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We have analyzed the chemical bonding and reactivity in the cubic molecule octahydridosilsesquioxane, Si8H8O12, and its counterpart Ge8H8O12 by means of ab initio quantum chemical methods and group theory. Density functional theory and MP2 methods combined with the basis sets 6-311+G(d) and 6-311++G(2d,p) were used for geometry optimization and vibrational frequency analysis. The geometries of Si8H8O12 and Ge8H8O12 are unstable under Oh symmetry and distort to the rare Th molecular symmetry. The energy gained from this pseudo-Jahn–Teller distortion ranges from 0.78 to 6.14 kcal mol−1 depending on methodological treatment. The Fukui functions and the molecular electrostatic potential were both used as DFT-based reactivity descriptors. Our study shows that Si8H8O12 and Ge8H8O12 are both hard amphoteric molecules. The cavity within each cage is acidic and able to encapsulate hard small bases such as F−. The exterior of the cages is basic and can form stable exohedral complexes with hard acids, as in the case of H+. The insertion of F− in Si8H8O12 and Ge8H8O12 cages gives the most stable endohedral complexes of the series studied, characterized by formation energies of −3.50 and −3.45 eV at CAM-B3LYP/6-311+G(d) and −3.61 and −3.68 eV at the MP2/6-311++G(d,p) level, respectively. The calculated formation energies of the exohedral and endohedral complexes align with the DFT reactivity descriptor analysis. [ABSTRACT FROM AUTHOR]

Herein, we report a quantum chemistry investigation of the interaction between µ-truxinic acid, referred to as TXA0, and Y+ (Y = Li, Na, K) and Z− (Z = F, Cl, Br) ions using M06-2X, B3LYP and ω B97XD functionals in conjunction with the 6–31 + + G(d,p), aug-cc-pVDZ(-X2C) and 6–311 + + G (d, p) basis sets. Our computations suggest that Y+ cations can bind to TXA0 through several combinations of cation...O and cation-π interactions, while Z− anions generally establish anion...H–O contacts. Predicted binding energies at the M06-2X/6–311 + + G(d,p) level range between − 26.6 and − 70.2 kcal/mol for cationic complexes and − 20.4 and − 62.3 kcal/mol for anionic ones. As such, TXA0 appears as an amphoteric molecule with a slight preference for electrophilic (cation... O) attacks. Furthermore, the most favourable binding site for cations allows for the formation of O...cation...O interactions where the cation is trapped between O37 and O38 atoms of TXA0. Anions do not behave uniformly towards TXA0: while the fluoride anion F− induces the deprotonation of TXA0, Br− and Cl− do not. All of these structural insights are supported by topological calculations in the context of the quantum theory of atoms in molecules (QTAIM). Finally, SAPT0 analyses suggest that TXA0...Y+ and TXA0...Z− complexes are mainly stabilized by electrostatic and inductive effects, whose combined contributions account for more than 60 percent of the total interaction energy. [ABSTRACT FROM AUTHOR]

The ambident reactivity of small-sized XAHs (X=H, F, Cl, Br, CH3, and A=S, Se, Te) molecules towards the imidazole molecule (IMZ) has been investigated using wave function (MP2) and Density Functional Theory (B3LYP, B3LYP-D3). Molecular electrostatic potentials (MEPs) and frontier molecular orbitals of monomers are computed to rationalise the regioselectivity of IMZ towards XAHs. The chemical bonding of each complex is described in the framework of the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) paradigms. The symmetry-adapted perturbation theory (SAPT) is employed to assess the physical nature of the interactions. Our findings suggest that XAHs mainly bind to IMZ through H-bonding and chalcogen-bonding interactions of weak to moderate strength, with binding energies ranging from −3.1 to −17.6 kcal/mol at the MP2/aug-cc-pVDZ(-PP) level. Topological QTAIM descriptors reveal all H-bonds between IMZ and XAHs to be purely noncovalent contacts, while chalcogen bonds of halogenated XAHs (X = F, Cl, Br) show a partial covalent character. SAPT2 calculations indicate that both H-bonded and chalcogen-bonded complexes are mainly stabilised by electrostatic interactions. Insights drawn from this study are expected to constitute the bedrock for further investigations about noncovalent interaction between middle to big-sized chalcogen-containing molecules and imidazole derivatives. [ABSTRACT FROM AUTHOR]

