Natural Population Analysis Charges Research Articles

A theoretical and experimental study on isonitrosoacetophenone nicotinoyl hydrazone: Crystal structure, spectroscopic properties, NBO, NPA and NLMO analyses and the investigation of interaction with some transition metals

A new hydrazone oxime compound, isonitrosoacetophenone nicotinoyl hydrazone (inapNH2), was synthesized and characterized by spectroscopic techniques (FT-IR, 1H-NMR and 13C-NMR) and single-crystal X-ray diffraction. The molecular geometry, NMR chemical shift values and vibrational frequencies of the inapNH2 in the ground state have been calculated by using the Density Functional Method (DFT/B3LYP) with 6-31G(d) and 6-311++G(d,p) basis sets. The computational results obtained were in agreement with the experimental results. The thermodynamic parameters of the inapNH2 were calculated at different temperatures, and the changes in thermodynamic properties were studied with increasing temperature. The molecular stability originating from charge transfer and hyperconjugative interactions in the title compound was analyzed using Natural Bond Orbital (NBO) and Natural Localized Molecular Orbital (NLMO) analyzes. The Natural Population Analysis (NPA) charges obtained from NBO analysis were used in order to find out the possible coordination modes of the inapNH2 compound with metal ions. To predict the chemical reactivity of the molecule, the molecular electrostatic potential (MEP) surface map of inapNH2 was investigated and some of its global reactivity descriptors (chemical potential μ, electronegativity χ, hardness η and electrophilicity index ω) were calculated using DFT. Furthermore, the strength of metal–ligand interaction between chlorides of Co(II), Ni(II), Cu(II), Zn(II) and inapNH2, in both aqueous and ethanol phases, was elucidated by using the values of Charge Transfer (ΔN) and Energy Lowering (ΔE). The results indicated that the best interaction in both solvents is between CuCl2 and inapNH2.

Intra- and Intermolecular Charge Transfer in a Novel Dimer: Cooperatively Enhancing Second-Order Optical Nonlinearity

Based on s-indaceno[1,2,3-cd;5,6,7-c′d′]diphenalene (1) consisting of two phenalenyl moieties, the monomer 2 and its dimer 22 are designed by boron and nitrogen atoms substituting the central carbon atoms of phenalenyl moieties. Calculated energy decompose analysis (EDA) shows that the orbital interaction for 22 possesses a large attractive contribution of −18.31 kcal mol–1, which is dominated by the π–π stacking interaction between the upper and the lower π-conjugated units. Interestingly, the natural population analysis (NPA) charge and the transition density matrix (TDM) show that both intramolecular charge transfer and intermolecular charge transfer (CT) exist in 22. Further, the first hyperpolarizability (βtot = 4.56 × 104 au) of 2 with intramolecular CT is greatly larger than that of reported molecule 3 (5.45 × 103 au) with intermolecular CT. Significantly, 22 exhibits the largest βtot value to be 1.42 × 105 au, which is caused by combining the intra- and intermolecular CT transitions (βx = 1.40 × 1...

Frustrated Lewis Pair Chemistry with Magnesium Lewis Acids

Anilido imine–magnesium bromide complexes, (LHMgBr)2 and (LMeMgBr)2, have been prepared [LH = DIPP‐N(C6H4)C(H)N‐DIPP and LMe = DIPP‐N(C6H4)C(Me)N‐DIPP (DIPP = 2,6‐iPr2C6H3)]. Their dimeric crystal structures are compared to the dimer (DIPP‐nacnacMgBr)2 [DIPP‐nacnac = DIPP‐NC(Me)C(H)C(Me)N‐DIPP]. The anilido imine ligands show some degree of charge delocalization but are clearly more asymmetric than the DIPP‐nacnac complex: one of the N atoms has considerable anilido character, whereas the other one is close to an imine. Calculated natural population analysis (NPA) charges (B3PW91/6‐311++G**) and an atoms‐in‐molecules (AIM) study on model systems quantify the asymmetry in charge distribution. Quantification of the Lewis acidity of LHMgBr and LMeMgBr by the Gutmann–Beckett test gave acceptor numbers of 58.9 and 58.3, respectively. The complexes themselves are inert to a number of electrophiles; however, in combination with PPh3 the substrate 1‐butene oxide was ring‐opened. The resulting betaine‐type alkoxide complex is unstable and decomposes at room temperature through a Wittig‐type reaction. At higher temperatures also a reverse Wittig‐type decomposition is observed.

