BUSCADOR RECOLECTA

The effect of changing the nature of the R substituent from the first row (H, Li, BeH, BH, CH, NH, OH and F) to second row (Na, MgH, AlH, SiH, PH, SH and Cl) on the intrinsic acidity and basicity of R–C≡COH and R–C≡CSH compounds was investigated through the use of G4 high-level ab initio calculation. The variation of the acidity and basicity of the R–C≡CSH derivatives as a function of R is practically parallel to that found for the corresponding R–C≡COH analogs; though the basicities of the former are 9–14% higher than those of the latter, the acidity gap being very small (~ 2%). When this analysis is extended to the derivatives in which the triple CC bond is replaced by a double or single bond, it is found that the acidity gap increases systematically as the CC bond goes from triple to single; whereas, as expected for the basicity, the trend is the opposite. Quite surprisingly, however, the variation of the basicity of R–C≡CX (X = OH, SH) compounds with the nature of the first-row substituents, R, is remarkably different from that produced by the second-row analogs. The same is observed as far as intrinsic acidities are concerned. These dissimilarities reflect the rather different changes in the strength of the CC and the CX (X = OH, SH) bonds when a first-row substituent is replaced by the second-row analog, as reflected in the atoms in molecules (AIM), natural bond orbital (NBO) and the electron localization function (ELF) analyses of the corresponding species., This work was carried out with fnancial support from the projects PID2021-125207NB-C31, PID2021-125207NB-C32 and PID2019-110091GB-I00 of the Ministerio de Ciencia, Innovación y Universidades of Spain (MICINN). Finally, the authors thank the Centro de Computación Científca of the UAM (CCC-UAM) for the generous allocation of computer time and continued technical support. J.-C.G. thanks the CNES for a grant (50006558), Peer reviewed

Reduced nucleophilicities И of axially symmetric molecules B were determined from, where D is the equilibrium dissociation energy of the complexes B⋅⋅⋅XY, N is the nucleophilicity of B, E is the electrophilicity of the halogen-bond donor XY and (Formula presented.) is the minimum electrostatic surface potential of B. The series B⋅⋅⋅ClY, B⋅⋅⋅BrY, B⋅⋅⋅IY (Y=F, Cl, Br, I, CN, and CCH) as well as (B⋅⋅⋅XY, XY=F, Cl, Br,and BrCl) of complexes were investigated. Molecules B were grouped so that the terminal atom involved in the halogen bond was fixed within the group. Groups having N as the terminal atom were RCN (R=CH, H, and F) or RN (R=N and P), those with C as the terminal atom were RNC (R=H and F) and RC (R=O, S and Se), and those with a terminal O atom were R=C=O (R=O or S). Graphs of (Formula presented.) versus E for each group were straight lines through the origin, with generally different gradients, hence implying different N. By contrast, when (Formula presented.) was the ordinate the lines conflated to give a single straight line, which then defines a common (reduced) nucleophilicity И for that group of B. Hence it was concluded that И is an intrinsic property of the terminal atom, independent of the remainder of B, and only weakly dependent on the type (C, N or O) of the terminal atom. Moreover, И for each B was the same as determined previously from the hydrogen-bonded series B⋅⋅⋅HX, (X=F, Cl, Br, I, CN, CCH, and CP)., ACL thanks the University of Bristol for theawardof a University Senior Research Fellowship. IA acknowledges the financial support from the Ministerio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32)., Peer reviewed