Photodynamic antimicrobial activities of gallium and indium porphyrins as well as their quaternized derivatives have been investigated against S. aureus and E. coli biofilms, as well as on their planktonic (free floating) cells using a light emitting diode lamp at 415 nm. The studied photosensitizers show considerable ability to generate singlet oxygen and the quaternized molecules 2a and 3a are potential photodynamic antimicrobial chemotherapy (PACT) agents with log10 colony forming units >9 for E. coli and S. aureus planktonic cells. The quaternized derivatives are found to have higher ability to significantly suppress the biofilms of both S. aureus and E. coli in vitro. Therefore, this demonstrates that they are potentially suitable photosensitive agents for PACT use. The TD-B3LYP/LanL2DZ calculations were performed to evaluate the singlet excitation energies of quaternized and non-quaternized porphyrins in vacuo. Our study shows excellent agreement between time-dependent density-functional theory (TD-DFT) excited energies and experimental S1 > S0 excitation energies. The small deviation observed between the calculated and experimental spectra arises from the solvent effect. The excitation energies observed in these UV-visible spectra mostly originated from electron promotion between the highest occupied molecular orbital (HOMO) for the less intense band and the HOMO−1 for the most intense band of the ground states to the lower unoccupied molecular orbital (LUMO) of the excited states. [ABSTRACT FROM AUTHOR]

Two new structural motifs of the B24 clusters are constructed by use of the leapfrog transformation. The resulting leapfrog B24 has either a bowl shape with a square vacancy or a quasi‐planar 2D close‐packed triangular boron sheet. The neutral and ionic forms of the latter are found to be more stable than their homologous leapfrog bowl clusters, with the exception of the dicationic B24+2. While the leapfrog isomer is less stable than the tubular double ring in the neutral state, it becomes competitive in some ionic states. The nucleus independent chemical shift, electron localization function, ring current maps and the electronic structure of leapfrog B24 clusters reveal them to behave as aromatics. [ABSTRACT FROM AUTHOR]

Two new structural motifs of the B24 clusters are constructed by use of the leapfrog transformation. The resulting leapfrog B24 has either a bowl shape with a square vacancy or a quasi‐planar 2D close‐packed triangular boron sheet. The neutral and ionic forms of the latter are found to be more stable than their homologous leapfrog bowl clusters, with the exception of the dicationic B24+2. While the leapfrog isomer is less stable than the tubular double ring in the neutral state, it becomes competitive in some ionic states. The nucleus independent chemical shift, electron localization function, ring current maps and the electronic structure of leapfrog B24 clusters reveal them to behave as aromatics. [ABSTRACT FROM AUTHOR]

The lowest-lying isomer of the B50 boron cluster is confirmed to have a quasi-planar shape with two hexagonal holes. By applying a topological (leap-frog) dual operation followed by boron capping, we demonstrated that such a quasi-planar structure actually comes from the smallest elongated B102−, and its high thermodynamic stability is due to its inherent disk aromaticity arising from its 32 valent π electrons that fully occupy a disk configuration of [(1σ)2(1π)4(1δ)4(2σ)2(1φ)4(2π)4(1γ)4(2δ)4(1η)4]. The aromatic character of the quasi-planar B50 is further supported by a strong diatropic magnetic current flow. The sudden appearance of a quasi-planar B50 again points out that the growth pattern of pure boron clusters is still far from being completely understood. [ABSTRACT FROM AUTHOR]

Abstract: A furano sesquiterpenoid, known as siphonochilone (1), is commonly reported as the major compound in the roots and the rhizomes of Siphonochilus aethiopicus together with related oxidized sesquiterpenoids (2‐5). As part of investigating the UPLC QTOF MS ES+ chemical profiles of n‐hexane/dichloromethane (1:1) extracts from crushed fresh rhizomes, dried and powdered rhizomes and the dried powders held under storage at room temperature, we have recently realized that decomposition of 1 occurs during the processing of the rhizomes and the storage of the powders. This decomposition which involves autoxidation of the furan moiety leads to formation of the artefact sesquiterpenoid lactone (3) and potentially (4), which numerous papers misreport as naturally present in the plant. MP2/6‐31+G(d,p), B3LYP/6‐31+G(d,p) and B3LYP/6‐311+G(2d,p) calculations were performed on siphonochilone (1) and the sesquiterpenoid lactone artifacts (3) and (4) and results rationalized the observed autoxidation. [ABSTRACT FROM AUTHOR]

