Showing papers by "José Elguero published in 2023"
TL;DR: In this article , four mechanisms have been proposed in the literature to explain beryllium toxicity; they can be divided in two groups of two mechanisms: (i) replacement type: models 1 and 2; (ii) addition type: model 3 and 4.
Abstract: Abstract Four mechanisms have been proposed in the literature to explain beryllium toxicity; they can be divided in two groups of two mechanisms: (i) replacement type: models 1 and 2; (ii) addition type: models 3 and 4. At this moment is not possible to select the best model not even to establish if one of these models will be the ultimate mechanism of beryllium toxicity. However, it is important to know the still open discussion about something so important associated with one of the simplest elements of the periodic table.
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TL;DR: In this paper , the geometric and electronic structure of the paramagnetic salt of the metallacarborane sandwich complex [Fe(1,2-C2B9H11)2]Cs = FeSanCs.
Abstract: Mössbauer and X-ray photoelectron spectroscopies (XPS) are complemented with high-level quantum-chemical computations in the study of the geometric and electronic structure of the paramagnetic salt of the metallacarborane sandwich complex [Fe(1,2-C2B9H11)2]Cs = FeSanCs. Experimental 57Fe isomer shifts and quadrupole splitting parameters are compared with the theoretical prediction, with good agreement. The appearance of two sets of Cs(3d) doublets in the XPS spectrum, separated by 2 eV, indicates that Cs has two different chemical environments due to ease of the Cs(+) cation moving around the sandwich complex with low-energy barriers, as confirmed by quantum-chemical computations. Several minimum-energy geometries of the FeSanCs structure with the corresponding energies and Mössbauer parameters are discussed, in particular the atomic charges and spin population and the surroundings of the Fe atom in the complex. The Mössbauer spectra were taken at different temperatures showing the presence of a low-spin Fe atom with S = 1/2 and thus confirming a paramagnetic FeIII species.
TL;DR: Theoretical chemistry (M06-2x/aug-cc-pVDZ) was used to design a system based on ammonia boranes catalyzed by pyrazoles with the aim of producing dihydrogen, nowadays of high interest as clean fuel as discussed by the authors .
Abstract: Theoretical chemistry (M06-2x/aug-cc-pVDZ) was used to design a system based on ammonia boranes catalyzed by pyrazoles with the aim of producing dihydrogen, nowadays of high interest as clean fuel. The reactivity of ammonia borane and cyclotriborazane were investigated, including catalytic activation through 1H-pyrazole, 4-methoxy-1H-pyrazole, and 4-nitro-1H-pyrazole. The results point toward a catalytic cycle by which, at the same time, ammonia borane can initially store and then, through catalysis, produce dihydrogen and amino borane. Subsequently, amino borane can trimerize to form cyclotriborazane that, in presence of the same catalyst, can also produce dihydrogen. This study proposes therefore a consistent progress in using environmentally sustainable (metal free) catalysts to efficiently extract dihydrogen from small B-N bonded molecules.
TL;DR: In this paper , the reactivity of a B 3 P 3 -doped hexa-cata-hexabenzocoronene, as a model of nanographene, towards carbon dioxide was studied at the DFT M06-2X/6-311++G(3df,3pd)//M06 2X/ 6-31+G* level of theory.
Abstract: Abstract The reactivity of a B 3 P 3 -doped hexa-cata-hexabenzocoronene, as a model of nanographene (B 3 P 3 -NG), towards carbon dioxide was studied at the DFT M06-2X/6-311++G(3df,3pd)//M06-2X/6-31+G* level of theory. This compound can be classified as a poly-cyclic poly-Frustrated Lewis Pair (FLP) system, as it presents more than one Lewis Acid/Lewis Base pair on its surface, making the capture of several carbon dioxide molecules possible. Two scenarios were considered to fully characterize the capture of CO 2 by this multi-FLP system: (i) fixation of three CO 2 molecules sequentially one by one; and (ii) simultaneous contact of three CO 2 molecules with the B 3 P 3 -NG surface. The resulting adducts were analyzed as function of activation barriers and the relative stability of the CO 2 capture. A cooperativity effect due to the π-delocalization of the hexa-cata-hexabenzocoronene is observed. The fixation of a CO 2 molecule modifies the electronic properties. It enhances the capture of additional CO 2 molecules by changing the acidy and basicity of the rest of the boron and phosphorus atoms in the B 3 P 3 -NG system.
TL;DR: In this paper , the reaction of seventeen borane derivatives of five-membered N-heterocyclic rings (BNHRs) with CO 2 has been studied by means of DFT calculations.