SUBJECTS:Anions,Conformation,Energy,Molecular structure,Quantum mechanics, 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-CBH)]Cs = FeSanCs. Experimental Fe 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 Fe species., We are grateful to Prof. Ibon Alkorta (IQM-CSIC) for providing the MEP of trans-FeSan anion conformer. J.F.M. and J.Z.D.-P. acknowledge financial support from grant RTI2018-095303-B-C51 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe” and from grant S2018-NMT-4321 funded by the Comunidad de Madrid and by “ERDF A way of making Europe”. M.F., J.E., and J.M.O.-E. are grateful to Ministerio de Ciencia, Innovacióny Universidades, for financial support with grant number PID2021-125207NB-C32. O.B.O. and D.R.A. acknowledge the financial support from the Universidad de Buenos Aires (grant no. 20020190100214BA), the Consejo Nacional de Investigaciones Científicas y Técnicas (grant nos PIP11220200100467CO, PIP 11220130100377CO, and PIP11220130100311CO), and the Agencia Nacional de Promoción Científica y Tecnológica, Argentina (grant no. PICT-201-0381)., Peer reviewed

The strength of binding, as measured by the equilibrium dissociation energy Dof an isolated hydrogen-bonded complex B···HX, where B is a simple Lewis base and X = F, Cl, Br, I, CN, CCH, or CP, can be determined from the properties of the infinitely separated components B and HX. The properties in question are the maximum and minimum values σ(HX) and σ(B) of the molecular electrostatic surface potentials on the 0.001 e/bohriso-surfaces of HX and B, respectively, and two recently defined quantities: the reduced electrophilicity Ξof HX and the reduced nucleophilicity Иof B. It is shown that Dis given by the expression D= {σ(HX)σ(B)} ИΞ. This is tested by comparing Dcalculated ab initio at the CCSD(T)(F12c)/cc-pVDZ-F12 level of theory with that obtained from the equation. A large number of complexes (203) falling into four categories involving different types of hydrogen-bonded complex B···HX are investigated: those in which the hydrogen-bond acceptor atom of B is either oxygen or nitrogen, or carbon or boron. The comparison reveals that the proposed equation leads to Dvalues in good agreement in general with those calculated ab initio., A.C.L. thanks the University of Bristol for the award of a University Senior Fellowship. I.A. acknowledges grants from Ministerio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32)., Peer reviewed

A theoretical study of the reaction between several borataacenes (1-methylboratabenzene, 9-methyl-9-borataanthracene and cis and trans diboratapentacene) and CO2 has been carried out at the M06-2X computational level. The influence of a counterion (potassium cation), the cation complexation by 18-crown-6-ether and solvent effects have been explored. The computational results predict anti/syn selectivity as found experimentally in the cis- and trans-diboratapentacene reaction with CO2 (Baker et al., J. Am. Chem. Soc., 2023, 145, 2028)., This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades (Projects PID2021-125207NB-C32). Thanks are given to the Centro de Supercomputación de Galicia (CESGA), CTI (CSIC) and the Irish Centre for High-End Computing (ICHEC, Dublin) for their continued computational support., Peer reviewed

This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32).Thanks are also given to the CTI (CSIC) for their continued computational support .M.D.G.acknowledges Universidad de Alcalá for a Starting Research Scholarship (“Ayuda de iniciación en la actividad investigadora”), Peer reviewed

Dedicated to Juan J. Novoa Vide, in memoriam, A comprehensive comparison between known benzene mono-substituted compounds R−Ph and the corresponding isoelectronic unknown R-cyclohexaborane(12) molecules is carried out from a geometric and electronic structure point of view, with R={H, BH, CH, NH, OH, F; AlH, SiH, PH, SH, Cl; NO, OCH}. We suggest new chemical names for the 2D borane compounds and analyze the geometric and electronic structure carbon vs. boron comparatives by means of HOMO-LUMO gaps, bonding schemes, electron density topological properties and predicted NMR chemical shifts. The predictions on the properties in planar hexagonal cyclic boranes may help in the design of synthesis procedures for these yet-unkown compounds., MF, JMOE, IA and JE are grateful to the Spanish Ministry of Science and Innovation with project PID2021-125207NB-C32.JMOE is grateful to Carlos Cuevas (Instituto de Química-Física“Blas Cabrera”,CSIC) for helpful discussions, Peer reviewed

