In Silico Design and Characterization of a New Molecular Electride: Li@Calix[3]Pyrrole.

Electrides, in which anionic electrons are localized independently of the atoms in the compound, have shown promise, especially as catalysts and optoelectronic materials. Here, we present a new computationally designed molecular electride, Li@calix[3]pyrrole (Li@C3P). Electron density and electron localization function analyses unequivocally confirm the existence of localized electride electron density, outside the system, independent of any specific atoms. Non-covalent interaction plots further validate the character of the isolated localized electron, suggesting that the system can be accurately represented by Li+@calix[3]pyrrole ⋅ e-, denoting its distinct charge separation. The remarkable non-linear optical properties of Li@C3P, including average polarizability, α ‾ ${\bar{\alpha }}$ =412.4 au, first hyperpolarizability, ß=4.46×104 au, and second hyperpolarizability, γ ∥ ${{\gamma }_{\parallel }}$ =18.40×106 au, are unparalleled in the previously reported and similar Li@C4P molecular electride. Furthermore, energy decomposition analysis in combination with natural orbital for chemical valence theory sheds light on the mechanism of electron density transfer from Li to the C3P cage, yielding the charge-separated Li@C3P complex. In addition to the electron transfer, a key factor to its electride nature is the electronic structure of the CnP cage, which has its lowest unoccupied molecular orbital located in the void adjacent to the N-H groups at the back of the bowl-shaped CnP cage.

Defect-Free Synthesis of a Fully π-Conjugated Helical Ladder Polymer and Resolution into a Pair of Enantiomeric Helical Ladders.

Fully π-conjugated ladder polymers with a spiral geometry represent a new class of helical polymers with great potential for organic nanodevices, but there is no precedent for an optically active helical ladder polymer totally composed of achiral units. We now report the defect-free synthesis and resolution of a fully π-conjugated helical ladder polymer with a rigid helical cavity, which has been achieved by quantitative and chemoselective acid-promoted alkyne benzannulations of a rationally designed, random-coil achiral polymer followed by chromatographic enantioseparation. Because of a sufficiently high helix-inversion barrier, the isolated excess one-handed helical ladder polymer with a degree of polymerization of more than 15 showed a strong circular dichroism with a dissymmetry factor of up to 1.7×10-2 and is thermally stable, maintaining its optical activity in solution even at 100 °C, as well-supported by molecular dynamics simulation.

One-Handed Helical Tubular Ladder Polymers for Chromatographic Enantioseparation.

Defect-free one-handed contracted helical tubular ladder polymers with a π-electron-rich cylindrical helical cavity were synthesized by alkyne benzannulations of the random-coil precursor polymers containing 6,6'-linked-1,1'-spirobiindane-7,7'-diol-based chiral monomer units. The resulting tightly-twisted helical tubular ladder polymers showed remarkably high enantioseparation abilities toward a variety of chiral hydrophobic aromatics with point, axial, and planar chiralities. The random-coil precursor polymer and analogous rigid-rod extended helical ribbon-like ladder polymer with no internal helical cavity exhibited no resolution abilities. The molecular dynamics simulations suggested that the π-electron-rich cylindrical helical cavity formed in the tightly-twisted tubular helical ladder structures is of key importance for producing the highly-enantioseparation ability, by which chiral aromatics can be enantioselectively encapsulated by specific π-π and/or hydrophobic interactions.

Chiral Calix[3]pyrrole Derivatives: Synthesis, Racemization Kinetics, and Ring Expansion to Calix[9]- and Calix[12]pyrrole Analogues.

Chiral pyrrolic macrocycles continue to attract interest. However, their molecular design remains challenging. Here, we report a calixpyrrole-based chiral macrocyclic system, calix[1]furan[1]pyrrole[1]thiophene (1), synthesized from an oligoketone. Macrocycle 1 adopts a partial cone conformation in the solid state, and undergoes racemization via ring inversion. Molecular dynamics simulations revealed that inversion of the thiophene is the rate determining step. Pyrrole N-methylation suppressed racemization and permitted chiral resolution. Enantioselective N-methylation also occurred in the presence of a chiral ammonium salt, although the stereoselectivity is modest. A unique feature of 1 is that it acts as a useful synthetic precursor to yield several calix[n]furan[n]pyrrole[n]thiophene products (n=2-4), including a calix[12]pyrrole analogue that to our knowledge constitutes the largest calix[n]pyrrole-like species to be structurally characterized.

Molecular Electrides: An In Silico Perspective.

