Bond Paths Show Preferable Interactions: Ab Initio and QTAIM Studies on the X−H···π Hydrogen Bond

Ca(II) and Yb(II) complexes featuring M(C≡C)4 structural motif: enforced proximity or genuine η2 -bonding?

Bis(carbazolide) complexes M[3,6-tBu2 -1,8-(RC≡C)2 Carb]2 (THF)n (R=SiMe3 , n=0, M=Ca, Yb; R=Ph, n=1, M=Ca, Yb; n=0, M=Yb) were synthesized through transamination reaction of M[N(SiMe3 )2 ]2 (THF)2 with two molar equivalents of carbazoles. The complexes feature M(η2 -C≡C)4 structural motif composed of M(II) ions encapsulated by four acetylene fragments due to atypical for alkaline- and rare-earth metals η2 -interactions with triple C≡C bond. This interaction is evidenced experimentally by X-ray diffraction, Raman spectroscopy in the solid state and by NMR-spectroscopy in the solution. According to QTAIM analysis there are 4 bond critical points (3;-1) between the metal atom and each of the triple bonds, which are connected by a strongly curved, almost T-shaped bond pathway.

Comprehensive Investigation of Cu2+ Adsorption from Wastewater Using Olive-Waste-Derived Adsorbents: Experimental and Molecular Insights

This study investigates the efficacy of adsorbents from locally sourced olive waste-encompassing olive skins, leaves, and pits, recovered from the initial centrifugation of olives (OWP)-and a composite with sodium alginate (OWPSA) for the removal of Cu2+ ions from synthetic wastewater. Experimental analyses conducted at room temperature, with an initial Cu2+ concentration of 50 mg/L and a solid/liquid ratio of 1 g/L, showed that the removal efficiencies were approximately 79.54% and 94.54% for OWP and OWPSA, respectively, highlighting the positive impact of alginate on adsorption capacity. Utilizing statistical physics isotherm models, particularly the single-layer model coupled to real gas (SLMRG), allowed us to robustly fit the experimental data, providing insights into the adsorption mechanisms. Thermodynamic parameters affirmed the spontaneity and endothermic nature of the processes. Adsorption kinetics were interpreted effectively using the pseudo-second-order (PSO) model. Molecular modeling investigations, including the conductor-like screening model for real solvents (COSMO-RS), density functional theory (DFT), and atom-in-molecule (AIM) analysis, unveiled intricate molecular interactions among the adsorbent components-cellulose, hemicellulose, lignin, and alginate-and the pollutant Cu2+, confirming their physically interactive nature. These findings emphasize the synergistic application of experimental and theoretical approaches, providing a comprehensive understanding of copper adsorption dynamics at the molecular level. This methodology holds promise for unraveling intricate processes across various adsorbent materials in wastewater treatment applications.

Quince seed mucilage/β-cyclodextrin/Mmt-Na+-co-poly (methacrylate) based pH-sensitive polymeric carriers for controlled delivery of Capecitabine

In current work, quince seed mucilage and β-Cyclodextrin based pH regulated hydrogels were developed using aqueous free radical polymerization to sustain Capecitabine release patterns and to overcome its drawbacks, such as high dose frequency, short half-life, and low bioavailability. Developed networks were subjected to thermal analysis, Fourier transforms infrared spectroscopy, powder x-ray diffraction, elemental analysis, scanning electron microscopy, equilibrium swelling, and in-vitro release investigations to assess the network system's stability, complexation, morphology, and pH responsiveness. Thermally stable pH-responsive cross-linked networks were formed. Nanocomposite hydrogels were prepared by incorporating Capecitabine-containing clay into the swollen hydrogels. All the formulations exhibited equilibrium swelling ranging from 67.98 % to 92.98 % at pH 7.4. Optimum Capecitabine loading (88.17 %) was noted in the case of hydrogels, while it was 74.27 % in nanocomposite hydrogels. Excellent gel content (65.88 %-93.56 %) was noticed among developed formulations. Elemental analysis ensured the successful incorporation of Capecitabine. Nanocomposite hydrogels released 80.02 % longer than hydrogels after 30 h. NC hydrogels had higher t1/2 (10.57 h), AUC (121.52 μg.h/ml), and MRT (18.95 h) than hydrogels in oral pharmacokinetics. These findings imply that the pH-responsive carrier system may improve Capecitabine efficacy and reduce dosing frequency in cancer therapy. Toxicity profiling proved the system's safety, non-toxicity, and biocompatibility.