Context A Conceptual DFT (CDFT) study has been carry out to analyse the coupling reactions of the simplest amine
(CH 3 NH 2 ), alcohol (CH 3 OH), and thiol (CH 3 SH) compounds with CO 2 to form the corresponding adducts CH 3 NHCO 2 H,
CH 3 OCO 2 H, and CH 3 SCO 2 H. The reaction mechanism takes place in a single step comprising two chemical events: nucleo-
philic attack of the non-metallic heteroatoms to CO 2 followed by hydrogen atom transfer (HAT). According to our calcula-
tions, the participation of an additional nucleophilic molecule as HAT assistant entails important decreases in activation
electronic energies. In such cases, the formation of a six-membered ring in the transition state (TS) reduces the angular
stress with respect to the non-assisted paths, characterised by four-membered ring TSs. Through the analysis of the energy
and reaction force profiles along the intrinsic reaction coordinate (IRC), the ratio of structural reorganisation and electronic
rearrangement for both activation and relaxation energies has been computed. In addition, the analysis of the electronic
chemical potential and reaction electronic flux profiles confirms that the highest electronic activity as well as their changes
take place in the TS region. Finally, the distortion/interaction model using an energy decomposition scheme based on the
electron density along the reaction coordinate has been carried out and the relative energy gradient (REG) method has been
applied to identify the most important components associated to the barriers., This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades
(PID2021-125207NB-C32). L.M.A. is a Ramón y Cajal fellow (ref.
RYC2021-030994-I) and thanks MCIN/AEI and NextGeneration EU/
PRTR for support., Peer reviewed

7 pags., 5 figs., 3 tabs. -- Dedicated to Professor Russell N. Grimes, In 1977 Weiss and Grimes, by means of mass spectrometry and 1H and 11B NMR spectroscopy, proposed two structures (I and II) for the ferraborane (η5-C5H5)Fe(B5H10), isoelectronic with ferrocene. In this work, by means of high-level quantum-chemical computations, we confirm the experimental structures of the two isomers with their corresponding energies, and assign the reported 1H and 11B NMR chemical shifts. A striking result from this study is the planarization (3D→2D) of the B5H10 - ligand - an unknown isolated anion, isoelectronic with aromatic cyclopentadienyl anion C5H5 - - when attached to the (η5-C5H5)Fe+ moiety, thus resulting in a more stable ferraborane isomer II., This work was carried out with financial support from the Ministerio deCiencia, Innovación y Universidades (Project PID2021-125207NB-C32) and Comunidad de Madrid (PS2018/EMT-4329AIRTEC-CM). W.T. and J.B-Ll. acknowledge the financial supportof the National Agency for Research and Development (ANID)through FONDECYT project 1211128, and ANID/ScholarshipProgram/Becas Doctorado Nacional/2022-21221331 (J.B-Ll.)., Peer reviewed

11 pags., 8 figs., 4 tab., The reactivity of B3N3-doped hexa-cata-hexabenzocoronene (B3N3-NG), Al3N3-NG, B3P3-NG and Al3P3-NG, models of doped nanographenes (NGs), towards carbon dioxide was studied with density functional theory (DFT) calculations at the M06-2X/6-311++G(3df,3pd)//M06-2X/6-31+G* level of theory. The NG systems exhibit a poly-cyclic poly-frustrated Lewis pair (FLP) nature, featuring multiple Lewis acid/Lewis base pairs on their surface enabling the capture of several CO2 molecules. The capture of CO2 by these systems was investigated within two scenarios: (A) sequential capture of up to three CO2 molecules and (B) capture of CO2 molecules in the presence of a sodium cation. The resulting adducts were analyzed in terms of the activation barriers and relative stabilities. The presence of aluminium atoms changes the asynchrony of the reaction favoring the aluminium-oxygen bond and influences the regioselectivity of the multi-capture. A cooperative effect is predicted due to π-electron delocalization, with the sodium cation stabilizing the stationary points and favoring the addition of CO2 to the NGs., This work was carried out with financial support from the Ministerio de Ciencia, Innovacion y Universidades (Project PID2021-125207NB-C32). We are also grateful to the Centro de Supercomputacion de Galicia (CESGA), CTI (CSIC) and the Irish Centre for High-End Computing (ICHEC, Dublin) for their continued computational support., Peer reviewed

