Intramolecular and intermolecular hydrogen bonding in electronic excited states of calixarene building blocks bis(2-hydroxyphenyl)methane (2HDPM) monomer and hydrogen-bonded 2HDPM-H2O complex were studied theoretically using the time-dependent density functional theory (TDDFT). Twenty-four stable conformations (12 pairs of enantiomers) of 2HDPM monomer have been found in the ground state. From the calculation results, the conformations 1a and 1b which both have an intramolecular hydrogen bond are the most stable ones. The infrared spectra of 2HDPM monomer and 2HDPM-H2O complex in ground state and S1 state were calculated. The stretching vibrational absorption band of O2???H3 group in the monomer and complex disappeared in the S1 state. At the same time, a new strong absorption band appeared at the C=O stretching region. From the calculation of bond lengths, it indicates that the O2???H3 bond is significantly lengthened in the S1 state. However, the C1???O2 bond is drastically shortened upon electronic excitation to the S1 state and has the characteristics of C=O band. Furthermore, the intramolecular hydrogen bond O2???H3?·?·?·?O4 of the 2HDPM monomer and the intermolecular hydrogen bonds O2???H3?·?·?·?O7 and O7???H9?·?·?·?O4 of 2HDPM-H2O complex are all shortened and strengthened in the S1 state.
Figure
Intramolecular and intermolecular hydrogen bonding in electronic excited states of calixarene building blocks bis(2-hydroxyphenyl)methane (2HDPM) monomer and hydrogen-bonded 2HDPM-H2O complex were studied by TDDFT method 相似文献
The DFT-B3LYP/6-311++G(3df,2p) and MP2(full)/6-311++G(3df,2p) calculations were carried out on the binary complex formed by HM (M?=?Li, Na, K) and HF or the π-electron donor (C2H2, C2H4, C6H6), as well as the ternary system FH???HM???C2H2/C2H4/C6H6. The cooperativity effect between the dihydrogen-bonding and H–M???π interactions was investigated. The result shows that the equilibrium distances RH???H and RM???π in the ternary complex decrease and both the H???H and H–M???π interactions are strengthened when compared to the corresponding binary complex. The cooperativity effect of the dihydrogen bond on the H–M???π interaction is more pronounced than that of the M???π bond on the H???H interaction. Furthermore, the values of cooperativity effect follow the order of FH???HNa???π?>?FH???HLi???π?>?FH???HK???π and FH???HM???C6H6?>?FH???HM???C2H4?>?FH???HM???C2H2. The nature of the cooperativity effect was revealed by the analyses of the charge of the hydrogen atoms in H???H moiety, atom in molecule (AIM) and electron density shifts methods.
Figure
Shifts of electron density upon ternary-complex formation indicate the cooperativity effect between the dihydrogen-bonding and H–M???π interactions 相似文献
Molecular interaction between dioxane and methanol involves certain polar and nonpolar bonding to form a one to one complex. Interatomic distances between hydrogen and oxygen within 3 Å have been considered as hydrogen bonding. Optimizations of the structures of dioxane-methanol complexes were carried out considering any spatial orientation of a methanol molecule around a chair/boat/twisted-boat conformation of dioxane. From 45 different orientations of dioxane and water, 23 different structures with different local minima were obtained and the structural characteristics like interatomic distances, bond angles, dihedral angles, dipole moment of each complex were discussed. The most stable structure, i.e., with minimum heat of formation is found to have a chair form dioxane, one O-H…O, and two C-H…O hydrogen bonds. In general, the O-H…O hydrogen bonds have an average distance of 1.8 Å while C-H…O bonds have 2.6 Å. The binding energy of the dioxane-methanol complex is found to be a linear function of number of O-H…O and C-H…O bonds, and hydrogen bond length. Graphical Abstract
Sixteen orientations of methanol around dioxane converge to six local minima including the global minima with one H-O…H and two C-H…O hydrogen bonds.相似文献
In this work, computations of density functional theory (DFT) were carried out to investigate the nature of interactions in solid 2,6-dibromo-4-nitroaniline (DBNA). This system was selected to mimic the hydrogen/halogen bonding found within crystal structures as well as within biological molecules. DFT (M06-2X/6-311++G**) calculations indicated that the binding energies for different of interactions lie in the range between ?1.66 and ?9.77 kcal mol?1. The quantum theory of atoms in molecules (QTAIM) was applied to provide more insight into the nature of these interactions. Symmetry-adapted perturbation theory (SAPT) analysis indicated that stability of the Br···Br halogen bonds is predicted to be attributable mainly to dispersion, while electrostatic forces, which have been widely believed to be responsible for these types of interactions, play a smaller role. Our results indicate that, for those nuclei participating in hydrogen/halogen bonding interactions, nuclear quadrupole resonance parameters exhibit considerable changes on going from the isolated molecule model to crystalline DBNA.
