Influence of insertion of a noble gas atom on halogen bonding in H2O···XCCNgF and H3N···XCCNgF (X = Cl and Br; Ng = Ar, Kr, and Xe) complexes

The H₂O···XCCNgF and H₃N···XCCNgF (X = Cl and Br; Ng = Ar, Kr, and Xe) complexes have been studied with quantum chemical calculations at the MP2/aug-cc-pVTZ level. The results show that the inserted noble gas atom has an enhancing effect on the strength of halogen bond, and this enhancement is weakened with the increase of noble gas atomic number. The methyl and Li substituents in the electron donor strengthen the halogen bond. The interaction energy increases from ?3.75 kcal/mol in H₃N–BrCCF complex to ?9.66 kcal/mol in H₂LiN–BrCCArF complex. These complexes have been analyzed with atoms in molecules, natural bond orbital, molecular electrostatic potentials, and energy decomposition calculations.     

Theoretical Prediction of Adsorption Properties of Carmustine Drug on Various Sites of the Outer Surface of the Single-Walled Boron Nitride Nanotube and Investigation of Urea Effect on Drug Delivery by DFT and MD

In this work, the adsorption behavior of Carmustine (BCNU) drug over the (6,0) zigzag single-wall boron nitride nanotube (SWBNNT) is studied by means of density functional theory calculations and molecular dynamics simulations (MD). The calculated adsorption energies proved that the adsorption of BCNU molecule on SWBNNT is a physisorption process. The natural bond orbital calculations demonstrated that existence of a charge transfer from the SWBNNT to the BCNU molecule. Moreover, quantum theory of atoms in molecules showed that the hydrogen bonds and electrostatic interactions are two major factors contributed to the overall stabilities of the complexes. Furthermore, interaction of BCNU with the surface of single wall BNNT at 310 K and 1 bar in the present of water and different concentration of Urea molecules has been studied by MD simulation. The MD results confirm that the highest number of hydrogen bond and the lowest value of Lennard-Jones (L-J) energy between nanotube and drug exist in the simulation system with concentration of 1 mol L^?1 Urea.     

A π‐Stacked Porphyrin–Fullerene Electron Donor–Acceptor Conjugate That Features a Surprising Frozen Geometry

A “frozen” electron donor–acceptor array that bears porphyrin and fullerene units covalently linked through the ortho position of a phenyl ring and the nitrogen of a pyrrolidine ring, respectively, is reported. Electrochemical and photophysical features suggest that the chosen linkage supports both through‐space and through‐bond interactions. In particular, it has been found that the porphyrin singlet excited state decays within a few picoseconds by means of a photoinduced electron transfer to give the rapid formation of a long‐lived charge‐separated state. Density functional theory (DFT) calculations show HOMO and LUMO to be localized on the electron‐donating porphyrin and the electron‐accepting fullerene moiety, respectively, at this level of theory. More specifically, semiempirical molecular orbital (MO) configuration interaction (CI) and unrestricted natural orbital (UNO)‐CI methods shed light on the nature of the charge‐transfer states and emphasize the importance of the close proximity of donor and acceptor for effective electron transfer.     

Theoretical study of molecular interactions of sulfur ylide with HF, HCN, and HN3

The molecular interactions between sulfur ylide (SY) and HX molecules (X = F, CN, and N₃) were investigated using the MP2 method at 6-311++G(2d,2p) basis set. Three different patterns including non-classical hydrogen bond (HB) H···C and classical HB H···X were found for complex formation between SY and HX molecules. Stability of the H···C type complexes are greater than H···X complexes. Quantum theories of atoms in molecules, natural bond orbitals, and energy decomposition analysis methods have been applied to analyze the intermolecular interactions. Good correlations have been found between the interaction energies (SE), the second-order perturbation energy E ⁽²⁾ and the charge transfer qCT in the studied systems.     