Bis(selone) Complexes of Palladium(II), Platinum(II), and Gold(III): Synthesis and Structural Studies

New bis(selone)‐based metal complexes, [MnLxCly] {M = Pd, L = 3,3′‐[(2‐bromo‐1,3‐phenylene)bis(methylene)]bis(1‐mesityl‐1,3‐dihydro‐2H‐imidazole‐2‐selone) (15), n = 2, x = 2, y = 4, C64H66N8Cl4Br2Se4Pd2) (17); M = Pt, L = 15, n = 2, x = 2, y = 4, C64H66N8Cl4Br2Se4Pt2 (18); M = Au, L = 15, n = 1, x = 1, y = 1, C32H33N4Se2BrAuCl (19)} were synthesized by the reaction of bis(selone) (15) with Pd(COD)Cl2 (yield 31 %), Pt(COD)Cl2 (yield 34 %), and [AuCl(SMe2)] (yield 57 %), respectively. Single‐crystal X‐ray diffraction analysis reveals that 17 and 18 exist as [2+2] dinuclear self‐assembled 24‐membered metallamacrocycles, while the spectroscopic data for the gold(III) complex 19 indicate that it exists as a new organogold(III) bromide, where a facile oxidative addition occurs across the C–Br bond. Natural bond orbital analysis showed the variation of the natural population analysis (NPA) charge on the Se atoms, from negative to positive, after complexation (15: –0.25; 17: 0.08; 18: 0.09–0.13). Moreover, the NPA charge on the metal atom is found to be negative for complexes 17 and 18 (Pd: –0.133 for 17; Pt: –0.23 and –0.251 for 18). However, for complex 19, the gold atom carries a positive charge (0.15).

A DFT study of 3d (d1–d10) transition-metal phthalocyanines (TMPcs): Bonding natures, electronic adsorption spectroscopy

The structures, electronic properties, bonding characters and UV–Vis spectra of [Formula: see text] ([Formula: see text]–[Formula: see text]) transition-metal phthalocyanines (TMPcs) molecules have been studied with different density function theory (DFT) methods. The calculated structural parameters agree well with previous experimental or theoretical values. Natural Population Analysis (NPA) charge revealed that [Formula: see text]–[Formula: see text] hybridizations occur when [Formula: see text] TM atoms are involved in chemical bondings. The spin magnetic moments of TMPcs are mainly from the contribution of [Formula: see text] electrons. Conceptual density functional theory (CDFT) results indicate that [Formula: see text] TMPcs molecules are willing to accept further electrons. The TM–N chemical bonds show very weak covalent nature, and are consistent with bond order analyses. Time-dependent density function theory (TD-DFT) calculations were carried out to simulate the UV–Vis spectra, and corresponding electronic transfers for dominant peaks were also obtained.

Exploring Promising Catalysts for Chemical Hydrogen Storage in Ammonia Borane: A Density Functional Theory Study

Density functional theory (DFT) has been applied to study potential ammonia borane (AB) dehydrogenation pathways via new bifunctional ruthenium-based catalysts, alongside their computationally-designed iron-based counterparts (i.e., four catalysts), using the wB97XD (dispersion-included) functional. The efficiency of each catalyst was under scrutiny based on the addition of ammonia borane, with a focus on the associated activation-energy barriers, whilst hydrogen release from the catalyst was also studied in detail. Here, natural-population analysis charges were key quantities of interest. It was found that the iron-based catalysts display more promising dehydrogenation energy barriers vis-

Reactions of the halonium ions of carenes and pinenes: An experimental and theoretical study