Five pyrazagalloles bearing H and CH substituents on the gallium atom and/or in the pyrazole ring have been calculated. The theoretical results have been compared with literature results concerning geometries from the Cambridge Data Base with very good agreement.HandC NMR results from the literature, scarce, and unpublished from our group are also well reproduced from GIAO calculations. The most important conclusion from this work is the assignment to a pzGa trimer as the isomer present in theH NMR spectra of dimeric pyrazagalloles. A mechanism connecting dimers and trimers has been found and the transition states identified., Peer reviewed

Equilibrium dissociation energies De of the hydrogen-bonded complexes HAl⋅⋅⋅HX and HGa⋅⋅⋅HX (X=F, Cl, Br, I, CN, CCH, and CP) were calculated ab initio at the CCSD(T)-(F12c)/cc-pVDZ−F12 level of theory. The gradients of graphs of De versus the electrophilicity EHX of the Lewis acids HX yielded the nucleophilicities NM−X of the Group 13 atoms M in these diatomic molecules. Molecular electrostatic surfaces potentials reveal that H−Al and H−Ga are bi-nucleophilic and that the H ends of these H−M molecules are more nucleophilic than the M ends for M=Al and Ga, but not when M=boron. Therefore, the complexes M−H⋅⋅⋅HX were investigated using the same approach. It was concluded for M=Al and Ga that, for a given X, the M−H⋅⋅⋅HX complexes were more strongly bound than the corresponding H−M⋅⋅⋅HX complexes for both M=Al and Ga but the reverse order applies for M = boron. The effects of substituting the H atoms in the M−H molecules by F atoms and by methyl groups were investigated to measure the −I and +I inductive effects relative to H, respectively, on the nucleophilicities of the molecules M−H when M is acting as hydrogen-bond acceptor in complexes H−M⋅⋅⋅H−X., The investigations reported in this article were enabled by the
award of financial support to IA from the Ministerio de Ciencia,
Innovación y Universidades (PID2021-125207NB-C32) and the
award to ACL of a Senior Research Fellowship by the University
of Bristol., Peer reviewed

15 pags., 12 figs., 2 tabs. -- 2024 SANIBEL PROCEEDINGS .-- Dedicated to José (Jepi) Arnó Prenafeta (1965–2024), in memoriam., Quantum-chemical computations were carried out for a series of circumferences (unknots), trefoil and toric trefoil knots of X30 systems, with X with atomic numbers Z = {1-6}. Relaxed structures lead to different configurations, with the striking cases of C30 and B30, with the former leading to a relaxed trefoil knot and the latter relaxing to a Möbius band, both corresponding to energy minima., This work was supported by Ministerio de Ciencia e Innovación [grant number PID2021-125207NB-C32 and PID2022-142024NB-100]., Peer reviewed

The properties (geometry, bond-dissociation enthalpies and proton affinities) of three azoles, pyrrole, imidazole and pyrazole, with twenty-two N-substituents R covering a significant part of the periodic table [1 (lithium group, alkaline), 2 (beryllium group, alkaline earth), 13 (boron group, triel), 14 (carbon group, tetrel), 15 (nitrogen group, pnictogen), 16 (oxygen group, chalcogen) and 17 (fluorine group, halogen) of the periods 2, 3 and 4 plus the hydrogen] have been calculated with the G4 composite ab initio method. These three properties were discussed with regard to the azole and to the group R using as model compound the amines HN–R. The large set of compounds and their consistency allowed finding many equations that related different calculated properties. General properties such as bond-dissociation enthalpies, BDH, N–R bond lengths and proton affinities were tested in search of simple equations that explain the calculated properties., Open Access funding provided thanks to the CRUE-CSIC
agreement with Springer Nature. This work has also been supported
by Project PID2021-125207NB-C32 from the Ministerio de Ciencia e
Innovación (MICINN) of Spain.

