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DFT and ab initio calculations are performed on tetramethyltin (SnMe4, TMSn) and its cation. A set of spectroscopic constants for both species are derived. They include equilibrium geometries, rotational constants and vibrational wavenumbers. All quantities are in close agreement with the available experimental data. For the cation, our calculations confirm the C3v charge transfer structure proposed earlier through the analysis of electron paramagnetic resonance (EPR) experimental data. Using multi reference configuration interaction and time dependant density functional theory (TD-DFT) methodologies, the vertical electronic excitation energies of TMSn and TMSn+ are determined. For the singlet-singlet neutral molecule, our calculated transition energies are distinctly lower than those previously computed. For the TMSn ( $\tilde X$1A1 → 11T2) absorption transition, our computed excitation energy coincides, however, with the experimental value. Predictive data are also given for the TMSn triplets. At the best level of theory, the vertical and the adiabatic ionization energies of TMSn are computed 9.86 eV and 8.74 eV, respectively. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012 [ABSTRACT FROM AUTHOR]

Four octahedral complexes of the type SnCl4.2L [L = (R2N)3P(E): E = Se; R = Me(1), Et(2) and E = S; R = Me(3), Et(4)] have been studied in solution by multinuclear (31P, 77Se, and 119Sn) NMR spectroscopy. 31P and 77Se NMR data were informative of changes associated with complex formation. The solution structure of the complexes was confirmed by their 119Sn NMR spectra that showed two triplet features for each complex, attributed to a mixture of the expected cis and trans isomers. The triplet signal is due to the coupling with two equivalent phosphorus atoms, consistent with an octahedral geometry around the tin center. In addition, density functional theory (DFT)/B3LYP calculations have been carried out to support the interpretations of NMR data. The results are discussed and compared with those reported for related complexes. GRAPHICAL ABSTRACT [image omitted] [ABSTRACT FROM AUTHOR]

Abstract: The reactions of allylic and aliphatic alcohols with ethyl acetoacetate have been investigated at the DFT/B3LYP level using 6-311G(d) basis set. Analysis results of frontier molecular orbital (FMO) interactions, chemical potential μ and electrophilicity index ω according to Fukui and Pearson respectively, provide a good prediction of experimental results. Alkylation or transesterification reaction is predicted reliably by the calculations. [Copyright &y& Elsevier]

Abstract: Tin tetrachloride adducts of the type SnCl4·2L (L=(Me2N)3P(O) (1), (Me2N)2P(O)F (2), Me2NP(O)F2 (3) and P(O)F3 (4)) have been theoretically studied by means of DFT geometry optimisation (B3LYP/LANL2DZ) and 119Sn chemical shift calculations (B3LYP/SV). A good correlation was found between calculated and experimental data. On going from complex 1 to 4, the Snderwent considerable lengthening, while that of Snortened (Snn cis-1 vs. 2.37Å in cis-4; Snin cis-1 vs. 2.37Å in cis-4). In the same way, the Snh name="sbnd" />P bond angle was found to decrease from 147° for cis-1 to 136° for cis-4. The trends are in good agreement with the calculated metal–ligand binding energies of complexes 1–4. Interestingly, the structural changes are accompanied by increased 119Sn chemical shifts towards higher frequencies as the Me2N groups in the ligand are substituted by fluorine atoms. The theoretical results showed that the use of the all-electron SV basis set for tin, together with the 6-31G∗ basis set for the other atoms could efficiently predict the 119Sn NMR chemical shifts in the complexes SnCl4·2L. [Copyright &y& Elsevier]

Abstract: A systematic theoretical DFT study of the bonding between the cation Fe3+ and the anion H2PO4- was carried out. By interesting in tetrahedral, bipyramidal and octahedral environments around the iron ion, several isomers were studied and their geometries were established in each case. Calculated infra-red spectra were also done. [Copyright &y& Elsevier]

Abstract: Two octahedral complexes of the general formula SnCl4 ·2(O)PF2NR2 (R=Me (1) or Et (2)) have been synthesised from SnCl4 and the ligand R2NP(O)F2 in anhydrous CHCl3. The new adducts have been characterised by multinuclear (119Sn, 31P, 19F and 1H) NMR, IR spectroscopy and elemental analysis. When compared with previously described hexamethylphosphoramide (HMPA) and trimethylphosphate (TMPA) analogues, the NMR data of the two complexes prepared suggest the presence of only the cis isomer in solution. Steric factors and the Lewis basicity of the ligand may explain the stereochemistry observed. Low temperature 31P and 119Sn NMR spectra show that the compounds partially dissociate in dichloromethane. Additionally, DFT/B3LYP calculations on complex 1 and its ligand have been carried out to support the interpretations of NMR data. [Copyright &y& Elsevier]