Temozolomide was paired with guanine, 6-selenoguanine, and 6-thioguanine, as well as the SH tautomer of the latter. The potential energy surface of each heterodimer was searched for all minima, using Dispersion-Corrected Density Functional Theory and MP2 methods. Among the dozens of minima, three categories were observed. Stacked geometries place the aromatic systems of the two molecules parallel to one another, while the two systems are roughly perpendicular to one another in a second category. Also found are coplanar structures held together by H-bonds. Dispersion proves to be a dominating attractive force for the stacked structures, less so for perpendicular, and smallest for the coplanar dimers. Geometries and energetics are relatively insensitive to S and Se substitution, but tautomerization reverses relative stabilities of different geometries. [ABSTRACT FROM AUTHOR]

B3LYP, B3LYP-D3 and MP2 calculations are used to predict the preferred site of binding of HCl to temozolomide (TMZ). Binding energies, bond length perturbations, and infrared spectra of the various heterodimers indicate that the O-atom of the terminal amide group is the preferred attack site. The interaction is strong with binding energy of roughly 30 kJ mol −1 . The molecular electrostatic potential surrounding TMZ is consistent with this preference, but is unable to fully account for the energetic ordering of the other minima. [ABSTRACT FROM AUTHOR]

Highlights: [•] All possible binding sites of TMZ with water are considered, and binding energies evaluated. [•] The terminal amide group represents the strongest binding site, with water bound by 40kJ/mol. [•] The global minimum is cyclic, with water acting as simultaneous proton donor and acceptor. [•] Molecular electrostatic potential (MEP) and Natural Bond Orbital (NBO) data aid in understanding the binding preferences. [ABSTRACT FROM AUTHOR]

A density functional theory (DFT) study is performedto determine the stability of the complexes formed between eitherthe N or O site of 3-methyl-4-pyrimidone and 1-methyl-2-pyrimidonemolecules and different ligands. The studied ligands are boron andalkali Lewis acids, namely, B(CH3)3, HB(CH3)2, H2B(CH3), BH3, H2BF, HBF2, BF3, Li+, Na+, and K+. The acids are divided into twogroups according to their hardness. The reactivity predictions, accordingto the molecular electrostatic potential (MEP) map and the naturalbond orbital (NBO) analysis, are in agreement with the calculatedrelative stabilities. Our findings reveal a strong regioselectivitywith borane and its derivatives preferring the nitrogen site in bothpyrimidone isomers, while a preference for oxygen is observed forthe alkali acids in the 3-methyl-4-pyrimidone molecule. The complexationof 1-methyl-2-pyrimidone with these hard alkali acids does not showany discrimination between the two sites due to the presence of acontinuous delocalized density region between the nitrogen and theoxygen atoms. The preference of boron Lewis acids toward the N siteis due to the stronger B–N bond as compared to the B–Obond. The influence of fluorine or methyl substitution on the boronatom is discussed through natural orbital analysis (NBO) concentratingon the overlap of the boron empty p-orbital with the F lone pairsand methyl hyperconjugation, respectively. The electrophilicity ofthe boron acids gives a good overall picture of the interaction capabilitieswith the Lewis base. [ABSTRACT FROM AUTHOR]

The ipsocentric method at the coupled Hartree–Fock level is used for the calculation of magnetically induced ring currents in the boron buckyball B80, for both Ihand distorted Thgeometries. A close similarity between the current patterns in boron and carbon buckyballs is noted, but with a higher current density in B80. Paratropic currents on the pentagons are predominant in the boron buckyball, and the central NICS value is positive. These observations support the conclusion that B80should be considered (weakly) anti-aromatic. The largest orbital contributions to the ring currents in both molecules are identified and related to specific excitations in the frontier orbital region. [ABSTRACT FROM AUTHOR]

