Activation of dinitrogen as a dipolarophile in 1,3-Dipolar Cycloadditions: A theoretical study using nitrile imines as “Octet” 1,3-Dipoles

Theoretical calculations at the G4MP2 level of theory demonstrate that it is possible to activate dinitrogen to make it react in dipolar cycloadditions using neutral beryllium derivatives and other neutral metallic compounds. For the particular case of beryllium, the barrier decreases more than 40 kJ·mol -1 with respect to the non-catalysed reaction. The activation achieved is lower than using diazonium salts (models of protonated N 2 ), but still in a range that can be experimentally attainableThis work was carried out with financial support from the Ministerio de Economía y Competitividad (Project No. CTQ2015-63997-C2-2-P) and Comunidad Autónoma de Madrid (Project FOTOCARBON, ref. S2013/MIT-2841). Computer, storage and other resources from the CTI (CSIC) are gratefully acknowledged. M. M. Montero-Campillo also thanks Project FOTOCARBON for her research contrac

Hydrogen bonds are never of an “anti-electrostatic” nature : a brief tour of a misleading nomenclature

This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades (projects PID2021-125207NB-C31 and PID2021-125207NB-C32).A large amount of scientific works have contributed through the years to rigorously reflect the different forces leading to the formation of hydrogen bonds, the electrostatic and polarization ones being the most important among them. However, we have witnessed lately with the emergence of a new terminology, anti-electrostatic hydrogen bonds (AEHBs), that seems to contradict this reality. This nomenclature is used in the literature to describe hydrogen bonds between equally charged systems to justify the existence of these species, despite numerous proofs showing that AEHBs are, as any other hydrogen bond between neutral species, mostly due to electrostatic forces. In this Viewpoint, we summarize the state of the art regarding this issue, try to explain why this terminology is very misleading, and strongly recommend avoiding its use based on the hydrogen bond physical grounds.Peer reviewe

A theoretical survey of the UV–visible spectra of axially and peripherally substituted boron subphthalocyanines

The UV–visible spectra of a series of subphthalocyanines (SubPcs) characterized by three different axial substituents (An ) in combination with H, F, NO2, SO2 H and SO2 CH3 peripheral substituents (Ri ) were predicted and analyzed by means of time-dependent DFT calculations, including chloroform as a solvent. In this analysis, we paid particular attention to the Q band, which remained almost unchanged regardless of the nature of the axial substituent. For the same axial substituent, changes in the Q band were also rather small when hydrogens at the periphery were replaced by R1 = SO2 H and R1 = R2 = SO2 H. However, the shifting of the Q band was almost 10 times larger when R1 = NO2 and R1 = R2 = NO2 due to the participation of this substituent in the π SubPc cloud. In most cases, the characteristics of the spectra can be explained considering only the transitions involving the HOMO-1, HOMO, LUMO and LUMO + 1 orbitals, where the Q band can be decomposed into two main contributions, leading to charge separation. Only for SubPc(A3,F,F,H) would one of the two contributions from the deepest orbital involved not lead to charge transfer. For this latter case, the HOMO-2 orbital must also be taken into account. In summary, the results obtained with the analysis of the MO indicate that the studied SubPcs are appropriate for photochemical device

Significant bonding rearrangements triggered by Mg4 clusters

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Chemical Physics 154.4 (2021): 044302 and may be found at https://doi.org/10.1063/5.0038047The structure, stability, and bonding of the complexes formed by the interaction of Mg4 clusters and first row Lewis bases, namely, ammonia, water, and hydrogen fluoride, have been investigated through the use of high-level G4 single-reference and CASPT2 multireference formalisms. The adducts formed reflect the high electrophilicity of the Mg4 cluster through electron density holes in the neighborhood of each metallic center. After the adduct formation, the metallic bonding of the Mg4 moiety is not significantly altered so that the hydrogen shifts from the Lewis base toward the Mg atoms lead to new local minima with enhanced stability. For the particular case of ammonia and water, the global minima obtained when all the hydrogens of the Lewis base are shifted to the Mg4 moiety have in common a very stable scaffold with a N or an O center covalently tetracoordinated to the four Mg atoms, so the initial bonding arrangements of both reactants have completely disappeared. The reactivity features exhibited by these Mg4 clusters suggest that nanostructures of this metal might have an interesting catalytic behaviorThis work was supported by the projects PGC2018-094644-BC21, PGC2018-094644-B-C22, and PID2019-110091GB-I00 (MICINN) of the Ministerio de Ciencia, Innovación y Universidades of Spai

