Search

The discovery of fullerenes was a huge milestone in the scientific community, and with it came the urge to discover and analyze various small and large atomic and molecular clusters having a cavity. These cavitands of varied shapes and sizes have wide applications in the encapsulation of rare gas atoms to induce bond formation between them, storage of hydrogen and hydrocarbons to be used as alternative sources of fuel, catalyzation of otherwise slow reactions without using a catalyst, activation of small gas molecules, etc. Various cavitands like fullerenes, [ExBox]4+, cucurbit[n]urils, borospherenes, octa acid, etc. have been used for this purpose. Some clusters including cavitands exhibit fluxional behaviour. Systems in a confined environment often manifest interesting variations in their properties and behaviour, compared to their unconfined counterparts, facilitating the aforementioned applications. In this perspective article, we explore the possibility of making use of this extra degree of freedom, viz., the fluxionality, in changing the catalytic activity of the cavitand.

Ab initio calculations have been performed for a series of binuclear sandwich complexes, M2(η5-L)2. It has been observed that the eclipsed and staggered conformations have almost equal amount of energies. The M-M bond lengths are comparable with those in the free M2 molecules (M = Be, Mg). The nuclear-independent chemical shift (NICS) values indicate the aromaticity of these complexes. The stability of Be2(η5-L)2 complexes is higher than that of the Mg2(η5-L)2 complexes. The natural bond orbital (NBO) analysis and electron density descriptors proved the existence of a single covalent M-M bond in an M22+ fragment. It has been observed that each M-M bond contains a non-nuclear attractor (NNA) at the center of the respective bond. The Laplacian of electron density [∇2ρ(r)] is negative at the NNAs. The energy decomposition analysis (EDA) showed that M22+ and 2L- represent the bonding interaction in the complexes. All of the designed binuclear sandwich complexes behave as electrides.

Due to its high specificity and reliability, “click chemistry” has become a valuable tool to prepare functional materials in several research disciplines. Apart from the modular and orthogonal appr...

The cycloaddition of ethylene, cyanoethylene, and propylene to a five-membered P/B frustrated Lewis pair (FLP) is shown to be highly favorable under normal conditions, as confirmed by the computed thermodynamic and kinetic data. All of these cycloaddition reactions are concerted as highlighted by the intrinsic reaction coordinate (IRC) and Wiberg bond index calculations. Almost 70% of the reaction force is required for structural orientation to initiate electronic activity. The reactions are interpreted by the frontier molecular orbital (FMO) analysis and conceptual density functional theory (DFT)-based reactivity descriptors. It appears that ethylene and propylene will act as nucleophiles, while the FLP will act as an electrophile throughout the cycloaddition reaction, however, cyanoethylene will act as an electrophile and the FLP as a nucleophile. Regioselectivities of the cycloadditon of cyanoethylene and propylene to the FLP are further verified through philicity and dual descriptors. It is demonstrated that an FLP can be forced to act as an electrophile or a nucleophile by intelligently selecting its partner in a cycloaddition reaction. Even the P and B centers would behave differently within the same FLP. This strategy may be properly exploited by the experimentalists in designing a suitable reaction for the synthesis of any useful molecule possessing the desired property.

Two azo functionalized Zn(II)-based MOFs, {[Zn(SDB)(3,3′-L)0.5]·xG}n, IITKGP-13A, and {[Zn2(SDB)2(4,4′-L)]·xG}n, IITKGP-13B (IITKGP stands for Indian Institute of Technology Kharagpur), have been c...

Density functional theory (DFT) based calculations have been carried out for the endohedral encapsulation of magnesium dimer inside fullerene, that is, Mg2 @C60 . It is observed that the minimum energy structure of the Mg2 @C60 system is C2h symmetry. The MgMg bond distance in the Mg2 @C60 system is much shorter than that in the free Mg2 and Mg22+ ion. The formation of the endohedral Mg2 @C60 system is thermochemically spontaneous in nature. The natural bond orbital (NBO) analysis showed the presence of an Mg22+ fragment with an MgMg bond inside the C60 cage. The electron density descriptors have identified the covalency in the MgMg bond. A non-nuclear attractor (NNA) is present in the middle of the two Mg-atoms. The bonding interaction between the Mg2 and C60 fragments is ionic in nature and the [Mg22+ ] and [C602- ] represent the bonding pattern in the Mg2 @C60 system. The designed endohedrally encapsulated system behaves as an electride.

Two Cu(II)-based metal–organic frameworks (MOFs) having paddle-wheel secondary building units (SBUs), namely, 1Me and 1ipr, were synthesized solvothermally using two new bent di-isophthalate ligand...

Using the electron density and its associated quantities in a molecular system to quantify chemical reactivity in density functional theory is of considerable recent interest. Local temperature based on the kinetic energy density is an intrinsic property of a molecular system, which can be employed for this purpose. In this work, we explore such a possibility. To this end, we examine the local behavior of local temperature with a few choices of the kinetic energy density, apply it to determine regioselectivity of nucleophilic and electrophilic compounds, and then investigate its performance in appreciating reactions along the intrinsic reaction pathway for exothermic, endothermic, and thermoneutral transformations. Our results confirm that local temperature can be used as an effective descriptor of molecular reactivity.

Is it possible to facilitate the formation of a genuine Be-Be or Mg-Mg single bond for the E2 species while it is in its neutral state? So far, (NHCR )Be-Be(NHCR ) (R=H, Me, Ph) have been reported where Be2 is in 1 Δg excited state imposing a formal Be-Be bond order of two. Herein, we present the formation of a single E-E (E=Be, Mg) covalent bond in E2 (NHBMe )2 (E=Be, Mg; NHBMe =(HCNMe )2 B) complexes where E2 is in 3 ∑u + excited state having (nσg + )2 (nσu + )1 ((n+1)σg + )1 (n=2 for Be and n=4 for Mg) valence electron configuration and it forms electron-shared bonding with two NHBMe radicals. The effects of bonding with nσu + and (n+1)σg + orbitals will cancel each other, providing the former E-E bond order as one. Be2 (NHBMe )2 complex is thermochemically stable with respect to possible dissociation channels at room temperature, whereas the two exergonic channels, Mg2 (NHBMe )2 → Mg + Mg(NHBMe )2 and Mg2 (NHBMe )2 → Mg2 + (NHBMe )2 , are kinetically inhibited by a free energy barrier of 15.7 and 18.7 kcal mol-1 , respectively, which would likely to be further enhanced in cases of bulkier substituents attached to the NHB ligands. Therefore, the title complexes are first viable systems which feature a neutral E2 moiety with a single E-E covalent bond.