Biosorption of zinc (II) from synthetic wastewater by using Inula Viscosa leaves as a low-cost biosorbent: Experimental and molecular modeling studies

The use of biosorption as a strategy for lowering the amount of pollution caused by heavy metals is particularly encouraging. In this investigation, a low-cost and efficient biosorbent, Inula Viscosa leaves were used to remove zinc ions (Zn²⁺) from synthetic wastewater. A Fourier transform infrared spectroscopy experiment, a scanning electron microscopy experiment, and an energy dispersive X-ray spectroscopy experiment were used to describe the support. Several different physicochemical factors, such as the beginning pH value, contact duration, initial zinc concentration, biosorbent dose, and temperature, were investigated in this study. When the Langmuir, Freundlich, Temkin, Toth, and Redlich-Peterson models were used to match the data from the Inula Viscosa leaves biosorption isotherms, it was found that the biosorption isotherms correspond most closely with the Langmuir isotherm. On the other hand, the kinetic biosorption process was investigated using pseudo-first-order, pseudo-second-order (PS2), and Elovich models. The PS2 model was the one that provided the most accurate description of the biosorption kinetics. The thermodynamics process shows the spontaneous and endothermic character of Zn²⁺ sorption on Inula Viscosa leaves, which also entails the participation of physical interactions. In addition, the atom-in-molecule analysis, density functional theory, and the conductor like screening model for real solvents, were used to investigate the relationship that exists between quantum calculations and experimental outcomes.

Effective removal of cationic dye on activated carbon made from cactus fruit peels: a combined experimental and theoretical study

This article investigates experimentally and theoretically the adsorption of Basic Red 46 cationic dye (BR46) using activated carbon generated from cactus fruit peels (ACCFP). The prepared adsorbent was characterized by different analytical tools showing a good surface for the uptake of pollutants. A maximum batch adsorption capacity of 806.38 mg g^-1 was achieved at optimal conditions. The Freundlich model best represented the equilibrium data, although the pseudo-second-order kinetic model best described the adsorption kinetics. The thermodynamic studies demonstrated that the adsorption process was spontaneous (ΔG° < 0) and endothermic (ΔH° = 32.512 kJ mol^-1). DFT descriptors were combined with COSMO-RS and AIM theory to provide a complete picture of the adsorbate/adsorbent system and its molecular interactions. Last, the ACCFP was regenerable up to four times, emphasizing the idea of using it as an adsorbent to treat textile wastewaters.

Adjusting the balance between hydrogen and chalcogen bonds

A complex is assembled which pairs a carboxyl group of X₁COOH with a 1,2,5-chalcogenadiazole ring containing substituents on its C atoms. The OH of the carboxyl group donates a proton to a N atom of the ring to form a OH⋯N H-bond (HB), while its carbonyl O engages in a Y⋯O chalcogen bond (ChB) with the ring in which Y = S, Se, Te. The ChB is strengthened by enlarging the size of the Y atom from S to Se to Te. Placement of an electron-withdrawing group (EWG) X₁ on the acid strengthens the HB while weakening the ChB; the reverse occurs when EWGs are placed on the ring. By selection of the proper substituents on the two units, it is possible to achieve a near perfect balance between the strengths of these two bonds. These bond strengths are also reflected in the NMR spectroscopic properties of the chemical shielding of the various atoms and the coupling between the nuclei directly involved in each bond.

Corrosion protection performance of silicon-based coatings on carbon steel in NaCl solution: a theoretical and experimental assessment of the effect of plasma-enhanced chemical vapor deposition pretreatment

Using a plasma-assisted chemical vapor deposition (PACVD) process, carbon steel samples were coated with an organosilicon layer less than 2.5 microns thick. Ellipsometry, Fourier transform infrared (FTIR) spectroscopy, contact angle, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used to analyze the films. Additionally, gravimetric experiments were used to determine the electrochemical properties of the organosilicon coatings. Organosilicon-coated carbon steel specimens demonstrated significantly enhanced resistance to corrosive conditions, such as 3% aqueous sodium chloride solutions. The surface preparation method has a considerable influence on the morphological and electrochemical properties of the steel. Argon pretreatment significantly enhances the corrosion resistance of organosilicon-coated steel. Gravimetric research demonstrated that pretreatment with argon plasma resulted in less weight loss and corrosion than pretreatment with nitrogen plasma. The link between quantum computing and experimental data using density functional theory (DFT) and molecular dynamics (MD) was used.

