The mechanism of the ozonolysis on the surface of C70 fullerene: the electron localizability indicator study.

The formation of C70O from C70O3 monomolozonide is a three-step process with the isomer dependent last step leading either to c,c-C70O epoxide or d,d-C70O oxidoannulene. The process involves the open intermediate (first O-O then Cc-Cc/Cd-Cd bonds broken), oxidoannulene-like structure intermediate (new Cc-O/Cd-O bond formed) and finally the oxide product. On the formation of c,c-C70O isomer, the final release of O2 is followed by the restoration of Cc-Cc bond, which stabilizes the product. Neither Cd-Cd bond is restored nor the total energy essentially lowered upon d,d-C70O formation. At all steps of the studied process, the four CC bonds adjacent to Cc-Cc or Cd-Cd bond, respectively, play a crucial role donating or withdrawing the necessary electron density. C70(O)O2 products, with O2 bridging one of the bonds adjacent to the parent Cc-Cc/Cd-Cd one, may compete with the oxide products. The OO bond in such structures is weak as suggested by its low electron population. For both c,c-C70O3 and d,d-C70O3, the shape of the potential energy surfaces (0 K) and the related, reported earlier, room temperature-free energy surfaces differ. Graphical abstract.

Effects of xenon insertion into hydrogen bromide. Comparison of the electronic structure of the HBr···CO2 and HXeBr···CO2 complexes using quantum chemical topology methods: electron localization function, atoms in molecules and symmetry adapted perturbation theory.

Quantum chemistry methods have been applied to study the influence of the Xe atom inserted into the hydrogen-bromine bond (HBr → HXeBr), particularly on the nature of atomic interactions in the HBr···CO2 and HXeBr···CO2 complexes. Detailed analysis of the nature of chemical bonds has been carried out using topological analysis of the electron localization function, while topological analysis of electron density was used to gain insight into the nature of weak nonbonding interactions. Symmetry-adapted perturbation theory within the orbital approach was applied for greater understanding of the physical contributions to the total interaction energy.

Homoleptic aminophenolates of Zn, Mg and Ca. Synthesis, structure, DFT studies and polymerization activity in ROP of lactides.

The reaction of MgBu2, ZnEt2 or Ca(O(i)Pr)2 with 2 eq. of three-coordinating N-[methyl(2-hydroxy-3,5-dimethylphenyl)]-N-methyl-N-methyl-1,3-oxolaneamine (mpoa-H) or N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-methyl-1,3-oxolaneamine (tbpoa-H) gave neutral, monomeric [Mg(mpoa)2], [Zn(mpoa)2], [Zn(tbpoa)2], and [Ca(tbpoa)2] as white powders in 58-90% yields. The resulting aminophenolates were characterized in solution by NMR showing, in the case of [Zn(tbpoa)2], interesting dynamics. [Zn(tbpoa)2] and [Ca(tbpoa)2] were characterized by X-ray crystallography to show the Zn atom to be pseudo-octahedrally coordinated and the Ca atom in six-coordination mode. The new homoleptic complexes were tested in the polymerization of lactide with an external alcohol to reveal stable behaviour (during the polymerization process) only in the case of [Zn(tbpoa)2]. The high activity of the catalyst was correlated with a ligand flexibility that was further supported by theoretical studies.

OH-induced oxidative cleavage of dimethyl disulfide in the presence of NO.

We report the results of the theoretical study of (•)OH-induced oxidative cleavage of dimethyl disulfide (DMDS) and the experimental study of the CH3SSCH3 + (•)OH reaction in the presence of (•)NO. Infrared low temperature argon matrix studies combined with ab initio calculations allowed us to identify cis-CH3SONO, which evidences the formation of the CH3SO(•) and CH3SH molecules in the course of the CH3SSCH3 + (•)OH reaction. Ab initio/quantum chemical topology calculations revealed details of the oxidative cleavage of dimethyl disulfide, which is a complex multistep process involving an alteration of S-O and S-S covalent bonds as well as a hydrogen atom transfer. The ability of delocalization of the unpaired electron density by sulfur atoms and a formation of a hydrogen bond by CH3SO(•) and CH3SH are the factors which seem to explain antiradical properties of DMDS.

Investigations of the very short hydrogen bond in the crystal of nitromalonamide via Car-Parrinello and path integral molecular dynamics.

In this paper are presented the results of theoretical studies of the structure in proton motion in a very short O···O and two weak N-H···O intramolecular hydrogen bonds in the nitromalonamide crystal. The dynamics of proton motion in hydrogen bonds were investigated in the NVT ensemble at 298 K using the Car-Parrinello and the path integral molecular dynamics. A very large delocalization of proton in the slightly asymmetrical single well of free energy potential of O-H···O intramolecular hydrogen bond was noted especially in the path integral simulation where quantum effects are taken into account. This hydrogen bond is very strong with the estimated energy of hydrogen bond ca. -27 kcal/mol. The nature of intra- and intermolecular interactions was studied by means of quantum theory of atoms in molecules. The infrared spectra were calculated and compared with available experimental data. CPMD vibrational results appear to be in good agreement with the experimental ones.

Matrix-isolated hydrogen-bonded and van der Waals complexes of hydrogen peroxide with OCS and CS2.

