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Density and viscosity values of the binary mixture of ethylbenzene and aniline have been experimentally measured in different mole fractions at temperatures of 293.15 to 313.15 K and at an absolute pressure of 86.7 kPa. Based on the obtained experimental data, the excess molar volume and viscosity deviations have been reported, which can interpret the interactions in this mixture. The obtained data were fitted with the Redlich‐Kister equation. In addition, the viscosity results are discussed using the equation proposed by Gruenberg‐Nissan. After experimental studies, in order to investigate the interactions of these two components and their mixture, quantum mechanical calculations and molecular dynamics simulation have been used. In this way, the structures of the desired molecules have been optimized. Then Atoms in Molecules (AIM) and frontier molecular orbital (FMO) techniques have been used for a more detailed investigation. Finally, by plotting radial distribution functions (RDFs) obtained from molecular dynamics, these interactions have been investigated in a more comprehensive way. In addition, the simulated densities at 298.15 K have been reported. At the end, clear pictures of the interactions of molecules in mixtures were obtained by comparing the achievements of experimental measurements, quantum chemical and calculations MD simulation. [ABSTRACT FROM AUTHOR]

The pharmaceutical proprieties of the 2,6-dimethylpiperazine-1,4-diium oxalate oxalic acid compound have been studied and the relevant drug design has been considered. The investigated organic compound with formula (2,6-(CH3)C4H10N2)2(C2O4)2·H2C2O4 (2DPOA) has been synthesized by slow evaporation technique at room temperature of a molar ratio 3:2 mix of oxalic acid and 2,6-dimethylpiperazine. Then 2DPOA has been characterized by IR, 13C NMR, UV–visible and the DFT calculation at the B3LYP level of theory has been made. The molecular structure and parameters (bond angles and lengths) of the molecule have been optimized using the Gaussian 09 software and compared with the XRD data. The atoms-in-molecules (AIM), electron localization function (ELF), and localized orbital locator (LOL) methods have been utilized to determine the types and nature of noncovalent interactions present within the 2DPOA molecule. These methods offer insights into the characteristics and behavior of these interactions. Furthermore, the presence of these interactions has been confirmed through the Hirshfeld Surface (HS) and reduced density gradient (RDG) analysis. The NBO analysis is employed to assess the charge exchange occurring within the studied compound. The molecular reactive sites have been examined using the molecular potential surface and Mulliken atomic charges. The energy gap between HOMO–LUMO and chemical properties of 2DPOA have been determined within the frontier molecular orbital theory. The UV–Vis spectrum of the 2DPOA molecule has been recorded and examined. The calculated and experimental infrared absorption and nuclear magnetic resonance spectra of 2DPOA molecule have been investigated. Finally, the molecular docking simulation has been used to find novel inhibitors and drugs for the cancer and epilepsy disease treatment. [ABSTRACT FROM AUTHOR]

The microwave‐assisted extraction of the main phenolic component of green coffee beans, chlorogenic acid (CGA), was carried out employing deep eutectic solvents based on choline chloride and five different hydrogen bond donors (HBD) in a 1:2 ratio. The best performance for the extraction process of CGA was reached by the mixtures of choline chloride/ethylene glycol and choline chloride/urea. To understand the various interactions between the phenolic compound and the two most efficient deep eutectic solvents, computational calculations were carried out at the density functional theory (DFT) level, as well as Atoms in Molecules (AIM) and Non‐Covalent Interactions (NCIs) analyses. In that way, a variety of hydrogen bond types were found in every structure. Nevertheless, the CGA does not disrupt the hydrogen bond network established between ChCl and the HBD. Among the strongest interactions are those hydrogen bonds between the quinic acid moiety and the ethylene glycol or the urea. In addition, the thermochemistry of the formation of the two main deep eutectic solvents and their corresponding complexes with CGA was calculated, where the formation of urea‐based structures was slightly more effective by ~3 kcal/mol. [ABSTRACT FROM AUTHOR]

The nature of chemical bonding in BeF− anion is investigated quantum mechanically. Topological analyses within the realm of quantum theory of atoms in molecules (QTAIM) and electron localization function (ELF) clearly establish the bonds as having "Charge shift" character. The laplacian of electron density is significantly positive and the basin population is lower with a large covariance, indicating significant charge shift character. Detailed analysis reveals no multiple bonding character in this anion and its heavier analogues. [ABSTRACT FROM AUTHOR]

Polarisabilities of atoms within molecules can be calculated from molecular electron densities using the density partitioning method known as Iterated Stockholder Atoms (ISA). Non-local polarisation effects are removed by optimising the ISA functional for the perturbed electron density, with the additional constraint that the atomic charges do not change. The resulting atomic polarisabilities are chemically reasonable, tend to become smaller as the atomic charge becomes more positive, and are approximately transferable between atoms in similar chemical environments. The methodology can be extended to calculate local higher-rank polarisabilities and dispersion energy coefficients. [ABSTRACT FROM AUTHOR]

