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Alkorta I.,Institute Quimica Medica IQM CSIC | Elguero J.,Institute Quimica Medica IQM CSIC
Chemistry - A European Journal | Year: 2013

The association of BeX2 (X: H, F, Cl) derivatives with azoles leads to a dramatic increase of their intrinsic acidity. Hence, whereas 1H-tetrazole can be considered as a typical N base in the gas phase, the complex 1H-tetrazole-BeCl2 is predicted to be, through the use of high-level G4 ab initio calculations, a nitrogen acid stronger than perchloric acid. This acidity enhancement is due to a more favorable stabilization of the deprotonated species after the beryllium bond is formed, because the deprotonated anion is a much better electron donor than the neutral species. Consequently, this is a general phenomenon that should be observed for any Lewis base, including those in which the basic site is a hydroxy group, an amino group, a carbonyl group, an aromatic N atom, a second-row atom, or the π system of unsaturated hydrocarbons. The consequence is that typical bases like aniline or formamide lead to BeX2 complexes that are stronger acids than phosphoric or chloric acids. Similarly, water, methanol, and SH2 become stronger acids than sulfuric acid, pyridine becomes a C acid almost as strong as acetic acid, and unsaturated hydrocarbons such as ethylene and acetylene become acids as strong as nitric and sulfuric acids, respectively. When is a base not a base? The association of BeX2 derivatives with conventional bases converts them into superacids. Hence, whereas 1H-tetrazole can be considered as a typical N base in the gas phase, the 1H-tetrazole-BeCl2 complex is a stronger acid than perchloric acid (see scheme). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Alkorta I.,Institute Quimica Medica IQM CSIC | Elguero J.,Institute Quimica Medica IQM CSIC | Yanez M.,Autonomous University of Madrid | Mo O.,Autonomous University of Madrid
Physical Chemistry Chemical Physics | Year: 2014

A theoretical study of the beryllium bonded clusters of the (iminomethyl)beryllium hydride and (iminomethyl)beryllium fluoride [HC(BeX)NH, X = H, F] molecules has been carried out at the B3LYP/6-311++G(3df,2p) level of theory. Linear and cyclic clusters have been characterized up to the decamer. The geometric, energetic, electronic and NMR properties of the clusters clearly indicate positive cooperativity. The evolution of the molecular properties, as the size of the cluster increases, is similar to those reported in polymers held together by hydrogen bonds. This journal is © 2014 the Owner Societies.


Alkorta I.,Institute Quimica Medica IQM CSIC | Elguero J.,Institute Quimica Medica IQM CSIC | Mo O.,Autonomous University of Madrid | Yanez M.,Autonomous University of Madrid | Del Bene J.E.,Youngstown State University
Physical Chemistry Chemical Physics | Year: 2015

Ab initio MP2/aug′-cc-pVTZ calculations have been carried out to investigate the structures, binding energies, and bonding characteristics of binary complexes HFBe:FCl, R2Be:FCl, and FCl:N-base, and of ternary complexes HFBe:FCl:N-base and R2Be:FCl:N-base for R = H, F, Cl; N-base = NH3, NHCH2, NCH. Dramatic synergistic cooperative effects have been found between the Be⋯F beryllium bonds and the Cl⋯N halogen bonds in ternary complexes. The Cl⋯N traditional halogen bonds and the Be⋯F beryllium bonds in binary complexes become significantly stronger in ternary complexes, while the F-Cl bond weakens. Charge-transfer from F to the empty p(σ) orbital of Be leads to a bending of the XYBe molecule and a change in the hybridization of Be, which in the limit becomes sp2. As a function of the intrinsic basicity of the nitrogen base and the intrinsic acidity of the Be derivative, the halogen-bond type evolves from traditional to chlorine-shared to ion-pair bonds. The mechanism by which an ion-pair complex is formed is similar to that involved in the dissociative proton attachment process. EOM-CCSD spin-spin coupling constants 1XJ(Cl-N) across the halogen bond in these complexes also provide evidence of the same evolution of the halogen-bond type. © the Owner Societies 2015.


Alkorta I.,Institute Quimica Medica IQM CSIC | Elguero J.,Institute Quimica Medica IQM CSIC | Solimannejad M.,Arak University
Journal of Physical Chemistry A | Year: 2014

A theoretical study of the complexes formed by monosubstituted phosphines (XH2P) and the methyl radical (CH3) has been carried out by means of MP2 and CCSD(T) computational methods. Two minima configurations have been obtained for each XH2P:CH3 complex. The first one shows small P-C distances and, in general, large interaction energies. It is the most stable one except in the case of the H3P:CH3 complex. The second minimum where the P-C distance is large and resembles a typical weak pnicogen bond interaction shows interaction energies between -9.8 and -3.7 kJ mol-1. A charge transfer from the unpaired electron of the methyl radical to the P-X σ* orbital is responsible for the interaction in the second minima complexes. The transition state (TS) structures that connect the two minima for each XH2P:CH3 complex have been localized and characterized. © 2014 American Chemical Society.


