Complexes of adamantane-based group 13 Lewis acids and superacids: Bonding analysis and thermodynamics of hydrogen splitting

The electronic structure and chemical bonding in donor-acceptor complexes formed by group 13 element adamantane and perfluorinated adamantane derivatives EC9R15 (E=B, Al; R=H, F) with Lewis bases XR3 and XC9H15 (X=N, P; R= H, CH3) have been studied using energy decomposition analysis at the BP86/TZ2P level of theory. Larger stability of complexes with perfluorinated adamantane derivatives is mainly due to better electrostatic and orbital interactions. Deformation energies of the fragments and Pauli repulsion are of less importance, with exception for the boron-phosphorus complexes. The MO analysis reveals that LUMO energies of EC9R15 significantly decrease upon fluorination (by 4.7 and 3.6 eV for E=B and Al, respectively) which results in an increase of orbital interaction energies by 27-38 (B) and 15-26 (Al) kcal mol(-1). HOMO energies of XR3 increase in order PH3<NH3<PMe3<PC9H15<NMe3<NC9H15. For the studied complexes, there is a linear correlation between the dissociation energy of the complex and the energy difference between HOMO of the donor and LUMO of the acceptor. The fluorination of the Lewis acid significantly reduces standard enthalpies of the heterolytic hydrogen splitting H-2+D+A=[HD](+)+[HA](-). Analysis of several types of the [HD](+)center dot center dot center dot[HA](-) ion pair formation in the gas phase reveals that structures with additional H center dot center dot center dot F interactions are energetically favorable. Taking into account the ion pair formation, hydrogen splitting is predicted to be highly exothermic in case of the perfluorinated derivatives both in the gas phase and in solution. Thus, fluorinated adamantane-based Lewis superacids are attractive synthetic targets for the construction of the donor-acceptor cryptands

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10&nbsp;years; 78.2% included were male with a median age of 37&nbsp;years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

On the use of energy decomposition analyses to unravel the origin of the relative stabilities of isomers

Structural isomers are molecules that have the same number and type of atoms but arranged in different manner. The isomerization energy is the energy difference between two isomers, i.e. the energy cost corresponding to the transformation of one isomer into another. In this thesis, the PhD student has focused on isomers that can be built from the same fragments, but simply connecting them differently, with a new methodology called "turn-upside-down." Basically one starts with the same two fragments and they are connected in different way to build the two isomers. Later, the energies involved in the bonding between the fragments are studied by an energy decomposition analysis in order to find the reason for the difference in stability between the two isomers. The computational results obtained have allowed us to justify the energy of isomerization of organic or inorganic or organometallic compoundsIsòmers estructurals són molècules que presenten el mateix nombre i tipus d’àtoms, però ordenats de diferent manera. L’energia d’isomerització és la diferència d’energia entre dos isòmers, o sigui, el cost energètic corresponent a la transformació d’un isòmer a l’altre. En aquesta tesi, el doctorand s’ha centrat en isòmers que es poden construir a partir dels mateixos fragments, però simplement unint-los de diferent manera, amb una nova metodologia anomenada “turn-upside-down”. Bàsicament es parteix dels mateixos dos fragments que unim de diferent manera per construir els dos isòmers. Posteriorment, les energies involucrades en la unió entre els fragments s’estudien amb una anàlisi de descomposició de l’energia per tal de saber la raó de la diferència d’estabilitat entre els dos isòmers. Els resultats computacionals obtinguts han permès justificar l’energia d’isomerització de compostos tant orgànics com inorgànics o organometàl·lic

An Analysis of the Isomerization Energies of 1,2-/1,3-Diazacyclobutadiene, Pyrazole/Imidazole, and Pyridazine/Pyrimidine with the Turn-Upside-Down Approach

The isomerization energies of 1,2- and 1,3-diazacyclobutadiene, pyrazole and imidazole, and pyridazine and pyrimidine are 10.6, 9.4, and 20.9 kcal/mol, respectively, at the BP86/TZ2P level of theory. These energies are analyzed using a Morokuma-like energy decomposition analysis in conjunction with what we have called turn-upside-down approach. Our results indicate that, in the three cases, the higher stability of the 1,3-isomers is not due to lower Pauli repulsions but because of the more favorable σ-orbital interactions involved in the formation of two C–N bonds in comparison with the generation of C–C and N–N bonds in the 1,2-isomers

Comparison between Alkalimetal and Group 11 Transition Metal Halide and Hydride Tetramers: Molecular Structure and Bonding