Hydrogen-bond interactions in hydrated 6-selenoguanine tautomers: a theoretical study

A comprehensive theoretical investigation has been performed to study the six most stable complexes of isolated, mono, and hexahydrated 6-selenoguanine tautomers. The ground state geometries are studied at the density-functional theory and Møller–Plesset Perturbation theory implementing the 6-311++G (2d, 2p) basis set. The intermolecular distances between the water molecule and the acceptor atom of 6-selenoguanine is about 0.6 Å longer for hydrogen bonds involving selenium atom. The relative Gibbs free energy of the 6-selenoguanine tautomers favors the selenone tautomer. The majority of the stable monohydrated complexes are the one in which the oxygen atom of water accepts the acidic N7-H proton while donating a proton to the carbonyl selenium atom of 6-selenoguanine; the interaction toward N7-H being stronger than that with the selenium site. The amino group planarity has been found to be increased in the hydrated complexes. The examination of molecular orbital reveals a moderate band gap between the donor and acceptor atoms of isolated and hydrated complexes. An excellent linear correlation is found to exist between electron density and laplacian of electron density with hydrogen-bond length through atoms in molecule analysis. The natural bond orbital analysis shows a maximum charge transfer of 0.060e for selenium acceptors and around 0.025e for selenium donors.     

Proton Transfer Influence on Geometry and Electron Density in Benzoic Acid–Pyridine Complexes

The influence of the proton transfer on the geometry of donor and acceptor molecule in benzoic acid–pyridine complexes is investigated by theoretical calculations at the B3LYP/6‐311++G** level of theory. Systematic shifts of the H‐atom in the H‐bond are reflected in the geometry of the COOH group and the lengths of aromatic ring bond lengths of the proton acceptor. Changes in electron densities have been studied by atoms in molecules analysis. A systematic natural bond orbital analysis has been performed to study the proton transfer mechanism. Two donor orbitals are engaged in the proton transfer process which is accompanied by a change in orbital delocalization of H‐atom that can switch between two donor orbitals so the path of proton transfer in intermolecular H‐bond is not determined by the orbital shape. Theoretical results have been confirmed by experimental results published previously.     

O–H···C hydrogen bond in the methane–water complex

Quantum chemical calculations were performed at different levels of theory (SCF, DFT, MP2, and CCSD(T)) to determine the geometry and electronic structure of the HOH···CH₄ complex formed by water and methane molecules, in which water is a proton donor and methane carbon (sp³) is an acceptor. The charge distribution on the atoms of the complex was analyzed by the CHelpG method and Hirshfeld population analysis; both methods revealed the transfer of electron charge from methane to water. According to the natural bond orbital (NBO) analysis data, the charge transfer upon complexation is caused by the interaction between the σ orbital of the axial С–H bond of methane directed along the line of the O–H···C hydrogen bridge and the antibonding σ* orbital of the О–H bond of the water molecule. Topological analysis of electron density in the HOH···CH₄ complex by the AIM method showed that the parameters of the critical point of the bond between hydrogen and acceptor (carbon atom) for the O–H···C interaction are typical for Н-bonded systems (the magnitude of electron density at the critical point of the bond, the sign and value of the Laplacian). It was concluded that the intermolecular interaction in the complex can be defined as an Н bond of O–H···σ(С–H) type, whose energy was found to be 0.9 kcal/mol in MP2/aug-cc-pVQZ calculations including the basis set superposition error (BSSE).     

Charge transfer in the TCNQ-sexithiophene complex

Molecular crystals from thiophene molecules can be doped with TCNQ-F4 molecules for use in all-organic optoelectronic and semiconductor devices. The charge transfer and the molecular orbital energy level formation in between these two organic molecules are investigated here by density functional theory calculations. The isolated molecules are calculated nonbonded and bonded together, forming a charge transfer complex (CTC). The relaxed structure of the complex shows essentially coplanar and centered molecules with the alpha-sexithiophene rings tilted alternatingly by 4.8 degrees. The bond formation of these molecules results in a charge transfer of approximately 0.4 e from the alpha-sexithiophene to the TCNQ-F4 molecule. The highest occupied molecular orbital-lowest unoccupied molecular orbital gap width is reduced as compared to the isolated molecules due to the newly formed orbitals in the CTC. Upon adsorption on a Au(111) surface, electrons are transferred onto the molecule complex, thereby causing the molecular levels to align asymmetric with respect to the charge neutrality level. The theoretical results for the single molecule and CTC layer are compared to experimental photoemission and scanning tunneling spectroscopy results.     