Mata I.,CSIC - Institute of Materials Science | Alkorta I.,Institute Quimica Medica IQM CSIC | Molins E.,CSIC - Institute of Materials Science | Espinosa E.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling
Chemistry - A European Journal | Year: 2010

Topological analyses of the theoretically calculated electron densities for a large set of 163 hydrogenbonded complexes show that H··· X interactions can be classified in families according to X (X=atom or π orbital). Each family is characterised by a set of intrinsic dependencies between the topological and energetic properties of the electron density at the hydrogenbond critical point, as well as between each of them and the bonding distance. Comparing different atom-acceptor families, these dependencies are classified as a function of the van der Waals radius rX or the electronegativity χX, which can be explained in terms of the molecular orbitals involved in the interaction. According to this ordering, the increase of χX leads to a larger range of H···X distances for which the interaction is of pure closed-shell type. Same dependencies observed for H···O interactions experimentally characterised by means of high-resolution X-ray diffraction data show a good agreement with those obtained from theoretical calculations, in spite of a larger dispersion of values around the expected fitting functions in the experimental case. Theoretical dependencies can thus be applied to the analysis of the experimental electron density for detecting either unconventional hydrogen bonds or problems in the modelling of the experimental electron density. © 2010 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim.


Mata I.,CSIC - Institute of Materials Science | Alkorta I.,Institute Quimica Medica IQM CSIC | Espinosa E.,CNRS Laboratory of Crystallography, Nuclear Magnetic Resonance and Modelling | Molins E.,CSIC - Institute of Materials Science
Chemical Physics Letters | Year: 2011

The hydrogen bond interaction energy (EHB) of HF⋯HR (R = H, Li, Al, Cl, CCH) complexes under external electric fields is investigated in terms of the bonding distance and of several properties at the bond critical point. All these properties can be used for the estimation of EHB, being the positive curvature along the hydrogen bond path the most suited for the application to experimental electron densities. © 2011 Elsevier B.V. All rights reserved.


Del Bene J.E.,Youngstown State University | Alkorta I.,Institute Quimica Medica IQM CSIC | Elguero J.,Institute Quimica Medica IQM CSIC
Journal of Physical Chemistry A | Year: 2014

Ab initio MP2/aug′-cc-pVTZ calculations have been carried out in search of equilibrium structures with P⋯Cl pnicogen bonds or halogen bonds on the potential energy surfaces H2FP:ClY for Y = F, NC, Cl, CN, CCH, CH3, and H. Three different types of halogen-bonded complexes with traditional, chlorine-shared, and ion-pair bonds have been identified. Two different pnicogen-bonded complexes have also been found on these surfaces. The most electronegative substituents F and NC form only halogen-bonded complexes, while the most electropositive substituents CH 3 and H form only pnicogen-bonded complexes. The halogen-bonded complexes involving the less electronegative groups Cl and CN are more stable than the corresponding pnicogen-bonded complexes, while the pnicogen-bonded complexes with CCH are more stable than the corresponding halogen-bonded complex. Traditional halogen-bonded complexes are stabilized by charge transfer from the P lone pair to the Cl-A σ* orbital, where A is the atom of Y directly bonded to Cl. Charge transfer from the Cl lone pair to the P-F σ* orbital stabilizes pnicogen-bonded complexes. As a result, the H2FP unit becomes positively charged in halogen-bonded complexes and negatively charged in pnicogen-bonded complexes. Spin-spin coupling constants 1XJ(P-Cl) for complexes with traditional halogen bonds increase with decreasing P-Cl distance, reach a maximum value for complexes with chlorine-shared halogen bonds, and then decrease and change sign when the bond is an ion-pair bond. 1pJ(P-Cl) coupling constants across pnicogen bonds tend to increase with decreasing P-Cl distance. © 2014 American Chemical Society.


Del Bene J.E.,Youngstown State University | Alkorta I.,Institute Quimica Medica IQM CSIC | Elguero J.,Institute Quimica Medica IQM CSIC
Journal of Physical Chemistry A | Year: 2013