Literature reports provide ample evidence of the dynamical studies of various fluorophores in different room-temperature ionic liquid (RTIL)-cosolvent mixtures. However, most of the experimental and simulation studies reveal that ∼50% of the spectral relaxation dynamics is fast and cannot be resolved using traditional time correlated single photon counting (TCSPC) measurements. Our group has also investigated the dynamics of a solvatochromic probe coumarin 153 (C153) in a RTIL-cosolvent mixture using a TCSPC setup (S. Sarkar, R. Pramanik, C. Ghatak, P. Setua and N. Sarkar, J. Phys. Chem. B, 2010, 114, 2779-2789). Consequently, a major portion of the solvation dynamics remained undetected and moreover we could not monitor the dynamics beyond 0.4 mole fraction of the cosolvents. Thus in this study, we have rekindled our interest to sufficiently capture the rotational anisotropy and solvation dynamics of C153 beyond 0.4 mole fraction of the cosolvents in the RTIL-cosolvent mixture employing femtosecond fluorescence upconversion measurements. Additionally, we have utilized another RTIL with a higher alkyl chain length and viscosity to obtain a comprehensive and quantitative picture of the role of viscosity on the dynamics of the probe molecule. The most interesting observation of the present work is that the viscosities of different RTIL-cosolvent mixtures can efficiently control the cis-trans isomerization kinetics of the anionic fluorophore merocyanine 540 (MC 540) and the translational diffusion of a hydrophobic probe. The optimization of geometrical structures of [EmimOs]- and [EmimOs]-cosolvent mixtures followed by frequency analyses in both gas and solution phases have been carried out using quantum chemical calculations with the aid of density functional theory (DFT) methods. The computation based on the bond distances, electron densities and non-covalent interactions (NCI) has also been used to investigate the existence of the hydrogen-bond (H-bond). Again to comprehend van der Waals interactions and the conventional hydrogen-bond, the evolution of NCI plots are simulated. Therefore, the detailed experimental and theoretical studies presented in this manuscript lead to the inference that addition of the conventional solvents finely tunes the physicochemical properties of RTILs and broadens their scope of applications in the fields of chemistry and biology.

A DFT-based computational study has been performed on the hydrogenation of CO2, catalyzed by a bridged FLP. Formic acid might be formed in two possible pathways as revealed by this study. In one way, the Lewis basic center of the FLP activates H2, and the Lewis acidic center activates CO2 simultaneously in the first step of the reaction. Alternatively, the Lewis basic center of the FLP activates CO2, and the Lewis acidic center activates H2. The simultaneous activation of CO2 and H2 through single TS is confirmed by NBO analysis. Free energy profiles are also generated for both the possible pathways in solvent phase. It appears from these profiles that the first step, i.e., simultaneous activation of CO2 and H2, is the rate determining for both the reaction pathways. A significant amount of barrier height is reduced in comparison to that in the corresponding uncatalyzed reaction as observed in these profiles. The nature of donor-acceptor interactions present in the transition state geometries is further analyzed by energy decomposition analysis (EDA) methods. The EDA analysis shows that the HOMO of the FLP donates electron density to the LUMO of H2, the HOMO of H2 donates electron density to the LUMO of CO2, and several occupied MOs of CO2 donate electron density to the LUMO of FLP at the TS geometry.

This Review presents the current status of the noble gas (Ng)‐noble metal chemistry, which began in 1977 with the detection of AuNe+ through mass spectroscopy and then grew from 2000 onwards; currently, the field is in a somewhat matured state. On one side, modern quantum chemistry is very effective in providing important insights into the structure, stability, and barrier for the decomposition of Ng compounds and, as a result, a plethora of viable Ng compounds have been predicted. On the other hand. experimental achievement also goes beyond microscopic detection and characterization through spectroscopic techniques and crystal structures at ambient temperature; for example, (AuXe4)2+(Sb2F11 −)2 have also been obtained. The bonding between two noble elements of the periodic table can even reach the covalent limit. The relativistic effect makes gold a very special candidate to form a strong bond with Ng in comparison to copper and silver. Insertion compounds, which are metastable in nature, depending on their kinetic stability, display an even more fascinating bonding situation. The degree of covalency in Ng–M (M=noble metal) bonds of insertion compounds is far larger than that in non‐insertion compounds. In fact, in MNgCN (M=Cu, Ag, Au) molecules, the M−Ng and Ng−C bonds might be represented as classical 2c–2e σ bonds. Therefore, noble metals, particularly gold, provide the opportunity for experimental chemists to obtain sufficiently stable complexes with Ng at room temperature in order to characterize them by using experimental techniques and, with the intriguing bonding situation, to explore them with various computational tools from a theoretical perspective. This field is relatively young and, in the coming years, a lot of advancement is expected experimentally as well as theoretically.

We investigate the underlying principle behind the occurrence of bond stretch isomerism in Be32-, which has not been revealed yet. Various computational studies of the different isomers are carried out at the complete active space self-consistent field (CASSCF) level of theory in addition to the B3LYP level in conjunction with the 6-311++G(d) basis set. The potential energy surfaces linking the different isomers through transition states and conical intersections are investigated at the CASSCF level, connecting various geometrical isomers of Be32-. The linear intermediate of the Be32- cluster is considered to be of profound importance since its excited state is found to be degenerate and undergoing the Renner-Teller effect, producing two triangular bond stretch isomers. Ab initio molecular dynamics simulations based on the Atom Centered Density Matrix Propagation (ADMP) method also further elucidate the phenomenon of isomerization via the linear intermediate. The variation of the global reactivity descriptors and free energy profile along the bond stretch isomerization path is also investigated. The estimated aromatic stabilization energy also corroborates the stability ordering of the bond stretch isomers.