Abstract: Abstract The reaction of seventeen borane derivatives of five-membered N-heterocyclic rings (BNHRs) with CO 2 has been studied by means of DFT calculations. Several non-covalent complexes between the BNHRs and CO 2 which evolve through a TS in a single adduct for each BNHR have been identified. The calculated IRC of the TS has allowed to identify the non-covalent complex involved in the reaction in each case. The stationary points of the reactions have been analyzed with the distortion/interaction partition model. In addition, empirical models have been attempted to correlate the acid (fluoride ion affinity) and basic (proton affinity) properties of the isolated BNHR with the TS barriers and adduct energies. The energetics of the reactions are influenced by the number of nitrogen atoms in the ring.
TL;DR: In this paper , the structure, stability, and bonding characteristics of triel hydride dimers and trimers involving BX3 and AlX3 (X = H, F, Cl) in the gas phase, many of them explored for the first time, were investigated using different DFT (B3LP, B3LYP/D3BJ, and M06-2X) and ab initio (MP2 and G4) methods together with different energy decomposition formalisms, namely, many-body interaction-energy and localized molecular orbital energy decompposition analysis.
Abstract: The structure, stability, and bonding characteristics of dimers and trimers involving BX3 and AlX3 (X = H, F, Cl) in the gas phase, many of them explored for the first time, were investigated using different DFT (B3LYP, B3LYP/D3BJ, and M06-2X) and ab initio (MP2 and G4) methods together with different energy decomposition formalisms, namely, many-body interaction-energy and localized molecular orbital energy decomposition analysis. The electron density of the clusters investigated was analyzed with QTAIM, electron localization function, NCIPLOT, and adaptive natural density partitioning approaches. Our results for triel hydride dimers and Al2X6 (X = F, Cl) clusters are in good agreement with previous studies in the literature, but in contrast with the general accepted idea that B2F6 and B2Cl6 do not exist, we have found that they are predicted to be weakly bound systems if dispersion interactions are conveniently accounted for in the theoretical schemes used. Dispersion interactions are also dominant in both homo- and heterotrimers involving boron halide monomers. Surprisingly, B3F9 and B3Cl9 C3v cyclic trimers, in spite of exhibiting rather strong B-X (X = F, Cl) interactions, were found to be unstable with respect to the isolated monomers due to the high energetic cost of the rehybridization of the B atom, which is larger than the two- and three-body stabilization contributions when the cyclic is formed. Another important feature is the enhanced stability of both homo- and heterotrimers in which Al is the central atom because Al is systematically pentacoordinated, whereas this is not the case when the central atom is B, which is only tri- or tetra-coordinated.
TL;DR: In this article , the energy of the NO3 radical and its influence in the reaction profiles of the reaction with CH2ClBr, CH2ICl, CH 2BrI, CHCl2Br, and CHClBr2 were investigated.
Abstract: In this Reply, we answer the main argument raised in the Comment about the energy of the NO3 radical and its influence in the reaction profiles of the reaction of the NO3 radical with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2 by C. J. Nielsen and Y. Tang. The optimized geometry of the NO3 radical has been obtained using 49 DFT functionals: 26 functionals predict a minimum with D3h symmetry and 23 with C2v symmetry. The former functionals have been used to calculate the thermodynamic values of three reactions (X + HNO3 → XH + NO3, X= OH, CH3 and CCl3) and compared with experimental data. Those functionals with smaller errors have been used to recalculate the barriers of the reaction of NO3 with CH2ClBr, CH2ICl, CH2BrI, CHCl2Br, and CHClBr2. The results show differences of 10.5 kJ mol-1 when compared to those obtained with the M08HX functional.
TL;DR: In this article , a complete crystallographic study of three series of N1-aryl substituted-2-pyrazolines, the aryl group being 4-nitrophenyl (series 1), 2,4-dinitrophenymethylene (series 2), and 2, 4,6-trinitrophensyl(series 3) is presented and compared with data for related heterocycles found in the Cambridge Structural Database (2020.2.0).
Abstract: Herein, we present a complete crystallographic study of three series of N1-aryl substituted-2-pyrazolines, the aryl group being 4-nitrophenyl (series 1), 2,4-dinitrophenyl (series 2), and 2,4,6-trinitrophenyl (series 3). The structural features, bond distances and angles as well as torsions for each single compound will be described and comparatively discussed with data for related heterocycles found in the Cambridge Structural Database (2020.2.0). A deeper look at the data has been achieved to know the influence of the substituents on the molecular structures. In the crystals of compounds with stereogenic centers at positions 4 and 5, the presence of both enantiomers has been encountered in 12 cases out of 14 that include a literature result. Finally, molecular packings in all series have been analyzed reaching the conclusion that they follow several patterns depending on the existence or not, and the type of intermolecular interactions. A general pattern has been observed which implies a certain tendency of the molecules to arrange into chains, whose additional contacts could extend the dimensionality of the network.