氯化钕异丙醇配合物的电子结构与络合活化的研究

本文用INDO方法计算了氯化钕异丙醇配合物的电子结构。计算结果指出, 配位后, 与Nd-Cl键对应的分子轨道能量升高, Nd-Cl键级降低, Nd的正电荷降低, Cl的负电荷增多。从而表明。由于配位发生轨道重迭, 使得异丙醇氧的孤对电子移向钕离子的空价轨道。钕离子上的电子云密度增高加强了对Nd—Cl键的价电子的推斥作用, 使Nd-Cl间的价电子密度减小, 导致Nd-Cl键的削弱, 降低了键的能量, 有效地活化了Nd-Cl键,有利于生成活性物种的烷基化反应的进行。同时表明, 对Nd-Cl的络合催化有某种选择性。     

Observations on the Crystal Structures of Electron Donor-Acceptor Complexes

The theoretical interpretation of electron donor-acceptor complex formation in terms of charge transfer interactions has stimulated many structure determinations for these complexes. These fall into three classes, depending on the type of orbitals involved in charge transfer. In σ-σ complexes, intermolecular bonds become shorter and intramolecular bonds become longer as charge transfer increases. Relative orientations correspond to overlap of donor and acceptor molecules in directions of “preferred polarizability”. Intermolecular bond lengths in σ-π complexes show similar trends, and the axial orientation in the benzene-halogen complexes is probably the result of the best compromise between orbital overlap and energy factors. π-π Complexes contain stacks of alternate plane-to-plane donor and acceptor molecules, arranged in three characteristic ways. There is little correlation between interplanar spacing in these stacks and charge transfer properties. The relative orientations of donor and acceptor molecules within the stacks are determined by a combination of charge transfer interactions (maximized when aromatic rings of donor and acceptor molecules are displaced by half a ring diameter) and dipole-induced dipole interactions (maximized, for example, when a polar bond of one molecule overlaps a polarizable region of another). Crystal packing requirements and dispersion forces modify these effects, and no satisfactory theoretical treatment of this complex combination of interactions is yet available.     

Structure of a Hydrated Sulfonatotitanyl(IV) Complex in Aqueous Solution and the Dimethylsulfoxide Solvated Titanyl(IV) Ion in Solution and Solid State

The coordination chemistry of oxotitanium(IV) or titanyl(IV), TiO²⁺, has been studied in solution by X-ray methods. The titanyl(IV) ion hydrolyzes easily in aqueous systems to solid titanium dioxide as long as it is not stabilized through complexation. In this study the structures of the hydrated bissulfatotitanyl(IV) complex and the dimethylsulfoxide (DMSO) solvated titanyl(IV) ions have been determined. In isolated monomeric titanyl complexes titanium(IV) binds strongly to a doubly bound oxo group at ca. 1.64 Å, to four ligands in the equatorial plane almost perpendicular to the Ti=O bond at ca. 2.02 Å, and there is one weakly bound ligand, trans to the Ti=O bond, at ca. 2.22 Å, for oxygen donor ligands; the O=Ti–O_eq bond angles are 95°–100°. The structure of the DMSO solvated titanyl(IV) ion in the solid state is maintained in DMSO solution.     

The Effect of Intermolecular Hydrogen Bonding on the Polyaniline Water Complex

The polyaniline water hydrogen-bonded complex was studied by first-principles calculation. The density functional theory method was used to calculate the structure characters, natural bond orbital charge distribution, infrared spectra and the frontier molecular orbital. Results showed that the H–O···H–N and C–N···H–O type intermolecular hydrogen bonds were formed. The bonds involved in the intermolecular H-bond were all influenced by the hydrogen bonding interaction. During the hydrogen bond formation, the polymer chains in the complexes were all charged, which can be an important factor contributing to the increase of electrical conductivity. The N1–H vibration was strongly influenced, and the locations as well as the intensities of N1–H absorption bands were all changed in the complexes. In the orbital transition of HOMO to LUMO, the electron density transferred from benzenoid ring to quinoid ring.     

Ab initio study of mechanism of forming a spiro-ge-heterocyclic ring compound

The mechanism of cycloaddition reaction between singlet state dichloromethylenegermene (Cl₂C=Ge:) and ethene has been investigated with the CCSD(T)//B3LYP/6-31G* method. From the potential energy profile, it could be predicted that the reaction has one dominant reaction channel. The reaction rule presented is that the 4p unoccupied orbital of Ge in dichloromethylenegermene and the π orbital of ethene forming a π → p donor–acceptor bond resulting in the formation of a three-membered ring intermediate. Ring-enlargement effect make the three-membered ring intermediate isomerizes to a four-membered ring germylidene. Because the 4p unoccupied orbital of Ge atom in the four-membered ring germylidene and the π orbital of ethene form a π → p donor–acceptor bond, the four-membered ring germylidene further combines with ethene to form another intermediate. Because the Ge atom in the intermediate happens sp ³ hybridization after transition state, the intermediate isomerizes to a spiro-Ge-heterocyclic ring compound.     

