Atoms In Molecules Approach Research Articles

How the addition of atomic hydrogen to a multiple bond can be catalyzed by water molecules.

Observational data show complex organic molecules in the interstellar medium (ISM). Hydrogenation of small unsaturated carbon double bond could be one way for molecular complexification. It is important to understand how such reactivity occurs in the very cold and low-pressure ISM. Yet, there is water ice in the ISM, either as grain or as mantle around grains. Therefore, the addition of atomic hydrogen on double-bonded carbon in a series of seven molecules have been studied and it was found that water catalyzes this reaction. The origin of the catalysis is a weak charge transfer between the π MO of the unsaturated molecule and H atom, allowing a stabilizing interaction with H2O. This mechanism is rationalized using the non-covalent interaction and the quantum theory of atoms in molecules approaches.

Noncovalent Dualism in Perylene-Diimide-Based Keggin Anion Complexes: Theoretical and Experimental studies.

We report the synthesis and comprehensive characterization of organic-inorganic hybrid salts formed by bis-cationic N,N'-bis(2-(trimethylammonium)ethylene)perylene-3,4,9,10-tetracarboxylic acid bisimide (PTCD2+) and Keggin-type [XW12O40]n- (X = Si, n = 4; X = P, n = 3) polyoxometalates. (PTCD)3[PW12O40]2·3DMSO·2H2O (2) and (PTCD)2[SiW12O40]·DMSO·2H2O (3) were structurally characterized by single crystal X-ray diffraction. The cations in both structures exhibited infinite chainlike arrangements through π-π interactions, contrasting with the previously reported cation-anion stacking observed in naphthalene diimide derivatives. A detailed theoretical study employing topological analysis of the electron density distribution within the quantum theory of atoms in molecules approach provided further insights into this structural dualism. Atomic force microscopy analyses revealed the formation of self-assembled supramolecular structures on graphite from molecular monolayers (3 nm of thick) to submicrometer aggregates for 2. Hyperspectral Raman spectroscopy imaging revealed that such heterostructures are likely formed by an enhanced π-π interactions. Both complexes demonstrated interesting electrochemical behavior, photoluminescence and X-ray-induced luminescence. Electron spin resonance analysis confirmed charge separation in both compounds, with enhanced efficiency observed in compound 2. Our findings of these perylene-based organic-inorganic hybrid salts offer the potential for their application in optoelectronic devices and functional materials.

Weak noncovalent interactions in two positional isomers of acrylonitrile derivatives: inputs from PIXEL energy, Hirshfeld surface and QTAIM analyses.

A single crystal X-ray diffraction analysis was performed on two positional isomers (m-tolyl and p-tolyl) of acrylonitrile derivatives, namely, (Z)-3-(4-(pyridin-2-yl) phenyl)-2-(m-tolyl) acrylonitrile (1) and (Z)-3-(4-(pyridin-2-yl)phenyl)-2-(p-tolyl) acrylonitrile (2). Compound 1 crystallized in the monoclinic P21/n space group with two crystallographically independent molecules. Compound 2 also possesses two crystallographically independent molecules and crystallized in the triclinic P-1 space group. The Hirshfeld surface analysis revealed that, in both isomers, intermolecular H⋅⋅⋅H/C/N contacts contribute significantly to the crystal packing. More than 40% of the contribution arises from intermolecular C-H⋅⋅⋅C(π) contacts. In both compounds, the relative contribution of these contacts is comparable, indicating that the positional isomeric effects are marginal. The structures in which these isomers are arranged in the solid state are very similar, and the lattice energies are also comparable between the isomers. The Coulomb-London-Pauli-PIXEL (CLP-PIXEL) energy analysis identified the energetically significant dimers. The strength of the intra- and intermolecular interactions was evaluated using the quantum theory of atoms in molecules approach. The UV-Vis absorbance in three different solvents (chloroform, ethanol, and ethyl acetate) for isomers 1 and 2 are very similar. This result is in good agreement with the time-dependent density-functional theory (TD-DFT) calculations.