Two new Co(II) and Cu(II) azido complexes with 4-picoline (4-Pic) and pyridine-2-carboxaldoxime (HAld) were synthesized by self-assembly of the organic ligand and the M(II) nitrate in the presence of azide as a co-ligand. Their structures were determined to be [Co(4-Pic)4(H2O)(N3)]NO3*H2O*4-Pic (1) and [Cu(HAld)(Ald)(N3)] (2) using X-ray single crystal diffraction. In complex 1, the coordination geometry is a slightly distorted octahedron with a water molecule and azide ion located trans to one another. On the other hand, complex 2 has a distorted square pyramid CuN5 coordination sphere with N-atoms of the organic ligand as a basal plane and azide ion as apical. All types of intermolecular contacts and their contributions in the molecular packing were analyzed using Hirshfeld analysis. The intermolecular contacts, H...H (53.9%), O...H (14.1%), N...H (11.0%) and H...C (18.8%) in 1, and H...H (27.4%), N...H (27.7%), O...H (14.7%) and H...C (13.6%) in 2 have the largest contributions. Of all the contacts, the O...H, N...H and C...C interactions in 2 and the O...H, N...H and H...C in 1 are apparently shorter than the van der Waals radii sum of the interacting atoms. Atoms in molecules (AIM) topological parameters explained the lower symmetry of the coordinated azide in 1 than 2. [ABSTRACT FROM AUTHOR]

The assumption, common at the undergraduate level, that hydrogen with its single electron can form only one covalent bond is belied by the many structures that have been characterized with hydrogens bonded to two atoms. The 3‐center bond responsible for such bridging hydrogens is facilitated by the spherical distribution inherent to the 1s electron. Here we demonstrate how topological analysis of the electron density of molecules with bridging hydrogens can inform a deeper appreciation of the character and complexity of the chemical bond. DFT calculations are performed to generate the electron density for the experimental structures of a range of complexes with bridging hydrogens. Analysis using both the Atoms in Molecules (AIM) perspective and a range of electron indicators and localization functions demonstrates the utility of topological analysis for the detection and characterization of multi‐center bonding. [ABSTRACT FROM AUTHOR]

The important aspects of bonding are discussed in this perspective article, focusing on common misconceptions regarding 'covalent' and 'ionic' bonds. Special attention is given to the calculation of percentage covalent and ionic characters in a bond. In a course on chemical bonding, the graduate students were given an assignment: "Covalent versus ionic bonding in molecules." The outcome shows the majority of the students are unaware of the fact that no bond is purely ionic or covalent. To that end, a set of compounds are considered that are commonly used as examples of 'covalent' and 'ionic' compounds in standard textbooks, along with some 'partially covalent' noble gas (Ng) compounds containing noble coinage metals (M = Cu and Ag). State-of-the-art quantum chemical tools are utilized to analyze the bonding nature. The set contains alkali and alkaline earth metal halides, hydrogen halides, and main-group molecules like dihydrogen, dinitrogen, fluorine, chlorine, carbon monoxide, ammonia, and water, simple hydrocarbons, and noble gas- noble metal complexes. A perspective towards utilizing the most popular techniques in understanding the nature of bonding to eliminate certain common misconceptions among students including researchers, and a caution against the impetuous usage of the terms 'ionic' and 'covalent' to describe a bond. [ABSTRACT FROM AUTHOR]

The C–X bond cleavage in different methyl halides (CH3X; X = Cl, Br, I) mediated by 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(II) (CoIICbx) was theoretically investigated in the present work. An SN2-like mechanism was considered to simulate the chemical process where the cobalt atom acts as the nucleophile and the halogen as the leaving group. The reaction path was computed by means of the intrinsic reaction coordinate method and analyzed in detail through the reaction force formalism, the quantum theory of atoms in molecules (QTAIM), and the calculation of one-electron density derived quantities, such as the source function (SF) and the spin density. A thorough comparison of the results with those obtained in the same reaction occurring in presence of 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(I) (CoICbx) was conducted to reveal the main differences between the two cases. The reactions mediated by CoIICbx were observed to be endothermic and possess higher activation energies in contrast to the reactions where the CoICbx complex is present. The latter was supported by the reaction force results, which suggest a relationship between the activation energy and the ionization potentials of the different nucleophiles present in the cleavage reaction. Moreover, the SF results indicates that the lower axial ligand (i.e., 5,6-dimethylbenzimidazole) exclusively participates on the first stage of the reaction mediated by the CoIICbx complex, while for the CoICbx case, it appears to have an important role along the whole process. Finally, the QTAIM charge analysis indicates that oxidation of the cobalt atom occurs in both cases; at the same time, it suggests the formation of an uncommon two-center one-electron bond in the CoIICbx case. The latter was confirmed by means of electron localization calculations, which resulted in a larger electron count at the Co–C interatomic region for the CoICbx case upon comparison with its CoIICbx counterpart. [ABSTRACT FROM AUTHOR]