Nucleophilicities for a range of simple carbene molecules acting as hydrogen bond acceptors B in forming complexes B⋯HX are reported. The carbenes chosen to fulfil the roles of a Lewis base are B = RM, cyclo-(CH)M, HC=C=M and two N-heterocyclic carbenes, where M is one of the group 14 tetrel atoms, C, Si, Ge or Sn and R = H, CH, and F. All the carbenes but CH have a singlet electronic ground state. The Lewis acids, HX, involved are HF, HCl, HBr, HI and HCN, HCCH, and HCP. Nucleophilicities, N, of the carbenes were determined graphically from equilibrium dissociation energies, D, for the process B⋯HX = B + HX by using the equation D = c·N·E, where c = 1.0 kJ mol and the E are known numerical electrophilicities of the Lewis acids HX. D values were calculated ab initio at the CCSD(T)-F12c/cc-pVDZ-F12 level of theory, which for CH refers to the singlet electronic excited state. It was established that NRM values lie in the order of M = C ≫ Si ∼ Ge ∼ Sn for a given R and in the order R = CH > H > F for a given M. Reduced nucleophilicities, N/σ, were determined by using the molecular electronic surface potential σ at atom M (which lies on the C axis) on the 0.001 e Bohr iso-surface of each carbene molecule, as calculated at the MP2/aug-cc-pVTZ level. For RM having R = CH and H and cyclo-(CH)-M carbenes, the determined values of N/σ are shown to be independent of R and M., A thanks the Ministerio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32) for a grant of financial support and ACL is pleased to acknowledge the University of Bristol for the award of a University Senior Research Fellowship and for the award of an account on the Blue Pebble HPC.

The H and F spectra of 5-(perfluoroethyl)-3,4,5-tris(trifluoromethyl)-pyrazolidin-3-ol reported unassigned in the literature were compared with GIAO/ B3LYP/6-311++G(d,p) calculations for the different isomers and conformers, the latter structures were searched using the CREST program. The signal assignment corresponds to the 3S,4R,5R or 3R,4S,5S diastereoisomers., This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32). Thanks are also given to the CTI (CSIC) for their continued computational support

The thermodynamic properties of 778 azaboles, including the known pyrazaboles, imidazaboles, and triazaboles, have been theoretically calculated at the CBS-QB3 level. Pólya enumeration theorem was used to determine the number of skeletons of azaboles (237 neutral systems), followed by an exploration and generation of the whole space of N–H tautomers. The experimental X-ray geometries, B–C and B–N distances and folding angles, were compared with those of the calculated geometries. Using Free-Wilson (or absence-presence) matrices and multiple regression analysis, the fragments’ contribution to different enthalpies was calculated. Finally, a machine learning model based on Gaussian Process Regression has been created to predict the ΔH°f of the azaboles together with their structural characteristics., This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32). Open Access funding is provided thanks to the CRUE-CSIC agreement with Springer Nature., Peer reviewed

The structure of the ferrocene-water ((Cp)2Fe:H2O) complex has been characterized by combining state of the art rotational spectroscopy and computational chemistry. Two structures have been retrieved experimentally where water interacts with two distinguished binding sites, the exo Cp π cloud and the planetary-like planar orbit around iron. The spectra of both conformers exhibit significant averaging effects due to the nearly free rotational dynamics of water. This is in good agreement with the exploration of the potential energy surface of (Cp)2Fe:H2O. For water interacting with the exo Cp π cloud, we found three axial conformers giving rise to twenty minima with small internal rotation barriers. Theoretical calculations reveal two minima for the observed equatorial complex. Water interacts with ferrocene quite strongly, exhibiting binding energies above −11 kJ/mol in all binding sites and contributing to small deformations in the structure of bare ferrocene., This work was carried out with financial support from the
projects PID2021-125207NB-C31, PID2021-125207NB-C32 and
PID2021-125207NB-C33 of the Ministerio de Ciencia, Innovación
y Universidades of Spain (MICINN). The authors also thank the
Centro de Computación Científica of the UAM (CCC-UAM) for
the generous allocation of computer time and continued
technical support. SB, AV and JCL thank the Junta de Castilla y
León (INFRARED-FEDER IR2020-1-UVa02) for research funds. A.V.
would like to thank the University of Valladolid and Banco de
Santander for his Ph.D. grant, Peer reviewed

