Papers by Jose L Mendoza-cortes
Chemical Society Reviews, 2009
This <i>critical review</i> covers the application of computer simulations, including... more This <i>critical review</i> covers the application of computer simulations, including quantum calculations (<i>ab initio</i> and DFT), grand canonical Monte-Carlo simulations, and molecular dynamics simulations, to the burgeoning area of the hydrogen storage by metalorganic ...
Bilayer graphene (BLG) is a semiconductor whose band gap and properties can be tuned by various m... more Bilayer graphene (BLG) is a semiconductor whose band gap and properties can be tuned by various methods such as doping or applying gate voltage. Here, we show how to tune electronic properties of BLG by intercalation of transition metal (TM) atoms between two monolayer graphene (MLG) using a novel dispersion-corrected first-principle density functional theory (DFT) approach. We intercalated V, Nb, and Ta atoms between two MLG. We found that the symmetry, the spin, and the concentration of TM atoms in BLG-intercalated materials are the important parameters to control and to obtain a Dirac cone in their band structures. Our study reveals that the BLG intercalated with one vanadium (V) atom, BLG-1V, has a Dirac cone at the K-point. In all the cases, the present DFT calculations show that the 2p z sub-shells of C atoms in graphene and the 3d yz sub-shells of the TM atoms provide the electron density near the Fermi energy level (E F) which controls the material properties. Thus, we show that out-of-plane atoms can influence in-plane electronic densities in BLG and enumerate the conditions necessary to control the Dirac point. This study offers insight into the physical properties of 2D BLG intercalated materials and presents a new strategy for controlling the electronic properties of BLG through TM intercalation by varying the concentration and spin arrangement of the metals resulting in various conducting properties, which include: metal, semi-metal and semiconducting states. Published by AIP Publishing. https://doi.org/10.1063/1.5008996
Covalent−organic frameworks (COFs) are intriguing platforms for designing functional molecular ma... more Covalent−organic frameworks (COFs) are intriguing platforms for designing functional molecular materials. Here, we present a computational study based on van der Waals dispersion-corrected hybrid density functional theory (UB3LYP-D2, i.e., DFT-D) to design boroxine-linked and triazine-linked COFs intercalated with Fe. Keeping the original P−6m2 symmetry of the pristine COF (COF-Fe-0), we have computationally designed seven new COFs by intercalating Fe atoms between two organic layers. The equilibrium structures and electronic properties of both the pristine and Fe-intercalated COF materials are investigated here. We predict that the electronic properties of COFs can be fine-tuned by adding Fe atoms between two organic layers in their structures. Our calculations show that these new intercalated-COFs are promising semiconductors. The effect of Fe atoms on the electronic band structures and density of states (DOSs) has also been investigated using the aforementioned DFT-D method. The contribution of the d-subshell electron density of the Fe atoms plays an important role in improving the semiconductor properties of these new materials. These intercalated-COFs provide a new strategy to create semiconducting materials within a rigid porous network in a highly controlled and predictable manner.
We show a comprehensive study on the structure and electronic properties of a layered manganese o... more We show a comprehensive study on the structure and electronic properties of a layered manganese oxide commonly known as birnessite. We present the effects of substituting different intercalated cations (Li+, Na+, K+, Be2+, Mg2+, Ca2+, Sr2+, Zn2+, B3+, Al3+, Ga3+, Sc3+, and Y3+) and the role of waters in the intercalated layer. The importance of the Jahn–Teller effect and ordering of the Mn3+ centers due to cation intercalation are addressed to explain the ability to tune the indirect band gap (Egi) from 2.63 to ∼2.20 eV and the direct band gap (Egd) from 3.09 to ∼2.50 eV. By aligning the structures’ bands, we noted that structures with Sr, Ca, B, and Al have potential for usage in water splitting, and anhydrous B-birnessite is predicted to have a suitable direct band gap for light capturing. Furthermore, we also demonstrate how the effects of cations in the bulk differ from the behavior on single layer surfaces. More specifically, we show that an indirect to direct band transition is observed when we separate the bulk into a single layer oxide. This study shows a new strategy for tuning the band gap of layered materials to capture light which may couple to its intrinsic water-splitting catalytic properties, thus resembling photosynthesis.