The complexation behavior of diprotonated phenylenediamine isomers with decamethylene cucurbit[6]uril (Me12Q[6]) in 1:1 and 1:2 stoichiometry was investigated in vacuum and solution using density functional theory (DFT). Among the isomers, o-phenylenediamine (oPDA) forms an exclusion complex in 1:1 stoichiometry, while others form an inclusion complex. In the 1:2 stoichiometry, at least one of the guest molecule lie on the surface of the Me12Q[6] cavity. The structural reorganization was found to depend on the mode of interaction of the guest molecule. In the gas phase, the enthalpy and Gibbs free energy are negative for all the complexes demonstrating the encapsulation process is spontaneous and thermodynamically favorable. In the solution phase, the enthalpy and entropy are negative for complexes with guest molecules meta- and para-isomers of phenylenediamine. For oPDA as a guest, the enthalpy and entropy are positive indicating the complex formation to be nonspontaneous. The MESP isosurface of complexes shows a higher accumulation of charge in the 1:2 stoichiometry, which reduces their stability. AIM analysis shows the interaction between oPDA and Me12Q[6] is due to hydrogen bonding with moderate strength, while for the other isomers, interactions between the benzene group and the Me12Q[6] cavity were noticed. EDA analysis shows the larger contribution is the electrostatic attraction and it decreases with the increase in the guest ratio. The formation of inclusion complexes by mPDA and pPDA and the surface adsorption of oPDA on Me12Q[6] and the higher accumulation of positive charge during solvation in oPDA@Me12Q[6] complexes make them labile in the solution phase. [ABSTRACT FROM AUTHOR]

The computational modeling supported with experimental results can explain the overall structural packing by predicting the hydrogen bond interactions present in any cocrystals (active pharmaceutical ingredients + coformer) as well as salts. In this context, the hydrogen bonding synthons, physiochemical properties (chemical reactivity and stability), and drug-likeliness behavior of proposed nicotinamide–oxalic acid (NIC–OXA) salt have been reported by using vibrational spectroscopic signatures (IR and Raman spectra) and quantum chemical calculations. The NIC–OXA salt was prepared by reactive crystallization method. X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) techniques were used for the characterization and validation of NIC–OXA salt. The spectroscopic signatures revealed that (N7–H8)/(N23–H24) of the pyridine ring of NIC, (C═O), and (C–O) groups of OXA were forming the intermolecular hydrogen bonding (N–H⋯O–C), (C–H⋯O═C), and (N–H⋯O═C), respectively, in NIC–OXA salt. Additionally, the quantum theory of atoms in molecules (QTAIM) showed that (C10–H22⋯O1) and (C26–H38⋯O4) are two unconventional hydrogen bonds present in NIC–OXA salt. Also, the natural bond orbital analysis was performed to find the charge transfer interactions and revealed the strongest hydrogen bonds (N7–H8⋯O5)/(N23–H24⋯O2) in NIC–OXA salt. The frontier molecular orbital (FMO) analysis suggested more reactivity and less stability of NIC–OXA salt in comparison to NIC–CA cocrystal and NIC. The global and local reactivity descriptors calculated and predicted that NIC–OXA salt is softer than NIC–CA cocrystal and NIC. From MESP of NIC–OXA salt, it is clear that electrophilic (N7–H8)/(N23–H24), (C6═O4)/(C3═O1) and nucleophilic (C10–H22)/(C26–H38), (C6–O5)/(C3–O2) reactive groups in NIC and OXA, respectively, neutralize after the formation of NIC–OXA salt, confirming the presence of hydrogen bonding interactions (N7–H8⋯O5–C6) and (N23–H24⋯O2–C3). Lipinski’s rule was applied to check the activeness of salt as an orally active form. The results shed light on several features of NIC–OXA salt that can further lead to the improvement in the physicochemical properties of NIC.

Two new Co(II) and Cu(II) azido complexes with 4-picoline (4-Pic) and pyridine-2-carboxaldoxime (HAld) were synthesized by self-assembly of the organic ligand and the M(II) nitrate in the presence of azide as a co-ligand. Their structures were determined to be [Co(4-Pic)4(H2O)(N3)]NO3*H2O*4-Pic (1) and [Cu(HAld)(Ald)(N3)] (2) using X-ray single crystal diffraction. In complex 1, the coordination geometry is a slightly distorted octahedron with a water molecule and azide ion located trans to one another. On the other hand, complex 2 has a distorted square pyramid CuN5 coordination sphere with N-atoms of the organic ligand as a basal plane and azide ion as apical. All types of intermolecular contacts and their contributions in the molecular packing were analyzed using Hirshfeld analysis. The intermolecular contacts, H…H (53.9%), O…H (14.1%), N…H (11.0%) and H…C (18.8%) in 1, and H…H (27.4%), N…H (27.7%), O…H (14.7%) and H…C (13.6%) in 2 have the largest contributions. Of all the contacts, the O…H, N…H and C…C interactions in 2 and the O…H, N…H and H…C in 1 are apparently shorter than the van der Waals radii sum of the interacting atoms. Atoms in molecules (AIM) topological parameters explained the lower symmetry of the coordinated azide in 1 than 2.