Physicochemical Properties and Atomic-Scale Interactions in Polyaniline (Emeraldine Base)/Starch Bio-Based Composites: Experimental and Computational Investigations

The processability of conductive polymers still represents a challenge. The use of potato starch as a steric stabilizer for the preparation of stable dispersions of polyaniline (emeraldine base, EB) is described in this paper. Biocomposites are obtained by oxidative polymerization of aniline in aqueous solutions containing different ratios of aniline and starch (% w/w). PANI-EB/Starch biocomposites are subjected to structural analysis (UV-Visible, RAMAN, ATR, XRD), thermal analysis (TGA, DSC), morphological analysis (SEM, Laser Granulometry), and electrochemical analysis using cyclic voltammetry. The samples were also tested for their solubility using various organic solvents. The results showed that, with respect to starch particles, PANI/starch biocomposites exhibit an overall decrease in particles size, which improves both their aqueous dispersion and solubility in organic solvents. Although X-ray diffraction and DSC analyses indicated a loss of crystallinity in biocomposites, the cyclic voltammetry tests revealed that all PANI-EB/Starch biocomposites possess improved redox exchange properties. Finally, the weak interactions at the atomic-level interactions between amylopectin–aniline and amylopectin–PANI were disclosed by the computational studies using DFT, COSMO-RS, and AIM methods.

Non-conventional hydrogen bonding and dispersion forces that support embedding mesitylgold into a tailored bis(amidine) framework

A bis(amidine) ligand operates as a molecular lock for two AuMes fragments. The resulting complex retains a flexible double macrocycle with two non-conventional N-H⋯C_ipso hydrogen bonds and distinct intramolecular dispersion forces. Instead of unfolding of the double-ring structure through bond rupture in solution, a conformational ring inversion is observed.

Hydrogen bonds and dispersion forces serving as molecular locks for tailored Group 11 bis(amidine) complexes

A flexible polydentate bis(amidine) ligand LH2 operates as a molecular lock for various coinage metal fragments and forms the dinuclear complexes [LH2(MCl)2], M = Cu (1), Au (2), the coordination...

Theoretical study of hydrogen bonding interactions in substituted nitroxide radicals

Interaction energy (E_int) of hydrogen bonded complexes of nitroxide radicals can be assessed in terms of the deepest minimum of molecular electrostatic potential (V_min).

Probing the bent bonds in cyclopropane systems for gas storage and separation process: A computational study

The hydrogen, carbon dioxide, and carbon monoxide gas adsorption and storage capacity of lithium-decorated cyclopropane ring systems were examined with quantum chemical calculations at density functional theory, DFT M06-2X functional using 6-31G(d) and cc-pVDZ basis sets. To examine the reliability of M06-2X DFT functional, a few representative systems are also examined with complete basis set CBS-QB3 method and CCSD-aug-cc-pVTZ level of theory. The cyclopropane systems can bind to one Li⁺ ion; however, the corresponding the methylated systems can bind with two Li⁺ ions. The cyclopropane systems can adsorb six hydrogen molecules with an average binding energy of 3.8 kcal/mol. The binding free energy (ΔG) values suggest that the hydrogen adsorption process is feasible at 273.15 K. The calculation of desorption energies indicates the recyclable property of gas adsorbed complexes. The same number of CO₂ and CO gas molecules can also be adsorbed with an average binding energy of -14.4 kcal/mol and -10.7 kcal/mol, respectively. The carbon dioxide showed ~3-4 kcal/mol better binding energy as compared to carbon monoxide and hence such designed systems can function as a potential candidate for the separation of these flue gas molecules. The nature of interactions in complexes was examined with atoms in molecules analysis revealed the electrostatic nature for the interaction of Li⁺ ion with cyclopropane rings. The chemical hardness and electrophilicity calculations showed that the gas adsorbed complexes are rigid and therefore robust as gas storage materials.