Electrides are defined as the ionic compounds where the electron(s) serves as an anion. These electron(s) is (are) not bound to any atoms, bonds, or molecules but are rather localized into the space, crystal voids, or interlayer between two molecular slabs. There are three major categories of electrides, known as organic electrides, inorganic electrides, and molecular electrides. The computational techniques have proven as a great tool to provide emphasis on the electride materials. In this review, we have focused on the computational methodologies and criteria that help to characterize molecular electrides. A detailed account of the computational methods and basis sets applicable for molecular electrides have been discussed along with their limitations in this field. The main criterion for the identification of the electrides has also been discussed thoroughly with proper examples. The molecular electrides presented here have been justified with all the required criteria that support and proved their electride characteristics. We have also presented few systems which have similar properties but are not considered as molecular electrides. Moreover, the applicability of the electrides in catalytic processes have also been presented.

Encapsulation of Mg2 inside a C60 cage forms an electride.

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 Mg2 2+ 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 Mg2 2+ 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 [Mg2 2+ ] and [C60 2- ] represent the bonding pattern in the Mg2 @C60 system. The designed endohedrally encapsulated system behaves as an electride.

Two Closely Related Zn(II)-MOFs for Their Large Difference in CO2 Uptake Capacities and Selective CO2 Sorption.

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 constructed through the self-assembly of isomeric N,N'-donor spacers (3,3'-L = 3,3'-azobispyridine and 4,4'-L = 4,4'-azobispyridine) with organic ligand 4,4'-sulfonyldibenzoic acid (SDBH2) and Zn(NO3)2·6H2O (G represents disordered solvent molecules). Single-crystal X-ray diffraction studies reveal the 2D structure with sql topology for both MOFs. However, the subtle change in positions of coordinating N atoms of spacers makes IITKGP-13A noninterpenetrated, while IITKGP-13B bears a 2-fold interpenetrated structure. IITKGP-13A exhibits higher uptake of CO2 over CH4 and N2 with high IAST selectivities for mixed CO2/CH4 (50:50, biogas) and CO2/N2 (15:85, flue gas) gas systems. In contrast, IITKGP-13B takes up very low amount of CO2 gas (0.4 mmol g-1) compared to IITKGP-13A (1.65 mmol g-1) at 295 K. Density functional theory (DFT)-based electronic structure calculations have been performed to explain the origin of the large differences in CO2 uptake capacity between the two MOFs at the atomistic level. The results show that the value of the change in enthalpy (ΔH) at 298 K temperature and 1 bar pressure for the CO2 adsorption is more negative in IITKGP-13A as compared to that in IITKGP-13B, thus indicating that CO2 molecules are more favored to get adsorbed in IITKGP-13A than in IITKGP-13B. The computed values for the Gibbs' free energy change (ΔG) for the CO2 adsorption are positive for both of the MOFs, but a higher value is observed for the IITKGP-13B. The noncovalent types of interactions are the main contribution toward the attractive energies between the host MOF frameworks and guest CO2 molecules, which has been studied with the help of energy decomposition analysis (EDA).

Metal-Organic Frameworks of Cu(II) Constructed from Functionalized Ligands for High Capacity H2 and CO2 Gas Adsorption and Catalytic Studies.

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 ligands incorporating different substituents. The MOFs showed high porosity (BET surface area, 2191 m2/g for 1Me and 1402 m2/g for 1ipr). For 1Me, very high CO2 adsorption (98.5 wt % at 195 K, 42.9 wt % at 273 K, 23.3 wt % at 298 K) at 1 bar was found, while for 1ipr, it was significantly less (14.3 wt % at 298 K and 1 bar, 54.4 wt % at 298 K at 50 bar). 1Me exhibited H2 uptake of 3.2 wt % at 77 K and 1 bar of pressure, which compares well with other benchmark MOFs. For 1ipr, the H2 uptake was found to be 2.54 wt % under similar experimental conditions. The significant adsorption of H2 and CO2 for 1Me could be due to the presence of micropores as well as unsaturated metal sites in these MOFs besides the presence of substituents that interact with the gas molecules. The experimental adsorption behavior of the MOFs could be justified by theoretical calculations. Additionally, catalytic conversions of CO2 and CS2 into useful chemicals like cyclic carbonates, cyclic trithiocarbonates, and cyclic dithiocarbonates could be achieved.

Intriguing structural, bonding and reactivity features in some beryllium containing complexes.

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.

How Far Can One Push the Noble Gases Towards Bonding?: A Personal Account.