Even though molecules are fundamentally quantum entities, the concept of a molecule retains certain classical attributes concerning its constituents. This includes the empirical separability of a molecule into its three-dimensional, rigid structure in Euclidean space, a framework often obtained through experimental methods like X-Ray crystallography. In this work, we delve into the mathematical implications of partitioning a molecule into its constituent parts using the widely recognized Atoms-In-Molecules (AIM) schemes, aiming to establish their validity within the framework of Information Theory concepts. We have uncovered information-theoretical justifications for employing some of the most prevalent AIM schemes in the field of Chemistry, including Hirshfeld (stockholder partitioning), Bader's (topological dissection), and the quantum approach (Hilbert's space definition). In the first approach we have applied the generalized principle of minimum relative entropy derived from the Sharma-Mittal two-parameter functional, avoiding the need for an arbitrary selection of reference promolecular atoms. Within the ambit of topological-information partitioning, we have demonstrated that the Fisher information of Bader's atoms conform to a comprehensive theory based on the Principle of Extreme Physical Information avoiding the need of employing the Schwinger's principle, which has been proven to be problematic. For the quantum approach we have presented information-theoretic justifications for conducting Löwdin symmetric transformations on the density matrix to form atomic Hilbert spaces generating orthonormal atomic orbitals with maximum occupancy for a given wavefunction., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

An X‐ray diffraction study aimed at establishing the subtle details of the electron density and anharmonicity of the atomic vibrations in a stoichiometric monodomain single crystal of potassium niobate, KNbO3, has been conducted at room temperature (orthorhombic ferroelectric phase Amm2). The cation and anion displacements obtained from the experiment are weakly anharmonic without any manifestation of structural disorder. The chemical bond and interatomic interactions inside and between crystal substructures at the balance of intracrystalline forces are characterized in detail. The role of each of the ions in the formation of the ferroelectric phase was studied and the features of the electron‐density deformation in the niobium and oxygen substructures, and the role of each of them in the occurrence of spontaneous polarization are established. The position‐space distribution of electrostatic and quantum forces in KNbO3 is restored. It is emphasized that for the completeness of the analysis of the nature of the ferroelectric properties it is necessary to consider both static and kinetic electronic factors, which are of a quantum origin. The experimental results and theoretical estimations by the Kohn–Sham calculation with periodic boundary conditions are in reasonable agreement, thus indicating the physical significance of the findings of this study. [ABSTRACT FROM AUTHOR]

An X‐ray diffraction study aimed at establishing the subtle details of the electron density and anharmonicity of the atomic vibrations in a stoichiometric monodomain single crystal of potassium niobate, KNbO3, has been conducted at room temperature (orthorhombic ferroelectric phase Amm2). The cation and anion displacements obtained from the experiment are weakly anharmonic without any manifestation of structural disorder. The chemical bond and interatomic interactions inside and between crystal substructures at the balance of intracrystalline forces are characterized in detail. The role of each of the ions in the formation of the ferroelectric phase was studied and the features of the electron‐density deformation in the niobium and oxygen substructures, and the role of each of them in the occurrence of spontaneous polarization are established. The position‐space distribution of electrostatic and quantum forces in KNbO3 is restored. It is emphasized that for the completeness of the analysis of the nature of the ferroelectric properties it is necessary to consider both static and kinetic electronic factors, which are of a quantum origin. The experimental results and theoretical estimations by the Kohn–Sham calculation with periodic boundary conditions are in reasonable agreement, thus indicating the physical significance of the findings of this study. [ABSTRACT FROM AUTHOR]

Three new Hg(II) complexes with general formula [Hg(L)X2]2 (X = Cl (Hg 1), Br (Hg 2), and I (Hg 3)) have been synthesized using the novel ferrocenyl functionalized ligand 3‐ferrocenyl methyl‐thiazolidine‐2‐thione (L). The ligand (L) and the complexes have been characterized by Fourier transform infrared (FTIR), multinuclear nuclear magnetic resonance (NMR), electronic absorption, photoluminescence spectroscopies, and single crystal X‐ray diffraction. The single crystal X‐ray diffraction studies indicated that Hg 1 and Hg 2 are centrosymmetric dimers with distorted tetrahedral geometry around the Hg(II) centers generated by the two bridging halides, a terminal halide, and an exocyclic sulfur of ligand. Hg 3 possess two monomers with trigonal planar geometries around Hg(II), which are further held by weak Hg⋯I interactions. Variation in geometrical parameters have been attributed to differences in the nature of the halide donors attached to the Hg(II). The cyclic voltammetry experiments for all the compounds suggested their quasi‐reversible redox properties. Also, the photoluminescent investigation for Hg 1 and Hg 2 indicated medium strong photoluminescence emission at ~500 nm arising due to metal‐to‐ligand charge‐transfer (MLCT) transitions of the ferrocenyl moiety. The solid‐state structure of complexes are stabilized by varied interactions, namely, C–H⋯C and bifurcated H⋯Cl⋯H interactions in Hg 1, C–H⋯C, C–H⋯S, S⋯C (Cp), and C–H⋯Br interactions in Hg 2 and C–H⋯C, C–H⋯S, and C⋯S interactions in Hg 3. The nature and percentage contribution of all these interactions have been studied by the Hirshfeld surface analyses. The interaction energies for the dimers of all four compounds have been assessed with the help of density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM). [ABSTRACT FROM AUTHOR]