Dynamical Stability and Physical Properties of Fe Dihalide Nanowires

AbstractAn extensive first‐principles and atomistic Monte Carlo study on isolated Fe ( = F, Cl, Br, I) nanowires is presented. The structural properties of the Fe chains are determined and compared with their bulk structures. The results indicate that in the lowest energy configuration, the wires crystalize in a system that belongs to the space group (No. 131, Z = 2, point group ), with antiferromagnetic arrangement. The stability is determined by calculating the phonon frequencies in the whole Brillouin zone within the supercell approach. The relative stability of the periodic chains is also determined by calculating the elastic properties and comparing them with bulk cases. The band structure, the density of states, the magnetic properties, the anisotropy energy, and topological analysis, performed with the Quantum Theory of Atoms in Molecules approach, are also reported and discussed. The results support the idea that these Fe nanowire systems are promising materials for practical applications, like lithium‐ion batteries.

How Water Interacts with the NOH Group: The Rotational Spectrum of the 1:1 N,N-diethylhydroxylamine·Water Complex

The rotational spectrum of the 1:1 N,N-diethylhydroxylamine-water complex has been investigated using pulsed jet Fourier transform microwave spectroscopy in the 6.5-18.5 GHz frequency region. The most stable conformer has been detected as well as the 13C monosubstituted isotopologues in natural abundance and the 18O enriched water species, allowing to determine the nitrogen nuclear quadrupole coupling constants and the molecular structure in the vibrational ground state. The molecule has a Cs symmetry and the water lies in the bc symmetry plane forming two hydrogen bonds with the NOH frame with length: dHOH·NOH = 1.974 Å and dH2O·HON = 2.096 Å. From symmetry-adapted perturbation theory calculations coupled to atoms in molecule approach, the corresponding interaction energy values are estimated to be 24 and 13 kJ·mol-1, respectively. The great strength of the intermolecular interaction involving the nitrogen atom is in agreement with the high reactivity of hydroxylamine compounds at the nitrogen site.

Structural and Energetic Properties of Weak Noncovalent Interactions in Two Closely Related 3,6-Disubstituted-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole Derivatives: In Vitro Cyclooxygenase Activity, Crystallography, and Computational Investigations.

Two 3,6-disubstituted-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole derivatives, namely, 3-(adamantan-1-yl)-6-(2-chloro-6-fluorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole 1 and 6-(2-chloro-6-fluorophenyl)-3-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole 2, were prepared, and the detailed analysis of the weak intermolecular interactions responsible for the supramolecular self-assembly was performed using X-ray diffraction and theoretical tools. Analyses of Hirshfeld surface and 2D fingerprint plot demonstrated the effect of adamant-1-yl/phenyl moieties on intermolecular interactions in solid-state structures. The effect of these substituents on H···H/Cl/N contacts was more specific. The CLP-PIXEL and density functional theory methods provide information on the energetics of molecular dimers observed in these compounds. The crystal structure of compound 1 stabilizes with a variety of weak intermolecular interactions, including C–H···N, C–H···π, and C–H···Cl hydrogen bonds, a directional C–S···π chalcogen bond, and unconventional short F···C/N contacts. The crystal structure of compound 2 is stabilized by π-stacking interactions, C–H···N, C–H···π, and C–H···Cl hydrogen bonds, and highly directional attractive σ–hole interactions such as the C–Cl···N halogen bond and the C–S···N chalcogen bond. In addition, S(lp)···C(π) and short N···N contacts play a supportive role in the stabilization of certain molecular dimers. The final supramolecular architectures resulting from the combination of different intermolecular interactions are observed in both the crystal packing. The molecular electrostatic potential map reveals complementary electrostatic potentials of the interacting atoms. The quantum theory of atoms in molecules approach was used to delineate the nature and strength of different intermolecular interactions present in different dimers of compounds 1 and 2. The in vitro experiments suggest that both compounds showed selectivity against COX-2 targets rather than COX-1. Molecular docking analysis showed the binding pose of the compounds at the active sites of COX-1/2 enzymes.