A comparison between alkalimetal (M = Li, Na, K, and Rb) and group 11 transition metal (M = Cu, Ag, and Au) (MX)₄ tetramers with X = H, F, Cl, Br, and I has been carried out by means of the Amsterdam Density Functional software using density functional theory at the BP86/QZ4P level of theory and including relativistic effects through the ZORA approximation. We have obtained that, in the case of alkalimetals, the cubic isomer of <i>T</i>_<i>d</i> geometry is more stable than the ring structure with <i>D</i>_4<i>h</i> symmetry, whereas in the case of group 11 transition metal tetramers, the isomer with <i>D</i>_4<i>h</i> symmetry (or <i>D</i>_2<i>d</i> symmetry) is more stable than the <i>T</i>_<i>d</i> form. To better understand the results obtained we have made energy decomposition analyses of the tetramerization energies. The results show that in alkalimetal halide and hydride tetramers, the cubic geometry is the most stable because the larger Pauli repulsion energies are compensated by the attractive electrostatic and orbital interaction terms. In the case of group 11 transition metal tetramers, the <i>D</i>_4<i>h</i>/<i>D</i>_2<i>d</i> geometry is more stable than the <i>T</i>_<i>d</i> one due to the reduction of electrostatic stabilization and the dominant effect of the Pauli repulsion

Complexes of adamantine-based group 13 Lewis acids and superacids: bonding analysis and thermodynamics of hydrogen splitting

The electronic structure and chemical bonding in donor-acceptor complexes formed by group 13 element adamantine and perfluorinated adamantine derivatives EC9Rʹ15 (E = B, Al; R´= H, F) with Lewis bases XR3 and XC9H15 (X=N, P; R= H, CH3) have been studied using energy decomposition analysis (EDA) at the BP86/TZ2P level of theory. Larger stability of complexes with perfluorinated adamantine derivatives is mainly due to better electrostatic and orbital interactions. Deformation energies of the fragments and Pauli repulsion are of less importance, with exception for the boron-phosphorus complexes. The MO analysis reveals that LUMO energies of EC9Rʹ15 significantly decrease upon fluorination (by 4.7 and 3.6 eV for E = B and Al, respectively) which results in an increase of orbital interaction energies by 27-38 (B) and 15-26 (Al) kcal mol-1. HOMO energies of XR3 increase in order PH3 < NH3 < PMe3 < PC9H15 < NMe3 < NC9H15. For the studied complexes, there is a linear correlation between the dissociation energy of the complex and the energy difference between HOMO of the donor and the LUMO of the acceptor molecules. The fluorination of the Lewis acid significantly reduces standard enthalpies of the heterolytic hydrogen splitting H2 + D + A = [HD]+ + [HA]-. Analysis of the several types of the [HD]+ ··[HA]- ion pair formation reveals that orientation with additional H···F interactions is the most favorable energetically. Taking into account the ion pair formation, hydrogen splitting is predicted to be highly exothermic in case of the perfluorinated derivatives. Thus, fluorinated adamantine-based Lewis superacids are attractive synthetic targets and good candidates for the construction of the donor-acceptor cryptandsThis work was financially supported by St. Petersburg State University research grant 12.50.1194.2014. Excellent service of the Centre de Serveis Científiics i Acadèmmics de Catalunya (CESCA) and computer cluster at St. Petersburg State University is gratefully acknowledged. J.P. thanks the Netherlands Organization for Scientific Research (NWO-CW, NWO-EW, NWO-ALW) for financial support. M. S. thanks the following organizations for financial support: the Spanish government (MINECO, project number CTQ2014-54306-P), the Generalitat de Catalunya (project number 2014SGR931, ICREA Academia 2014 prize for excellence in research, and Xarxa de Referència en Química Teòrica i Computacional), and the FEDER fund (European Fund for Regional Development) for the grant UNGI10-4E-80

X₂Y₂ Isomers: Tuning Structure and Relative Stability through Electronegativity Differences (X = H, Li, Na, F, Cl, Br, I; Y = O, S, Se, Te)

We have studied the XYYX and X₂YY isomers of the X₂Y₂ species (X = H, Li, Na, F, Cl, Br, I; Y = O, S, Se, Te) using density functional theory at the ZORA-BP86/QZ4P level. Our computations show that, over the entire range of our model systems, the XYYX isomers are more stable than the X₂YY forms except for X = F and Y = S and Te, for which the F₂SS and F₂TeTe isomers are slightly more stable. Our results also point out that the Y–Y bond length can be tuned quite generally through the X–Y electronegativity difference. The mechanism behind this electronic tuning is the population or depopulation of the π* in the YY fragment

Analysis of the Relative Stabilities of Ortho, Meta, and Para MClY(XC₄H₄)(PH₃)₂ Heterometallabenzenes (M = Rh, Ir; X = N, P; Y = Cl and M = Ru, Os; X = N, P; Y = CO)

Density functional theory calculations of the relative stabilities of the ortho, meta, and para MClY­(XC₄H₄)­(PH₃)₂ heterometallabenzenes (M = Rh, Ir; X = N, P; Y = Cl and M = Ru, Os; X = N, P; Y = CO) have been carried out. The ortho isomer is the most stable for X = P, irrespective of the metal M. For X = N and M = Ir, Rh the meta is the lowest-lying isomer, whereas for M = Ru, Os the ortho and meta isomers are almost degenerate. The electronic structure and chemical bonding have been investigated with energy decomposition analyses of the interaction energy between various fragments, to discuss the origin of the differences observed. The values of the multicenter index of aromaticity and nucleus-independent chemical shifts indicate that the heterometallabenzenes studied should be classified as aromatic or slightly aromatic