Noble gases (Ngs) are the least reactive elements in the periodic table towards chemical bond formation when compared with other elements because of their completely filled valence electronic configuration. Very often, extreme conditions like low temperatures, high pressures and very reactive reagents are required for them to form meaningful chemical bonds with other elements. In this personal account, we summarize our works to date on Ng complexes where we attempted to theoretically predict viable Ng complexes having strong bonding to synthesize them under close to ambient conditions. Our works cover three different types of Ng complexes, viz., non-insertion of NgXY type, insertion of XNgY type and Ng encapsulated cage complexes where X and Y can represent any atom or group of atoms. While the first category of Ng complexes can be thermochemically stable at a certain temperature depending on the strength of the Ng-X bond, the latter two categories are kinetically stable, and therefore, their viability and the corresponding conditions depend on the size of the activation barrier associated with the release of Ng atom(s). Our major focus was devoted to understand the bonding situation in these complexes by employing the available state-of-the-art theoretic tools like natural bond orbital, electron density, and energy decomposition analyses in combination with the natural orbital for chemical valence theory. Intriguingly, these three types of complexes represent three different types of bonding scenarios. In NgXY, the strength of the donor-acceptor Ng→XY interaction depends on the polarizing power of binding the X center to draw the rather rigid electron density of Ng towards itself, and sometimes involvement of such orbitals becomes large enough, particularly for heavier Ng elements, to consider them as covalent bonds. On the other hand, in most of the XNgY cases, Ng forms an electron-shared covalent bond with X while interacting electrostatically with Y representing itself as [XNg]+Y-. Nevertheless, in some of the rare cases like NCNgNSi, both the C-Ng and Ng-N bonds can be represented as electron-shared covalent bonds. On the other hand, a cage host is an excellent moiety to examine the limits that can be pushed to attain bonding between two Ng atoms (even for He) at high pressure. The confinement effect by a small cage-like B12N12 can even induce some covalent interaction within two He atoms in the He2@B12N12 complex.

Unprecedented Bonding Situation in Viable E2 (NHBMe )2 (E=Be, Mg; NHBMe =(HCNMe )2 B) Complexes: Neutral E2 Forms a Single E-E Covalent Bond.

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.

Boron Nanowheels with Axles Containing Noble Gas Atoms: Viable Noble Gas Bound M©B10- Clusters (M=Nb, Ta).

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.

Ligand-Supported E3 Clusters (E=Si-Sn).

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.

The strongest CO binding and the highest C-O stretching frequency.

A coupled-cluster study is performed on CO bound BeY complexes (Y = O, CO3, SO4, NH, NCN, and NBO) to understand the effect of attached ligands (Y) on the CO binding ability and C-O stretching frequency (νCO). Herein, we report that BeNCN has the highest CO binding ability (via both C- and O-side binding) among the studied neutral Be-based clusters, whereas OCBeSO4 has the highest νCO among the neutral carbonyls. The nature and extent of shift in νCO compared to free CO are explained in terms of change in polarization in the bonding orbitals of CO and relative contribution from OC→BeY or CO→BeY σ-donation, and OC←BeY or CO←BeY π-back-donation. The largest blue-shift in OCBeSO4 and the largest red-shift in COBeNH are consequences of the smallest OC←BeSO4 π-back-donation and the largest CO←BeNH π-back-donation, respectively.

NgMCp+: Noble Gas Bound Half-Sandwich Complexes (Ng = He-Rn, M = Be-Ba, and Cp = η5-C5H5).

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 density analysis reveals that Ng-Be (Ng = Kr, Xe, Rn) and Ng-Mg (Ng = Xe, Rn) bonds are partly covalent in nature, the orbital interaction (ΔEorb) is found to be the most important term in the Ng-M attractive energy as revealed by the EDA-NOCV. For all Ngs, the major contribution toward the ΔEorb energy term originates from Ng→MCp+ σ-donation. Additionally, CpBeNgF (Ng = Xe, Rn) and CpNgF (Ng = Kr-Rn) are found to be viable systems with kinetic protection for the exergonic dissociation channels, CpBeNgF → Ng + CpBeF and CpNgF → Ng + CpF, respectively, where the activation free energy barrier in the latter systems (24.1-34.7 kcal mol-1) is significantly larger than that in the former ones (6.6-8.9 kcal mol-1). CpNgF (Ng = Kr-Rn) complexes are predicted to be stable even above 300 K, whereas CpBeNgF (Ng = Xe, Rn) would be viable up to ∼100 K. While the F-Ng bonds are ionic in nature, the Ng-Be and Ng-C bonds in these complexes have significant covalent character.

A Spinning Umbrella: Carbon Monoxide and Dinitrogen Bound MB12- Clusters (M = Co, Rh, Ir).

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 Å 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) over L→M σ-donation. The binding of L enhances the energy barrier for the rotation of the inner B3 unit within the outer B9 ring by 0.4-1.8 kcal/mol, which can be explained by a reduction in the distance of the longest bond between inner B3 and outer B9 rings upon complexation. A good correlation is found between the change in rotational barrier relative to that in MB12- and the energy associated with the L→M σ-donation. Born-Oppenheimer molecular dynamics simulations further support that the M-L bonds in the studied systems are kinetically stable enough to retain the original forms during the internal rotation of inner B3 unit.

σ-Aromatic cyclic M3(+) (M = Cu, Ag, Au) clusters and their complexation with dimethyl imidazol-2-ylidene, pyridine, isoxazole, furan, noble gases and carbon monoxide.