Deformations of cyclodextrins and their influence to form inclusion compounds

AbstractDeformations of the three most common cyclodextrins (,, and) were induced to form inclusion compounds with sertraline and abacavir. The deformations were obtained from classical molecular dynamics (CMD) using as starting point X‐ray structures. The molecular dynamics were performed in two ways, over the cyclodextrins with and without the presence of a guest. Two characteristic rings within these cyclodextrins were used to measure the distortions observed along with the molecular dynamics. A docking approach was used to build inclusion compounds over the structures obtained from CMD without the presence of sertraline or abacavir. Thus, we compared structures of inclusion compounds obtained from deformations induced by the presence of a guest or with intrinsic deformations exhibited by each cyclodextrin. After this step, each structure was optimized by the PBE0‐D3/6‐31G(d,p) method, and the electron density delivered by this method was used to perform the quantum theory of atoms in molecules approach to analyze intermolecular contacts between sertraline, or abacavir, and three cyclodextrins. From this procedure, we found that inclusion compounds obtained from X‐ray structures present the highest energies over the potential energy surface. Thus, for getting low‐lying energy structures of inclusion compounds, deformations on cyclodextrins are necessary.

Structure-property relationship in thioxotriaza-spiro derivative: Crystal structure and molecular docking analysis against SARS-CoV-2 main protease

Detailed structural and non-covalent interactions in thioxotriaza-spiroderivative (DZ2) are investigated by single crystal structure anslysis and computational approaches. Its results were compared with the previously reported spiroderivative (DZ1). The crystal structure analysis revealed various C–H…O, N–H…O, C–H…N and N–H…S hydrogen bonds involved in constructing several dimeric motifs to stabilize the crystal packing. The differences and similarities in the relative contribution of non-covalent interactions in DZ1 and DZ2 compounds are compared using the Hirshfeld surface analysis and 2D fingerprint plots. The binding energies of specific molecular pairs and homodimers have been obtained using molecule–molecule interaction energy calculation. The hierarchy and topology of pair-wise intermolecular interactions are visualized through energy frameworks. The nature and strength of intra and intermolecular interactions were characterized using non-covalent interaction index analysis and the quantum theory of atoms in molecule approach. Further, molecular docking of compounds (DZ1 and DZ2) with SARS-CoV-2 main protease for COVID-19 is performed. And the superposition of these ligands and inhibitor N3, which is docked into the binding pocket of 7BQY, is presented. The binding affinity of −6.7 kcal/mol is observed, attributed to hydrogen bonding and hydrophobic interactions between the ligand and the amino acid residues of the receptor.

Photophysics and Excited State Dynamics of Cyclometalated [M(Phbpy)(CN)] (M = Ni, Pd, Pt) Complexes: A Theoretical and Experimental Study.

Cyclometalated complexes [M(Phbpy)(CN)] (HPhbpy = 6-phenyl-2,2'-bipyridine) of the group 10 metals (Ni, Pd, and Pt) bearing a carbanionic -C∧N∧N pincer ligand were synthesized and studied in a combined experimental and computational DFT approach. All three complexes were crystallographically characterized showing closely packed dimers with head-to-tail stacking and short metal-metal contacts in the solid state. The computational models for geometries, excited states, and electronic transitions addressed both monomeric (Ni-mono, Pd-mono, and Pt-mono) and dimeric (Ni-dim, Pd-dim, and Pt-dim) entities. Photophysical properties and excited state dynamics of all title complexes were investigated in solution and in the solid at 298 and 77 K. [Ni(Phbpy)(CN)] and [Pd(Phbpy)(CN)] are virtually nonemissive in solution at 298 K, whereas [Pt(Phbpy)(CN)] shows phosphorescence in CH2Cl2 (DCM) solution (λem = 562 nm) stemming from a mixed 3MLCT/ILCT (metal-to-ligand charge transfer/intraligand charge transfer) state. At 77 K in a glassy frozen DCM:MeOH matrix, [Pd(Phbpy)(CN)] shows a remarkable emission (λem = 571 nm) with a photoluminescence quantum yield reaching almost unity, whereas [Ni(Phbpy)(CN)] is again nonemissive. Calculations on the monomeric models M-mono show that low-lying metal-centered states (MC, i.e., d-d* configuration) with dissociative character quench the photoluminescence. In the solid state, the complexes [M(Phbpy)(CN)] show defined photoluminescence bands (λem = 561 nm for Pd and 701 nm for Pt). Calculations on the dimeric models M-dim shows that the axial M···M interactions alter the photophysical properties of Pd-dim and Pt-dim toward MMLCT (metal-metal-to-ligand charge transfer) excited states with Pd-dim showing temperature-dependent emission lifetimes, suggesting thermally activated delayed fluorescence, whereas Pt-dim displayed phosphorescence with excimeric character. The metal-metal interactions were analyzed in detail with the quantum theory of atoms in molecules approach.