The C–X bond cleavage in different methyl halides (CH3X; X = Cl, Br, I) mediated by 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(II) (CoIICbx) was theoretically investigated in the present work. An SN2-like mechanism was considered to simulate the chemical process where the cobalt atom acts as the nucleophile and the halogen as the leaving group. The reaction path was computed by means of the intrinsic reaction coordinate method and analyzed in detail through the reaction force formalism, the quantum theory of atoms in molecules (QTAIM), and the calculation of one-electron density derived quantities, such as the source function (SF) and the spin density. A thorough comparison of the results with those obtained in the same reaction occurring in presence of 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(I) (CoICbx) was conducted to reveal the main differences between the two cases. The reactions mediated by CoIICbx were observed to be endothermic and possess higher activation energies in contrast to the reactions where the CoICbx complex is present. The latter was supported by the reaction force results, which suggest a relationship between the activation energy and the ionization potentials of the different nucleophiles present in the cleavage reaction. Moreover, the SF results indicates that the lower axial ligand (i.e., 5,6-dimethylbenzimidazole) exclusively participates on the first stage of the reaction mediated by the CoIICbx complex, while for the CoICbx case, it appears to have an important role along the whole process. Finally, the QTAIM charge analysis indicates that oxidation of the cobalt atom occurs in both cases; at the same time, it suggests the formation of an uncommon two-center one-electron bond in the CoIICbx case. The latter was confirmed by means of electron localization calculations, which resulted in a larger electron count at the Co–C interatomic region for the CoICbx case upon comparison with its CoIICbx counterpart.

This work extends the orbital‐free density functional theory to the field of quantum crystallography. The total electronic energy is decomposed into electrostatic, exchange, Weizsacker and Pauli components on the basis of physically grounded arguments. Then, the one‐electron Euler equation is re‐written through corresponding potentials, which have clear physical and chemical meaning. Partial electron densities related with these potentials by the Poisson equation are also defined. All these functions were analyzed from viewpoint of their physical content and limits of applicability. Then, they were expressed in terms of experimental electron density and its derivatives using the orbital‐free density functional theory approximations, and applied to the study of chemical bonding in a heteromolecular crystal of ammonium hydrooxalate oxalic acid dihydrate. It is demonstrated that this approach allows the electron density to be decomposed into physically meaningful components associated with electrostatics, exchange, and spin‐independent wave properties of electrons or with their combinations in a crystal. Therefore, the bonding information about a crystal that was previously unavailable for X‐ray diffraction analysis can be now obtained. [ABSTRACT FROM AUTHOR]

The present contribution elucidates the non-covalent interactions present within the molecular frameworks of a miscellany of mono and dihalo-salicylic acid derivatives from the viewpoint of the "atoms-in-molecule" (AIM) formalism. The pivotal roles of hydrogen bonds (HBs) and other short-contact non-covalent interactions, such as H···H and O···O/O···X (X = F, Cl, Br), toward the conformational preferences of the studied aromatic systems have been depicted in detail. Moreover, the modulations of the π-aromaticity of the studied systems in the presence of the concerned non-covalent interactions have been ascertained employing the nucleus-independent chemical shift (NICS) descriptor. [ABSTRACT FROM AUTHOR]

Amide metathesis has been used to generate the first structurally characterized boryl complexes of calcium and strontium, {(Me3Si)2N}M{B(NDippCH)2}(thf)n (M=Ca, n=2; M=Sr, n=3), through the reactions of the corresponding bis(amides), M{N(SiMe3)2}2(thf)2, with (thf)2Li‐ {B(NDippCH)2}. Most notably, this approach can also be applied to the analogous potassium amide K{N(SiMe3)2}, leading to the formation of the solvent‐free borylpotassium dimer [K{B(NDippCH)2}]2, which is stable in the solid state at room temperature for extended periods (48 h). A dimeric structure has been determined crystallographically in which the K+ cations interact weakly with both the ipso‐carbons of the flanking Dipp groups and the boron centres of the diazaborolyl heterocycles, with K⋅⋅⋅B distances of >3.1 Å. These structural features, together with atoms in molecules (QTAIM) calculations imply that the boron‐containing fragment closely approaches a limiting description as a "free" boryl anion in the condensed phase. [ABSTRACT FROM AUTHOR]

The electrostatic potential at the nucleus of an atom, whether in the free state or in a molecule, is qualitatively a characteristic property of the atom. It changes remarkably little from one molecular environment to another. The energies of atoms and molecules can be expressed both rigorously and approximately in terms of the electrostatic potentials at their nuclei. Molecular energies can be written entirely as summations over atomic contributions, with no explicit interatomic terms. This provides a basis for estimating the energy of an atom in a molecule. Overall, the present study supports the validity of the atoms-in-molecules concept. [ABSTRACT FROM AUTHOR]

Amide metathesis has been used to generate the first structurally characterized boryl complexes of calcium and strontium, {(Me3Si)2N}M{B(NDippCH)2}(thf)n (M=Ca, n=2; M=Sr, n=3), through the reactions of the corresponding bis(amides), M{N(SiMe3)2}2(thf)2, with (thf)2Li‐ {B(NDippCH)2}. Most notably, this approach can also be applied to the analogous potassium amide K{N(SiMe3)2}, leading to the formation of the solvent‐free borylpotassium dimer [K{B(NDippCH)2}]2, which is stable in the solid state at room temperature for extended periods (48 h). A dimeric structure has been determined crystallographically in which the K+ cations interact weakly with both the ipso‐carbons of the flanking Dipp groups and the boron centres of the diazaborolyl heterocycles, with K⋅⋅⋅B distances of >3.1 Å. These structural features, together with atoms in molecules (QTAIM) calculations imply that the boron‐containing fragment closely approaches a limiting description as a “free” boryl anion in the condensed phase. [ABSTRACT FROM AUTHOR]