The role of boron–ligand cooperation in activating molecular hydrogen by a set of six frustrated Lewis pair (FLP) systems is explored using density functional theory. The results obtained from thermochemical calculations show that all the studied FLP systems are capable of activating molecular hydrogen as the activation free energies are not too high (17.6–25.6 kcal mol−1). Sulphur based FLP 6 is the most promising one as it results in the smallest activation barrier among the studied sets. For a given FLP, the introduction of an electron donating –NMe2 group at the para position of the pyridine ring somewhat lowers the barrier and enhances the B–X (X = O, N, S) interaction. The B–X bond present within the FLPs plays a crucial role in facilitating the H2 activation process where it gets changed from the B+–X− type of interaction in the FLP to the B ← X dative bond upon H2 activation as understood from the energy decomposition analysis in combination with the natural orbital for chemical valence theory (EDA-NOCV). This mode of operation is termed as boron–ligand cooperation in analogy with the metal–ligand cooperation in transition metal complexes. The EDA-NOCV results obtained at the TS also support an electron transfer model where simultaneous electron transfer takes place from the Lewis basic center (N) of the FLP to σ*(H2) and from σ(H2) to the Lewis acidic center (B) of the FLP, resulting in a weakened H–H bond. The change in the aromaticity of the pyridine rings during the course of H2 activation is also monitored by nucleus independent chemical shift calculations. Finally, the ability of the studied FLP systems to act as hydrogenation catalysts is elucidated by studying the hydrogenation of CO2 to yield formic acid.

Since the last decade, the synthesis of self-healable polymers using Diels–Alder (DA) ‘click’ chemistry has been one of the major focus areas in the chemical community. Reversible covalent DA linkages lead to the synthesis of several materials which can be applicable from the biological to industrial fields. Herein, we report a new type of healable fluorescent polymer material based on an anthracene and 1,2,4-triazoline-3,5-dione (TAD) system which has several advantages over the conventional bismaleimide-based DA reaction. In this case, a reversible addition fragmentation chain-transfer (RAFT) polymerization technique was employed to prepare copolymers of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA). The methacrylate copolymers bearing repeating pendant hydroxyl groups were coupled with anthracyl derivatives, where the aromatic groups acted as the ‘click’ partner to the TAD moiety. The addition of TAD derivatives to the anthracyl-modified copolymers led to the synthesis of an ultrafast cross-linked network under ambient conditions without any need of modular reagents. Rationalization of the ultrafast DA reaction mechanism of the TAD–anthracene system was carried out via density functional theory (DFT) calculations by taking different anthracene and TAD derivatives. Thermoreversible properties and healing characteristics were analyzed by DSC and microscopic analyses.

A density functional theory-based computation has been carried out to reveal the geometrical and electronic structures of Mg2EP (1), where EP is an extended (3.1.3.1) porphyrinoid system. EP is a 2...

The possible interaction of the unprecedented but recently predicted inorganic double-helices made up of lithium and phosphorous (LinPn; n = 7–9) with dihydrogen (H2) molecules is explored via density functional theory-based computations. Because of the large amount of Li → P electron transfer, the Li chain carries a high positive charge, which can be utilized to interact with quite less-reactive elements such as H2. Despite low polarizability of the target species to be bound, these double-helices are found to interact with H2 molecules, having binding energies within a range of 1.7–3.2 kcal/mol per H2 molecule. Further, the periodic calculation with the LiP helix reveals that each Li center binds with two H2 molecules with an average binding energy of 2.5 kcal/mol per H2, and this leads to a 9.6 wt % of H2 uptake. The interactions in Li···H2 are mainly originating from both orbital and electrostatic contributions as reflected in the energy decomposition analysis. However, a global minimum search for H2@...

Minimization of the energy of a molecule is an important research problem in quantum chemistry. The use of appropriate global optimization algorithms for determining the most stable configuration is a matter of active interest, and various efforts have been made toward achieving the same. Instead of using single method-based techniques, a recent method has been developed for constructing new models where particle swarm optimization can be made use of. In the present study, we propose a convolutional neural network (CNN) model for learning and predicting the energy of a system by training geometries of cluster units containing both metal and non-metal atoms, viz. C5, N42−, N64−, Aun (n = 2 − 8) and AunAgm (2 ≤ n + m ≤ 8) clusters as prototype examples. Initially, several random clusters are generated within a given range in the three-dimensional space and their energies determined using the atom-centered density matrix propagation molecular dynamics simulation (ADMP). A CNN model is constructed from this initial set of clusters, which is later used for generating a huge number of systems required while searching for the stable structure, instead of using time-consuming quantum mechanical calculations in an iterative process. While several global optimization algorithms could have been used, we choose to employ particle swarm optimization (PSO) due to its ease of implementation and efficient rate of convergence.

Confinement causes drastic changes in bonding, reactivity and dynamics. Alkali metal atoms are excellent reducing agents due to their low ionization energies. On the other hand, high electron affinity values allow the halogen atoms to behave as powerful oxidizing agents. In this article, we have shown that those properties get changed in a confined environment created by two fullerenes differing in size.

The mechanism of dihydrogen activation has been theoretically investigated by means of DFT calculation. An experimentally synthesized bridged P/B frustrated Lewis pair (FLP) and two designed FLPs are used for this purpose. The model FLPs 2 and 3 are more efficient than FLP 1 for H2 activation as revealed by the thermochemical and kinetic data. A significant amount of electron density is transferred from H2 molecule to the FLPs at the transition states (TSs) during the process of H2 activation, and this is greater at the corresponding TSs of FLPs 2 and 3 than that of FLP 1. The NICS(0) and NICS(1zz) of the boron heterocycle at the FLPs 2 and 3, and at the corresponding TSs and the product geometries of H2 activation demonstrate that the anti-aromatic character of the rings in the FLPs is remarkably reduced at the TSs and finally at the products and that is most likely responsible for enhanced activity of FLPs 2 and 3 by decreasing the activation barrier.

Although the toxicity of beryllium compounds causes impediments in experiments involving them, beryllium chemistry has seen a recent upsurge of interest and considerable progress. Computations play a very important complementary role in analyzing the structure, stability and bonding of these compounds. In this perspective article, we highlighted our contribution to beryllium chemistry which is either completely through theoretical results or sometimes supported by experimental findings. It starts with the smallest 2π aromatic system, Be32-, which also exhibits rare bond-stretch isomerism. Furthermore, its reactivity towards different transformations is mentioned. Because of the ability of beryllium to attain a high ionic potential, the beryllium center in an appropriate situation can act as an excellent Lewis acid which is utilized to bind noble gas (Ng) atoms, carbon monoxide and dinitrogen through donor-acceptor types of interactions. We made several efforts to have strong Ng-Be bonds which led us to NgBeNCN that is recorded to have the strongest Ng-Be bond among the neutral Ng-Be complexes reported so far. Significant dinitrogen activation was also achieved in (NN)2Be(η2-N2) and OCBeNN complexes. In the latter case, a complete cleavage of the N-N bond producing the most stable NBeNCO molecule has occurred. We also found viable M2(NHBMe)2 (M = Be, Mg) complexes having unusual bonding where the interacting fragments are best described as the neutral M2 and (NHBMe)2 but M2 still possesses a single bond. We finally discussed the complex comprising an unusual Be(i) oxidation state, [BeI(cAACAr)2]+˙ and di-ortho-beryllated carbodiphosphorane exhibiting Be⇇C double dative bonds.