Density functional theory calculations at the B3LYP/SVP and B3LYP/6-31lG(d) levels were carried out for a series of XH3B80 complexes with X = {N, P, As, B, Al}. To probe the regioselectivity of B80, the electronic Fukui function, the molecular electrostatic potential (MEP), and the natural bond orbital (NBO) were determined. These indices were shown to provide reliable guides to predict the relative reactivities of the boron buckyball sites. Thermodynamic stabilities of the complexes formed by the reaction of B80 with nucleophiles (NH3, PH3, AsH3) and electrophiles (BH3, A1H3) are in good agreement with the prediction of regioselectivity indicated on the basis of Fukui and MEP indices. The qualitative results suggest the boron buckyball to be an amphoteric and hard molecule. It has two distinct reactive sites localized on caps and frame, which act as acids and bases, respectively. Most of the complexes are stable with formation energies comparable to that of the analogous complexes of the borane molecule, BH3BH3, BH3NH3, and BH3A1H3. The B-H-B bond characteristics of diborane are recovered in B80BH3. Exohedral complexes are more stable than endohedral complexes. The most stable complexes are those with NH3 on the caps and BH3 on the pentagonal ring of B80. [ABSTRACT FROM AUTHOR]

Two leapfrogisomers of a B112boron fullerene are constructed from small C28fullerenes (Tdand D2symmetries) by the leapfrogtransformation combined with omnicapping of the new hexagons. Their electronic structure is analyzed using the density functional theory at the B3LYP/SVP and BHLYP/SVP levels. Both isomers are characterized as minima on the potential energy hypersurface with a HOMO–LUMO gap at B3LYP/SVP of 1.7 eV and 1.6 eV (3.1 and 3.0 eV at BHLYP/SVP), respectively. The optimized structure of the helical D2-leapfrogis asymmetric, due to radial displacements of the capping atoms. The computed cohesive energies amount to −4.2 eV (∼0.04 eV lower than B80). The B112isomers are isoelectronic to Td-C84and D2-C84, and HOMO and LUMO orbitals in both isomers closely resemble those of their C84homologues. Energetic stability of leapfrogboron fullerenes depends on the isolation of empty hexagoncriterion, which is defined by the empty hexagon indexbased on the total number of empty hexagon pairs and empty hexagon–pentagon fused pairs. The switch of the cap atom to the nearest or farthest empty hexagon destabilizes the cage by 1.6 and 2.7 eV, respectively. The destabilization becomes more enhanced in non-leapfrogstructures wherein more caps are displaced. [ABSTRACT FROM AUTHOR]

Density functional theory (B3LYP, B3LYP‐D3, wB97XD, M062X, and M06L) and ab initio methods (MP2 and CCSD(T)) in conjunction with 6‐31+G(d,p) and LanL2DZ were employed to investigate the interaction energies between [Co(NH3)5NO2]2+ linkage isomers and chloride and nitrate in both gas phase and solid state. The nature of the chemical bonding has been analyzed by means of the atoms in molecules, electron density shift, natural bond orbitals, symmetry adapted perturbation theory, and energy decomposition analysis. The electronic structures of the two lowest laying singlet states (So and S1) of [Co(NH3)5NO2](NO3)Cl isomers were also investigated using CASSCF(6,6) with LanL2DZ and 6‐31G(d) basis sets. Our results show that [Co(NH3)5NO2]2+ linkage isomers interact more strongly with chloride than nitrate. The structures of [Co(NH3)5NO2](NO3)Cl linkage isomers and their relative stabilities were examined in gas phase and in solid state and confirmed the nitro‐complex as the most stable following by a viable intermediate endo‐complex. Study of the nitro‐nitrito linkage isomerization in [Co(NH3)5NO2](NO3)Cl revealed that anions form strong electrostatic bonds with [Co(NH3)5NO2]2+ leading to decrease in an activation energy compared to the [Co(NH3)5ONO]2+ isomers. A concerted action of ionic interactions and hydrogen bonds are suspected of regulating the isomerization in solid state. Assessment of various DFT methods with respect to CCSD(T) suggests M062X suitable method for [Co(NH3)5NO2](NO3)Cl linkage‐isomerization study. Potential energy surface calculations at the CASSCF/6‐31G(d) level of theory shows that the conical intersection (S1/So) might play an important role in the photoisomerization of [Co(NH3)5NO2](NO3)Cl. [ABSTRACT FROM AUTHOR]

