Halogen-π Interactions between Benzene and X/CX (X = Cl, Br): Assessment of Various Density Functionals with Respect to CCSD(T).

Various types of interactions between halogen (X) and π moiety (X-π interaction) including halogen bonding play important roles in forming the structures of biological, supramolecular, and nanomaterial systems containing halogens and aromatic rings. Furthermore, halogen molecules such as X and CX (X = Cl/Br) can be intercalated in graphite and bilayer graphene for doping and graphene functionalization/modification. Due to the X-π interactions, though recently highly studied, their structures are still hardly predictable.

Halides with Fifteen Aliphatic C-H···Anion Interaction Sites.

Since the aliphatic C-H···anion interaction is relatively weak, anion binding using hydrophobic aliphatic C-H (Cali-H) groups has generally been considered not possible without the presence of additional binding sites that contain stronger interactions to the anion. Herein, we report X-ray structures of organic crystals that feature a chloride anion bound exclusively by hydrophobic Cali-H groups. An X-ray structure of imidazolium-based scaffolds using Cali-H···A(-) interactions (A(-) = anion) shows that a halide anion is directly interacting with fifteen Cali-H groups (involving eleven hydrogen bonds, two bidentate hydrogen-bond-type binding interactions and two weakly hydrogen-bonding-like binding interactions).

Disulfuric acid dissociated by two water molecules: ab initio and density functional theory calculations.

We have studied geometries, energies and vibrational spectra of disulfuric acid (H2S2O7) and its anion (HS2O7(-)) hydrated by a few water molecules, using density functional theory (M062X) and ab initio theory (SCS-MP2 and CCSD(T)). The most noteworthy result is found in H2S2O7(H2O)2 in which the lowest energy conformer shows deprotonated H2S2O7. Thus, H2S2O7 requires only two water molecules, the fewest number of water molecules for deprotonation among various hydrated monomeric acids reported so far.

Interactions of CO2 with various functional molecules.

The CO2 capturing and sequestration are of importance in environmental science. Understanding of the CO2-interactions with various functional molecules including multi-N-containing superbases and heteroaromatic ring systems is essential for designing novel materials to effectively capture the CO2 gas. These interactions are investigated using density functional theory (DFT) with dispersion correction and high level wave function theory (resolution-of-identity (RI) spin-component-scaling (scs) Möller-Plesset second-order perturbation theory (MP2) and coupled cluster with single, double and perturbative triple excitations (CCSD(T))).

Highly stable CO2/N2 and CO2/CH4 selectivity in hyper-cross-linked heterocyclic porous polymers.

The largest obstacles for landfill/flue gas separation using microporous materials are small adsorption values and low selectivity ratios. This study demonstrates that these adsorption and selectivity challenges can be overcome by utilizing a series of hyper-cross-linked heterocyclic polymer networks. These microporous organic polymers (MOPs) were synthesized in a single step by inexpensive Friedel-Crafts-catalyzed reactions using dimethoxymethane as an external linker.

CO capture and conversion to HOCO radical by ionized water clusters.

The CO molecule can interact with the hydroxyl radical ((•)OH) via either a weak noncovalent interaction or strong covalent bonding. Upon the ionization of neutral water clusters, the resulting water cluster cations produce protonated water clusters and hydroxyl radicals. In this regard, we investigate the interactions of a CO molecule with water dimer and trimer cations using density functional theory (DFT), Möller-Plesset second-order perturbation theory (MP2), and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)].

Dynamics and structural changes of small water clusters on ionization.

Despite utmost importance in understanding water ionization process, reliable theoretical results of structural changes and molecular dynamics (MD) of water clusters on ionization have hardly been reported yet. Here, we investigate the water cations [(H2O)(n = 2-6)(+)] with density functional theory (DFT), Möller-Plesset second-order perturbation theory (MP2), and coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)]. The complete basis set limits of interaction energies at the CCSD(T) level are reported, and the geometrical structures, electronic properties, and infrared spectra are investigated.

Observable structures of small neutral and anionic gold clusters.

Since gold clusters have mostly been studied theoretically by using DFT calculations, more accurate studies are of importance. Thus, small neutral and anionic gold clusters (Au(n) and Au(n)(-) , n = 4-7) were investigated by means of coupled cluster with singles, doubles, and perturbative triple excitations [CCSD(T)] calculations with large basis sets, and some differences between DFT and CCSD(T) results are discussed. Interesting isomeric structures that have dangling atoms were obtained.

Anion Binding by Electron-Deficient Arenes Based on Complementary Geometry and Charge Distribution.

