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Quantum-Chemical Studies for Superspecies—in Celebration of Professor Jean-François Gal’s 80th Birthday

A special issue of Molecules (ISSN 1420-3049).

Deadline for manuscript submissions: 31 December 2026 | Viewed by 3355

Special Issue Editor

Prof. Dr. Ewa Raczyńska

E-Mail Website
Guest Editor
Department of Chemistry, Warsaw University of Life Sciences, 02-787 Warsaw, Poland
Interests: physical organic chemistry; structural chemistry; computational chemistry; gas-phase and solution acid-base equilibria; HB and metal cation adduct formation; tautomerism; substituent and solvent effects
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Special Issue Information

Dear Colleagues,

This Special Issue is dedicated to Professor Jean-François Gal on the occasion of his 80th birthday. He was born on May 7, 1945, in Antibes in the south of France, where he lives now with his wife, Juliette. He graduated {PhD, 1972; Doctorat d’Etat (Habilitation), 1979} from the Université Côte d’Azur (UniCA, formerly Université Nice-Sophia-Antipolis), and was appointed Assistant Professor in 1970, then Associate Professor (Maître de conferences) in 1981, and full Professor in 1991 at the same University. Now, he is Emeritus Professor at his Alma Mater.

During his career at UniCA, he taught physical and analytical chemistry, as well as spectroscopy, and administered a class of technicians for several years in collaboration with industrial laboratories. He was a postdoctoral fellow with Prof. R. W. Taft, University of California, Irvine (UCI, USA), in 1981–1982, and a research associate in 1986 in the same group. In 1991 and 1999, he went to the University of California, Davis (USA), and collaborated with Prof. C. B. Lebrilla as a research associate. In 2014, he was nominated Professor Honoris Causa of the University of Tartu (Estonia).

His research is mainly focused on basicity, substituent and solvent effects, molecular interactions, and gas-phase ion/molecule reactions, with special focus on the thermochemistry of acid/base processes. After establishing a calorimetric Lewis basicity scale based on the enthalpy of adduct formation with boron trifluoride in collaboration with Prof. P.-C. Maria, he turned to gas-phase proton-transfer measurements, using a home-built Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. One significant achievement accomplished with this instrument in the 1980s-2000s, was the extension of the gas-phase basicity scale into superbases in collaboration with Profs. E. D. Raczyńska and P.-C. Maria. The gas-phase lithium cation basicity was also largely developed in this period using the same technique. More recently, Prof. J.F. Gal studied the gas-phase reactivity of Lewis superacids, especially those used as catalysts, using electrospray ionization mass spectrometry. Prof. Gal published more than 200 articles in peer-reviewed journals, several book chapters and a book on Lewis basicity.

Taking into account the pivotal achievements of Prof. J.-F. Gal in chemistry of Lewis superacids and Brønsted superbases, this Special Issue is devoted, in general, to superspecies. The term "super” has been frequently employed in chemistry and refers to the species that display exceptional properties. For example, superatoms are clusters of atoms that mimic properties of classical atoms: superalkalis possess extreme ionization energies in comparison to alkali metals, and superhalogens have extreme electron affinities in comparison to halogens. Consequently, they can form supersalts with the complete electron transfer.

On the other hand, supermolecules, such as organic or inorganic superacids and superbases, exhibit extreme acid-base properties. For example, superacids show the Brønsted acidity stronger than 100 wt.% of H2SO4, and superbases display the Brønsted basicity stronger than DMAN. The neutralization reaction with the complete proton transfer, although possible in solution, has not yet been experimentally proved for the pairs of the neutral species in the gas phase, i.e., between superacids and superbases.

Quantum-chemical methods give the opportunity to examine the structure of superspecies, their stability and different types of possible isomerism, e.g., constitutional (prototropic tautomerism), conformational and/or geometric isomerism (rotations about single and/or double bonds, respectively). They give also the possibility to determine their physicochemical properties and distinguish some principal internal effects. In particular cases, experiment(s) can also be performed in parallel, and support theoretical examinations.

Chemists and physicists are invited to submit original articles or reviews on quantum-chemical investigations for superatoms, supersalts, superacids, superbases, and other species exhibiting exceptional (super or even hyper) chemical, physicochemical, or physical properties.

Prof. Dr. Ewa Raczyńska
Guest Editor

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Keywords

  • structure of superspecies
  • neutral, ionic, and/or radical forms
  • isomerism
  • electron delocalization
  • energetic parameters of electron transfer
  • thermochemistry of proton transfer
  • quantum-chemical studies

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Published Papers (5 papers)

