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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]

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]

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]

Abstract: A symmetry analysis of the valence shell in the boron buckyball B80 shows a perfect match with the symmetry of the valence shell in C60. The cap atoms participate in the bonding by 30 orbitals which transform as the σ-bonds along the 6–6 edges. Far reaching consequences for chemical and physical properties of B80, which until now only exists in silico, are expected. [Copyright &y& Elsevier]

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]