The reactions of vinylcyclopropane (+)-2-carene (1) and vinylcyclobutanes (-)-β-pinene (7), (-)-α-pinene (11), and (-)-nopol (12) with electrophilic halogens in the presence of oxygen and nitrogen nucleophiles in various solvents have been investigated. The halonium ion intermediates that were presumably formed were very reactive and led to opening of the conjugated cyclopropane or cyclobutane. Reactions of chloramine-T trihydrate with compound 1 in acetonitrile gave amidine 13 and diazepine 14. Reactions of chloramine-T trihydrate with pinenes in methylene chloride gave allylic tosylamines 22, 16B and 24. Mechanisms to explain the observations are proposed and supported by ab initio and Density Functional Theory calculations on the carenes and pinenes in this report and their bromonium ion intermediates. For comparisons, the relative extent of conjugation with the bromonium ion moiety of these, as well as select cyclohexene and cyclohexadiene systems and their corresponding bromonium ions, were optimized at the B3LYP/cc-pVDZ level of theory, and then these geometries were analyzed using the absolute hardness index at the Hartree-Fock/aug-cc-pVDZ and B3LYP/aug-cc-pVDZ levels of theory. Additionally, Natural Population Analysis charges were calculated for these systems using Moller-Plessett Second-Order Perturbation Theory electron densities and the aug-cc-pVDZ basis set. Combining the results of these theoretical methods with analysis of structural details of their optimized geometries gives much electronic structure insight into the extent of conjugation of bromonium ions of the carenes and pinenes reported here, and places them in relative context of more traditional conjugated and non-conjugated bromonium ion systems. In particular, bromonium ions of compounds 1, 7, and 11 display structural distortions, charge delocalizations and hardness values comparable with those of traditional conjugated cyclohexadienes, with possible reasons for subtle differences presented.

Pentafluoro-oxotellurate(VI) anions of mercury(II); syntheses and structures of [Hg(OTeF5)4](2-), [Hg(OTeF5)5](3-), [Hg2(OTeF5)6](2-), [Hg(OTeF5)4](2-)·Hg(OTeF5)2, and [Hg2(OTeF5)7](3-)·Hg(OTeF5)2.

Mercury(II) anions derived from the F5TeO- (teflate) group were synthesized and structurally characterized. The salts, [N(CH2CH3)4]2[Hg(OTeF5)4], [N(CH3)4]3[Hg(OTeF5)5], [N(CH2CH3)4]3[Hg(OTeF5)5], [N(CH3)4]2[Hg2(OTeF5)6], Cs2[Hg(OTeF5)4]·Hg(OTeF5)2, and {Cs3[Hg2(OTeF5)7]·Hg(OTeF5)2}·4SO2ClF, were obtained by reaction of Hg(OTeF5)2 with [M][OTeF5] (M = [N(CH3)4](+), [N(CH2CH3)4](+), Cs(+)) and were characterized by low-temperature single-crystal X-ray diffraction and low-temperature Raman spectroscopy. Unlike in the extensively fluorine-bridged solid-state structures of [HgF3](-) and [HgF4](2-), the less basic and more sterically demanding teflate ligands of the Hg(II) anions show less tendency to bridge. The anions exhibit a variety of structural motifs, ranging from well-isolated tetrahedral [Hg(OTeF5)4](2-) and square-pyramidal [Hg(OTeF5)5](3-) to the chain structures, [Hg2(OTeF5)6](2-) and [Hg2(OTeF5)7](3-)·Hg(OTeF5)2. The geometrical parameters and vibrational frequencies of [Hg(OTeF5)4](2-) (S4), [Hg(OTeF5)5](3-) (C1), and [Hg2(OTeF5)6](2-) (D2) anions, as well as the hypothetical [Hg3(OTeF5)8](2-) (C1) anion, were calculated using density functional theory methods (PBE1PBE/def2-TZVPP), which aided in the assignment of the Raman spectra of [Hg(OTeF5)4](2-), [Hg(OTeF5)5](3-), [Hg2(OTeF5)6](2-), and Cs2[Hg(OTeF5)4]·Hg(OTeF5)2. The calculated geometries were used to assess the effects of solid-state interionic interactions on the anion geometries. For the most part, the gross gas-phase trigonal bipyramidal (tbp) geometry of [Hg(OTeF5)5](3-) adheres to the predicted VSEPR geometry but contrasts with the solid-state anion structures, which have square-pyramidal geometries or geometries that lie between square pyramidal- and tbp-geometries. However, the bond length order calculated for the Hg-O bonds of tbp-[Hg(OTeF5)5](3-), Hg-Oeq > Hg-Oax, is opposite to that predicted by the VSEPR model of molecular geometry. Natural bond orbital analyses provided the associated Mayer bond orders, Mayer valencies, and natural population analysis charges.