Nucleophilicities N-HnA of hydrides of atoms A acting as hydrogen-bond acceptors in complexes H(n)AHX are reported. The H(n)A initially chosen are HB, H2C, H3N, H2O, and HF, that is from groups 13, 14, 15, 16, and 17, respectively, of row 1 of the Periodic Table. The Lewis acids HX involved are HF, HCl, HBr, HI, HCCH, and HCP. Nucleophilicities are determined from dissociation energies D-e for the process H(n)AHX = H(n)A + HX by using D-e = cN(HnA).E-HX, where E-HX are electrophilicities of the Lewis acids HX. This procedure is also followed for hydrides H(n)A in which the atoms A are from the same groups, but from rows 2, 3, and 4 of the Periodic Table. The order of N-HnA values found is row 1 > row 2 approximate to row 3 approximate to row 4 in each of groups 13, 15, 15, 16, and 17, with a large decrease from row 1 to row 2 but with small decreases from rows 2 to 3 to 4. The series RgHX is similarly investigated to give the order of nucleophilicities Rg = Xe > Kr > Ar. > Ne, which is reversed from that in the hydrides of groups 13 to 17., I.A. thanks the Ministerio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32) for a grant of financial support. ACL is pleased to acknowledge the University of Bristol for a University Senior Research Fellowship and an account on the (Blue Pebble)High Performance Computer., Peer reviewed

Although boron usually behaves as a Lewis acid, some molecular structures containing B-B bonds can act as electron donors. Inspired in reported crystalline structures, the basicity and the hydrogen bond (HB) acceptor capability of diborane derivatives of dipyrazole 1 have been studied theoretically using M06-2x and CCSD(T) computational methods. The topology of the electron density and molecular electrostatic potential of compound 1 reveal that the richest electron region is located above the B-B bond, making it suitable to be a strong donor and a very effective proton catcher. A key finding is the remarkably high proton affinity of the parent derivative, which exceeds that of very strong nitrogen-containing organic bases such as guanidines. In line with this finding, the hydrogen-bonded complexes exhibit binding energies up to 37 kJ mol-1, which is a significant interaction considering the electronegativity of boron in comparison with elements typically involved in hydrogen bonds. We have also designed substituted structures where the inductive effect improves the proton affinity and HB acceptor capabilities. The proton affinities of 1b reach 1096 kJ mol-1, among the highest reported for molecules in the gas-phase., This work was carried out with financial support from Projects PID2021-125207NB-C31 and PID2021-125207NB-C32 of the Ministerio de Ciencia, Innovación y Universidades of Spain (MICINN)., Peer reviewed

This publication presents the geometries of 157 nitro- and polynitropyrazoles. Among these, 109 compounds were theoretically studied using mainly the B3LYP/6–311++G(d,p) level of theory. Three-parameter Lee-Yang-Parr (B3LYP) is a density functional theory (DFT) method widely used in computational chemistry and constitutes an acceptable compromise for such a large set of compounds, some of them of considerable mass. The data set includes crystallographic parameters for 91 polynitropyrazoles; the remaining 67 compounds comprise 40 known and 27 newly reported structures. Several key issues are addressed: the investigation of 3,4-dinitro-1H-pyrazole, including nine X-ray structures (solvates and cocrystals); the prototropic tautomerism observed in four pairs of pyrazoles and the factors influencing the preference for a tautomer; the analysis of twelve 1-trinitromethyl-1H-pyrazoles; and a discussion of the detonation properties of 30 polynitro compounds. No previous work has included such a broad set of compounds. While comparing experimental data with theoretical calculations does not guarantee agreement in advance, in our case, the accordance regarding geometries is very good, except for some observed discrepancies. In the section on detonation properties, the consonance in terms of densities, planarity, and heats of formation is less strong but still sufficient to draw interesting conclusions., This work was carried out with financial support from theMinisterio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32). Thanks are also given to the CTI (CSIC) fortheir continued computational support. Library and scientific technical services of the Universidad Nacional de Educación a Distancia (UNED) are greatly acknowledged., Peer reviewed