Insights into the structure-property relationship of pharmaceutical co-crystals: Charge density and quantum chemical approaches

A subset of co-crystal systems of the antipyretic and analgesic drug, propyphenazone, are used to probe the nature of the drug···co-former interactions. The experimental electron density distribution, based on very high-resolution single crystal diffraction, has been modelled and an analysis undertaken using Bader's Atoms in Molecules approach. Atomic charges, intermolecular interactions and their energies have been subsequently derived and compared between systems. Complementary theoretical calculations are used to derive interaction energies for intermolecular interactions beyond atom···atom contacts. These permit the deconvolution of the intermolecular interactions into their constituent energy components for a comprehensive analysis. This approach provides an insight into the factors affecting the assembly of the solid state, with the case of pharmaceutical co-crystals being highlighted in this work. Furthermore, this approach enables analysis of the effect of the co-former on various influencing factors that determine the physicochemical properties of these multi-component systems.

Inclusion induced water solubility and binding investigation of acenaphthene-1,2-dione with p-sulfonatocalix[4]arene

An increase in the water solubility of acenaphthene-1,2-dione (AD) with p-sulfonatocalix[4]arene (p-SC4) is studied by means of simple method using UV chamber and analysed quantitatively using LC. The host guest interaction of AD with p-SC4 is studied using UV–visible absorption and emission spectral studies. The electrochemical properties of AD in the presence of p-SC4 is investigated using cyclic voltammetry method. The mode of binding is investigated using 1H NMR and ROESY techniques. Computational modelling shows that there are various kinds of non-covalent interactions favour the stability of the complexes. The presence of bond critical points between phenyl rings of p-SC4 and AD molecules are confirmed through density functional theory (DFT) and atoms in molecules approaches. Our study clearly reveals that there is strong charge transfer process between p-SC4 (SO3 group) and AD (aryl C-H…O) molecule during the inclusion process. In addition to this, dispersion interaction plays a vital role in the AD absorption on p-SC4 moiety which is confirmed through BE calculations and bond critical points between aromatic clouds.

Combined Experimental and Computational Approach for the Vibrational Characteristics and Theoretical Evaluation of Binding Activities and ADME Descriptors of 2,6-Di-tert-butyl-p-cresol

A crystalline sample of multipotent molecule “2,6-di-tert-butyl-p-cresol” (DBPC) was characterized by FT-IR, FT-Raman and its spectroscopic signatures were analyzed using density functional theory (DFT) computations. The weaker intermolecular interactions such as π-π, alkyl-alkyl, π-alkyl in the extended molecular framework were analyzed by Quantum topological atoms in molecule approach. The conformational analysis of the structure and the optimized geometrical parameters of the minimum energy conformer were discussed in detail. The excitation energies corresponding to one electron transition from various HOMO and LUMO energy levels were predicted using DFT. The second-order perturbation approach has been implemented to determine interaction energies between the molecular species. The predicted nonlinear optical (NLO) properties (second-order hyperpolarizabilities) suggest that DBPC can act as NLO materials. Since it has been already found as an anti-oxidant agent, an attempt was performed to find its active binding sites on phase II metabolism isoenzyme. The adsorption, distribution, metabolism and excretion descriptors were predicted to evaluate its drug-likeness. Also, the Swiss BOİLED-Egg model indicates that DBPC can be passively permeated through the blood-brain barrier and is predicted not to be effluated from the central nervous system by p-glycoprotein (PGP¯).

Effects of the inter- and intra-molecular hydrogen bonding interactions in forming atmospheric malonic acid-containing clusters

The possible involvement of chemical compounds in atmospheric new particle formation has received increased attention in recent years. Extensive density functional theory calculations were performed to characterize the effects of the inter- and intra-molecular hydrogen bonding interactions in forming atmospheric malonic acid (MOA)-containing clusters. Methanol, water, formaldehyde, and acetone are common atmospheric nucleation precursors, and they were chosen as the counterpart to interact with MOA. There are two types of hydrogen bonds: addition and insertion. When MOA behaves as the donor of a hydrogen bond, the formation of an inter-molecular hydrogen bond lightly increases the strength of the intra-molecular hydrogen bonds. Strong hydrogen bonds were formed when MOA executes as a hydrogen bond donor. The strength of the insertion conformer depends on the inserting molecule. The IR frequencies of the hydrogen bonded system were investigated. Furthermore, geometrically identified inter- and intra-molecular hydrogen bonds were provided by atoms in molecules approach.