The noble gas (Ng) binding ability of a monocationic [(FLP)Au]+ species has been investigated by a computational study. Here, the monocationic [(FLP)Au]+ species is formed by coordination of Au(I) cation with the phosphorous (Lewis base) and the boron (Lewis acid) centers of a frustrated Lewis pair (FLP). The bonds involving Au and P, and Au and B atoms in [(FLP)Au]+ are partially covalent in nature as revealed by Wiberg bond index (WBI) values, electron density analysis and energy decomposition analysis (EDA). The zero point energy corrected bond dissociation energy (D0), enthalpy and free energy changes are computed for the dissociation of Au-Ng bonds to assess the Ng binding ability of [(FLP)Au]+ species. The D0 ranges from 6.0 to 13.3 kcal/mol, which increases from Ar to Rn. Moreover, the dissociation of Au-Ng bonds is endothermic as well as endergonic for Ng = Kr-Rn, whereas the same for Ng = Ar is endothermic but exergonic at room temperature. The partial covalent character of the bonds between Au and Ng atoms is demonstrated by their WBI values and electron density analysis. The Ng atoms get slight positive charges of 0.11–0.23 |e|, which indicates some amount of charge transfer takes place from it. EDA demonstrates that electrostatic and orbital interactions have equal contributions to stabilize the Ng-Au bonds in the [(FLP)AuNg]+ complex.

Noble gas can be no noble in certain situations from the perspective of structure, bonding, and reactivity. These situations could be extreme experimental conditions or others. In this contribution, we systematically investigate the impact of fullerene encapsulation on molecular structure and chemical reactivity of noble gas dimers (Ng2) in a few fullerene molecules. To that end, we consider He2, Ne2, and Ar2 dimers encapsulated in C50, C60, and C70 fullerenes. We unveil that bond distances of Ng2 inside fullerene become substantially smaller and noble gas atoms become more electrophilic. In return, these noble gas dimers make fullerene molecules more nucleophilic. Using analytical tools from density functional theory, conceptual density functional theory, and information-theoretic approach, we appreciate the nature and origin of these structure and reactivity changes. The results and conclusions from this work should provide more new insights from the viewpoint of changing the perspectives of noble gas reactivity.

The effect of substitution in the dodecahedrane (C20 H20 ) cage on bonding in the confined He dimer is analyzed. The HeHe distances inside the halogenated dodecahedrane C20 X20 (X = FBr) cages are found to be less than half of that in the free He dimer. Comparing the equilibrium structure of He2 @C20 H20 with He2 @C20 X20 at ωB97XD/def2-TZVPP level, it is found that the He-He distances are relatively larger in the latter cases indicating the influence of halogen groups on the interaction between the cage and the trapped He pair. The viability of the He2 @C20 X20 complexes is reflected in the presence of a very high activation energy barrier against the thermochemically feasible dissociation process producing free He2 and C20 X20 . Quantum theory of atoms in molecules (QTAIM) approach reveals a partial covalent interaction between He pair.

This paper results from a round table discussion at the CCTC2018 Conference in Changsha City, Hunan, China, in December 2018. It presents a report on the status, prospects, and issues of conceptual density functional theory (CDFT). After a short exposition on the history of CDFT, its fundamentals, philosophy, and successes are highlighted. Then ten issues for reflection on the future of conceptual DFT are formulated and discussed, ending with one or more summarizing statements on the present status of various concepts/principles/practices and proposed directions for future research. The issues include the further analysis of the energy functional, E[N,v], extended to include effects of temperature, solvent, and mechanical forces, basic requirements for physically acceptable response functions as reactivity descriptors, the use of the grand canonical ensemble, the relevance of CDFT for chemical kinetics and thermodynamics, the domain of validity of CDFT-based principles, the combination of CDFT with reaction path calculations, information-theoretic descriptors, and the treatment of excited states and time dependence. The final issue advocates the transition of CDFT from an interpretative to a predictive mode; we believe this is of utmost importance for promoting CDFT as a viable alternative to wave function-based methods for the practicing chemist, a separate issue treated in the final section.

A series of three positional isomers of organic cages namely o-OC, m-OC, and p-OC, have been self-assembled using dynamic covalent chemistry. Their room temperature controlled fabrication with pall...

The crux of quantum chemistry lies in the minimization of energy functional to obtain the optimized geometry of a molecule. This involves formulating the energy minimization task as a global optimization (GO) problem and using an appropriate algorithm for determining the best solution out of a number of feasible solutions. Several new and unconventional algorithms are proposed that augment the efforts toward GO of clusters of atoms using rigorous quantum chemical methods. Among these, swarm intelligence-based nature-inspired metaheuristic algorithms have particularly drawn considerable attention. However, it still has certain drawbacks. In this work, we propose the use of firefly algorithm (FA) in conjunction with density functional theory (DFT)-based calculations for solving the GO problem and establish its superioriority in performance over particle swarm optimization (PSO) through extensive computational studies. Specifically, we show how such a “FA + DFT” approach can be used for GO of Al42− clusters. Each possible structure in the three-dimensional search space is treated as a firefly particle. Starting with an initial pool of particles, newer sets of particles are generated using an evolutionary mechanism, thereby moving toward solutions with particles having “better” structures. This novel approach also enables the possibility of incorporating molecule specific domain knowledge. For example, knowing that Al42− clusters are planar, we can restrict the search space so that only planar structures are explored, thereby achieving faster convergence of the algorithm. As an extension of the current technique, an important correlation between energy stabilization and aromaticity is established.