Ab initio MP2/aug′-cc-pVTZ searches of the potential surfaces of (H2C=PX)2 complexes, with X = F, Cl, OH, CN, NC, CCH, H, CH3, and BH2, have been carried out to identify and characterize the properties of complexes with P···P pnicogen bonds. All (H2C=PX)2 form equilibrium conformation A dimers with C2h symmetry in which A- P···P-A approaches a linear alignment, with A the atom of X directly bonded to P. Conformation A dimers containing the more electronegative substituents are stabilized by a P···P pnicogen bond, have shorter P-P distances, and have binding energies which correlate with the P-P distance. Dimers stabilized by a P···P pnicogen bond and two P···Hb interactions consist of those with the more electropositive substituents, have shorter P-Hb distances, and have binding energies which are too high for their P-P distances. Conformation A complexes with P···Hb interactions in addition to the P···P bond are more stable than the corresponding (PH2X)2 complexes, while with only one exception, complexes stabilized by only a P···P bond are less stable than the corresponding (PH2X)2 complexes. In the region of the potential surfaces with C-P···P-C approaching linearity (conformation B), the only planar equilibrium complex is (H2C=POH)2, which is stabilized primarily by two O-H···P hydrogen bonds. The remaining (H 2C=PX)2 complexes are not stabilized by pnicogen bonds, but by π interactions between the two H2C=PX monomers which are in parallel planes. When A-P···P-C approaches linearity, two types of equilibrium structures with P···P bonds exist. Of the conformation C dimers, (H2C=POH)2 is planar and the most stable, with a P···P pnicogen bond and an O-H···P hydrogen bond. (H2C=PH)2 and (H2C=PCH3)2 are also planar, and stabilized by a P···P pnicogen bond and a P···H b interaction. The absence of a P···H b interaction results in nonplanar C′ conformations with structures in which the monomers essentially retain their symmetry plane, but the plane of one molecule is rotated about the P···P bond relative to the other. C and C′ dimers are less stable than the corresponding A dimers, except for (H2C=PCH3)2. 31P chemical shielding patterns are consistent with the changing nature of the interactions which stabilize (H2C=PX)2 complexes. EOM-CCSD 31P-31P spin-spin coupling constants increase quadratically as the P-P distance decreases. © 2013 American Chemical Society.


Alkorta I.,Institute Quimica Medica IQM CSIC | Elguero J.,Institute Quimica Medica IQM CSIC | Del Bene J.E.,Youngstown State University
Journal of Physical Chemistry A | Year: 2013

Ab initio MP2/aug'-cc-pVTZ calculations have been carried out to determine the structures and binding energies of cyclic trimers (PH2X) 3 with X = F, Cl, OH, NC, CN, CH3, H, and BH2. Except for [PH2(CH3)]3, these complexes have C3h symmetry and binding energies between -17 and -63 kJ mol -1. Many-body interaction energy analyses indicate that the two-body terms are dominant, accounting for 97-103% of the total binding energy. Except for the trimer [PH2(OH)]3, the three-body terms are stabilizing. Charge transfer from the lone pair on one P atom to an antibonding σ* orbital of the P atom adjacent to the lone pair plays a very significant role in stabilization. The charge-transfer energies correlate linearly with the trimer binding energies. NBO, AIM, and ELF analyses have been used to characterize bonds, lone pairs, and the degree of covalency of the P⋯P pnicogen bonds. The NMR properties of chemical shielding and 31P-31P coupling constants have also been evaluated. Although the 31P chemical shieldings in the five most strongly bound trimers increase relative to the corresponding isolated monomers, there is no correlation between the chemical shieldings and the charges on the P atoms. EOM-CCSD 31P-31P spin-spin coupling constants computed for four (PH2X)3 trimers fit nicely onto a plot of 1pJ(P-P) versus the P-P distance for (PH2X)2 dimers. A coupling constant versus distance plot for the four trimers has a second-order trendline which has been used to predict the values of 1pJ(P-P) for the remaining trimers. © 2013 American Chemical Society.


Bauza A.,University of the Balearic Islands | Alkorta I.,Institute Quimica Medica IQM CSIC | Frontera A.,University of the Balearic Islands | Elguero J.,Institute Quimica Medica IQM CSIC
Journal of Chemical Theory and Computation | Year: 2013

In this article, we report a comprehensive theoretical study of halogen, chalcogen, and pnicogen bonding interactions using a large set of pure and hybrid functionals and some ab initio methods. We have observed that the pure and some hybrid functionals largely overestimate the interaction energies when the donor atom is anionic (Cl- or Br-), especially in the halogen bonding complexes. To evaluate the reliability of the different DFT (BP86, BP86-D3, BLYP, BLYP-D3, B3LYP, B97-D, B97-D3, PBE0, HSE06, APFD, and M06-2X) and ab initio (MP2, RI-MP2, and HF) methods, we have compared the binding energies and equilibrium distances to those obtained using the CCSD(T)/aug-cc-pVTZ level of theory, as reference. The addition of the latest available correction for dispersion (D3) to pure functionals is not recommended for the calculation of halogen, chalcogen, and pnicogen complexes with anions, since it further contributes to the overestimation of the binding energies. In addition, in chalcogen bonding interactions, we have studied how the hybridization of the chalcogen atom influences the interaction energies. © 2013 American Chemical Society.

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