Dispersion, rehybridization, and pentacoordination: keys to understand clustering of boron and aluminum hydrides and halides

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-coordinatedPID2021-125207NB-C31, PID2021-125207NB-C32, PID2019-110091GB-I0

Cations brought together by hydrogen bonds: The protonated pyridine-boronic acid dimer explained

According to the Cambridge Structural Database, protonated pyridine-boronic acid dimers exist in the solid phase, apparently defying repulsive coulombic forces. In order to understand why these cation-cation systems are stable, we carried out M06-2X/6-311++G(3df,2pd) electronic structure calculations and used a set of computational tools (energy partitioning, topology of the electron density and electric field maps). The behavior of the charged dimers was compared with the corresponding neutral systems, and the effect of counterions (Br - and BF 4- ) and the solvent (PCM model) on the binding energies has been considered. In the gas-phase, the charged dimers present positive binding energies but are local minima, with a barrier (16-19 kJ mol -1 ) preventing dissociation. Once the environment is included via solvent effects or counterions, the binding energies become negative; remarkably, the strength of the interaction is very similar in both neutral and charged systems when a polar solvent is considered. Essentially, all methods used evidence that the intermolecular region where the HBs take place is very similar for both neutral and charged dimers. The energy partitioning explains that repulsion and electrostatic terms are compensated by the desolvation and exchange terms in polar solvents, thus giving stability to the charged dimerThis work was carried out with financial support from the Ministerio de Economía, Industria y Competitividad (Projects No. CTQ2015-63997-C2-2-P, CTQ2014-57393-C2-1-P and CTQ2017-85821-R FEDER funds) and Comunidad Autónoma de Madrid (S2013/MIT2841, Fotocarbon

Intramolecular magnesium bonds in malonaldehyde-like systems. A critical view of the resonance-assisted phenomena

Through the use of high-level G4-theory calculations we have investigated the structure, stability and bonding of a set of Mg derivatives formed by replacing the –OH group of malonaldehyde or only the hydrogen atom of this group by a –MgH group. To give insight on the resonance-assisted phenomenon, which might be involved in the stabilization of these compounds, we also included the corresponding saturated analogues in our survey. The effect of the rigidity of the molecular framework was considered by analyzing the Mg-derivatives of (Z)-4-(hydroxymethylene)cyclobut-2- enone, obtained through the same substitutions mentioned above. The effect of replacing the carbonyl group by an imino group was also contemplated. In all cases, the global minimum is a cyclic conformer stabilized through the formation of rather strong intramolecular magnesium bonds. The strength of these interactions is directly related with the intrinsic basicity of the carbonyl group (or the imino group) and the intrinsic acidity of the –MgH group, rather than with a resonance-assisted phenomenon. As a matter of fact, for all the investigated systems, the conclusion is that resonance in the cyclic conformer is directly correlated with the strength of the intramolecular magnesium bond, and not vice-versa. Interestingly, the strength and characteristics of these interactions for these Mg-containing derivatives are very similar to those of the corresponding Be-containing analoguesWork supported by the Projects CTQ2015-63997-C2 and CTQ2016-76061-P of the Ministerio de Economía y Competitividad of Spain, FOTOCARBON-CM S2013/MIT-2841 of the Comunidad Autónoma de Madrid and by the COST Action CM1204 of the EU Framework Programme. Horizon 202