Five new heteroleptic complexes of Cu(I), Ag(I), and Ni(II) having formulae [Cu3(dtc)2(dppf)2]PF6 (Cu‐I), [Cu3(dtc)2(dppe)2]PF6 (Cu‐II), [Cu(PPh3)2(dtc)] (Cu‐III), [Ag3(dtc)2(PPh3)2]NO3 (Ag‐I), and [Ni(dtc)(dppf)]PF6 (Ni‐I) (dtc = N‐ethanol‐N‐methylferrocenyl‐dithiocarbamate; dppf = 1,1′‐bis(diphenylphosphino)ferrocene; dppe = 1,1′‐bis(diphenylphosphino)ethane; PPh3 = tripheylphosphine) have been synthesized and characterized using elemental analysis, Fourier‐transform infrared, multinuclear nuclear magnetic resonance, UV–Vis spectroscopy, and single‐crystal X‐ray diffraction. The single‐crystal X‐ray diffraction studies indicate that Ag‐I forms a rare trinuclear cluster in which the geometry around the two silver centers Ag1 and Ag3 is distorted tetrahedral, whereas the third silver center Ag2 shows a distorted trigonal planar geometry. The Ni‐I complex has a distorted square‐planar geometry around the Ni center. In addition, a side product [Ag2{S2(dppf)2}] (Ag‐II) was obtained during an attempt to synthesize [Ag(dppf)(dtc)], where the two Ag centers are bridged by two sulfido centers and coordinated with two phosphorus centers of the dppf ligand to give rise to a distorted tetrahedral geometry. The solid‐state structures of Ag‐I, Ni‐I, and Ag‐II are stabilized by a variety of weak interactions. The nature of these interactions has been addressed with the help of Hirshfeld surface analyses. In addition, the weak argentophilic interaction in Ag‐I and Ag‐II have been studied using quantum theory of atoms in molecules and natural bond orbital calculations. The electrochemical properties of the complexes have been investigated using cyclic voltammetry, where Cu‐I and Cu‐II exhibited two quasi‐reversible waves, whereas Cu‐III, Ag‐I, Ag‐II, and Ni‐I exhibited only one quasi‐reversible peak. [ABSTRACT FROM AUTHOR]

Quantum theory of atoms in molecules and the orbital‐free density functional theory (DFT) are combined in this work to study the spatial distribution of electrostatic and quantum electronic forces acting in stable crystals. The electron distribution is determined by electrostatic electron mutual repulsion corrected for exchange and correlation, their attraction to nuclei and by electron kinetic energy. The latter defines the spread of permissible variations in the electron momentum resulting from the de Broglie relationship and uncertainty principle, as far as the limitations of Pauli principle and the presence of atomic nuclei and other electrons allow. All forces are expressed via kinetic and DFT potentials and then defined in terms of the experimental electron density and its derivatives; hence, this approach may be considered as orbital‐free quantum crystallography. The net force acting on an electron in a crystal at equilibrium is zero everywhere, presenting a balance of the kinetic Fkin(r) and potential forces F(r). The critical points of both potentials are analyzed and they are recognized as the points at which forces Fkin(r) and F(r) individually are zero (the Lagrange points). The positions of these points in a crystal are described according to Wyckoff notations, while their types depend on the considered scalar field. It was found that F(r) force pushes electrons to the atomic nuclei, while the kinetic force Fkin(r) draws electrons from nuclei. This favors formation of electron concentration bridges between some of the nearest atoms. However, in a crystal at equilibrium, only kinetic potential vkin(r) and corresponding force exhibit the electronic shells and atomic‐like zero‐flux basins around the nuclear attractors. The force‐field approach and quantum topological theory of atoms in molecules are compared and their distinctions are clarified. [ABSTRACT FROM AUTHOR]

[Ni{2‐H2NC(=O)C5H4N}2(H2O)2][Ni{2,6‐(O2C)2C5H3N}2]·4.67H2O, a new complex salt containing a bis(2,6‐dicarboxypyridine)nickel(II) anion and a bis(2‐amidopyridine)diaquanickel(II) cation, was synthesized and characterized. The crystal is stabilized by an extensive network of hydrogen bonds. Alternate layers of anions and cations/water molecules parallel to (010) can be distinguished. Computational studies of the network packing of the title compound by high‐level DFT‐D/B3LYP calculations indicate stabilization of the networks with conventional and non‐conventional intermolecular O—H...O, N—H...O and C—H...O hydrogen bonds along with π‐stacking contacts. Due to the presence of water molecules and the importance of forming hydrogen bonds with the involvement of water clusters to the stability of the crystal packing, the importance and role of these water clusters, and the quantitative stability resulting from the formation of hydrogen bonds and possibly other noncovalent bonds such as π‐stacking are examined. The binding energies obtained by DFT‐D calculations for these contacts indicate that hydrogen bonds, especially O—H...O and N—H...O, control the construction of the crystalline packing. Additionally, the results of Bader's theory of AIM for these interactions agree reasonably well with the calculated energies. [ABSTRACT FROM AUTHOR]