Theoretical Search for an Iron‐Based Magnetic Superhalogen with Halogen or Interhalogen as Ligand

By using density functional theory, we have investigated the geometrical structures, electrophilic properties, magnetic properties, and fragmentation channels of FeXn (X = Cl, Br; n = 1–6) clusters as well as the “mixed species” that contain interhalogen compounds. Our main objectives are to design new iron-based magnetic superhalogens and to explore whether the interhalogen compounds are suitable for the superhalogen ligand. By calculating their adiabatic electron affinities (AEAs) and vertical detachment energies (VDEs), we found that both FeCln and FeBrn can be classified as superhalogens for n ≥ 3. Among mixed species, FeClF3, FeBrF3, FeClF5, and FeBrF5 are superhalogens, but their AEA values are still smaller than those of the correspondingly sized FeFn clusters. Their superhalogen properties are further supported by the natural population analysis (NPA) charge distribution and the HOMO of anions. However, in mixed species, the extra electron and HOMO do not uniformly delocalize over the different halogen atoms. This might be the reason why FeXYn possesses relatively small AEA values. In addition, we also studied the superhalogen salts formed with these superhalogen anions and Na+, which greatly enhance the reliability of our obtained superhalogens.

Substituent effects in 1-nitro-4-substituted bicyclo[2.2.2]octane derivatives: inductive or field effects?

Interactions between the NO2 group and 13 different substituents (BF2, BH2, CF3, CH3, CHO, CN, F, NH2, NMe2, NO2, NO, OH, OMe) were investigated computationally for bicyclo[2.2.2]octane (BCO) and benzene substituted at 1,4 and 1,3 positions in the ring. Three methods were employed to estimate the character and strength of the substituent effect: substituent effect stabilization energy (SESE), sigma/pi electron donor acceptor index (sEDA/pEDA) and substituent active region (cSAR) parameter. For the first time the sEDA/pEDA parameters were calculated not for the ring but for the NO2 group. All calculations were performed at the B3LYP/6-31G(d,p) level of theory. For 1,4 derivatives, a direct comparison of slopes of linear regressions between BCO and benzene reveals a much better transmission of the substituent effect in the latter. The ratio of slopes (benzene over BCO) is always larger than 4. It follows that the resonance effects, which are absent in the BCO, dominate in this case. For 1,3 derivatives, because of much lower correlation coefficients, estimated standard deviations (ESD) were used to calculate the ratio instead of the slopes. For these systems the ratio is much closer to the unity, which indicates that only the sigma/through space effects are present and they are of similar magnitude in benzene and BCO. It follows from natural population analysis (NPA) charges that the substituent effect in the studied systems is due mainly to through-space interactions.

Understanding the impact of the central atom on the ionic liquid behavior: Phosphonium vs ammonium cations

The influence of the cation's central atom in the behavior of pairs of ammonium- and phosphonium-based ionic liquids was investigated through the measurement of densities, viscosities, melting temperatures, activity coefficients at infinite dilution, refractive indices, and toxicity against Vibrio fischeri. All the properties investigated are affected by the cation's central atom nature, with ammonium-based ionic liquids presenting higher densities, viscosities, melting temperatures, and enthalpies. Activity coefficients at infinite dilution show the ammonium-based ionic liquids to present slightly higher infinite dilution activity coefficients for non-polar solvents, becoming slightly lower for polar solvents, suggesting that the ammonium-based ionic liquids present somewhat higher polarities. In good agreement these compounds present lower toxicities than the phosphonium congeners. To explain this behavior quantum chemical gas phase DFT calculations were performed on isolated ion pairs at the BP-TZVP level of theory. Electronic density results were used to derive electrostatic potentials of the identified minimum conformers. Electrostatic potential-derived CHelpG and Natural Population Analysis charges show the P atom of the tetraalkylphosphonium-based ionic liquids cation to be more positively charged than the N atom in the tetraalkylammonium-based analogous IL cation, and a noticeable charge delocalization occurring in the tetraalkylammonium cation, when compared with the respective phosphonium congener. It is argued that this charge delocalization is responsible for the enhanced polarity observed on the ammonium based ionic liquids explaining the changes in the thermophysical properties observed.