TDDFT Study on Excited-State Hydrogen Bonding of 2'-Deoxyguano-sine in H2O Solution

The mono and dihydrated complexes of 2'-deoxyguanosine have been used to elucidate the importance of the 2'-hydroxy group in the hydration. Density functional theory and time-dependent density functional theory methods were performed to investigate the ground-and excited-state hydrogen bonding properties of 2'-deoxyguanosine-water (2'-dG-W) and 2'-deoxyguanosine-2water (2'-dG-2W). Infrared spectra, geometric optimizations, frontier molecular orbitals and Mulliken charges have also been studied. The results demonstrated that the excited-state intramolecular hydrogen bonding dynamics of complexes 2'-dG-W and 2'-dG-2W behaves differently upon photoexcitation, while their intermolecular hydro-gen bonding dynamics behaves similarly. Moreover, the significant weakening of the inter-molecular hydrogen bond O4···H1?N1 and the formation of the new strong hydrogen bond O4···H3?N2 in the 2'-dG-2W upon photoexcitation were due to the geometric structure bending of guanine and the rigidity of related molecules. In addition, the charge transfer properties were theoretically investigated by analysis of molecular orbital.     

Synthesis,spectroscopic properties,density functional theory calculations and nonlinear optical properties of novel complexes of 5‐hydroxy‐4,7‐dimethyl‐6‐(phenylazo)coumarin with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions

5‐Hydroxy‐4,7‐dimethyl‐6‐(phenylazo)coumarin (L) has been synthesized and its novel complexes with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) metal ions have also been prepared and identified using various analytical tools. The complexes are octahedral binding via one/two oxygen, nitrogen atoms for 1:1 and 1:2 complexes and two/three coordinated water molecules. All the prepared solid complexes behave as neutral in dimethylformamide. The optimized structures of the studied complexes were theoretically investigated at the B3LYP/6‐311G** level. Molecular stability and bond strengths were investigated by applying natural bond orbital analysis. The geometries of the studied complexes are non‐planar as indicated from the values of dihedral angles. The global properties of hardness, global softness and electronegativity were computed. The calculated small energy gap between highest occupied and lowest unoccupied molecular orbital energies shows that charge transfer occurs within the complexes. The obtained total static dipole moment, mean polarizability, anisotropy of polarizability and mean first‐order hyperpolarizability (<β>) were compared with those of urea as a reference material. The results for <β> showed that the complexes are excellent candidates as nonlinear optical materials. The three‐dimensional plots of the molecular electrostatic potential for some selected complexes were investigated.     

Hydrogen bonding mediated by key orbital interactions determines hydration enthalpy differences of phosphate water clusters

Electronic structure calculations have been carried out to provide a molecular interpretation for dihydrogen phosphate stability in water relative to that of metaphosphate. Specifically, hydration enthalpies of biologically important metaphosphate and dihydrogen phosphate with one to three waters have been computed with second-order M?ller-Plesset perturbation and density functional theory (B3LYP) with up to the aug-cc-pvtz basis set and compared to experiment. The inclusion of basis set superposition error corrections and supplemental diffuse functions are necessary to predict hydration enthalpies within experimental uncertainty. Natural bond orbital analysis is used to rationalize underlying hydrogen bond configurations and key orbital interactions responsible for the experimentally reported difference in hydration enthalpies between metaphosphate and dihydrogen phosphate. In general, dihydrogen phosphate forms stronger hydrogen bonds compared to metaphosphate due to a greater charge transfer or enhanced orbital overlap between the phosphoryl oxygen lone pairs, n(O), and the antibonding O-H bond of water. Intramolecular distal lone pair repulsion with the donor n(O) orbital of dihydrogen phosphate distorts symmetric conformations, which improves n(O) and sigma*(O-H) overlap and ultimately the hydrogen bond strength. Unlike metaphosphate, water complexed to dihydrogen phosphate can serve as both a hydrogen bond donor and a hydrogen bond acceptor, which results in cooperative charge transfer and a reduction of the energy gap between n(O) and sigma*(O-H), leading to stronger hydrogen bonds. This study offers insight into how orbital interactions mediate hydrogen bond strengths with potential implications on the understanding of the kinetics and mechanism in enzymatic phosphoryl transfer reactions.     