A host–guest model designed between two hemispheres as Rebek imide receptor and different ligands via triple hydrogen bonding and π−π stacking interactions was surveyed to investigate the substituent effects. The association of Rebek imide with 2,6-di(isobutyramido)pyridine (X-Rebek imidepyr) in the presence of electron donating/withdrawing substituents was studied (X = (NCH3)2, OCH3, CH3, OH, H, F, Cl, Br and CN, CF3 and NO2, where and ∙∙∙ denote π–π stacking and hydrogen bonding). It was explained the variation in binding energies, energy decomposition, geometries, NMR properties, and electron density of mentioned complexes and effect of different types of the substituents in studied complexes was identified via computational chemistry at M05-2X/6-311++G** level of theory on π–π stacking and hydrogen bonding interactions. [ABSTRACT FROM AUTHOR]

Theoretical and experimental studies of bonding in the main group homonuclear diatomic molecules have been pursued for many years, and they possess serious challenges for scientists. Most of the early experimental work have been carried out by Herzberg.1,2 We take a relook at the bonding motifs of Period 2 homonuclear diatomic molecules (from Li2 to Ne2) using varieties of quantum chemical tools, commonly used for intermolecular bonding/interactions now. The methods employed include Atoms in Molecules (AIM), Non-covalent Index plot (NCI), Electrostatic potential (ESP), and Potential Acting on one Electron in a Molecule (PAEM). The spectroscopic constants i.e., equilibrium bond distances (re), harmonic frequencies (ω), bond dissociation energies (De) have all been evaluated using high-level ab initio methods and critically compared with the experimental results. Multi-reference calculations (CASSCF) on B2 and C2 have been carried out as they have a large number of low lying electronic states. Bonding within these homonuclear diatomic molecules show all the diversities that are encountered in inter/intra-molecular bonding in chemistry. Based on the AIM analysis, these 8 homonuclear diatomic molecules could be divided into three different groups, based on the correlation between binding energy and the electron density at the bond critical point. However, PAEM/ESP analysis allows us to analyse all eight of them as one group having a good correlation between binding energy and the PAEM/ESP at the critical point between the two atoms. Our results highlight the arbitrariness in relying on some computational tools to characterize a bond as covalent (shared) or ionic/electrostatic (closed). In contrast, they also show the usefulness of the various methods in exploring similarities and differences in bonding. We propose that from Li2 to Ne2, all homonuclear diatomic molecules are bound by 'chemical bonds'. The Period 2 homo-nuclear diatomic 'molecules' from the 'covalent Li2' to the 'van der Waals Ne2' show a rich diversity of 'bonds' that one can see in all inter- and intra-molecular interactions encountered in physics, chemistry and biology. Here, we show that these display a continuum in 'chemical bonds!' [ABSTRACT FROM AUTHOR]

[Display omitted] • Structure and stability of zwitterionic glycine-water governed by number of HO···HO and intramolecular water network. • Beyond n = 6, additional water molecules are added to the existing water cluster. • Benchmark calculations support M06-2X-D3 for computing binding energies of zwitterionic glycine-water complex. • Molecular dynamics results show the zwitterionic glycine floats on the surface due to its charged nature. • QTAIM and NCI-RDG shows water-water HBs are weak, and zGly.W interactions are of medium strength. • We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us. The putative global minima geometries of zwitterionic glycine-water complexes [zGly.Wn (1 = 1–10)] are controlled by the cyclic network of water molecules bonded to the zwitterionic glycine. Their stability is governed by the number of water-water interactions along with the existence of the intramolecular glycine-water bonds. The computed intramolecular distances suggest that water molecules tend to coordinate within themselves. The computed association energy attains saturation at 6, implying that up to 6 water molecules are coordinated to the zwitterionic glycine. Further addition of water molecules happens to be an intramolecular addition to the existing water. The computed incremental association energy decreases with the increase in the number of water molecules, except for the six and nine water molecules. This implies that compared to the water clusters, the zwitterionic clusters are less stable. The higher stability of n = 6 and 9 can be marked to the resemblance of the cyclic network of water molecules to the bare global minima water clusters. Benchmarking calculations suggest that M06-2X-D3 functional provides binding energy close to the PW6B97D3(BJ) method. The PGM clusters' thermodynamic parameters show that the reaction's enthalpy remains constant and is negative, indicating that the hydration process is exothermic and independent of the number of water molecules. The electron density difference (EDD) diagram shows the build-up of charge is more pronounced in the intramolecular hydrogen bonds (HBs) between water molecules than between zwitterionic glycine and water. QTAIM analysis shows that the water-water HBs are comparatively weaker than zwitterionic glycine-water interactions. [ABSTRACT FROM AUTHOR]