Theory, Calculations, and Experiments, 2015
The electron-impact mass spectra of the tris(pentafluorophenyl)boroxine (1) and triphenylboroxine... more The electron-impact mass spectra of the tris(pentafluorophenyl)boroxine (1) and triphenylboroxine were analyzed to probe the McLafferty type of rearrangements involving 1,3-fluorine or 1,3-hydrogen migrations to boron from the adjacent aromatic rings. 1,3-Sigmatropic fluorine migration leading to the McLafferty rearrangement of 1 results in the formation of the tetrafluorobenzyne radical cation (1c), whereas the similar rearrangement involving 1,3-hydrogen rearrangement is not observed for the nonfluorinated analog 2. The DFT calculations show that the activation barrier for the 1,3-fluorine migration in 1 is significantly lower than that for the 1,3-hydrogen migration in 2 (DDG z w33 kcal/ mol), which is in accordance with the observed 1,3-fluorine migration for the fluorinated boroxine and the lack of such rearrangement for the nonfluorinated boroxine. The 1:1 stoichiometry of the fluoride anion with 1 has also been demonstrated by high resolution electrospray ionization time-of-flight mass spectrometry.
![Research paper thumbnail of Visible Light Sensitized CO 2 Activation by the Tetraaza [Co II N 4 H(MeCN)] 2+ Complex Investigated by FT-IR Spectroscopy and DFT Calculations](https://attachments.academia-assets.com/45030850/thumbnails/1.jpg)
The Journal of Physical Chemistry C, 2015
In situ FT-IR measurements and electronic structure calculations are reported for the reduction o... more In situ FT-IR measurements and electronic structure calculations are reported for the reduction of CO 2 catalyzed by the macrocyclic complex [Co II N 4 H] 2+ (N 4 H = 2,12-dimethyl-3,7,11,17-tetraazabicyclo-[11.3.1]-heptadeca-1(17),2,11,13,15-pentaene). Beginning from the [Co II N 4 H] 2+ resting state of the complex in wet acetonitrile solution, two different visible light sensitizers with substantially different reducing power are employed to access reduced states. Accessing reduced states of the complex with a [Ru(bpy) 3 ] 2+ sensitizer yields an infrared band at 1670 cm −1 attributed to carboxylate, which is also observed for an authentic sample of the one-electron reduced complex [CoN 4 H(MeCN)] + in CO 2 saturated acetonitrile solution. The results are interpreted based on calculations using the pure BP86 functional that correctly reproduces experimental geometries. Continuum solvation effects are also included. The calculations show that Co is reduced to Co I in the first reduction, which is consistent with experimental d−d spectra of square Co(I) macrocycle complexes. The energy of the CO 2 adduct of the one-electron reduced catalyst complex is essentially the same as for [CoN 4 H(MeCN)] + , which implies that only a fraction of the latter forms an adduct with CO 2 . By contrast, the calculations indicate a crucial role for redox noninnocence of the macrocyclic ligand in the doubly reduced state, [Co I (N 4 H) −• ], and show that [Co I (N 4 H) −• ] binds partially reduced CO 2 fairly strongly. Experimentally accessing [Co I (N 4 H) −• ] with an Ir(bpy) 3 sensitizer with greater reducing power closes the catalytic cycle as FT-IR spectroscopy shows CO production. Use of isotopically substituted C 18 O 2 also shows clear evidence for 18 O-substituted byproducts from CO 2 reduction to CO. . Oxidation states of cobalt obtained for the different species discussed in this work in the gas phase and using implicit solvation. The boxes indicate the oxidation state obtained by the different functionals using the LOBA analysis.