The interplay and strength of the π⋯HF, C⋯HF, F⋯HF and F⋯HC hydrogen bonds upon the formation of multimolecular complexes based on C2H2⋯HF and C2H4⋯HF small dimers

The conception of this theoretical research was idealized aiming to unveil the intermolecular structures of complexes formed by acetylene or ethylene and hydrofluoric acid. At light of computational calculations by using the B3LYP/6-311++G(d,p) method, the geometries of the C₂H₂⋯(HF), C₂H₂⋯2(HF), C₂H₂⋯4(HF), C₂H₄⋯(HF), C₂H₄⋯2(HF) and C₂H₄⋯4(HF) hydrogen-bonded complexes were fully optimized. Moreover, the Post-Hartree-Fock calculations MP2/6-311++G(d,p), MP2/aug-cc-pVTZ, MP4(SDQ)/6-311++G(d,p) and CCSD/6-311++G(d,p) also were also used. The infrared spectra were analyzed in order to identify the new vibrational modes and frequencies of the proton donors shifted to red region. Through the modeling of charge-fluxes on the basis of the Quantum Theory of Atoms In Molecules (QTAIM) and, by contradicting the expectation of the hydrofluorination mechanisms of acetylene or ethylene, C⋯HF was recognized as a new type of hydrogen bond instead of the already well known π⋯H. The calculations of the Natural Bonding Orbital (NBO) and Charges derived from the Electrostatic Potential Grid-based (ChElPG) were also applied to interpret the shifting frequencies as well as measuring of the punctual charge-transfer after the formation of the complexes. Finally, the determination of the stabilization energy was carried out through the arguments of the Fock matrix in NBO basis and through the supermolecule approach. Also it is worthwhile to notice that some algebraic formulations were used for determining the electronic cooperative effect (CE).

π-Hydrogen bonding and aromaticity: a systematic interplay study

Quantum DFT calculations, corrected for long-range interactions, have been carried out on complex models formed between HF as a proton donor and 2-methylene-2H-indene derivatives as proton acceptors. Using various exocyclic X substitutions, mutual effects of the aromaticity and the strength of the resulting π-hydrogen bond (after its evaluation by AIM methodology) have been investigated. The results show that the aromaticity of 6-membered rings and the hydrogen bond strength increase upon increasing the electron-donating character of the X-substituents. Based on some aromaticity indices (HOMA, FLU, SA and NICS(1)zz), it has been shown that the formation of a π-hydrogen bond causes an increase of aromaticity of the 6-membered ring. Also, the strength of the resulting π-hydrogen bond (with an energy of about 4.0 to 7.0 kcal mol-1) depends on the aromaticity of the 6-membered ring and increases with an increase in the aromaticity. In addition, a linear relationship was found between the most negative value of the molecular electrostatic potential (Vmin) and the HOMA, which confirms that the Vmin in the region of the studied ring could be used as a new index to estimate the amount of aromaticity. The electronic properties of the complexes have also been evaluated by means of the molecular electrostatic potential (MEP), the atoms in molecules (AIM) and the natural bond orbital (NBO) analyses.

Perspective: Found in translation: Quantum chemical tools for grasping non-covalent interactions

Today's quantum chemistry methods are extremely powerful but rely upon complex quantities such as the massively multidimensional wavefunction or even the simpler electron density. Consequently, chemical insight and a chemist's intuition are often lost in this complexity leaving the results obtained difficult to rationalize. To handle this overabundance of information, computational chemists have developed tools and methodologies that assist in composing a more intuitive picture that permits better understanding of the intricacies of chemical behavior. In particular, the fundamental comprehension of phenomena governed by non-covalent interactions is not easily achieved in terms of either the total wavefunction or the total electron density, but can be accomplished using more informative quantities. This perspective provides an overview of these tools and methods that have been specifically developed or used to analyze, identify, quantify, and visualize non-covalent interactions. These include the quantitative energy decomposition analysis schemes and the more qualitative class of approaches such as the Non-covalent Interaction index, the Density Overlap Region Indicator, or quantum theory of atoms in molecules. Aside from the enhanced knowledge gained from these schemes, their strengths, limitations, as well as a roadmap for expanding their capabilities are emphasized.