Abstract In this study, a new organic-inorganic hybrid metal compound (C 5 H 14 N 2) 2 [SnCl 6 ] 2 ·5H 2 O was crystallized at room temperature in the orthorhombic system (space group P2 1 2 1 2 1) where the structure is determined by single crystal X-ray diffraction analysis. The examination of the structure shows the cohesion and stability of the atomic arrangement result from the establishment of N—H⋯Cl, O(W)—H(W)⋯Cl, N—H⋯O(W) and O(W)—H(W)⋯O(W) hydrogen bonds between 1-methylpiperazine-1,4-diium (C 5 H 14 N 2)2+cations, isolated (SnCl 6)2– anions and water molecules to form organic and inorganic layers parallel to the (a, c) plane and alternate along the b-axis. Hirshfeld surface analysis was used to investigate intermolecular interactions, as well 2D fingerprint plots were conducted to reveal the contribution of these interactions in the crystal structure quantitatively. The solid phase FTIR and FT-Raman spectra of this compound have been recorded in the regions 400–4000 and 100–500 cm−1, respectively. The vibrational frequencies were also predicted from the calculated intensities by DFT method and were compared with the experimental frequencies, which yield good agreement between observed and calculated frequencies. Besides, the optical proprieties were investigated by UV-visible and photoluminescence spectroscopy studies in the region 200–700 nm and the electronic properties HOMO and LUMO energies were measured by TD-DFT approach. Moreover, this compound was characterized by thermal analysis between 300 and 500 K which revealing two phase transitions. Finally, X-ray photoelectron spectroscopy (XPS) analysis is reported to determine the degree of oxidation of tin in this compound and analyzing the surface chemistry of (C 5 H 14 N 2) 2 [SnCl 6 ] 2 ·5H 2 O. Graphical abstract Image 1 The different characterization techniques of (C 5 H 14 N 2) 2 [SnCl 6 ] 2 ·5H 2 O. Highlights • The crystal structure exhibits organic and inorganic layers parallel to the (a, c) plane and alternate along the b-axis. • The 3D Hirshfield surfaces and the associated 2D fingerprint plots were investigated for intermolecular interactions. • The vibrational frequencies were also predicted from the calculated intensities by DFT method and were compared with the experimental frequencies. • The optical properties were studied by UV–visible absorption, photoluminescence spectroscopy studies and XPS technique. • This compound was characterized by thermal analysis between 300 and 500. [ABSTRACT FROM AUTHOR]

In this work, the optical properties of tetra(imidazole) of palladium phthalocyanine (PdPc(Im) 4 ) in solution form and thin films on glass and fluorine-doped tin oxide (FTO) substrates were investigated via the thermal evaporation technique. The optical band gap was evaluated by ultraviolet-visible spectroscopy (UV-Vis). The energy band gap values were determined based on the Tauc graph. In addition, time-dependent density functional theory (TD-DFT) was used to simulate the UV-Vis absorption spectrum of the (PdPc(Im) 4 ) molecule in the Dimethyl Sulfoxide (DMSO) solution phase. A good correlation was found between the DFT results and the experimental optical results. The band gap values between the experimental and DFT-simulated values are presented. The energy band gap of (PdPc(Im) 4 ) obtained from the DFT calculations showed that it can be efficiently regulated. Frontier molecular orbitals and molecular electrostatic potentials were also proposed in this work. The surface study of the layers deposited on FTO was considered by atomic force microscopy (AFM) and scanning electron microscopy (SEM), and the results demonstrated good homogeneity covering the entire surface. The SEM image showed a homogeneous distribution of the grains with some spherical or rod-shaped structures and no agglomeration structures. This work rendered a strategy for regulating the energy band gap and compared the experimental observations obtained with theoretical studies, which provides a fundamental insight into the optical band for optoelectronic and thin-film solar cells.

In this work, a comparative theoretical conformational analysis of the commercially most successful herbicide compound, glyphosate ( N -phosphonomethylglycine), has been made at various quantum chemical levels of theory, in the gas phase and aqueous solution, using the integral equation-formalism polarizable continuum model (IEFPCM) and the solvation model density (SMD) approaches. The stable conformers of non-ionized (NE) and ionized or zwitterionic (ZW) neutral forms of glyphosate and the inter-conversions between them are described. Calculations revealed that several NE conformers of glyphosate exist in the gas phase but the zwitterionic form (ZW) is unstable in vacuo at all levels of theory. In aqueous solution, the stabilization of the zwitterion form of glyphosate was unable to be predicted satisfactorily within the equilibrated framework of the IEFPCM polarizable continuum model and using the standard UFF-radii cavity. However, the calculation with the density-based solvation model (SMD) was consistent with the experimental findings and led to the identification of the phosphonate zwitterionic (ZWP) structure as the global minimum energy in aqueous solution. The ZWP ⇋ NE tautomeric equilibrium between the non-ionized and zwitterionic forms of glyphosate was studied in aqueous solution at the SMD-B3LYP-D3/6-311++(2d,2p) level. Zwitterion formation in solution could occur by means of a concerted intramolecular proton transfer from the nitrogen to the oxygen of the phosphonate group. An analysis of the intermolecular mechanism shows that the addition of one water molecule favours the process either thermodynamically or kinetically. The possibility that the tautomerization process of glyphosate via a nonconcerted mechanism with zwitterion carboxylate (ZWC) as the intermediate can be excluded and the ZWP → ZWC proton transfer conversion can be a nearly barrierless process in PES and FES surfaces. comparison with similarly related biologically active systems was made.