Matrix isolation spectroscopy has been combined with ab initio calculations to characterize the 1:1 complexes of H2O2 with OCS and CS2. The infrared spectra of the argon and nitrogen matrices doped with H2O2 and OCS or CS2 have been measured and analyzed. The geometries of the complexes were optimized at the MP2/6-311++G(3df,3pd) level of theory. Four structures were found for the OCS-H2O2 complex and five for the CS2-H2O2 one; every pair of the corresponding structures showed close correspondence. For every optimized structure the interaction energy was partitioned according to the SAPT Scheme and the topological distribution of the charge density (AIM theory) was performed. The SAPT analysis and AIM results indicate that only one complex among the nine optimized ones is stabilized by the hydrogen bonding, namely the OCS-H2O2 one with the OH group of H2O2 bonded to an oxygen atom of OCS. The other structures are stabilized by van der Waals interaction. The spectra analysis evidences that at least two types of the complexes are trapped in the argon matrices including the most stable ones: hydrogen bonded structure in the case of the OCS-H2O2 complex and the structure stabilized by the S···H and C···O interactions in the case of the CS2-H2O2 complex. The solid nitrogen environment triggers the formation of the structures of C2v symmetry with a sulfur atom of OCS or CS2 directed toward the center of O-O bond of H2O2, stabilized by S···O interactions.

Homo- and heteroleptic zinc aminophenolates as initiators for lactide polymerization.

The reaction of ZnEt2 with one or two equivalents of aminophenolate ligand N-[methyl(2-hydroxy-3,5-di-tert-butylphenyl)]-N-methyl-N-cyclohexylamine gives hetero- and homoleptic molecular compounds [(micro,eta2-L2)ZnEt]2 and [Zn(eta2-L2)2]. The later is most probably a mixture of diastereoisomers that in solution shows an interesting dynamic behaviour. Both complexes as well as the BnOH derivative of the latter, [(eta2-L2)Zn(micro-BnO)]2, proved excellent initiators for lactide polymerization.

Structure, spectra and stability of a tetrafluoromethane-water complex.

The complex formed between water and tetrafluoromethane has been studied by infrared matrix isolation spectroscopy and ab initio calculations. The geometries of the CF4-H2O complexes were optimized in two steps at the MP2/aug-cc-pVTZ level of theory. The structure found at this level was reoptimized on the CP-corrected potential energy surface. The interaction energy was partitioned according to the SAPT scheme and the topological analysis of the electron density was performed. The optimized structure corresponds to the nonhydrogen bonded complex with an oxygen atom of water oriented toward the carbon atom of CF4. The infrared spectra of CF4-H2O /Ne(Ar) matrices demonstrate the presence of a well defined CF4-H2O structure in accord with theoretical prediction. Two complex vibrations were identified in the spectra of neon matrices and four vibrations were observed in the spectra of argon matrices. The available experimental data are in accord with the CP-corrected calculated data.

Molecular modeling study of leflunomide and its active metabolite analogues.

Leflunomide is known as a compound with various sorts of biological activity, which found a practical application in medicine. Search of current literature revealed an active metabolite of Leflunomide together with its eight analogues synthesized as protein tyrosine kinase inhibitors with potential anticancer activity. Accurate description of the molecular structure of these compounds is valuable. The detailed geometrical parameters description was performed using DFT theory. The conformational analysis and intramolecular proton transfer were considered. Using the most stable conformation the detailed electronic structure description was obtained by analysis of electron density and electrostatic potential distribution in the first step. Next, the topological analysis of the electron density by AIM method and electron localization function (ELF) theories supplemented this study. The AIM and ELF theories were applied to study the topology of the molecules, atomic charges distribution, and details of bonding. The theoretical investigations were performed in the gas phase and by using SCRF/PCM solvent reaction field. In this study the molecular modeling results for Leflunomide and the analogues of its active metabolite are presented.

Experimental and theoretical study of the photophysics and structures of europium cryptates incorporating 3,3'-bi-isoquinoline-2,2'-dioxide.

A detailed photophysical study of [Eu within (biqO2.2.2)(CF3SO3)](CF3SO3)2. CH3CN.H2O (Eu within 1) and two other types of cryptates incorporating three 3,3'-biisoquinoline-2,2'-dioxide units has been performed. Structural crystallographic data of Eu within 1, electronic structure calculations and theoretical models were used to obtain the intramolecular energy transfer rates and the appropriate set of rate equations, which was solved numerically. Quantum yields and decay lifetimes were obtained from these results and compared to the experimental data. The role of the ligand-to-metal charge transfer (LMCT) states was ascertained. A theoretical ligand field and intensity analysis was carried out and the results agree very well with the emission spectra. The molecular structures of the lanthanide cryptates were successfully modelled by the YIII ion using the restricted Hartree-Fock (RHF) method, with the advantage of dealing with closed-shell systems. These molecular structures were used to explain the drastic differences in the photophysics of the three EuIII cryptates.

The first structurally characterized nonorganometallic titanium(III) alkoxo-bridged dinuclear complexes.

The reaction of [Ti4(OMe)14Cl2] (1) with an excess of AlMe3 gave the cocrystallite [Ti2(mu-OMe)2(mu-Cl)Cl3(thf)3].[Ti2(mu-OMe)3Cl3(thf)3] (2.3) species in a 1:1 ratio. Similar to 2, [Ti2(mu-OEt)2(mu-Cl)Cl3-(thf)3] (4) was obtained in the reaction of an equimolar mixture of TiCl4 and Ti(OEt)4 with Al/AlMe3. The short distance [2.543(1)av A in 2.3 and 2.599(1) A in 4] between "Ti(+3)" atoms, their diamagnetism, and ELF analysis indicate the presence of a Ti-Ti bond.