ,GENETIC algorithms ,ISOMERS - Abstract
Herein the performance of a modification within the hybrid algorithm implemented in the AUTOMATON program is introduced and evaluated. For the creation of the initial population, AUTOMATON combines a probabilistic automata procedure with a genetic algorithm used to evolve this population. The proposed modification is addressed to efficiently identify the minimum energy structures of systems composed of more than one type of atom and with a low computational cost. The effectiveness of this approach is evaluated in the determination of the minimum energy structures of Be
6 B11 − . The modification, aimed to explore the potential energy surface, consisted of filling the cells first with Be atoms in the process of creating the initial population. This order obeys the structural pattern established in the Be–B clusters reported to date. The results show that this variation not only identifies a more significant number of viable isomers but also to find a better putative global minimum than those previously reported in the literature. Therefore, it is recommended to be used as a complement to the standard searching process. [ABSTRACT FROM AUTHOR]- Published
- 2020
- Full Text
- View/download PDF
9. Carbon rings decorated with group 14 elements: new aromatic clusters containing planar tetracoordinate carbon.
- Author
-
Yañez, Osvaldo, Vásquez-Espinal, Alejandro, Báez-Grez, Rodrigo, Rabanal-León, Walter A., Osorio, Edison, Ruiz, Lina, and Tiznado, William
- Subjects
GROUP 14 elements ,INTRAMOLECULAR proton transfer reactions ,GROUP rings ,ANALYTICAL chemistry ,POTENTIAL energy surfaces ,CHEMICAL bonds - Abstract
A simple and chemically intuitive approach is used to design ptC-containing E–C clusters (E = Si–Pb). This approach consists in replacing three or two consecutive protons from an aromatic hydrocarbon by one E
2 4+ or one E2+ fragment, respectively. In the model, electrons from E are removed from the pz orbitals, emptying them. Si–Pb favors the formation of a 3c-2e (E–C–E) σ-bond, which involves the ptC. Additionally, the π-electronic cloud is delocalized through the E-pz orbitals allowing the E atoms to effectively take part in the electronic delocalization, preserving the 4n + 2 Hückel's rule from the parent hydrocarbon. Two aromatic monocycles and one aromatic bicycle – benzene (C6 H6 ), cyclopentadienyl anion (C5 H5 − ) and pentalene dianion (C8 H6 2− ) – have been transformed into C–E systems. After an extensive exploration of their potential energy surfaces, four new global minima with ptC are identified, resulting from the substitution of the protons by Si and Ge cations in C5 H5 − and C8 H6 2− (E3 C5 and E4 C8 ). The analysis of both the chemical bonding and the magnetic response to an external magnetic field confirms the aromatic character of these species. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
10. (Li6Si5)2–5: The Smallest Cluster‐Assembled Materials Based on Aromatic Si56− Rings.
- Author
-
Yañez, Osvaldo, Garcia, Victor, Garza, Jorge, Orellana, Walter, Vásquez‐Espinal, Alejandro, and Tiznado, William
- Subjects
POTENTIAL energy surfaces ,DENSITY functional theory ,AROMATIC compounds ,LITHIUM-ion batteries ,MICROPROBE analysis - Abstract
Extensive explorations of their potential energy surfaces, combined with high‐level quantum chemical computations, strikingly show that the lowest energy structures of the (Li6Si5)2–5 systems consist of 2–5 Si56− aromatic units, surrounded by Li+ counterions, respectively. These viable gas‐phase compounds are the pioneering reported cases of oligomers made by planar aromatic silicon rings. Based on the key evidence that these oligomers are energetically favored, and that their silicon rings aromaticity is thoroughly preserved, the Li6Si5 cluster is proposed as a potential assembly unit to build silicon‐lithium nanostructures, thus opening new paths to design Zintl compounds at the nanoscale level. Aromatic building blocks: After a systematic exploration of the potential energy surface of the (Li6Si5)2–5 clusters, it was found that the lowest energy structures in all cases are formed by multiple aromatic Si56− pentagonal units interacting electrostatically with lithium cations. These units maintain their geometric and electronic properties as revealed by chemical bonding and magnetic response analyses. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