In this study, we investigated the potential of palladium tetrakis (imidazole) phthalocyanine (PdPc(Imz) 4 ) for use as an organic semiconductor for improving the photovoltaic performance. In order to get more information about the prevailing model of the conduction mechanism (correlated barrier hopping (CBH)) for PdPc(Imz) 4 , electrical impedance measurements were performed at different temperatures and the obtained data were simulated by the Kohlraush Williams Watt (KWW) approach. Theoretical studies (density functional theory (DFT)) were performed and molecular electrostatic potential (MEP) maps were also extracted to understand the relationship between the molecular structures and the molecular electronic structure of PdPc(Imz) 4 and its semiconductor properties. Furthermore, studies on the AC electrical process as a function of temperature highlighted a hopping charge transport according to an equivalent electrical circuit composed of a parallel constant-phase element (CPE), capacitance in the grain boundary layer ( C g ), and resistance of the grain boundary ( R g ). To improve interpretation of the results, an in-depth analysis of the behavior of the electric transport was conducted. As a result, the correlated barrier hopping (CBH) conduction mechanism was shown to be the most suitable predominant conduction mechanism., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

A unified CO 2 -amine reaction mechanism applicable to absorption in aqueous or nonaqueous solutions and to adsorption on immobilized amines in the presence of both dry and humid conditions is proposed. Key findings supported by theoretical calculations and experimental evidence are as follows: (1) The formation of the 1,3-zwitterion, RH 2 N + -COO - , is highly unlikely because not only the associated four-membered mechanism has a high energy barrier, but also it is not consistent with the orbital symmetry requirements for chemical reactions. (2) The nucleophilic attack of CO 2 by amines requires the catalytic assistance of a Bro̷nsted base through a six-membered mechanism to achieve proton transfer/exchange. An important consequence of this concerted mechanism is that the N and H atoms added to the C=O double bond do not originate from a single amine group. Using ethylenediamine for illustration, detailed description of the reaction pathway is reported using the reactive internal reaction coordinate as a new tool to visualize the reaction path. (3) In the presence of protic amines, the formation of ammonium bicarbonate/carbonate does not take place through the widely accepted hydration of carbamate/carbamic acid. Instead, water behaves as a nucleophile that attacks CO 2 with catalytic assistance by amine groups, and carbamate/carbamic acid decomposes back to amine and CO 2 . (4) Generalization of the catalytic assistance concept to any Bro̷nsted base established through theoretical calculations was supported by infrared measurements. A unified six-membered mechanism was proposed to describe all possible interactions of CO 2 with amines and water, each playing the role of a nucleophile and/or Bro̷nsted base, depending on the actual conditions., Competing Interests: The authors declare no competing financial interest.

The formation of substituted 1,2-diamines via the regiospecific nucleophilic ring opening of 2-methylaziridine with methylamine was performed by nucleophilic attack at aziridine carbon atoms. A detailed theoretical study was investigated by density functional theory (DFT) at the B3LYP level and second order Moller Plesset perturbation theory (MP2) by using the 6-311G(d,p) basis set. The third Grimme correction term (D3) was used to take into account weak interactions. Solvent effects were computed in methanol and dimethylsulfoxide using the polarizable continuum model (PCM). Emphasis was placed on the ring opening mechanisms of neutral aziridines and aziridinium ions obtained through N-complexation with the BF 3 Lewis acid. Moreover, the effect of substituent groups on the regioselectivity of the ring opening was investigated. The nucleophilic attack was carried out via two pathways (frontside attack M1 and backside attack M2) where activation barriers proved the preference for ring opening through the backside attack at the C3 aziridine carbon atom. The obtained results showed that the frontside attack with methylamine takes place along a concerted mechanism that leads to formation of products through one transition state. However, the backside attack is carried via a stepwise process in which the methylamine attack takes place in an S N 2 fashion where the leaving group is the ring nitrogen. It first conduces a ring opening considered as the rate-determining step followed by formation of a zwitterionic intermediate. This latter undergoes a rotation to allow the proton transfer step and finally leads to formation of the thermodynamic products.