Solvothermal synthesis of a highly porous metal–organic framework (PMOF) of Cu(II) had been achieved with a bent tetracarboxylate linker, L4− incorporating an –NH2 group in the middle. The design of the linker afforded paddle-wheel secondary building unit (SBU) with metal bound solvent molecules. Upon activation by heating, the overall integrity of the structure remained intact with the result of a PMOF embellished with unsaturated metal centers (UMCs) and free –NH2 groups. This activated PMOF showed adsorption of 6.6% by weight of H2 gas at 77 K and 62 bar and very high 60% by weight of CO2 gas at 298 K and 32 bar. The adsorption/desorption properties of this MOF has been probed theoretically to obtain additional insights into physisorption of these strategically important gases. The binding energy values reveal the willingness of the CO2 and H2 gas molecules to get absorbed in Cu(II)-MOF. Temperature–pressure (T–P) phase diagrams have been generated for both of the gas absorption processes at ωB97x-D/TZVP level of theory. Temperature and pressure regions have been identified where Gibbs free energy is negative that is the absorption process is spontaneous. The ab initio molecular dynamics study reveals that the gas saturated Cu(II)-MOFs are stable. Thus this Cu(II)-MOF can be used as an effective gas storage material.

Density functional theory-based computations are carried out to analyze the electronic structure and stability of B2(MIC)2 complexes, where MIC is a mesoionic carbene, viz., imidazolin-4-ylidenes, pyrazolin-4-ylidene, 1,2,3-triazol-5-ylidene, tetrazol-5-ylidene, and isoxazol-4-ylidene. The structure, stability, and the nature of bonding of these complexes are further compared to those of the previously reported B2(NHC)2 and B2(cAAC)2. A thorough bonding analysis via natural bond order, molecular orbital, and energy decomposition analyses (EDA) in combination with natural orbital for chemical valence (NOCV) reveals that MICs are suitable ligands to stabilize B2 species in its (3)1∑g+ excited state, resulting in an effective B–B bond order of 3. Their high dissociation energy and endergonicity at 298 K for the dissociations L–BB–L → 2 B–L and L–BB–L → BB + 2 L (L = Ligand) indicate their viability at ambient condition. The donor property of MICs is comparable to that of NHCMe. The orbital interaction plays a greater role than the coulombic interaction in forming the B–L bonds. The EDA-NOCV results show that the sum of the orbital energies associated with the (+, +) and (+, −) L→[B2]←L σ-donations is far larger than that of L←[B2]→L π-back donation. It also reveals that cAACMe possesses the largest σ-donation and π-back donation abilities among the studied ligands, and the σ-donation and π-back donation abilities of MICs are comparable to those of NHCMe. Therefore, the present study shows that MICs would also be an excellent choice as ligands to experimentally realize new compounds having a strong B–B triple bond.

The hexagonal and heptagonal holes of B 39 - allow its complexation with a half sandwich complex ECp∗+ (E Si, Ge, Sn, Pb). Structure and the nature of bonding of (η6/7-B39)E(η5-Cp∗) are explored through the density functional theory based computation. (η6-B39)E(η5-Cp∗) isomers are more stable than (η7-B39)E(η5-Cp∗) and the energy difference between these two isomers decreases down the group from Si to Pb. The dissociation path, (η6/7-B39)E(η5-Cp∗) → B 39 - + ECp∗+ is studied. For all E, (η6/7-B39)E(η5-Cp∗) is formed exergonically at 298 K temperature as given by the ΔG values of dissociation path [60.1(Si) to 68.3(Pb) kcal/mol for (η6-B39)E(η5-Cp∗) and 58.3(Si) to 67.8(Pb) kcal/mol for (η7-B39)E(η5-Cp∗)]. The adduct becomes bent around the central E atom when B 39 - gets attached to ECp∗+ and the amount of bending increases gradually down the group from Si to Pb. Bonding analysis of the stable isomer, (η6-B39)E(η5-Cp∗) has been done by natural bonding orbital (NBO) and energy decomposition analyses (EDA). The electron density from B 39 - is transferred to the ECp∗+ moiety as revealed by the NBO analysis. All the complexes are mainly stabilized by the electrostatic and orbital interactions between B 39 - and ECp∗+ fragments as highlighted by the EDA results.

A theoretical investigation of the binding ability of different ligands [L = CO, H2O, H2S, N2, NH3, 1,3-dimethylimidazole (DMI), C2H2 and C2H4] with metal isocyanide and cyanide (MNC and MCN; M = Cu, Ag, Au) compounds has been carried out using quantum chemical computations. In order to analyze the thermochemical stability of these complexes, we have calculated the changes in the related dissociation energies and free energies by considering different possible dissociation pathways (four two-body and one three-body) such as (a) LMCN(/NC) = L + MCN(/NC); (b) LMCN = LM + CN; (c) LMCN = L + M + CN; (d) LMCN = LM+ + CN−; and (e) LMCN = L− + MCN+. The possible dissociation processes are endothermic in nature at room temperature suggesting non-spontaneity at 298 K. Our inspection suggests that MNC have higher binding ability than the MCN compounds in all of the L-bonding cases and both of them follow similar trends as Au > Cu > Ag. The natural bond orbital analysis, topological analysis of the electron density from atoms in molecules technique, and energy decomposition analysis have been carried out to characterize the nature of interaction between L and MCN which shows that the L‐M bonds acquire some degree of covalent character. Furthermore, in order to check the validity of the conceptual DFT-based electronic structure principles like maximum hardness and minimum electrophilicity principles, the change in the relevant global reactivity descriptors like chemical hardness (η), chemical potential (μ), and electrophilicity index (ω) is also studied along the isomerization path, LMNC → LMCN.

The intriguing question of whether it is possible to form a genuine M0–M0 single bond for the M2 species (M = Zn, Cd, Hg) is addressed here. So far, all the bonds reported in the literature are exclusively MI–MI. Herein, we present viable M2(NHBMe)2 (M = Zn, Cd, Hg; NHBMe = (HCNMe)2B) complexes in which the controlled donor–acceptor interaction leads to an M0–M0 single bond. In these complexes, M2 in the 1∑g ground state with the (nσg+)2(nσu+)2 (n = 7, 10 and 14 for M = Zn, Cd and Hg, respectively) valence electron configuration forms donor–acceptor bonding with singlet 2NHBMe ligands where a combined effect of dominant (+,−) σ-backdonation from the antibonding (nσu+)2 orbital of M2 to the 2NHBMe ligands and a somewhat weaker (+,+) σ-donation from the 2NHBMe ligands to the bonding (n + 1)σg+ orbital leads to the unorthodox bonding situation of forming an M–M single bond in the zero oxidation state by eventually nullifying one effect by another. This is an unprecedented situation in the sense that the NHBMe ligand acts as a strong σ-acceptor and a weaker σ-donor. A comparison with the experimentally reported M2(PhDipp)2 complexes reveals the uniqueness of the NHBMe ligand in exhibiting such a bonding scenario. The M2(NHBMe)2 complex is thermochemically viable with respect to possible dissociation channels at room temperature, except for metal extrusion processes, M2(NHBMe)2 → M + M(NHBMe)2 and M2(NHBMe)2 → M2 + (NHBMe)2. Although the latter two processes are exergonic, they are kinetically protected by a high free energy barrier of 26.5–39.5 kcal mol−1. The experimental characterization of M2(PhDipp)2 despite similar exergonic channels reveals such kinetic stability to be enough for the viability of the M2(NHBMe)2 complexes. Furthermore, the ligand exchange reaction considering M2(PhMe)2 as the starting material also turned out to be feasible. Therefore, the M2(NHBMe)2 complexes are the first cases that feature a neutral M2 moiety with a single M0–M0 covalent bond, where M is a Group 12 metal.