11. A Fukui function-guided genetic algorithm. Assessment on structural prediction of Si n ( n = 12-20) clusters.
- Author
-
Yañez, Osvaldo, Vásquez‐Espinal, Alejandro, Inostroza, Diego, Ruiz, Lina, Pino‐Rios, Ricardo, and Tiznado, William
- Subjects
GENETIC algorithms ,CLUSTER analysis (Statistics) ,POTENTIAL energy surfaces ,SILICON ,STRUCTURAL analysis (Science) - Abstract
Theoretical studies are essential for the structural characterization of clusters, when it comes to rationalize their unique size-dependent properties and composition. However, the rapid growth of local minima on the potential energy surface (PES), with respect to cluster size, makes the candidate identification a challenging undertaking. In this article, we introduce a hybrid strategy to explore the PES of clusters. This proposal involves the use of a biased initial population of a genetic algorithm procedure. Each individual in this population is built by assembling small fragments, according to the best matching of the Fukui function. The performance of a genetic algorithm procedure. The performance of the method is assessed on the PES exploration of medium-sized Si
n clusters ( n = 12-20). The most relevant results are: (a) the method converges at almost half of the time used by the canonical version of the GA and, (b) in all the studied cases, with the exception of Si13 and Si16 , the method allowed to identify the global minimum (GM) and other important low-lying structures. Additionally, the apparent deficiency of the proposal to identify the GM was corrected when a Si atom, or other low-lying isomers, were considered to build the clusters. © 2017 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]- Published
- 2017
- Full Text
- View/download PDF
12. Designing 3-D Molecular Stars.
- Author
-
Tiznado, William, Perez-Peralta, Nancy, Islas, Rafael, Toro-Labbe, Alejandro, Ugalde, Jesus M., and Merino, Gabriel
- Subjects
- *
POTENTIAL energy surfaces , *MOLECULES , *LIGANDS (Chemistry) , *CHEMICAL structure , *LITHIUM , *CATIONS - Abstract
We have explored in detail the potential energy surfaces of the Si5Lin5-6 (n = 5-7) systems. We found that it is feasible to design three-dimensional star-like silicon structures using the appropriate ligands. The global minimum structure for Si5Li7+ has a perfect seven-peak star-like structure. The title compounds comprise, essentially, the Si56- ring interacting with lithium cations. The ionic character of the Si-Li interactions induces the formation of a bridged structure. Concomitantly, our calculations show that the reduction of the Pauli repulsion and the maximization of the orbital contribution are also significant for the star-like structure formation. Additionally, the MO analysis of the systems suggests that the role of the lithium atoms is to provide the precise number of electrons to the central Si5 unit. This is confirmed by the magnetic properties, which show that electron delocalization enhances the stability of the star-like structures proposed here. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
13. Reply to the 'Comment on "Exploiting electronic strategies to stabilize a planar tetracoordinate carbon in cyclic aromatic hydrocarbons"' by V. S. Thimmakondu, Chem. Commun., 2019, DOI: 10.1039/c9cc04639a.
- Author
-
Yañez, Osvaldo, Vásquez-Espinal, Alejandro, Pino-Rios, Ricardo, Ferraro, Franklin, Pan, Sudip, Osorio, Edison, Merino, Gabriel, and Tiznado, William
- Subjects
AROMATIC compounds ,POTENTIAL energy surfaces ,CARBON - Abstract
The effectiveness of our proposed approach to stabilize a planar tetracoordinate carbon (ptC) in cyclic aromatic hydrocarbons, introduced in the title article, is unquestionable as our exhaustive searches on the singlet and triplet potential energy surfaces of the new ptC molecules identified as viable species are reproducible. Besides, the T
1 diagnostic value for the Si2 C5 H2 system reported in the comment seems to be the T1 amplitudes. We recomputed the T1 diagnostic value using different software (Gaussian and ORCA), which gave similar values to that reported in our communication. Additionally, a multiconfigurational (complete active space SCF) calculation fully confirms the mono-configurational character of the questioned Si2 C5 H2 ptC structure. We accept that the linear isomer for the C7 H2 system, in the triplet electronic state, is competitive with the isomer reported in our article, in the singlet electronic state, as mentioned in the title comment. However, this is a minor correction that does not affect the primary goal and main conclusions of our communication. [ABSTRACT FROM AUTHOR]- Published
- 2019
- Full Text
- View/download PDF
14. 1,3-Dipolar cycloaddition of nitrile imines with α,β-unsaturated lactones, thiolactones and lactams: synthesis of ring-fused pyrazoles
- Author
-
Chandanshive, Jay Zumbar, González, Pedro Blas, Tiznado, William, Bonini, Bianca Flavia, Caballero, Julio, Femoni, Cristina, and Comes Franchini, Mauro
- Subjects
- *
RING formation (Chemistry) , *NITRILES , *IMINES , *LACTONES , *LACTAMS , *PYRAZOLES , *POTENTIAL energy surfaces - Abstract
Abstract: 1,3-Dipolar cycloaddition of nitrile imines with α,β-unsaturated five- and six-membered lactones, thiolactones and lactams gave ring-fused pyrazoles. Regioisomeric mixtures have been obtained with the 5-substituted pyrazole as the major cycloadduct. Only with the five-membered lactone the major product was the 4-acyl derivative. Computational studies, the use of the topological analysis of the Fukui functions and the potential energy surfaces (PES) theory allowed a theoretical description of the local reactivity in agreement with the observed high regiochemistry and with the role of the heteroatom adjacent to the carbonyl group. [Copyright &y& Elsevier]
- Published
- 2012
- Full Text
- View/download PDF
15. Graphene-supported MB36 clusters (M=Fe, Co, Ni) as a single-atom electrocatalyst for the oxygen reduction reaction: A DFT study.