Alkaline-earth (Be, Mg and Ca) bonds at the origin of huge acidity enhancements

The interaction between alkaline-earth derivatives with the general formula X2M (X = H, F and Cl; M = Be, Mg and Ca) and a set of Lewis bases, including first and second-row hydrides, namely YHn(Y = O, N, F, S, P and Cl) hydrides, as well as other typical cyclic organic bases, such as aniline, 1H-1,2,3-triazole, 1H-tetrazole and phenylphosphine, was investigated using the G4 ab initio composite method. Contrary to what was expected, it was found that the interactions involving Mg and Ca derivatives were not necessarily weaker than those between beryllium bonds. The origin is two-fold: larger deformation of the interacting systems when Be-derivatives are involved and appearance of secondary non-covalent interactions in the formation of some of the Mg- and Ca-containing complexes. Hence, the dissociation of the latter complexes may require higher enthalpies than that of the Be complexes. These deformations are triggered by a significant redistribution of electron density of the two interacting moieties, which also result in dramatic changes in the reactivity of the interacting compounds and in particular in the intrinsic basicity of the Lewis bases investigated, to the point that conventional bases, such as ammonia or aniline, upon complexation with MCl2(M = Be, Mg and Ca), become stronger Brønsted acids than phosphoric acid, whereas other bases, such as 1H-tetrazole, become stronger acids than perchloric acid.This work was carried out with financial support from the Ministerio de Economía, Industria y Competitividad (projects CTQ2015-63997-C2 and CTQ2013-43698-P), by the COST Action CM1204 and Comunidad Autónoma de Madrid (S2013/MIT2841, Fotocarbon

Beryllium Subphthalocyanines Self-Assembling Properties

Beryllium subphthalocyanines have been recently shown to be suitable candidates for photochemical devices if combined with appropriate donor systems. The ability of beryllium subphthalocyanines to self-assemble is explored for the first time by means of Density Functional Theory calculations. Free dimers of beryllium subphtalocyanine and their corresponding complexes with water and pyridine are computed at the wB97X-D/6-311+G(d,p) level of theory. In contrast with the behavior reported for beryllium phthalocyanines, for beryllium subphtalocyanines, beryllium-aza-nitrogen intermolecular interactions are observed, suggesting that these species are likely to self-assemble. Aggregates of related structures such as beryllium subporphyrazines with axial groups confirm the importance of hydrogen bonds in the stacking.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Fostering the Basic Instinct of Boron in Boron-Beryllium Interactions

A set of complexes LHB···BeX (L = CNH, CO, CS, N, NH, NCCH, PH, PF, PMe, OH; X = H, F) containing a boron-beryllium bond is described at the M06-2X/6-311+G(3df,2pd)//M062-2X/6-31+G(d) level of theory. In this quite unusual bond, boron acts as a Lewis base and beryllium as a Lewis acid, reaching binding energies up to -283.3 kJ/mol ((HO)HB···BeF). The stabilization of these complexes is possible thanks to the σ-donor role of the L ligands in the LHB···BeX structures and the powerful acceptor nature of beryllium. According to the topology of the density, these B-Be interactions present positive laplacian values and negative energy densities, covering different degrees of electron sharing. ELF calculations allowed measuring the population in the interboundary B-Be region, which varies between 0.20 and 2.05 electrons upon switching from the weakest ((CS)HB···BeH) to the strongest complex ((HO)HB···BeF). These B-Be interactions can be considered as beryllium bonds in most cases.This work was carried out with financial support from the Ministerio de Economía y Competitividad (Project No. CTQ2015-63997-C2-2-P) and Comunidad Autónoma de Madrid (S2013/MIT2841, Fotocarbon). We also thank the Centro de Computación Cientí fica de la Universidad Autónoma de Madrid (CCC-UAM) and CTI (CSIC) for their continued computational supportPeer Reviewe