Tetrel Bonds with π-Electrons Acting as Lewis Bases-Theoretical Results and Experimental Evidences

MP2/aug-cc-pVTZ calculations were carried out for the ZFH₃-B complexes (Z = C, Si, Ge, Sn and Pb; B = C₂H₂, C₂H₄, C₆H₆ and C₅H₅⁻; relativistic effects were taken into account for Ge, Sn and Pb elements). These calculations are supported by other approaches; the decomposition of the energy of interaction, Quantum Theory of Atoms in Molecules (QTAIM) and Natural Bond Orbital (NBO) method. The results show that tetrel bonds with π-electrons as Lewis bases are classified as Z···C links between single centers (C is an atom of the π-electron system) or as Z···π interactions where F‒Z bond is directed to the mid-point (or nearly so) of the CC bond of the Lewis base. The analogous systems with Z···C/π interactions were found in the Cambridge Structural Database (CSD). It was found that the strength of interaction increases with the increase of the atomic number of the tetrel element and that for heavier tetrel elements the ZFH₃ tetrahedral structure is more deformed towards the structure with the planar ZH₃ fragment. The results of calculations show that the tetrel bond is sometimes accompanied by the Z-H···C hydrogen bond or even sometimes the ZFH₃-B complexes are linked only by the hydrogen bond interaction.

Hydrogen bonds and other interactions as a response to protect doublet/octet electron structure

MP2/aug-cc-pVTZ calculations were performed for complexes linked by hydrogen bonds. Three types of proton donating species were taken into account: H₂O, CCl₃H, and H₃O⁺. These calculations are supported by the natural bond orbital (NBO) method and the quantum theory of atoms in molecules (QTAIM) approach. Numerous correlations between parameters of H-bonded systems were found. The most important are those which show the response of the system on the H-bond formation; for example, the increase of polarization of the A-H bond correlates with the strength of the hydrogen bond. Similar relationships were found for the σ-hole bonds while the π-hole bonds do not follow the trends known for the hydrogen bonds. Graphical abstract Hydrogen bonds and other interactions as a response to protect doublet/octet electron structureᅟ.

New Type of Halogen Bond: Multivalent Halogen Interacting with π- and σ-Electrons

MP2/aug-cc-pVTZ calculations were performed for complexes of BrF₃ and BrF₅ acting as Lewis acids through the bromine centre, with species playing a role of Lewis base: dihydrogen, acetylene, ethylene, and benzene. The molecular hydrogen donates electrons by its σ-bond, while in remaining moieties—in complexes of hydrocarbons; such an electron transfer follows from π-electrons. The complexes are linked by a kind of the halogen bond that is analyzed for the first time in this study, i.e., it is the link between the multivalent halogen and π or σ-electrons. The nature of such a halogen bond is discussed, as well as various dependencies and correlations are presented. Different approaches are applied here, the Quantum Theory of Atoms in Molecules, Natural Bond Orbital method, the decomposition of the energy of interaction, the analysis of electrostatic potentials, etc.

Experimental evidence for the blue-shifted hydrogen-bonded complexes of CHF3 with π-electron donors

Blue-shifted hydrogen-bonded complexes of fluoroform (CHF₃) with benzene (C₆H₆) and acetylene (C₂H₂) have been investigated using matrix isolation infrared spectroscopy and ab initio computations. For CHF₃-C₆H₆ complex, calculations performed at the B3LYP and MP2 levels of theory using 6-311++G (d,p) and aug-cc-pVDZ basis sets discerned two minima corresponding to a 1:1 hydrogen-bonded complex. The global minimum correlated to a structure, where the interaction is between the hydrogen of CHF₃ and the π-electrons of C₆H₆ and a weak local minimum was stabilized through H…F interaction. For the CHF₃-C₂H₂ complex, computation performed at MP2/aug-cc-pVDZ level of theory yielded two minima, corresponding to the cyclic C-H…π complex A (global) and a linear C-H…F (n-σ) complex B (local). Experimentally a blue-shift of 32.3cm^-1 and 7.7cm^-1 was observed in the ν₁ C-H stretching mode of CHF₃ sub-molecule in Ar matrix for the 1:1 C-H…π complexes of CHF₃ with C₆H₆ and C₂H₂ respectively. Natural bond orbital (NBO), Atoms-in-molecule (AIM) and energy decomposition (EDA) analyses were carried out to explain the blue-shifting and the nature of the interaction in these complexes.