A combined computational and interpretational DFT study is performed to investigate the regioselectivity of B 18 and B 30 leapfrog boron sheets upon reaction with XH 3 -type electrophiles and nucleophiles (X = N, P, As, B, Al). The M062X, B3LYP, and B3LYP-D3 functionals are used combined with the 6-31+G(d,p) basis. The molecular electrostatic potential (MEP), Fukui functions, and the dual descriptor are employed to predict the local reactivity of B 18 and B 30 . Our results reveal that both clusters are hard and prefer to react with hard bases and acids, such as NH 3 and BH 3 . Further, these leapfrog B 6n clusters can play the role of catalysts as they break B-H and Al-H bonds of BH 3 and AlH 3 in s -BH 3 -B 6n and s -AlH 3 -B 6 n complexes, respectively. Leapfrog B 6 n -XH 3 complexes (X = B and Al) can be considered as an interaction between two electron-deficient systems. Therefore, the chemical reactivity between these systems cannot be interpreted in terms of the Hard-Soft-Acid-Base principle.

M pro , the main protease and a crucial enzyme in SARS-CoV-2 is the most fascinating molecular target for pharmacological treatment and is also liable for viral protein maturation. For antiviral therapy, no drugs have been approved clinically to date. Targeting the M pro with a compound having inhibitory properties against it can hinder viral replication. The therapeutic potential of the antiviral compound Nirmatrelvir (NMV) against SARS-CoV-2 M pro was investigated using a systematic approach of molecular docking, MD simulations, and binding free energy calculation based on the MM-GBSA method. NMV, a covalent inhibitor with a recently revealed chemical structure, is a promising oral antiviral clinical candidate with significant in vitro anti-SARS-CoV-2 action in third-phase clinical trials. To explore the therapeutic ability and possible drug resistance, the M pro system was studied for WT and two of its primary mutants (C145A & C145S). The protein-ligand (M pro /NMV) complexes were further examined through long MD simulations to check the possible drug resistance in the mutants. To understand the binding affinity, the MM-GBSA method was applied to the M pro /NMV complexes. Moreover, PCA analysis confirms the detachment of the linker region from the major domains in C145S and C145A mutants allowing for conformational alterations in the active-site region. Based on the predicted biological activities and binding affinities of NMV to WT and mutant (C145A & C145S) M pro , it can be stipulated that NMV may have conventional potency to act as an anti-viral agent against WT M pro , while the catalytic-dyad mutations may show substantial mutation-induced drug resistance.Communicated by Ramaswamy H. Sarma.

SARS-CoV-2 M pro is one of the most vital enzymes of the new coronavirus-2 (SARS-CoV-2) and is a crucial target for drug discovery. Unfortunately, there is not any potential drugs available to combat the action of SARS-CoV-2 M pro . Based on the reports HIV-protease inhibitors can be applied against the SARS by targeting the SARS-CoV-1 M pro , we have chosen few clinically trialed experimental and allophenylnorstatine (APNS) containing HIV-protease inhibitors (JE-2147, JE-533, KNI-227, KNI-272 & KNI-1931), to examine their binding affinities with SARS-CoV-2 M pro and to assess their potential to check for a possible drug candidate against the protease. Here, we have chosen a methodology to understand the binding mechanism of these five inhibitors to SARS-CoV-2 M pro by merging molecular docking, molecular dynamics (MD) simulation and MM-PBSA based free energy calculations. Our estimations disclose that JE-2147 is highly effective (Δ G Bind = -28.31 kcal/mol) due to an increased favorable van der Waals (Δ E vdw ) interactions and decreased solvation (Δ G solv ) energies between the inhibitor and viral protease. JE-2147 shows a higher level of interactions as compared to JE-533 (-6.85 kcal/mol), KNI-227 (-18.36 kcal/mol), KNI-272 (-15.69 kcal/mol) and KNI-1931 (-21.59 kcal/mol) against SARS-CoV-2 M pro . Binding contributions of important residues (His41, Met49, Cys145, His164, Met165, Glu166, Pro168, Gln189, etc.) from the active site or near the active site regions with ≥1.0 kcal/mol suggest a potent binding of the inhibitors. It is anticipated that the current study of binding interactions of these APNS containing inhibitors can pitch some valuable insights to design the significantly effective anti-SARS-CoV-2 M pro drugs.Communicated by Ramaswamy H. Sarma.