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Research

16 pages, 2934 KB  
Article
DFT Investigation into the Role of Superbases as the Auxiliary Groups in CO2 Reduction
by Zoran Glasovac, Borislav Kovačević and Davor Margetić
Molecules 2026, 31(7), 1167; https://doi.org/10.3390/molecules31071167 - 1 Apr 2026
Viewed by 434
Abstract
Non-metallic hydride donors have emerged as an interesting, highly tunable class of compounds capable of CO2 reduction, with benzimidazoles being simple, yet efficient and regenerable, representatives. In this work, the role of superbases as auxiliary groups attached to the benzimidazole framework was [...] Read more.
Non-metallic hydride donors have emerged as an interesting, highly tunable class of compounds capable of CO2 reduction, with benzimidazoles being simple, yet efficient and regenerable, representatives. In this work, the role of superbases as auxiliary groups attached to the benzimidazole framework was investigated using the CPCM(CH3CN)/ωB97xD/aug-cc-pVTZ//CPCM(CH3CN)/ωB97xD/6-31+G(d,p) approach. Three modes of operation were assessed through hydricity calculations and the modeling of two different CO2 reduction mechanisms. Among the superbases considered, phosphazene substituents yielded the largest increase in the hydride donation ability, lowering hydricity by 6 kcal mol−1 relative to 2-methylbenzimidazole, with the α-substitution exerting a stronger effect than β-substitution. For most systems, changes in hydricity correlate with changes in aromaticity, except in systems where steric congestion limits optimal substituent alignment. CO2 activation pathways encompassing guanidine/CO2 hydrogen bonding and guanidinium carboxamidine formation were modeled. In the former, transition state structures were significantly stabilized, and the overall exergonicity of the reduction is enhanced. Also, utilizing the longer and more flexible linker additionally decreases the barrier for the reaction. The carboxamidine pathway is disfavored because of the high stability of the carboxamidine intermediate and low barrier for the C–N bond cleavage, which reverses the mechanism to the reduction of isolated CO2. Full article
(This article belongs to the Special Issue Quantum-Chemical Studies for Superspecies—in Celebration of Professor Jean-François Gal’s 80th Birthday)
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21 pages, 3564 KB  
Article
Theoretical Survey of the Intrinsic Reactivity of Functionalized (CH2=C(R)XH) Enols, Enethiols and Eneselenols: Potential Interstellar Species
by Al Mokhtar Lamsabhi, Otilia Mó, Jean-Claude Guillemin and Manuel Yáñez
Molecules 2026, 31(6), 1040; https://doi.org/10.3390/molecules31061040 - 20 Mar 2026
Viewed by 377
Abstract
The conformational properties and intrinsic reactivity of unsaturated CH2=C(R)XH systems (R = –H, –CH=CH2, –C≡CH, –C≡N, –Cl, –phenyl, –cyclopentadienyl, –pyrrole; X = O, S, Se)—namely enols, enethiols, and eneselenols—have been investigated using G4 and CCSD(T) calculations. All compounds exhibit [...] Read more.
The conformational properties and intrinsic reactivity of unsaturated CH2=C(R)XH systems (R = –H, –CH=CH2, –C≡CH, –C≡N, –Cl, –phenyl, –cyclopentadienyl, –pyrrole; X = O, S, Se)—namely enols, enethiols, and eneselenols—have been investigated using G4 and CCSD(T) calculations. All compounds exhibit antiperiplanar (ap) and anticlinal (ac)-conformers that are nearly isoenergetic, as their relative stabilities are governed by subtle noncovalent interactions, which are analyzed in detail. Both conformers are therefore expected to coexist in the gas phase, and because the rotational barriers are very low, their interconversion is effectively barrierless under typical conditions. In contrast, the corresponding protonated species display significantly higher barriers, approximately three to five times larger. The keto–enol tautomerization involves activation barriers exceeding 180 kJ·mol−1, confirming that, as in other keto–enol rearrangements, the process is not monomolecular. Protonation generally occurs at the methylene carbon, with the exceptions of the –C≡CH and –C≡N derivatives. Strong linear correlations are found among the proton affinities of the three families studied, which follow the trend: enols > enethiols > eneselenols. All systems behave as strong carbon bases; some are predicted to be 20–21 orders of magnitude more basic than ketene and 3–5 orders of magnitude more basic than vinylimine in terms of equilibrium constants. Deprotonation preferentially occurs at the X–H group in nearly all cases. The only exception is the cyclopentadienyl-substituted enol, for which deprotonation of the cyclopentadienyl moiety is favored due to enhanced aromatic stabilization of the resulting anion. Overall, acidity increases along the series O < S < Se. Full article
(This article belongs to the Special Issue Quantum-Chemical Studies for Superspecies—in Celebration of Professor Jean-François Gal’s 80th Birthday)
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24 pages, 7945 KB  
Article
Polynuclear Superhalogen Anions with Heterovalent Central Atoms
by David Mekhael, Piotr Skurski and Iwona Anusiewicz
Molecules 2026, 31(6), 933; https://doi.org/10.3390/molecules31060933 - 11 Mar 2026
Viewed by 479
Abstract
This study explores a novel class of polynuclear superhalogen anions featuring heterovalent central atoms from groups 13 (B, Al) and 15 (P, As). The investigated species follow a modified general formula, (XnYn’F{(3n+5n’ [...] Read more.