Explaining the interactions between metaldehyde and acidic surface groups of activated carbon under different pH conditions

Metaldehyde (MA) is an organic compound widely used in agriculture all around the world as molluscicide. There are growing concerns that relatively high levels of MA have been detected in surface water, which could be ascribed to the fact that it is transparent to common wastewater treatment processes. A theoretical study of the influence of activated carbon (AC) surface groups (SGs) on MA adsorption is done in order to help to understand the process and to evaluate the influence of the acid SGs over the adsorption in AC filters. Multiple Minima Hypersurface methodology was employed in order to study the interactions of the MA with acid SGs (hydroxyl and carboxyl) at acidic and neutral pH, and at different hydration conditions explicitly taking into account the solvent influence. Selected structures were re-optimized using Density Functional Theory and posteriorly refined to achieve a well-defined electron density to characterize the interactions by the Quantum Theory of Atoms in Molecules approach. The obtained results showed that the presence of SGs enhances the adsorption process. The deprotonated carboxyl and hydroxyl SGs of AC models show the strongest interactions, suggesting greater adsorption at neutral pH which is in concordance with experimental data. The main interactions are of a dispersive nature between the pesticide and the π-cloud of the AC and hydrogen bonds between the MA and the acid SGs suggesting that the adsorption process is driven by a physisorption mechanism. Water acts as an intermediary between the AC and MA and competing with it for the adsorption sites.

GPUs as boosters to analyze scalar and vector fields in quantum chemistry

AbstractThe analysis of scalar and vector fields in quantum chemistry is an essential task for the computational chemistry community, where such quantities must be evaluated rapidly to perform a particular study. For example, the atoms in molecules approach proposed by Bader has become popular; however, this method demands significant computational resources to compute the involved tasks in short times. In this article, we discuss the importance of graphics processing units (GPU) to analyze electron density, and related fields, implementing several scalar, and vector fields within the graphics processing units for atoms and molecules (GPUAM) code developed by a group of the Universidad Autónoma Metropolitana in México City. With this application, the quantum chemistry community can perform demanding computational tasks on a desktop, where CPUs and GPUs are used to their maximum capabilities. The performance of GPUAM is tested in several systems and over different GPUs, where a GPU installed in a workstation converts it to a robust high‐performance computing system.

Experimental validation of calculated atomic charges in ionic liquids.

A combination of X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy has been used to provide an experimental measure of nitrogen atomic charges in nine ionic liquids (ILs). These experimental results are used to validate charges calculated with three computational methods: charges from electrostatic potentials using a grid-based method (ChelpG), natural bond orbital population analysis, and the atoms in molecules approach. By combining these results with those from a previous study on sulfur, we find that ChelpG charges provide the best description of the charge distribution in ILs. However, we find that ChelpG charges can lead to significant conformational dependence and therefore advise that small differences in ChelpG charges (<0.3 e) should be interpreted with care. We use these validated charges to provide physical insight into nitrogen atomic charges for the ILs probed.

Microscopic analysis of AgCl polymorphism

A detailed theoretical study of the structural properties of the phases involved in the pressure-induced polymorphic sequence of AgCl is reported. As many other binary ionic compounds, AgCl crystallizes in the B1 (NaCl-type) structure at ambient pressure and shows a high-pressure B2 (CsCl-type) structure under pressure. However, unlike alkali halides, there is not a direct transformation from one to the other. The greater polarizability of the silver chloride structure enables the stabilization of two other phases in between B1 and B2: the monoclinic (KOH-type) and the orthorhombic (TlI-type, B33) structures. This polymorphic sequence is specially interesting, since a concerted transition pathway within the monoclinic KOH-type symmetry has also been proposed as a transition pathway in the B1 → B2 transformation. This would point at a connection between symmetries that are thermodynamically and kinetically stabilized, with phases that appear under pressure being good candidates for mechanistic analyses. Our calculations yield cell parameters and structural behavior under pressure in overall good agreement with available experimental data for all these phases and extend the information previously observed for the four polymorphs (e.g., compressibilities). Computed transition pressures confirm the B1→KOH-type→B33 sequence. In order to analyze the occurrence of the KOH-type phase between the B1 and B33 phases, we have resorted to the Atoms In Molecules approach to obtain the evolution of charges with pressure. We find that the descent to the KOH-type symmetry provides a continuous change in ionic charges between B1 and B33 phases, which implies a smaller stress. Thus, coupling group–subgroup relationships to chemical bond analysis can provide microscopic insight into why a given symmetry is favored.