Two empirical equations have been devised to transform absolute shieldings (GIAO) into chemical shifts. Both correlations are excellent, but that based on M06-2X/aug-cc-pVDZ calculations needs a correction term for chlorine-substituted boron compounds with B-Cl bonds. These equations have been tested against a collection of closoboranes, neutrals, and dianionic., This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades (PID2021-125207NB-C32). Thanksare also given to the CTI (CSIC) for their continued computational support., Peer reviewed

Nucleophilicities NMA of diatomic Lewis bases MA acting as hydrogen-bond acceptors in complexes MA⋯HX are reported. The molecules MA were chosen so that the atom M adjacent to the atoms A directly involved in the hydrogen bonds belongs to Groups 13, 14, 15, 16 and 17 of the periodic table. The effects of changing atom M from rows 1 to 4 within a given group were also investigated. The hydrogen-bond donors HX involved in the complexes were HF, HCl, HBr, HI, HCCH, and HCP. Nucleophilicities NMA were determined from dissociation energies De for the process MA⋯HX = MA + HX by using De = cNMA·EHX + d, where EHX are electrophilicities of the Lewis acids HX, and c and d are constants. The order of NMA values was found to be Row 4 > Row 3 ∼ Row 2 ≫ Row 1 in each of the Groups 13, 15, 15, 16 and 17. The effect of adding an H atom to MA to give linear triatomic molecules HMA were considered. The reduced nucleophilicities ИMA = NMA/σmin (σmin is the minimum value of the molecular electrostatic surface potential of MA) as a function of the group and row of atom M were also discussed for diatomic molecules MA., I. A. thanks the Ministerio de Ciencia, Innovación y Universi-
dades (grant number PID2021-125207NB-C32) for financial
support. A. C. L. is pleased to acknowledge the University of
Bristol for a University Senior Research Fellowship and
accounts on the University High Performance Computers., Peer reviewed

The registered version of this article, first published in Journal of Molecular Structure 1351 (Part 1) 144176, is available online at the publisher's website: https://doi.org/10.1016/j.molstruc.2025.144176, La versión registrada de este artículo, publicado por primera vez en Journal of Molecular Structure 1351 (Part 1) 144176, está disponible en línea en el sitio web del editor: https://doi.org/10.1016/j.molstruc.2025.144176, This work was carried out with financial support from the Ministerio de Ciencia, Innovación y Universidades (PID2021–125207NB-C32). Library and scientific-technical services of the Universidad Nacional de Educación a Distancia (UNED) are greatly acknowledged. Thanks are also given to the CTI (CSIC) for their continued computational support, The structure of the title compound was determined both in the solid state by crystallography and in solution by NMR, particularly concerning the conformation around the C2–N8 bond. Hirshfeld surface (HS) analysis of this molecule was performed, using Crystal Explorer 25.09, in order to evaluate the zones of potential intermolecular contacts in the crystal as well as to determine the atoms involved. As crystals of the protonated form could not be obtained due to the rapid decomposition of the pyrimidine ring, multinuclear 1H, 13C, and 15N NMR spectroscopy was employed. This revealed that protonation occurs on the ring nitrogens in a 90/10 ratio. Theoretical calculations of geometries and energies have been carried out at the Becke Three-parameter Lee–Yang–Parr (B3LYP)/6–311++G(d,p) level, and the optimized structures used to calculate chemical shifts via the Gauge-Invariant Atomic Orbital (GIAO) method. These calculations were crucial to draw definitive conclusions., versión publicada