This study explores a novel class of polynuclear superhalogen anions featuring heterovalent central atoms from groups 13 (B, Al) and 15 (P, As). The investigated species follow a modified general formula, (XnYn’F{(3n+5n’)+1})− where X = B and/or Al, Y = P and/or As, and n + n′ = 2–4. Low-energy isomers were identified using the Coalescence Kick method and subsequently optimized at the MP2/aug-cc-pVDZ level of theory. Electronic stability was assessed via the outer valence Green’s function (OVGF) approach with the same aug-cc-pVDZ basis set. All examined anions exhibit exceptional electronic stability, with vertical electron detachment energies (VDEs) ranging from 10.70 to 12.37 eV, significantly exceeding the superhalogen threshold of 3.65 eV. Thermodynamic analyses indicate that aluminum atoms play a crucial role in stabilizing larger clusters by acting as a structural “glue”, thereby suppressing fragmentation through the loss of neutral XF3 or YF5 units. In contrast, larger non-metallic analogs show an increased propensity toward dissociation. The potential of the heterovalent polynuclear superhalogen anions as weakly coordinating anions (WCAs) was further evaluated through molecular electrostatic potential (ESP) analysis. The results demonstrate that combining different central atoms within boron-based frameworks leads to a more homogeneous charge distribution, enhancing weakly coordinating behavior. Full article
(This article belongs to the Special Issue Quantum-Chemical Studies for Superspecies—in Celebration of Professor Jean-François Gal’s 80th Birthday)
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11 pages, 870 KB  
Article
DFT Study of Americium and Europium Complexation with 2,9-Bis(1,2,4-triazin-3-yl)-1,10-Phenanthroline Ligand: The Influence of the Counteranions–Nitrate Versus Perchlorate
by Jaanus Burk, Lauri Sikk, Kaido Tämm and Peeter Burk
Molecules 2026, 31(4), 665; https://doi.org/10.3390/molecules31040665 - 14 Feb 2026
Viewed by 383
Abstract
2,9-Bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen)-based ligands show great promise in the separation of trivalent lanthanides and actinides. Experimental studies have shown that americium forms stronger complexes with the BTPhen ligands than europium; most theoretical studies have so far failed to reproduce these results. In the current [...] Read more.
2,9-Bis(1,2,4-triazin-3-yl)-1,10-phenanthroline (BTPhen)-based ligands show great promise in the separation of trivalent lanthanides and actinides. Experimental studies have shown that americium forms stronger complexes with the BTPhen ligands than europium; most theoretical studies have so far failed to reproduce these results. In the current study, three different metal forms (the naked cation, its nitrate or perchlorate salts and tetraaqua solvated salts) were used to study different complexation reactions. It was shown that in the case of naked cations and salts, europium forms the most stable complex with the 2,9-bis(1,2-triazin-3-yl)-1,10-phenanthroline ligand in all of the reactions compared. However, europium is also more strongly interacting (compared to americium) with anions and water molecules in the tetraaquatrinitrato or tetraaquatriperchlorato complexes. That shifts the energies of reactions like Am(NO3)3·4H2O + [Eu(H2O)4BTPhen]3+ = [Am(H2O)4BTPhen]3+ + Eu(NO3)3·4H2O in favor of the americium being complexed with BTPhen and europium with anions and water. Therefore, the americium complexes with BTPhen become the more stable form, in an agreement with the experimental studies. Comparison of counterion influence (nitrate vs. perchlorate) indicates that bigger preference for americium over europium complexation corresponds to the nitrate complexes and stems mainly from the fact that in M(NO3)3(H2O)4 europium is stabilized more than in M(ClO4)3(H2O)4. Full article
(This article belongs to the Special Issue Quantum-Chemical Studies for Superspecies—in Celebration of Professor Jean-François Gal’s 80th Birthday)
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10 pages, 581 KB  
Article
The Impact of Perfluoroalkyl Groups on Phosphane Basicity
by Marta-Lisette Pikma, Aleksander Trummal, Ivo Leito and Agnes Kütt
Molecules 2025, 30(10), 2220; https://doi.org/10.3390/molecules30102220 - 20 May 2025
Viewed by 814
Abstract
This study employed computational methods to investigate the basicity of a series of polyfluorinated phosphanes. Results revealed an exceptionally low basicity, with the computed pKaH values in acetonitrile approaching −30, a value significantly lower than anticipated. The good agreement between the [...] Read more.
This study employed computational methods to investigate the basicity of a series of polyfluorinated phosphanes. Results revealed an exceptionally low basicity, with the computed pKaH values in acetonitrile approaching −30, a value significantly lower than anticipated. The good agreement between the SMD and COSMO-RS methods provided confidence in the reliability of these values. This unexpected behavior challenges conventional perceptions of phosphane basicity and deepens our understanding of the electronic effects of fluorination. The findings hold important implications for catalysis, ligand design, and main-group chemistry, where a precise comprehension of phosphane electronic properties is crucial. pKaH(MeCN) values, gas-phase basicities, and steric parameters are reported for 14 phosphanes. Full article
(This article belongs to the Special Issue Quantum-Chemical Studies for Superspecies—in Celebration of Professor Jean-François Gal’s 80th Birthday)
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