Theoretical study of molecular interactions of phosphorus ylide with HF, HCN, and HN3

The molecular interactions between phosphorous ylide (PY) and HX molecules (X?=?F, CN, and N₃) were investigated using the MP2 method at 6-311++G(2d,2p) basis set. Three different patterns including non-classical hydrogen bond H···C, X···P interaction and classical hydrogen bond H···X were found for complex formation between PY and HX molecules. From the predicted models, stability of the H···C type complexes are greater than other types. Quantum theories of atoms in molecules and natural bond orbitals methods have been applied to analyze the intermolecular interactions. Good correlations have been found between the interaction energies (SE), the second-order perturbation energy E ⁽²⁾, and the charge transfer qCT in the studied systems.     

取代基对N-H…O=C氢键三聚体中氢键强度的影响

使用MP2方法研究了氢键三聚体中N—H…O=C氢键强度, 探讨了氢键受体分子中不同取代基对N—H…O=C氢键强度的影响. 研究表明, 不同取代基对氢键三聚体中N—H…O=C氢键强度的影响是不同的: 取代基为供电子基团, 氢键键长r(H…O)缩短, 氢键强度增强; 取代基为吸电子基团, 氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明, N—H…O=C氢键强度越强, 氢键中氢原子的正电荷越多, 氧原子的负电荷越多, 质子供体和受体分子间的电荷转移越多. 供电子基团使N—H…O=C氢键中氧原子的孤对电子n(O)对N—H的反键轨道滓*(N—H)的二阶相互作用稳定化能增加, 吸电子基团使这种二阶相互作用稳定化能减小. 取代基对与其相近的N—H…O=C氢键影响更大.     

取代基对1-甲基尿嘧啶与N-甲基乙酰胺氢键复合物中氢键强度的影响

使用密度泛函理论B3LYP方法和二阶微扰理论MP2方法对由1-甲基尿嘧啶与N-甲基乙酰胺所形成的氢键复合物中的氢键强度进行了理论研究, 探讨了不同取代基取代氢键受体分子1-甲基尿嘧啶中的氢原子对氢键强度的影响和氢键的协同性. 研究表明: 供电子取代基使N－H…O＝C氢键键长r(H…O)缩短, 氢键强度增强; 吸电子取代基使N－H…O＝C氢键键长r(H…O)伸长, 氢键强度减弱. 自然键轨道(NBO)分析表明: 供电子基团使参与形成氢键的氢原子的正电荷增加, 使氧原子的负电荷增加, 使质子供体和受体分子间的电荷转移量增多; 吸电子基团则相反. 供电子基团使N－H…O＝C氢键中氧原子的孤对电子轨道n(O)对N－H的反键轨道σ^*(N－H)的二阶相互作用稳定化能增强, 吸电子基团使这种二阶相互作用稳定化能减弱. 取代基对与其相近的N－H…O＝C氢键影响更大.     

Source of Cooperativity in Halogen‐Bonded Haloamine Tetramers

Inspired by the isostructural motif in α‐bromoacetophenone oxime crystals, we investigated halogen–halogen bonding in haloamine quartets. Our Kohn–Sham molecular orbital and energy decomposition analysis reveal a synergy that can be traced to a charge‐transfer interaction in the halogen‐bonded tetramers. The halogen lone‐pair orbital on one monomer donates electrons into the unoccupied σ*_N?X orbital on the perpendicular N?X bond of the neighboring monomer. This interaction has local σ symmetry. Interestingly, we discovered a second, somewhat weaker donor–acceptor interaction of local π symmetry, which partially counteracts the aforementioned regular σ‐symmetric halogen‐bonding orbital interaction. The halogen–halogen interaction in haloamines is the first known example of a halogen bond in which back donation takes place. We also find that this cooperativity in halogen bonds results from the reduction of the donor–acceptor orbital‐energy gap that occurs every time a monomer is added to the aggregate.