The Journal of Physical Chemistry A, 2012
The Yaghi laboratory has developed porous covalent organic frameworks (COFs), COF102, COF103, and... more The Yaghi laboratory has developed porous covalent organic frameworks (COFs), COF102, COF103, and COF202, and metalÀorganic frameworks (MOFs), MOF177, MOF180, MOF200, MOF205, and MOF210, with ultrahigh porosity and outstanding H 2 storage properties at 77 K. Using grand canonical Monte Carlo (GCMC) simulations with our recently developed first principles based force field (FF) from accurate quantum mechanics (QM), we calculated the molecular hydrogen (H 2 ) uptake at 298 K for these systems, including the uptake for Li-, Na-, and K-metalated systems. We report the total, delivery and excess amount in gravimetric and volumetric units for all these compounds. For the gravimetric delivery amount from 1 to 100 bar, we find that eleven of these compounds reach the 2010 DOE target of 4.5 wt % at 298 K. The best of these compounds are MOF200-Li (6.34) and MOF200-Na (5.94), both reaching the 2015 DOE target of 5.5 wt % at 298 K. Among the undoped systems, we find that MOF200 gives a delivery amount as high as 3.24 wt % while MOF210 gives 2.90 wt % both from 1 to 100 bar and 298 K. However, none of these compounds reach the volumetric 2010 DOE target of 28 g H 2 /L. The best volumetric performance is for COF102-Na (24.9), COF102-Li (23.8), COF103-Na (22.8), and COF103-Li (21.7), all using delivery g H 2 /L units for 1À100 bar. These are the highest volumetric molecular hydrogen uptakes for a porous material under these thermodynamic conditions. Thus, one can obtain outstanding H 2 uptakes with Li, Na, and K doping of simple frameworks constructed from simple, cheap organic linkers. We present suggestions for strategies for synthesis of alkali metal-doped MOFs or COFs.
Journal of Computational Chemistry, 2015
Previous calculations suggested that di-tetrazine-tetroxide (DTTO), aka tetrazino-tetrazine-tetra... more Previous calculations suggested that di-tetrazine-tetroxide (DTTO), aka tetrazino-tetrazine-tetraoxide, might have a particularly large density (2.3 g/cm 3 ) and high energy release (8.8 kJ/kg), but it has not yet been synthesized successfully. We report here density functional theory (DFT) (M06, B3LYP, and PBE-ulg) on 20 possible isomers of DTTO. For the two most stable isomers, c1 and c2 we predict the best packings (i.e., polymorphs) among the 10 most common space groups for organic molecular crystal using the Universal force field and Dreiding force field with Monte Carlo sampling. This was followed by DFT calculations at the PBE-ulg level to optimize the crystal packing. We conclude that the c1 isomer has the P2 1 2 1 2 1 space group with a density of 1.96 g/cm 3 , while the c2 isomer has the Pbca space group with a density of 1.98 g/cm 3 . These densities are among the highest of current energetic materials, RDX (1.81 g/cm 3 ) and CL20 (2.01 g/cm 3 ). We observe that the stability of the polymorphs increases with the density while the planarity decreases.
The Journal of Physical Chemistry A, 2011
ChemInform, 2009
ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance t... more ABSTRACT ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
The Journal of Physical Chemistry A, 2010
Chemical Society Reviews, 2009
This critical review presents a comprehensive study of transition-metal carboxylate clusters whic... more This critical review presents a comprehensive study of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) towards construction and synthesis of metal-organic frameworks (MOFs). We describe the geometries of 131 SBUs, their connectivity and composition. This contribution presents a comprehensive list of the wide variety of transition-metal carboxylate clusters which may serve as secondary building units (SBUs) in the construction and synthesis of metal-organic frameworks. The SBUs discussed here were obtained from a search of molecules and extended structures archived in the Cambridge Structure Database (CSD, version 5.28, January 2007) which included only crystals containing metal carboxylate linkages (241 references).
Physisorption in porous materials is a promising approach for meeting H 2 storage requirements fo... more Physisorption in porous materials is a promising approach for meeting H 2 storage requirements for the transportation industry, because it is both fully reversible and fast at mild conditions. However, most current candidates lead to H 2 binding energies that are too weak (leading to volumetric capacity at 298 K of <10 g/L compared to the DOE 2015 Target of 40 g/L). Using accurate quantum mechanical (QM) methods, we studied the H 2 binding energy to 48 compounds based on various metalated analogues of five common linkers for covalent organic frameworks (COFs). Considering the first transition row metals (Sc though Cu) plus Pd and Pt, we find that the new COF-301-PdCl 2 reaches 60 g total H 2 /L at 100 bar, which is 1.5 times the DOE 2015 target of 40 g/L and close to the ultimate (2050) target of 70 g/L. The best current materials, , are predicted to store 7.6 g/L (0.54 wt % excess) and 9.6 g/L (0.87 wt % excess), respectively, at 298 K and 100 bar compared with 60 g/L (4.2 wt % excess) for COF-301-PdCl 2 .
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Papers by Jose L Mendoza-cortes