Modulating of the pnicogen-bonding by a H⋯π interaction: An ab initio study

An ab initio study of the cooperativity in XH₂P⋯NCH⋯Z and XH₂P⋯CNH⋯Z complexes (X=F, Cl, Br, CN, NC; Z=C₂H₂,C₆H₆) connected by pnicogen-bonding and H⋯π interactions is carried out by means of MP2 computational method. A detailed analysis of the structures, interaction energies and bonding properties is performed on these systems. For each set of the complexes considered, a favorable cooperativity is observed, especially in X=F and CN complexes. However, for a given X or Z, the amount of cooperativity effects in XH₂P⋯CNH⋯Z complexes are more important than XH₂P⋯NCH⋯Z counterparts. Besides, the influence of a H⋯π interaction on a P⋯N (C) bond is more pronounced than that of a P⋯N (C) bond on a H⋯π bond. The quantum theory of atoms in molecules shows that ternary complexes have increased electron densities at their bond critical points relative to the corresponding binary systems. The results also indicate that the strength of the P⋯N(C) and H⋯π interactions increases in the presence of the solvent.

New insights about the hydrogen bonds formed between acetylene and hydrogen fluoride: π⋯H, C⋯H and F⋯H

A theoretical study of hydrogen bond strength and bond properties in the C₂H₂⋯(HF)-T, C₂H₂⋯2(HF)-T, C₂H₂⋯2(HF), C₂H₂⋯3(HF) and C₂H₂⋯4(HF) complexes was carried out at the B3LYP/6-311++G(d,p) theory level. In these systems, a strength competition between the π⋯H and C⋯H interactions was examined. Specifically the F⋯H hydrogen bond, its properties were studied through a comparison between the hydrogen fluoride and the higher-order complexes (trimer, tetramer and pentamer). Regarding the electronic properties, the hydrogen bond strength could not be determined by the supermolecule approach. Thus, the hydrogen bond energies were computed via NBO calculations. Additionally to NBO, the ChelpG charge calculations were used to interpret the intermolecular charge transfer. The QTAIM integrations were useful to predict the covalent character of the π⋯H, C⋯H and F⋯H hydrogen bonds. Moreover, values of hybrid orbitals (s and p) and atomic radii were also determined in order to justify the red shifts in the stretch frequencies of the HF bonds.

Understanding the behavior of caffeine on a boron-doped diamond surface: voltammetric, DFT, QTAIM and ELF studies

A cyclic and differential pulse voltammetry analysis by using a boron doped diamond electrode to understand the behavior of caffeine on its surface was carried out.

Assessment of DFT Functionals for QTAIM Topological Analysis of Halogen Bonds with Benzene

Halogen bonding, a noncovalent interaction between a halogen atom and a nucleophilic site, is receiving a growing attention in the chemical community stimulating a large number of theoretical investigations. The density functional theory (DFT) approach revealed to be one of the most suitable methods owing to its accuracy and low computational cost. We report here a detailed analysis of the performance of an extensive set of DFT functionals in reproducing accurate binding energies and topological properties for the halogen-bonding interaction of either NCX or PhX molecules (X = F, Cl, Br, I) with the aromatic system of benzene in the T-shaped configuration. It was found that the better performance for both sets of properties is provided by a small subset of functionals able to take into account, implicitly or explicitly (by inclusion of an additive pairwise potential), the dispersion contribution, that is, ωB97X, M06-2X, M11, mPW2PLYP-D, and B2PLYP-D3.

Interacting quantum fragments-rooted preorganized-interacting fragments attributed relative molecular stability of the Be(II) complexes of nitrilotriacetic acid and nitrilotri-3-propionic acid

A method designed to investigate, on a fundamental level, the origin of relative stability of molecular systems using Be(II) complexes with nitrilotriacetic acid (NTA) and nitrilotri-3-propionic acid (NTPA) is described. It makes use of the primary and molecular fragment energy terms as defined in the IQA/F (Interacting Quantum Atoms/Fragments) framework. An extensive classical-type investigation, focused on single descriptors (bond length, density at critical point, the size of metal ion or coordination ring, interaction energy between Be(II) and a donor atom, etc.) showed that it is not possible to explain the experimental trend. The proposed methodology is fundamentally different in that it accounts for the total energy contributions coming from all atoms of selected molecular fragments, and monitors changes in defined energy terms (e.g., fragment deformation, inter- and intra-fragment interaction) on complex formation. By decomposing combined energy terms we identified the origin of relative stability of Be(II) (NTA) and Be(II) (NTPA) complexes. We found that the sum of coordination bonds' strength, as measured by interaction energies between Be(II) ion and donor atoms, favours Be(II) (NTA) but the binding energy of Be(II) ion to the entire ligand correlates well with experimental trend. Surprisingly, the origin of Be(II) (NTPA) being more stable is due to less severe repulsive interactions with the backbone of NTPA (C and H-atoms). This general purpose protocol can be employed not only to investigate the origin of relative stability of any molecular system (e.g., metal complexes) but, in principle, can be used as a predictive tool for, e.g., explaining reaction mechanism. © 2016 Wiley Periodicals, Inc.