Two new structural motifs of the B 24 clusters are constructed by use of the leapfrog transformation. The resulting leapfrog B 24 has either a bowl shape with a square vacancy or a quasi-planar 2D close-packed triangular boron sheet. The neutral and ionic forms of the latter are found to be more stable than their homologous leapfrog bowl clusters, with the exception of the dicationic B 24 +2 . While the leapfrog isomer is less stable than the tubular double ring in the neutral state, it becomes competitive in some ionic states. The nucleus independent chemical shift, electron localization function, ring current maps and the electronic structure of leapfrog B 24 clusters reveal them to behave as aromatics., (© 2020 Wiley Periodicals LLC.)

Theoretical calculations were performed to investigate the interplay between σ-hole, anion-HC and cation-π interactions in the complexes of dibromo[2,2]paracyclophane (DBr[2,2]PCP) with alkali (Li + , Na + , K + ), alkaline earth metal cations (Be 2+ , Mg 2+ , and Ca 2+ ), and halogen anions (F - , Cl - , and Br - ) using the wave function (MP2) and density functional theory (M06-2X and B3LYP) methods with the 6-311++G(d,p) basis set. The study reveals that DBr[2,2]PCP behaves as amphoteric molecule with a predominance of basic character. It prefers to interact with hard cations and hard anions such as Be 2+ and F - through cation-π and anion···HC interactions, respectively. Substitution of Br by F and Cl atoms in DBr[2,2]PCP decreases slightly the interaction energies of DX[2,2]PCP-halogen complexes (X = F, Cl, and Br) by 2.0 and 0.3 kcal/mol (M06-2X), respectively. The anion-HC interactions in DBr[2,2]PCP complexes are ∼10 kcal/mol stronger (B3LYP; ∼15 kcal/mol at M06-2X and 7 kcal/mol at MP2) than the σ-hole interactions.

The electronic structure of Eu 2+ compounds results from a complex combination of strongly correlated electrons and relativistic effects as well as weak ligand-field interaction. There is tremendous interest in calculating the electronic structure as nowadays the Eu 2+ ion is becoming more and more crucial, for instance, in lighting technologies. Recently, interest in semiempirical methods to qualitatively evaluate the electronic structure and to model the optical spectra has gained popularity, although the theoretical methods strongly rely upon empirical inputs, hindering their prediction capabilities. Besides, ab initio multireference models are computationally heavy and demand very elaborative theoretical background. Herein, application of the ligand-field density functional theory (LFDFT) method that is recently available in the Amsterdam Modeling Suite is shown: (i) to elucidate the electronic structure properties on the basis of the multiplet energy levels of Eu configurations 4f 7 and 4f 6 5d 1 and (ii) to model the optical spectra quite accurately if compared to the conventional time-dependent density functional theory tool. We present a theoretical study of the molecular Eu(η 9 -C 9 H 9 ) 2 complex and its underlying photoluminescence properties with respect to the Eu 4f-5d electron transitions. We model the excitation and emission spectra with good agreement with the experiments, opening up the possibility of modeling lanthanides in complex environment like nanomaterials by means of LFDFT at much-reduced computational resources and cost.

The lowest-lying isomer of the B50 boron cluster is confirmed to have a quasi-planar shape with two hexagonal holes. By applying a topological (leap-frog) dual operation followed by boron capping, we demonstrated that such a quasi-planar structure actually comes from the smallest elongated B102-, and its high thermodynamic stability is due to its inherent disk aromaticity arising from its 32 valent π electrons that fully occupy a disk configuration of [(1σ)2(1π)4(1δ)4(2σ)2(1φ)4(2π)4(1γ)4(2δ)4(1η)4]. The aromatic character of the quasi-planar B50 is further supported by a strong diatropic magnetic current flow. The sudden appearance of a quasi-planar B50 again points out that the growth pattern of pure boron clusters is still far from being completely understood.