Noble-Gas Difluoride Complexes of Mercury(II): The Syntheses and Structures of Hg(OTeF5)2·1.5NgF2 (Ng = Xe, Kr) and Hg(OTeF5)2

The synthesis of high-purity Hg(OTeF5)2 has resulted in its structural characterization in the solid state by Raman spectroscopy and single-crystal X-ray diffraction (XRD) and in solution by (19)F NMR spectroscopy. The crystal structure of Hg(OTeF5)2 (-173 °C) consists of discrete Hg(OTeF5)2 units having gauche-conformations that interact through long Hg---O and Hg---F intramolecular contacts to give a chain structure. The Lewis acidity of Hg(OTeF5)2 toward NgF2 (Ng = Xe, Kr) was investigated in SO2ClF solvent and shown to form stable coordination complexes with NgF2 at -78 °C. Both complexes were characterized by low-temperature Raman spectroscopy (-155 °C) and single-crystal XRD. The complexes are isostructural and are formulated as Hg(OTeF5)2·1.5NgF2. The Hg(OTeF5)2 units of Hg(OTeF5)2·1.5NgF2 also have gauche-conformations and are linked through bridging NgF2 molecules, also resulting in chain structures. These complexes represent the only examples of coordination compounds where NgF2 coordinates to mercury in a neutral covalent compound and the only example of mercury coordinated to KrF2. Moreover, the Hg(OTeF5)2·1.5KrF2 complex is the only KrF2 complex known to contain a bridging KrF2 ligand. Energy-minimized gas-phase geometries and vibrational frequencies for the model compounds, [Hg(OTeF5)2]3 and [Hg(OTeF5)2]3·2NgF2, were obtained and provide good approximations of the local environments of Hg(OTeF5)2 and NgF2 in the crystal structures of Hg(OTeF5)2 and Hg(OTeF5)2·1.5NgF2. Assignments of the Raman spectra of Hg(OTeF5)2 and Hg(OTeF5)2·1.5NgF2 are based on the calculated vibrational frequencies of the model compounds. Natural bond orbital analyses provided the associated bond orders, valencies, and natural population analysis charges.

Probing the Structural, Bonding, and Magnetic Properties of Cobalt Coordination Complexes: Co–Benzene, Co–Pyridine, and Co–Pyrimidine

Neutral and anionic Co1,2(benzene)1,2, Co1,2(pyridine)1,2, and Co1,2(pyrimidine)1,2 complexes have been investigated within the framework of an all-electron gradient-corrected density functional theory. The ground-state structures for each size clusters were identified based on the geometry optimization. Meanwhile, their electron affinities and vertical detachment energies were predicted and compared with the experimental values. By analyzing the pattern of highest occupied molecular orbitals (HOMOs), we found that the bond formation of these Co-organic complexes mainly arises from the 3d/4s electrons of the cobalt atoms and the π-cloud of the organic molecules. More importantly, we presented an approach to map and analyze the Co-organic interactions from another perspective. The scatter plots of the reduced density gradient (RDG) versus ρ allow us to identify the different types of interactions, and the maps of the gradient isosurfaces show a rich visualization of chemical bond and steric effects. Their magnetic properties were studied by determining the spin magnetic moments and visualizing the spin density distributions. Finally, the natural population analysis (NPA) charge was calculated to achieve a deep insight into the distribution of electron density and the reliable charge-transfer information.