Extended electron-deficient arenes are investigated as potential neutral receptors for polyanions. Anion binds via σ interaction with extended arenes, which are composed solely of C and N ring atoms and CN substituents. As a result, the positive charge on the aromatic C is enhanced, consequently maximizing binding strength.

H2-Binding by Neutral and Multiply Charged Titaniums: Hydrogen Storage Capacity of Titanium Mono- and Dications.

Given that transition metal-hydrogen systems have been studied as a predecessor for hydrogen storage materials, we have investigated the neutral and multiply charged titanium-H2 systems (Ti-H2, Ti(+)-H2, Ti(2+)-H2, Ti(3+)-H2, and Ti(4+)-H2) using density functional theory (DFT) and high-level ab initio calculations, including coupled cluster theory with single, double, and perturbatively triple excitations [CCSD(T)]. These systems show different types of hydrogenation depending on their charged state. The neutral Ti-H2 system shows dihydride structure with covalent interaction where the Ti-H distance is 1.

Structural basis of triclosan resistance.

Triclosan (5-chloro-2-(2,4-dichloro-phenoxy)-phenol, TCL) is a well known inhibitor against enoyl-acyl carrier protein reductase (ENR), an enzyme critical for cell-wall synthesis of bacteria. The inhibitory concentration at 50% inhibition (IC(50)) of TCL against the Escherichia coli ENR is 150nM for wild type (WT), 380, 470 and 68,500nM for Ala, Ser and Val mutants, respectively. To understand this high TCL resistance in the G93V mutant, we obtained the crystal structures of mutated ENRs complexed with TCL and NAD(+).

Structure, Stabilities, Thermodynamic Properties, and IR Spectra of Acetylene Clusters (C2H2)n=2-5.

There are no clear conclusions over the structures of the acetylene clusters. In this regard, we have carried out high-level calculations for acetylene clusters (C2H2)2-5 using dispersion-corrected density functional theory (DFT-D), Møller-Plesset second-order perturbation theory (MP2); and coupled-cluster theory with single, double, and perturbative triple excitations [CCSD(T)] at the complete basis set limit. The lowest energy structure of the acetylene dimer has a T-shaped structure of C2v symmetry, but it is nearly isoenergetic to the displaced stacked structure of C2h symmetry.

Chiral transformation in protonated and deprotonated adipic acids through multistep internal proton transfer.

Protonated and deprotonated adipic acids (PAA: HOOC-(CH(2))(4)--COOH(2) (+) and DAA: HOOC-(CH(2))(4)-COO(-)) have a charged hydrogen bond under the influence of steric constraint due to the molecular skeleton of a circular ring. Despite the similarity between PAA and DAA, it is surprising that the lowest energy structure of PAA is predicted to have (H(2)O..

Comparison of cationic, anionic and neutral hydrogen bonded dimers.

Short Strong Hydrogen Bonds (SSHBs) play an important role in many fields of physics, chemistry and biology. Since it is known that SSHBs exist in many biological systems, the role of hydrogen bonding motifs has been particularly interesting in enzyme catalysis, bio-metabolism, protein folding and proton transport phenomena. To explore the characteristic features of neutral, anionic and cationic hydrogen bonds, we have carried out theoretical studies of diverse homogeneous and heterogeneous hydrogen bonded dimers including water, peroxides, alcohols, ethers, aldehydes, ketones, carboxylic acids, anhydrides, and nitriles.

Rules and trends of metal cation driven hydride-transfer mechanisms in metal amidoboranes.

Group I and II metal amidoboranes have been identified as one of the promising families of materials for efficient H(2) storage. However, the underlying mechanism of the dehydrogenation of these materials is not well understood. Thus, the mechanisms and kinetics of H(2) release in metal amidoboranes are investigated using high level ab initio calculations and kinetic simulations.

Ammonia-water cation and ammonia dimer cation.

We have investigated the structure, interaction energy, electronic properties, and IR spectra of the ammonia-water cation (NH(3)H(2)O)(+) using density functional theory (DFT) and high-level ab initio theory. The ammonia-water cation has three minimum-energy structures of (a) H(2)NH(+)..

Interaction of Benzene with Transition Metal Cations: Theoretical Study of Structures, Energies, and IR Spectra.

The cation-π interactions have been intensively studied. Nevertheless, the interactions of π systems with heavy transition metals and their accurate conformations are not well understood. Here, we theoretically investigate the structures and binding characteristics of transition metal (TM) cations including novel metal cations (TM(n+) = Cu(+), Ag(+), Au(+), Pd(2+), Pt(2+), and Hg(2+)) interacting with benzene (Bz).