This paper investigates the Jahn-Teller effect in the icosahedral cation B(80)(+) and compares the descent in symmetry with that in C(60)(+). For both cations the icosahedral ground state is a (2)H(u) state, which exhibits a H ⊗ (g ⊕ 2h) Jahn-Teller instability. A detailed construction of the potential energy surface of B(80)(+) using different DFT methods including B3LYP/6-31G(d), VWN/6-31G(d), PBE/TZP and PBE/6-31G(d) shows that, contrary to C(60)(+), which prefers D(5d) symmetry, the ground state of B(80)(+) adopts S(6) point group symmetry. A D(3d) structure is identified as a saddle point among the S(6) minima of B(80)(+). The distortion of D(3d) to S(6) in B(80)(+) is attributed to a superposition of Jahn-Teller and pseudo-Jahn-Teller effects. Imaginary modes, transforming as the g(g) representation, which are present in neutral icosahedral B(80), form the dominant symmetry breaking active modes. The pronounced difference between the JT effects in the boron and carbon buckyball cations is due to the plasticity of the boron caps. The calculated Jahn-Teller stabilization of B(80)(+) is nearly 1549 cm(-1) (PBE/TZP), which exceeds the stabilization of 596 cm(-1) computed for C(60)(+) at the same level.

The ipsocentric method at the coupled Hartree-Fock level is used for the calculation of magnetically induced ring currents in the boron buckyball B(80), for both I(h) and distorted T(h) geometries. A close similarity between the current patterns in boron and carbon buckyballs is noted, but with a higher current density in B(80). Paratropic currents on the pentagons are predominant in the boron buckyball, and the central NICS value is positive. These observations support the conclusion that B(80) should be considered (weakly) anti-aromatic. The largest orbital contributions to the ring currents in both molecules are identified and related to specific excitations in the frontier orbital region.

Density functional theory calculations at the B3LYP/SVP and B3LYP/6-311G(d) levels were carried out for a series of XH(3)B(80) complexes with X = {N, P, As, B, Al}. To probe the regioselectivity of B(80), the electronic Fukui function, the molecular electrostatic potential (MEP), and the natural bond orbital (NBO) were determined. These indices were shown to provide reliable guides to predict the relative reactivities of the boron buckyball sites. Thermodynamic stabilities of the complexes formed by the reaction of B(80) with nucleophiles (NH(3), PH(3), AsH(3)) and electrophiles (BH(3), AlH(3)) are in good agreement with the prediction of regioselectivity indicated on the basis of Fukui and MEP indices. The qualitative results suggest the boron buckyball to be an amphoteric and hard molecule. It has two distinct reactive sites localized on caps and frame, which act as acids and bases, respectively. Most of the complexes are stable with formation energies comparable to that of the analogous complexes of the borane molecule, BH(3)BH(3), BH(3)NH(3), and BH(3)AlH(3). The B-H-B bond characteristics of diborane are recovered in B(80)BH(3). Exohedral complexes are more stable than endohedral complexes. The most stable complexes are those with NH(3) on the caps and BH(3) on the pentagonal ring of B(80)., (© 2011 American Chemical Society)

A density functional theory study of small base molecules and tetrahedral and cubane-like group V clusters encapsulated in B(80) shows that the boron buckyball is a hard acid and prefers hard bases like NH(3) or N(2)H(4) to form stable off-centered complexes. In contrast, tetrahedral and cubane-like clusters of this family are metastable in the cage. The most favorable clusters are the mixed tetrahedral and cubane clusters formed by nitrogen and phosphorus atoms such as P(2)N(2)@B(80), P(3)N@B(80), and P(4)N(4)@B(80). The boron cap atoms are electrophilic centers, and prefer mainly to react with electron rich nucleophilic sites. The stability of the complexes will be governed by the size and electron donating character of the encapsulated clusters. B(80) forms stable complexes with hard materials where a bidentate interaction of the encapsulated molecule with two boron cap atoms is preferred over a single direct complex toward a single endohedral boron.