Metal acetylides (MCCH, M = Cu, Ag, Au) were already experimentally detected in molecular form. Herein, we investigate the possibility of noble gas (Ng) insertion within the C-H bond of MCCH and their stability is compared with those of the reported MNgCCH and HCCNgH molecules. Our coupled-cluster-level computations show that MCCNgH (Ng = Kr, Xe, Rn) systems are local minima on the corresponding potential energy surfaces, whereas their lighter analogues do not remain in the chemically bound form. Further, their stability is analyzed with respect to all possible dissociation channels. The most favorable dissociation channel leads to the formation of free Ng and MCCH. However, there exists a high free energy barrier (29.3-46.9 kcal/mol) to hinder the dissociation. The other competitive processes against their stability include two-body and three-body neutral dissociation channels, MCCNgH → MCC + NgH and MCCNgH → MCC + Ng + H, respectively, which are slightly exergonic in nature at 298 K for Ng = Kr, Xe and M = Cu, Ag, and for AuCCKrH. However, the Xe analogues for Cu and Ag and AuCCKrH would be viable at a lower temperature. AuCCNgH (Ng = Kr-Rn) molecules are the best candidates for experimental realization, since they have higher dissociation energy values and higher kinetic protection in the case of feasible dissociation channels compared to the Cu and Ag systems. A detailed bonding analysis indicates that the Ng-H bonds are genuine covalent bonds and there is also a substantial covalent character in Ng-C contacts of these molecules. Moreover, the possibility of insertion of two Xe atoms in AuCCH resulting in AuXeCCXeH and the stability of XeAuXeCCXeH are also tested herein.

Chemical reactivity properties such as regioselectivity, electrophilicity and nucleophilicity are important chemical concepts, yet their understanding and quantification are still far from being accomplished. Applying density functional theory (DFT) to appreciate these properties is one route to pursue in the literature. In this work, we present a comparative study to benchmark two approaches in DFT to predict regioselectivity, electrophilicity and nucleophilicity: one with the Hirshfeld charge and the other with the Fukui function. We also examine the impact of 15 different ways to compute atomic charges on the performance of their predictions about these chemical reactivity properties. Our results show that the Hirshfeld charge is able to reliably determine regioselectivity and simultaneously accurately quantify both electrophilicity and nucleophilicity. The Fukui function behaves reasonably well for the prediction of electrophilicity but performs poorly for nucleophilicity. Among all other atomic charges examined in this study, it is only the Voronoi deformation density charge that yields the similar result as the Hirshfeld charge. As the first systematic benchmark study in the literature to compare the two available approaches in DFT about reactivity predictions, this work should fill in the needed knowledge gap and provide an impetus for the future development of chemical reactivity theory using DFT language.

The viability of noble gas axled boron nanowheels Ngn M©B10- (Ng=Ar-Rn; M=Nb, Ta; n=1, 2) is explored by ab initio computations. In the resulting Ng2 -M complexes, the Ng-M-Ng nanorod passes through the center of the B10- ring, providing them with an inverse sandwich-like structure. While in the singly Ng bound analogue, the Ng binding enthalpy Hb at 298 K ranges from 2.5 to 10.6 kcal mol-1 , in doubly Ng bound cases it becomes very low for the Ng2 M©B10- →Ng+NgM©B10- dissociation channel, except for the case of Rn, for which the corresponding Hb values are 3.4 (Nb) and 4.0 kcal mol-1 (Ta). For a given Ng, Ta has slightly higher Ng-binding ability than Nb. The corresponding free-energy changes indicate that these systems, particularly the Xe and Rn complexes, are good candidates for experimental realization in a low-temperature matrix. The Ng-M bonds were found to be covalent in nature, as reflected in their large Wiberg bond indices, formation of a 2c-2e σ orbital between Ng and M centers in natural bond orbital and adaptive natural density partitioning (AdNDP) analyses, and the short Ng-M distances. Energy decomposition analysis and a study on the natural orbitals for chemical valence show that the Ng-M contact is supported mainly by the orbital and electrostatic interactions, with almost equal contributions. Although both the Ng→M σ donation and Ng←M π backdonation play roles in the origin of orbital interaction, the former is significantly dominant over the latter. Further, AdNDP analysis indicates that the doubly aromatic character (both σ and π) in MB10- clusters is not perturbed by the interaction with Ng atoms.

In this letter, a possible reason behind selective host-guest organization in the initial stage of sI methane hydrate nucleation is provided, through density functional theory based calculations. In doing so, we have connected earlier experimental and theoretical observations on the structure and energetics of sI methane hydrate to our findings. Geometry and relative stability of small (H 2 O) 5 and (H 2 O) 6 clusters, presence of CH 4 guest, integrity and cavity radius of (H 2 O) 20 and (H 2 O) 24 , as well as the weak van der Waals type of forces, particularly dispersion interaction, are major factors responsible for initial formation of methane encapsulated dodecahedron cavity over tetrakaidecahedron.

We report a family of systems having a planar pentacoordinate carbon (ppC) based on the next heavier analogue of CAl5+, the ppC system par excellence. Although because of the larger size of Ga, the ppC isomer is not even a local minimum in CGa5+, a single isoelectronic substitution of Ga by smaller sized Be maximizes the bonding in the ppC form. Retaining the 18 valence electron rule, the global minimum structures of CGa4Be, CGa3Be2−, CGa2Be32−, and CGaBe43− clusters and their corresponding lithium salts have a ppC.