Neutral and Anionic Gold Decamers: Planar Structure with Unusual Spatial Charge-Spin Separation.

We have investigated the issue of two-dimensional (2D) versus three-dimensional (3D) structures for neutral-state Au10 and clarified the lowest-energy structure among a few 2D Au10(-) isomers. Though almost all previous works were based on density functional theory (DFT), we here carried out not only extensive DFT calculations but also high levels of ab initio calculations of Möller-Plesset second order perturbation theory (MP2), and coupled cluster theory with single and double excitations (CCSD) including perturbative triple excitations [CCSD(T)]. While DFT favors 2D structures, MP2 and CCSD(T) favor 3D structures for moderate-sized basis sets.

Hydrogen-release mechanisms in lithium amidoboranes.

Alkali-metal amidoboranes have been recently highlighted as materials that satisfy many of the criteria required to make hydrogen-storage media. It is, therefore, crucial for us to understand the dehydrogenation mechanism of these materials for further development towards making successful hydrogen-storage media. In the present study, we attempt to shed light on the mechanisms involved in the loss of one molar equivalent of H(2) from solid lithium amidoboranes by using high-level ab initio calculations of monomeric and dimeric compounds in the gas phase.

Water Dimer Cation: Density Functional Theory vs Ab Initio Theory.

By using density functional theory (DFT) and high-level ab initio theory, the structure, interaction energy, electronic property, and IR spectra of the water dimer cation [(H2O)2(+)] are investigated. Two previously reported structures of the water dimer cation [disproportionated ionic (Ion) structure and hydrazine-like (OO) structure] are compared. For the complete basis set (CBS) limit of coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)], the Ion structure is much more stable (by 11.

Photoexcitation and photoionization dynamics of water photolysis.

Despite the importance of water photolysis in atmospheric chemistry, its mechanism is not well understood. Two different mechanisms for water photolysis have been proposed. The first mechanism is driven by water photoexcitation, followed by the reaction of the active hydrogen radical with water clusters.

Hydrogen detachment of the hydrated hydrohalogen acids upon attaching an excess electron.

High level ab initio calculations are employed to investigate the excess electron attachment to the hydrated hydrohalogen acids. The excess electron leads to the dissociation of hydrogen halide acids, which results in the release of a hydrogen radical. Neutral HCl, HBr, and HI are dissociated by tetrahydration.

Photodissociation of hydrated hydrogen iodide clusters.

Using high-level ab initio calculations and excited state ab initio molecular dynamics simulations, we show that hydrated iodic acids release hydrogen radicals and/or hydrogen molecules as well as iodine radicals upon excitation. Its photoreaction process involving charge transfer to the solvent takes place in four steps: 1) hydration of the acid, 2) charge transfer to water upon excitation of hydrated acid, 3) detachment of the neutral iodine atom, and 4) detachment of the hydrogen radical. The iodine detachment process from excited hydrated hydro-iodic acids is exothermic and the detachment of hydrogen radicals from hydrated hydronium radicals is spontaneous if the initial kinetic energy of the cluster is high enough to get over the activation barrier of the detachment.

Complete basis set limit of Ab initio binding energies and geometrical parameters for various typical types of complexes.

Using basis-set extrapolation schemes for a given data set, we evaluated the binding energies and geometries at the complete basis set (CBS) limit at the levels of the second order Møller-Plesset perturbation theory (MP2) and the coupled cluster theory with singles, doubles, and perturbative triples excitations [CCSD(T)]. The systems include the hydrogen bonding (water dimer), aromatic interaction (benzene dimer), pi-H interaction (benzene-water), cation-water, anion-water, pi-cation interaction (cation-benzene), and pi-anion interaction (anion-triazine). One extrapolation method is to exploit both BSSE-corrected and BSSE-uncorrected binding energies for the aug-cc-pVNZ (N = 2, 3, 4, .

Charge-transfer-to-solvent-driven dissolution dynamics of I- (H2O)2-5 upon excitation: excited-state ab initio molecular dynamics simulations.

In contrast to the extensive theoretical investigation of the solvation phenomena, the dissolution phenomena have hardly been investigated theoretically. Upon the excitation of hydrated halides, which are important substances in atmospheric chemistry, an excess electron transfers from the anionic precursor (halide anion) to the solvent and is stabilized by the water cluster. This results in the dissociation of hydrated halides into halide radicals and electron-water clusters.