The σ-aromaticity of M3(+) (M = Cu, Ag, Au) is analyzed and compared with that of Li3(+) and a prototype σ-aromatic system, H3(+). Ligands (L) like dimethyl imidazol-2-ylidene, pyridine, isoxazole and furan are employed to stabilize these monocationic M3(+) clusters. They all bind M3(+) with favorable interaction energy. Dimethyl imidazol-2-ylidene forms the strongest bond with M3(+) followed by pyridine, isoxazole and furan. Electrostatic contribution is considerably more than that of orbital contribution in these M-L bonds. The orbital interaction arises from both L → M σ donation and L ← M back donation. M3(+) clusters also bind noble gas atoms and carbon monoxide effectively. In general, among the studied systems Au3(+) binds a given L most strongly followed by Cu3(+) and Ag3(+). Computation of the nucleus-independent chemical shift (NICS) and its different extensions like the NICS-rate and NICS in-plane component vs. NICS out-of-plane component shows that the σ-aromaticity in L bound M3(+) increases compared to that of bare clusters. The aromaticity in pyridine, isoxazole and furan bound Au3(+) complexes is quite comparable with that in the recently synthesized Zn3(C5(CH3)5)3(+). The energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital also increases upon binding with L. The blue-shift and red-shift in the C-O stretching frequency of M3(CO)3(+) and M3(OC)3(+), respectively, are analyzed through reverse polarization of the σ- and π-orbitals of CO as well as the relative amount of OC → M σ donation and M → CO π back donation. The electron density analysis is also performed to gain further insight into the nature of interaction.

Statistical Significance of the Maximum Hardness Principle Applied to Some Selected Chemical Reactions.

The validity of the maximum hardness principle (MHP) is tested in the cases of 50 chemical reactions, most of which are organic in nature and exhibit anomeric effect. To explore the effect of the level of theory on the validity of MHP in an exothermic reaction, B3LYP/6-311++G(2df,3pd) and LC-BLYP/6-311++G(2df,3pd) (def2-QZVP for iodine and mercury) levels are employed. Different approximations like the geometric mean of hardness and combined hardness are considered in case there are multiple reactants and/or products. It is observed that, based on the geometric mean of hardness, while 82% of the studied reactions obey the MHP at the B3LYP level, 84% of the reactions follow this rule at the LC-BLYP level. Most of the reactions possess the hardest species on the product side. A 50% null hypothesis is rejected at a 1% level of significance.

A coupled-cluster study on the noble gas binding ability of metal cyanides versus metal halides (metal = Cu, Ag, Au).

A coupled-cluster study is carried out to investigate the efficacy of metal(I) cyanide (MCN; M = Cu, Ag, Au) compounds to bind with noble gas (Ng) atoms. The M-Ng bond dissociation energy, enthalpy change, and Gibbs free energy change for the dissociation processes producing Ng and MCN are computed to assess the stability of NgMCN compounds. The Ng binding ability of MCN is then compared with the experimentally detected NgMX (X = F, Cl, Br) compounds. While CuCN and AgCN have larger Ng binding ability than those of MCl and MBr (M = Cu, Ag), AuCN shows larger efficacy toward bond formation with Ng than that of AuBr. Natural bond orbital analysis, energy decomposition analysis in conjunction with the natural orbital for chemical valence theory, and the topological analysis of the electron density are performed to understand the nature of interaction occurring in between Ng and MCN. The Ng-M bonds in NgMCN are found comprise an almost equal contribution from covalent and electrostatic types of interactions. The different electron density descriptors also reveal the partial covalent character in the concerned bonds.

Comparative Study on the Noble-Gas Binding Ability of BeX Clusters (X = SO4, CO3, O).

Ab initio computations are carried out to assess the noble gas (Ng) binding capability of BeSO4 cluster. We have further compared the stability of NgBeSO4 with that of the recently detected NgBeCO3 cluster. The Ng-Be bond in NgBeCO3 is somewhat weaker than that in NgBeO cluster. In NgBeSO4, the Ng-Be bond is found to be stronger compared with not only the Ng-Be bond in NgBeCO3 but also that in NgBeO, except the He case. The Ar-Rn-bound BeSO4 analogues are viable even at room temperature. The Wiberg bond indices of Be-Ng bonds and the degree of electron transfer from Ng to Be are somewhat larger in NgBeSO4 than those in NgBeCO3 and NgBeO. Electron density and energy decomposition analyses are performed in search of the nature of interaction in the Be-Ng bond in NgBeSO4. The orbital energy term (ΔE(orb)) contributes the maximum (ca. 80-90%) to the total attraction energy. The Ar/Kr/Xe/Rn-Be bonds in NgBeSO4 could be of partial covalent type with a gradual increase in covalency along Ar to Rn.