The efficacy of B40 borospherene to act as a host for noble gas atoms is explored via density functional theory based computations. Although the Ng@B40 complexes are thermochemically unstable with respect to dissociation into free Ng and B40, it does not rule out their viability as all the systems possess a high activation free energy barrier (84.7-206.3 kcal mol-1). Therefore, once they are formed, it is hard to take out the Ng atom. Two Ng atoms can also be incorporated within B40 for the lighter Ng atoms (He and Ne). In fact, the destabilization offered by the encapsulation of one and two He atoms and one Ne atom inside B40 is significantly less than that in experimentally synthesized He@C20H20, highlighting their greater possibility for synthesis. Although Ar2 and Kr2 encapsulated B40 systems are very much destabilized by the repulsive interaction between Ng2 and B40, an inspection of the bonding situation reveals that the confinement can even induce some degree of covalent interaction between two otherwise non-bonded Ng atoms. Ng atoms transfer electrons towards B40 which is smaller for lighter Ng atoms and gradually increases along He to Rn. Even if the electrostatic interaction between Ng and B40 is the most predominant term in these systems, the extent of the orbital interaction is also considerable. However, the very large Pauli repulsion counterbalances the attractive interaction, eventually turning the interaction repulsive in nature. Ng@B40 also shows dynamical behaviour involving continuous exchange between hexagonal and heptagonal holes, similar to the host cage, as understood from the very little variation in the activation barrier because of the Ng encapsulation. Furthermore, sandwich complexes like [(η5-C5Me5)Fe(η6-B40)]+ and [(η5-C5Me5)Fe(η7-B40)]+ are noted to be viable with the latter being slightly more stable than the former. The encapsulation of Xe slightly improves the dissociation energy associated with the decomposition into Xe@B40 and [Fe(η5-C5Me5)]+ compared to that in the bare one.

The viability of sequestering gas molecules (CO, NO, CO2 , NO2 , N2 O, O2 , O3 , H2 O, NH3 , H2 , CH3 OH, CH3 F, C2 H5 F, C2 H2 , C2 H4 , HCN, and SO2 ) on the Al12 Be cluster is investigated by carrying out density functional theory based computations. Thermochemical as well as energetic considerations suggest that Al12 Be cluster adsorbs the chosen gas molecules in a favorable fashion. The gas molecules attain an activated state on getting adsorbed on the metal cluster as vindicated by Atoms-in-Molecule analysis. The possibility of CO oxidation, dissociative addition of CH3 F and C2 H5 F, NH bond decomposition in NH3 , dissociation of NO, and hydrogenation of C2 H2 reactions on Al12 Be cluster has been investigated. Results indicate that all the reactions take place in a thermodynamically favorable way at 298.15 K and one atmospheric pressure. The first five reactions aforementioned are kinetically favorable also and therefore are amenable to ambient temperature and pressure conditions. © 2017 Wiley Periodicals, Inc.

The activation of allene by a five-membered P/B frustrated Lewis pair (FLP) has been explored by DFT based computational study. It reveals the addition of allene to the FLP takes place via two thermodynamically favorable path. But, the attack of the P center of the FLP to the middle carbon of allene is kinetically more preferable. The reaction is further analysed by taking methyl-allene and cyano-allene and which produce four thermodynamically favorable regioisomers. However the attack of the P center of the FLP to the middle carbon is kinetically more preferable. The mechanism of the reactions are carefully analysed.

Two empirical formulae for estimating the standard entropies of some inorganic ionic solids are proposed. Linear relations are suggested between the standard entropy and the cube root of the formula unit volume as well as the cube root of the diamagnetic susceptibility, building a bridge between conceptual density functional theory and solid state chemistry. It is noted that the stabilities of inorganic ionic crystals are closely related to their molar diamagnetic susceptibilities. The suggested correlation provides a connection between the maximum entropy and minimum magnetizability principles.

The impact of geometrical confinement on the thermodynamic as well as kinetic aspects of a model cycloaddition reaction in between 1, 3 butadiene and ethylene have been investigated by carrying out density functional theory based calculations. To this end, two organic hosts, ExBox+4 and Cucurbit[7]uril (CB[7]) have been utilized to impose the effect of confinement on the reactants, transition state (TS) and product involved in the reaction. Results suggest that the shape of the host and thereby the nature of confining regime dictates the thermodynamic outcome of the studied reaction. The reaction becomes thermodynamically more spontaneous inside CB[7] as compared to ExBox+4 and that in the 'unconfined' gaseous state. Also the rate constant associated with the reaction increases manifold inside CB[7]. Atoms-in a-Molecule, non-covalent interaction, natural bond orbital as well as energy decomposition analyses suggest that the close geometrical proximity of the reactants inside CB[7] as well as extra stabilization of the TS in the encapsulated state may dictate the outcome.

The theoretical calculation at the M05-2X/6-311+G(d,p) level reveals that the B–B bond length in [N4-B2-N4]2− system (1.506 A) is slightly smaller than that of typical B=B bond in B2H2 (1.518 A). These systems interact with each M+ (M = Li, Na, K) ion very strongly with a binding energy of 213.5 (Li), 195.2 (Na) and 180.3 (K) kcal/mol. Additionally, the relief of the Coulomb repulsion due to the presence of counter-ion, M+, the B–B bond contracts to 1.484–1.488 A in [N4-B2-N4]M2. We have further extended our study to [N4-B2-N4-B2-N4]4− and [N4-B2-N4-B2-N4-B2-N4]6− systems. The B–B bond length is found to be 1.496 A in the former case, whereas the same is found to be 1.493 A and 1.508 A, respectively, for the two B–B bonds present in the latter one. The M + counter-ions stabilize such negatively charged systems and thus, create a possibility to design a long 1-D nanowire. Their utilities as probable hydrogen and noble gas (Ng) binding templates are explored taking [N4-B2-N4-B2-N4]Li4 system as a reference. It is found that each Li center binds with three H2 molecules with an average binding energy of 2.1 kcal/mol, whereas each Ng (Ar–Rn) atom interacts with Li center having a binding energy of 1.8–2.1 kcal/mol. The H2 molecules interact with Li centers mainly through equal contribution from orbital and electrostatic interaction, whereas the orbital interaction is found to be major term (ca. 51–58%) in Ng-Li interaction followed by dispersion (ca. 24–27%) and electrostatic interaction (ca. 17–24%).