The dimerization of hypobromous acid molecules was investigated using MP2 method with aug-cc-pVTZ basis set. Six different configurations were found as the local minima, corresponding to different dimers with one hydrogen bond or one halogen bond, or cyclic structures formed via simultaneously two hydrogen bonds or two halogen bonds, or one hydrogen bond along with one halogen-bonding-like interaction. These dimers exhibit different binding energies. The dimers with one O–H···O hydrogen bond and the cyclic one with an O–H···O HB and an O–Br···O interaction as well as another one with two O–H···Br hydrogen bonds are much stronger than the dimer with one O–Br···O halogen bond, while the dimer with one O–Br···Br halogen bond is even weaker. The topological property of the hydrogen bond or halogen bond in each dimer was assessed by AIM analysis. NBO analysis was employed to reveal the important roles of the intermolecular donor-acceptor orbital interactions and the charge transfer in each dimer. EDA analyses suggest that the electrostatic, exchange, polarization, and dispersion interactions are the attractive forces in stabilizing the complex, while the Pauli term is the repulsive force. [ABSTRACT FROM AUTHOR]

Abstract Acetyl-benzoic acid transformed into its phthalide form (so called Ph-2ABA) when it is crystalized. Also, in the crystalline structure is concerned, it contains four molecules in a unit cell including a dimer. The present study focuses the monomer and dimer structures of Ph-2ABAand their vibrational characteristics and electronic transitions. The FT-IR spectrum of Ph-2ABA was recorded in the region 4000-400 cm−1 and the bands were assigned by using potential energy distribution. The UV–vis absorption spectrum of the molecule in the water solution was recorded in the region 190-300 cm−1 and the molecular orbital contributions associated with the absorption bands were identified. TD-DFT calculations were also performed to elucidate the solvent effect on the electronic transitions. Moreover, the hidden bands (vibrational contributions) in the UV-absorption spectrum is resolved theoretically. Quantum topological atoms in molecule parameters of the molecule and FT-IR spectrum validates the dimer formation in the crystal structure. The charge transfer species corresponding to the hydrogen bonding interactions were identified by natural bond orbital analysis. The experimental results are well supported by the theoretical parameters. Graphical abstract Image 1 Highlights • Monomer and dimer geometries of Ph-2ABA were studied. • Electronic transitions between the energy levels were investigated. • Dimerization through hydrogen bonding interactions was explained. • Charge delocalization between the lone pair and antibonding orbitals were identified. • Assignments of normal modes (both monomer and dimer) of Ph-2ABA were done. [ABSTRACT FROM AUTHOR]

In the present study, the competition between the intramolecular hydrogen bond (IMHB) and the π-electron delocalization (π-ED) in some derivatives of triformylmethane (TFM) are investigated. In this regard, all of the hydrogen bonded structures are optimized by B3LYP and MP2 methods with the 6-311++G(d,p) basis set. The relative energies clearly predict that the B conformers (cis and trans) are more stable than the A and C ones; B < A < C. This order can be related to their IMHB strength and π-ED. Accordingly, IMHB and π-ED of all hydrogen bonded structures are comprehensively investigated. The IMHB results show that the O™H ⋯ O unit of A conformers is stronger than the corresponding interactions of other forms and is not consistent with the stability order. On the other hand, the π-electron delocalization of B forms are greater than those of A and C ones, which strongly support the stability order. Consequently, in the benchmark systems, the π-electron delocalization is a superior factor in determining the most stable structures. [ABSTRACT FROM AUTHOR]

The involved non-covalent interactions in 3D network construction of thiosemicarbazone. [Display omitted] • Facile condensation synthetization of two new ferrocenyl derivatives Fe complexes. • Structural characterization by FTIR, 1H &13C NMR, Mass, and single crystal X-ray diffraction. • DFT–D and AIM studies of non-covalent interactions constructing the appropriate 3D networks. • Stabilizing of 3D networks by N–H⋅⋅⋅S, C–H⋅⋅⋅N, C–H⋅⋅⋅Cl, and C–H⋅⋅⋅π. Two newly Schiff base conjugates formulated as C 22 H 25 FeN 3 S (1) and C 19 H 16 Cl 3 FeN 3 S (2) were synthesized by the facile condensation method of acetylferrocene with appropriate acidic ethanolic solution of thiosemicarbazides used as catalyst which protonate the carbonyl group present on ferrocene. The structures of these conjugates were determined by spectroscopic techniques of Infrared, 1H NMR, 13C NMR, Mass spectrometry, and single crystal X-ray diffraction. The crystal packings are stabilized with the sparse network of hydrogen bonds and stacking interactions. DFT–D/B3LYP high level calculations confirmed the main role of N–H⋅⋅⋅S, C–H⋅⋅⋅N, and C–H⋅⋅⋅Cl non-conventional hydrogen bonds especially the first one in the stabilization of the pertaining 1 - net and 2 - net networks. The presence of big chlorine substituting atoms in 2 , along with change of the spatial direction of the aryl ring plane relating to thioamide and ferrocenyl moieties, makes different C–H⋅⋅⋅Cl hydrogen bonds in 2 - net. However, DFT–D and AIM computational results with the good consistency about measurement of binding energy interactions, show that hydrogen bonds especially N–H⋅⋅⋅S ones have the bigger contribution in the network construction than stacking interactions. [ABSTRACT FROM AUTHOR]