Synthesis of 2-amino-3-cyano 4-H-chromenes containing quinoline in water: computational study on substituent effects

An efficient, high yielding and environmentally benign strategy to the synthesis of new 2-amino-3-cyano-4-H-chromene derivatives, via one-pot three-component reaction involving malononitrile, various α- or β-naphthol and appropriate aromatic aldehydes including 2-chloroquinoline-3-carbaldehydes in the presence of morpholine in water, was achieved. During the development of the synthesis five new chromene derivatives were fruitfully synthesized. It was found that employing this approach, aromatic aldehydes bearing electron-withdrawing groups give higher yields of the corresponding products in shorter reaction times. This observation was in agreement with topological analysis of calculated electron density functions using density functional theory and quantum theory of atoms in molecules approaches.

The substituent effect on the antioxidant capacity of catechols and resorcinols

The antioxidant capacity of polyphenols is widely recognized; especially, the catechol moiety is considered a key piece in the structure of natural compounds with this characteristic. The resorcinol is also a dihydroxybenzene that is present in natural antioxidants; however, fewer experimental and theoretical studies have been addressed to this moiety. This work reports a comparative study of the substituent effect on properties related to the antioxidant capacity, as energy ionization (I), and O–H bond dissociation enthalpy (BDE), to analyze the electron transfer and hydrogen atom transfer (HAT) mechanisms, in derivatives of phenols, catechols and resorcinols. In the set of substituents tested \(({-}\hbox {CH}_3, {-}\hbox {CH}_2\hbox {CH}_3, {-}(\hbox {CH}_2)_2{-}\hbox {CH}_3, {-}\hbox {CH}{=}\hbox {CH}_2, {-}\hbox {CH}{=}\hbox {CHCOOH}, {-}\hbox {COOH}\) and \({-}\hbox {CO}(\hbox {CH}_2)_4{-}\hbox {CH}_3)\) electron-withdrawing and electron-donating groups, including alkyl chains, are considered. We found that electron-donating substituents reduce I and O–H BDE of resorcinols and catechols derivatives. In addition, the length of the alkyl chains is not relevant on resorcinols neither on catechols. With regard to the HAT process, a double bond in a substituent favors it, while the –COOH group shows a contrary effect. The combination of a double bond with a –COOH group, in the substituent, increases the BDE and reduces the electron donor capacity, and this result suggests that this combination induces a reduction in the antioxidant capacity in one polyphenol compound. In several reports, an intramolecular hydrogen bond has been proposed within to the most stable structure of catechol. However, by using arguments from the atoms in molecules approach and the electron localization function, we show that such an interaction is not relevant to stabilize this conformation and consequently and this is the reason that explains the unimportance of this interaction in the properties studied here and in previous studies.

Application of topological analysis of the electron localization function to the complexes of molybdenum carbide nanoparticles with unsaturated hydrocarbons

The catalytic transformation of the heavy aromatics in bitumen into lighter components is the key to the upgrading and refining of the oil sands. To understand the chemical bonding in molybdenum carbide nanoparticle (MCNP) catalysts and the chemisorption bonds between the MCNPs and unsaturated hydrocarbons, the topological analysis of the electron localization function was applied to various MCNPs and their complexes with unsaturated hydrocarbons. For some of the smaller complexes, comparisons are made with the atoms in molecules approach, including the calculation of delocalization indices. The results are interpreted in the Lewis bonding scheme. It was found that the Mo–C bonding can be highly ionic in cases like Mo8C12 and MoC but shows significant covalent character in Mo2C, Mo3C, and Mo28C14. The chemisorption bonds between hydrocarbons and the MCNPs involve electron sharing of various types with strong covalent character. The strong three– or four–center interactions determine the adsorption configurations of the hydrocarbons on the MCNPs. Derivatives of benzene show some different bonding features, which depend strongly on the substituent or the heteroatom.