Formation and properties of iron-based magnetic superhalogens: A theoretical study

In order to explore new magnetic superhalogens, we have systematically investigated the structures, electrophilic properties, stabilities, magnetic properties, and fragmentation channels of neutral and anionic Fe(m)F(n) (m = 1, 2; n = 1-7) clusters using density functional theory. Our results show that a maximum of six F atoms can be bound atomically to one Fe atom, and the Fe-Fe bonding is not preferred in Fe2F(n)(0/-) clusters. The computed electron affinities (EAs) indicate that FeF(n) with n ≥ 3 are superhalogens, while Fe2F(n) can be classified as superhalogens for n ≥ 5. To further understand their superhalogen characteristic, the natural population analysis charge distribution and the HOMOs of anionic clusters were also analyzed. When the extra negative charge and the content of HOMO are mainly located on F atoms, the clusters could be classified as superhalogens with EAs substantially surpass that of Cl. By calculating the binding energies per atom and the HOMO-LUMO gaps, FeF3, FeF4(-), Fe2F4, Fe2F5(-), and Fe2F7(-) clusters were found to have higher stabilities, corresponding to the Fe atoms that are attained at their favorite +2 and +3 oxidation states. Furthermore, we also predicted the most preferred fragmentation channel and product for all the ground state clusters. Even more striking is the fact that both neutral and anionic Fe(m)F(n) (m = 1, 2; n = 1-7) clusters carry large magnetic moments which mainly come from 3d orbital of iron atom.

A protocol to evaluate one electron redox potential for iron complexes

Density functional theory calculation has been performed to calculate the redox potential and the correct ground spin state of iron complexes in acetonitrile. Widely used B3LYP functional is applied with the spin state corrected basis sets. The newly developed protocol for the set of 21 iron complexes is to optimize the structure at the level of the B3LYP/6-31G* and to calculate the single point electronic energy with the same functional and the modified basis sets s6-31G* for the iron atom and 6-31+G* for other ligand atoms. The solvation energy is considered through the polarized continuum model and the cavity creation energy is included for the accurate spin state description. Modifying the cavity size by employing the different scaling factor according to the mean absolute value of the natural population analysis charge (MA-NPA) is introduced. The molecule with the large MA-NPA requires the cavity size smaller than the less polar one. This protocol gives only 1 wrong ground spin state among the 18 iron complexes for which experimental data are known. For the open circuit voltage (OCV) calculation, our protocol performs well yielding the mean absolute error of 0.112 V for the test set. The close correlation between the calculated and the experimental OCV are obtained.

On the Factors Affecting H-Bonding : A CCSD(T) // B3LYP Study on Malonaldehyde Cation-Radical

Among the factors that may affect H-bond strength, the effect of the molecular ionization has not received any considerable attention. Here, malonaldehyde and its cation-radical as models were studied using DFT (B3LYP) and ab-initio theories (HF, MP2, and CCSD(T)). Based on establishing a comparison with the CCSD(T)/CBS energy barrier (from literature), we have found that the CCSD(T)/D95(d,p)//B3LYP/6-31G(d,p) computational protocol can be used as a reference for evaluating performance of the B3LYP and the MP2 methods on this model. In this computational organic chemistry study several aspects were investigated, they are: structures, energies, natural population analysis (NPA) charges, intramolecular charge transfer (delocalization) energies, and atoms in molecule (AIM) electron densities with regard to the Hbonding. The results indicate that loss of an electron can cause considerable effects on the various electronic structure aspects and the details are presented and discussed. All the aspects confirm that ionizing the molecule disturbs the electron density distribution in the HOMO orbital and makes the two oxygen atoms, relatively, electron deficient centers which consequently weakens both the H1-O1 bond and the O2/H1-O1 H-bond. The details of this investigation are new addition to the hydrogen bond theory. Other types of molecular models and computational protocols are of interest for future investigations. Keyword: Malonaldehyde cation-radical; DFT; MP2; CCSD(T); NBO; AIM; H-bond.

Electronic effect of ionic‐pair substituents

For conventional organic substituents, an almost linear relationship can be established between the para Hammett constants in aqueous solutions and chemical shifts or natural population analysis charges (NPA charges). Based on these correlations, the Hammett constants of six synthesized ionic‐pair substituents were estimated via the chemical shifts, which were well in agreement with the results calculated by NPA charges. The para Hammett constants of 89 different ionic‐pair substituents (77 anion‐cationic and 12 cation‐anionic) were therefore calculated in the gas phase based on the density functional theory method. The results show that both the anion‐cationic and cation‐anionic substituents are electron‐withdrawing groups and the different cation–anion combinations could tune the Hammett constants of the ionic‐pair substituents in a range from 0.03 to 0.77. Copyright © 2013 John Wiley & Sons, Ltd.