- Author
-
Solar-Encinas, José, Vásquez-Espinal, Alejandro, Yañez, Osvaldo, Tiznado, William, and Orellana, Walter
- Subjects
- *
OXYGEN reduction , *POTENTIAL energy surfaces , *WATER clusters , *ACTIVATION energy , *DYNAMIC simulation , *NICKEL catalysts - Abstract
This study delves into the potential of MB 36 clusters (where M = Fe, Co, Ni) supported on graphene as effective single-atom catalysts (SACs). Our research is methodically segmented into several stages, each designed to validate the feasibility of the proposed material. We begin by investigating the potential energy surface of MB 36 clusters. Our findings reveal a preference for metallic atoms to position themselves above the central hexagonal vacancy of the B 36 cluster. This factor significantly contributes to the stabilization of the resultant MB 36 system. Subsequently, we employ ab-initio molecular dynamic simulations to affirm the stability of the graphene-supported MB 36 clusters. In the final stage, we evaluate the system's catalytic capability for the oxygen reduction reaction (ORR) by calculating the dissociation energy of O 2 and OOH post their adsorption on the M atom of the graphene-supported MB 36 cluster. These simulations suggest that FeB 36 could maintain stability at room temperature, exhibiting activation energies for O 2 and OOH dissociation lower than those previously reported on Fe/N/C-type SACs, approaching those found on the Pt(111) surface, the most efficient ORR electrocatalyst. This computational study suggests that graphene-supported FeB 36 clusters could emerge as a promising candidate for SACs. [Display omitted] [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF
16. Isoelectronic substitution from Si52− to Al5H52−: Exploration of the series Si5−n(AlH)n2− (n = 0–5).
- Author
-
Fuenzalida-Valdivia, Isabel, Beltran, Maria J., Ferraro, Franklin, Vasquez-Espinal, Alejandro, Tiznado, William, and Osorio, Edison
- Subjects
- *
ISOELECTRONIC sequences , *POTENTIAL energy surfaces , *CHEMICAL bonds , *MOLECULAR clusters , *SILICON - Abstract
We established that the transformation from Si 5 2− to Al 5 H 5 2− could be possible by the successive isoelectronic substitution of silicon atoms by Al H units. The potential energy surfaces for the series Si 5− n (AlH) n 2− ( n = 0–5) systems were explored in detail, and the global minima maintained the same overall deltahedral structure as the one of the Si 5 2− cluster. The conservation of the overall structure upon isoelectronic substitution was proven to happen due to the preservation of the chemical bonding pattern. Theoretical VDEs were calculated for the series LiSi 5− n (AlH) n − ( n = 1–4) systems to facilitate their experimental detection. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
17. Structure and stability of the Si4Li n (n =1–7) binary clusters
- Author
-
Osorio, Edison, Villalobos, Valeria, Santos, Juan C., Donald, Kelling J., Merino, Gabriel, and Tiznado, William
- Subjects
- *
MOLECULAR structure , *STABILITY (Mechanics) , *SILICON compounds , *BINARY metallic systems , *MICROCLUSTERS , *POTENTIAL energy surfaces , *PHENOMENOLOGICAL theory (Physics) - Abstract
Abstract: The potential energy surfaces of the Si4Li n (n =1–7) systems have been explored in detail and the global minimum structures were identified. The stability and growth patterns of the title clusters is rationalized in terms of the phenomenological shell model in which the tetrahedral Si4Li4 cluster is a closed shell (20 valence electron) highly stable cluster. Given that the structures reported herein are global minima on their corresponding potential energy surfaces, we propose them as good candidates for experimental detection. [Copyright &y& Elsevier]
- Published
- 2012
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.