A theoretical study of weak interactions in phenylenediamine homodimer clusters

Utilizing dispersion-corrected density functional theory (DFT) calculations, we demonstrate the weak intermolecular interactions of phenylenediamine dimer (pdd) clusters, emphasizing the local lowest energy structures and decomposition of interaction energies by natural bond orbital (NBO) and atoms in molecule (AIM) analyses.

Insight into structural and π–magnesium bonding characteristics of the X2Mg⋯Y (X = H, F; Y = C2H2, C2H4and C6H6) complexes

Quantum chemical calculations have been performed to study the nature of interaction of complexes formed by MgX₂(X = H, F) molecules with acetylene, ethylene, and benzene.

An insight into Csp–H⋯π hydrogen bonds and stability of complexes formed by acetylene and its substituted derivatives with benzene and borazine

Theoretical calculations at the MP2/aug-cc-pVDZ level are used to investigate the C_sp–H⋯π interactions of C₂HX (X = H, F, Cl, Br, CH₃, NH₂) with C₆H₆ and B₃N₃H₆ molecules.

Theoretical study of intermolecular interactions in CB4H8-HOX (X=F, Cl, Br, I) complexes

The molecular aggregation based on intermolecular interactions between CB4H8 and HOX (X=F, Cl, Br and I) with particular emphasis on their bonding characteristics have been investigated using second order Moller-Plesset perturbation (MP2) method with aug-cc-pVDZ basis set. Different kinds of interactions including hydrogen bond (HB; H⋯O, XH; H⋯X), dihydrogen bond (DiHB; H⋯H) and non-classical B-B⋯H interactions were found between CB4H8 and HOX molecules. The structures of complexes have been analyzed using AIM and natural bond orbital methodologies. Good correlations have been found between the interaction energies (SE), the second-order perturbation energies E((2)), and the charge transfer qCT in the studied systems.

Triel Bonds, π-Hole-π-Electrons Interactions in Complexes of Boron and Aluminium Trihalides and Trihydrides with Acetylene and Ethylene

MP2/aug-cc-pVTZ calculations were performed on complexes of aluminium and boron trihydrides and trihalides with acetylene and ethylene. These complexes are linked through triel bonds where the triel center (B or Al) is characterized by the Lewis acid properties through its π-hole region while π-electrons of C₂H₂ or C₂H₄ molecule play the role of the Lewis base. Some of these interactions possess characteristics of covalent bonds, i.e., the Al-π-electrons links as well as the interaction in the BH₃-C₂H₂ complex. The triel-π-electrons interactions are classified sometimes as the 3c-2e bonds. In the case of boron trihydrides, these interactions are often the preliminary stages of the hydroboration reaction. The Quantum Theory of “Atoms in Molecules” as well as the Natural Bond Orbitals approach are applied here to characterize the π-hole-π-electrons interactions.

On the existence and characteristics of π-beryllium bonds

The existence of π-beryllium bonds explains the stability of the complexes between ethylene and acetylene and BeX2 (X = H, F, and Cl) derivatives. These linkers involve a significant charge transfer from the π(CC) bonding orbitals into the empty p orbitals of Be and to a much smaller degree into the σ(BeH)* antibonding orbitals. The significant deformation of the BeX2 moiety and the slight deformation of the unsaturated hydrocarbon result in distortion energies as high as the dissociation energy of the complex. The π-beryllium bonds are about four times stronger than conventional π-hydrogen bonds and even stronger than the strongest π-hydrogen bond reported to date in the literature. The topology of their electron density is characterized as being very flat in the bonding region between the π-system and Be, which leads to topologically unstable structures close to catastrophe points. Among the functionals considered in our study M06 is the one that leads to values in better agreement with CCSD(T)/aug-cc-pVTZ calculations used as a reference. B3LYP underestimates some interactions, whereas M06-2X overestimates all of them. MP2 also yields good agreement with the CCSD(T) method.