Assessment of atomic partial charge schemes for polarisation and charge transfer effects in ionic liquids

In this work, we assess several popular atomic partial charge schemes with the view of accurately quantifying charge distribution, dipole moments and charge transfer in routinely used ionic liquids (ILs). We investigated a series of ion pairs of imidazolium-based ILs such as [C((1-4))mim]X (where X = Cl, BF(4) and NTf(2)) and ionic clusters of [NMe(4)][BF(4)], [C(1)mim][BF(4)] and [C(1)mim]Cl that were composed of two, four and eight ion pairs. Assessed partial charge schemes include restrained electrostatic potentials (RESP) employing ChelpG, Connolly and Geodesic point selection algorithms, as well as density matrix partitioning schemes including Mulliken, Löwdin and Natural Population Analysis (NPA). The quality of charge distribution was analysed using the following criteria: (1) treatment of symmetry identical atoms, (2) invariance of charge in the imidazolium ring with increasing alkyl chain and (3) recalculation to dipole moments as a measure of electronic polarisation. The RESP schemes such as Connolly and Geodesic clearly outperform the ChelpG scheme as well as the density matrix-based schemes for these three criteria. Calculated partial charges reveal that dipole moments were best represented by the RESP schemes and confirmed the presence of charge transfer in ILs to a various degree. The degree of charge transfer was dependent on anions as well as cluster size. In the ion pairs, the chloride anion showed the largest charge transfer, followed by the NTf(2) and BF(4) anions. In ionic clusters the charge transfer was shown to gradually converge from two to eight ion pairs in the case of the [NMe(4)][BF(4)] and [C(1)mim][BF(4)] ILs to a value, close to that for corresponding ion pairs. In contrast, charge transfer in the [C(1)mim]Cl clusters converges to a lower value, showing an unusually strong inter-ionic bond with the chloride anion. NPA charges were found to perform poorly, with near-unity charges being retained on the anions and cations in ion pairs and ionic clusters. Mulliken and Löwdin charges were shown to be highly basis set dependent and unpredictable with marked fluctuations in partial charges and therefore their use for ILs is particularly discouraged. Ability of the partial charge schemes to capture fluctuations in the dipole moment within the ionic clusters was also examined. The Connolly and Geodesic RESP schemes were found to slightly outperform ChelpG. Evidence to suggest that chloride-based ILs might be poor model systems for ILs is also presented.

A new interaction mechanism of LiNH2 with MgH2: magnesium bond

Quantum chemical calculations were performed for LiNH2-HMgX (X=H, F, Cl, Br, CH3, OH, and NH2) complexes to propose a new interaction mechanism between them. This theoretical survey showed that the complexes are stabilized through the combinative interaction of magnesium and lithium bonds. The binding energies are in the range of 63.2-66.5 kcal mol(-1), i.e., much larger than that of the lithium bond. Upon complexation, both Mg-H and Li-N bonds are lengthened. Substituents increase Mg-H bond elongation and at the same time decrease Li-N bond elongation. These cyclic complexes were characterized with the presence of a ring critical point and natural population analysis charges.

Enhancing the function, non-additivity, and substitution position effect of the Li atom in the cation–π interaction and its mechanism: an ab initio study of Li+ ··· Li-substituted benzene complexes

Quantum chemical calculations have been performed to study the cation–π interaction in the Li+ ··· C6H6– n Li n (n = 0–6) complex. The results show that the cation–π interaction is enhanced by lithium substitution in the aromatic ring. With increasing number of lithium substituents in the aromatic ring, the total interaction energy becomes more negative. However, the average contribution from one Li substituent to the interaction energy becomes smaller. The lithium substituent in the aromatic ring displays negative non-additivity in enhancing the cation–π interaction. The substitution position of the lithium substituent in the aromatic ring has a prominent effect on the strength of the cation–π interaction. The largest interaction energy (–97.7 kcal mol−1) is found for the Li+ ··· 1,3,5-C6H3Li3 complex. The enhancing effect of the Li atom can be understood in terms of the natural population analysis (NPA) charge on the carbon atom in the aromatic ring, the most negative electrostatic potential at the center of the aromatic ring, and energy decomposition.