The viability of a series of small gas molecules (H2, N2, CO, CO2, H2O, H2S, C2H2, CH4, CH3Cl, C2H4, and C2H6) bound [M-(bipy)]+ (bipy = bipyridyl; M = Cu, Ag, Au) complexes is investigated at the PBE0/cc-pVTZ/cc-pVTZ-PP level with a special emphasis on the possible bond activation within the bound ligands. While the bond dissociation energy, enthalpy change, and free energy change are computed to show the stability of the complexes with respect to the dissociation into [M-(bipy)]+ and free gas molecule (L), natural bond orbital, electron density, and energy decomposition analyses in conjunction with natural orbitals for chemical valence are carried out to characterize the nature of L–M bonds. For a given L, the L binding ability is the highest for Au followed by Cu and Ag complexes, except for quite loosely bound CO2. For all ligand cases, the dissociation processes from the respective bound complexes are endergonic in nature at room temperature, except for the H2-, CH4-, and C2H6-bound Ag complexes and ...

Structures, bonding, and stability of half-sandwich complexes with general formula, NgMCp+ (Ng = He–Rn, M = Be–Ba, Cp = η5-C5H5) are analyzed through ab initio computation. MCp+ complexes possess remarkable Ng binding ability, particularly for M = Be and Mg. While for Ar–Rn bound analogues the bond dissociation energy in the former complex ranges within 17.5–28.0 kcal mol–1, it becomes 10.4–18.7 kcal mol–1 in the latter complex. In fact, BeCp+ is able to form a strong bond with the two most inert elements, He and Ne. Although the Ng binding ability of MCp+ gradually diminishes in moving from Be to Ba, the corresponding free energy change values show that Kr–Rn bound complexes involving the heavier congeners of Mg would remain in the bound state avoiding dissociation into Ng and MCp+. The nature of the Ng–M bond is characterized by natural bond orbital, electron density and energy decomposition analyses in conjunction with the natural orbital for chemical valence (EDA-NOCV) analysis. While the electron den...

Strong binding of carbon monoxide (CO) and dinitrogen (N2) by MB12– (M = Co, Rh, Ir) clusters results in a spinning umbrella-like structure. For OCMB12– and NNMB12– complexes, the bond dissociation energy values range within 50.3–67.7 kcal/mol and 25.9–35.7 kcal/mol, respectively, with the maximum value obtained in Ir followed by that in Co and Rh analogues. COMB12– complex is significantly less stable than the corresponding C-side bonded isomer. The associated dissociation processes for OCMB12– and NNMB12– into CO or N2 and MB12– are highly endergonic in nature at 298 K, implying their high thermochemical stability with respect to dissociation. In OCMB12– and NNMB12– complexes, the C–O and N–N bonds are found to be elongated by 0.022–0.035 A along with a large red-shift in the corresponding stretching frequencies, highlighting the occurrence of bond activation therein toward further reactivity due to complexation. The obtained red-shift is explained by the dominance of L←M π-back-donation (L = CO, OC, NN...

The interaction among E3 (E=Si, Ge, Sn) clusters and different ligands (L) encompassing five carbon-based donors (cyclic (alkyl)(amino)carbene (cAAC), N-heterocyclic carbene (NHC), saturated NHC (SNHC), mesoionic carbenes (MIC1, and MIC2)), two nitrogen-based donors (trimethylamine and pyridine), and two phosphorous-based donors (phosphinine and trimethylphosphine) in E3(L)3 complexes is explored through DFT computations. Although all carbenes form very strong bonds with E3 clusters, cAAC makes the strongest bond with Si3 and Ge3 clusters, and MIC1 with the Sn3 cluster. Nevertheless, other ligand-bound complexes are also viable at room temperature. This finding indicates that experimentalists may make use of them to synthesize the desired clusters based on precursor availability. The nature of the interaction in E−L bonds is analyzed through natural bond orbital analysis; energy decomposition analysis, in combination with the natural orbital for chemical valence; and adaptive natural density partitioning analysis. The L→E σ-donation and L←E π-back-donation play important roles in making contacts between L and E3 clusters favorable; where the former is significantly more dominant over the latter.

A porous Cu(II)-MOF shows an adsorption of 6.6 wt% of H2 at 77 K and 62 bar and a very high 60 wt% of CO2 at 298 K and 32 bar. When air is bubbled into a suspension of the activated MOF in the presence of different epoxides at room temperature, the CO2 in air is readily converted into the corresponding cyclic carbonates.

The impact of functionalization as well as guest encapsulation on the optoelectronic properties of the ExBox+4 moiety has been investigated with the aid of density functional theory (DFT) based calculations. To this end, three functionalized variants of the ExBox+4 moiety have been modelled in silico, viz. NH2-ExBox+4-F, CN-ExBox+4-NH2 and NO2-ExBox+4-NH2, whereas coronene (Cor), B-doped coronene (BCor), N-doped coronene (NCor), tetrathiafulvalene (TTF), biphenyl (BiPh), tetracyanoethylene (TCNE) and tetracyanoquinodimethane (TCNQ) molecules have been employed as guests. The results indicate that as a result of functionalization, the ExBox+4 moiety can exhibit tangible non-linear optical (NLO) response properties as vindicated by the first static hyperpolarizability (β). As a result of guest encapsulation, significant variation in the optoelectronic properties of the chosen hosts takes place. BCor/TCNQ/NCor molecules enhance the NLO activity of the hosts while TTF/TCNE suppresses the same. In particular, NCor@host moieties demonstrate very high β values at the static field limit. Time dependent DFT results suggest that in general, the ability of the guest in tuning the transition energy associated with the pivotal electronic transitions of the host plays the dominant role in the observed variation in β. In addition, BCor/NCor@host moieties demonstrate broadband optical absorption capability thereby elucidating the possibility of deriving multi-purpose optoelectronic features such as NLO activity as well as utility in photovoltaic systems. Thermochemical results suggest that all the guest@host systems are stable at 298.15 K. Non-covalent and electrostatic binding forces stabilize the studied systems.

The selectivity of cucurbit[7]uril (CB[7]) towards adsorbing a series of 14 molecules encompassing four hydrocarbons (C2H2, C2H4, C2H6, and CH4), diatomic molecules of halogens (F2 and Cl2), nitrogen oxides (NO2 and NO), carbon oxides (CO2 and CO), SO2, H2S, N2, and H2 is explored via a density functional theory based study. CB[7] is noted to have high selectivity towards adsorbing SO2 over the other considered molecules, highlighting its probable utility to separate SO2 from flue gas or other gas mixtures containing these molecules. The nature of bonding is deciphered via the computations of non-covalent interaction indices and energy decomposition analysis. Although in all cases the dispersion interaction turns out to be the most dominating contributor in stabilizing these complexes, the electrostatic contribution is also considerable. In fact, the combined effect of these two energy terms in SO2@CB[7] is responsible for the obtained selectivity.