Figure
Electrostatic potential mapped on the surface of 2,6-dibromo-4-nitroaniline (DBNA) molecular electron density (0.001 e au?3). Color ranges for VS(r), in kcal?mol?1: red > 26.5, yellow 26.5–5.7, green 5.7– ?15.1, blue < ?15.1. Black circles Surface maxima, blue surface minima 相似文献
The character of the cooperativity between the HOX···OH/SH halogen bond (XB) and the Y―H···(H)OX hydrogen bond (HB) in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes has been investigated by means of second-order Møller?Plesset perturbation theory (MP2) calculations and “quantum theory of atoms in molecules” (QTAIM) studies. The geometries of the complexes have been determined from the most negative electrostatic potentials (VS,min) and the most positive electrostatic potentials (VS,max) on the electron density contours of the individual species. The greater the VS,max values of HY, the larger the interaction energies of halogen-bonded HOX···OH/SH in the termolecular complexes, indicating that the ability of cooperative effect of hydrogen bond on halogen bond are determined by VS,max of HY. The interaction energies, binding distances, infrared vibrational frequencies, and electron densities ρ at the BCPs of the hydrogen bonds and halogen bonds prove that there is positive cooperativity between these bonds. The potentiation of hydrogen bonds on halogen bonds is greater than that of halogen bonds on hydrogen bonds. QTAIM studies have shown that the halogen bonds and hydrogen bonds are closed-shell noncovalent interactions, and both have greater electrostatic character in the termolecular species compared with the bimolecular species.
Figure
The character of the cooperativity between the X···O/S halogen bond (XB) and the Y―H···O hydrogen bond (HB) in OH/SH···HOX···HY (X=Cl, Br; Y=F, Cl, Br) complexes has been investigated by means of second-order Møller—Plesset perturbation theory (MP2) calculations and “quantum theory of atoms in molecules” (QTAIM) studies. 相似文献
A quantum chemistry study was carried out to investigate the strength and nature of halogen bond interactions in HXeH···XCCY complexes, where X = Cl, Br and Y = H, F, Cl, Br, CN, NC, C2H, CH3, OH, SH, NH2. Examination of the electrostatic potentials V(r) of the XCCY molecules reveals that the addition of substituents has a significant effect upon the most positive electrostatic potential on the surface of the interacting halogen atom. We found that the magnitude of atomic charges and multipole moments depends upon the halogen atom X and is rather sensitive to the electron-withdrawing/donating power of the remainder of the molecule. An excellent correlation was found between the most positive electrostatic potentials on the halogen atom and the interaction energies. For either HXeH···ClCCY or HXeH···BrCCY complexes, an approximate linear correlation between the interaction energies and halogens multipole moments are established, indicating that the electrostatic and polarization interactions are responsible for the stability of the complexes. According to energy decomposition analysis, it is revealed that the electrostatic interactions are the major source of the attraction in the HXeH···XCCY complexes. Furthermore, the changes in the electrostatic term are mainly responsible for the dependence of interaction energy on the halogen atom.
Graphical abstract
Electrostatic potential mapped on the surface of molecular electron density at the 0.001 electrons Bohr ?3 of HXeH. The color ranges in kcal mol?1 red >8.5, yellow 1.5 to 8.5, green ?5.5 to 1.5, blue <?5.5. Black and blue circles are referred to surface maxima and minima, respectively. 相似文献
The cooperativity effects between the O/N–H???F– anionic hydrogen-bonding and O/N–H???O hydrogen-bonding interactions and electrostatic potentials in the 1:2 (F–:N-(Hydroxymethyl)acetamide (signed as “ha”)) ternary systems are investigated at the B3LYP/6-311++G** and MP2/6-311++G** levels. A comparison of the cooperativity effect in the “F–???ha???ha” and “FH???ha–???ha” systems is also carried out. The result shows that the increase of the H???O interaction energy in the O–H???O–H, N–H???O–H or N–H???O?=?C link is more notable than that in the O–H???O?=?C contact upon ternary-system formation. The cooperativity effect is found in the complex formed by the O/N–H???F– and O/N–H???O interactions, while the anti-cooperativity effect is present in the system with only the O/N–H???F– H-bond or the “FH???ha–???ha” complex by the N–???H–F contact. Atoms in molecules (AIM) analysis and shift of electron density confirm the existence of cooperativity. The most negative surface electrostatic potential (VS,min) correlates well with the interaction energy E′int.(ha???F–) and synergetic energy Esyn., respectively. The relationship between the change of VS,min (i.e., ΔVS,min) and Esyn. is also found.
Figure
Surface electrostatic potential on the 0.001 au molecular surface 相似文献
O-H…X and O-H…O H-bonds as well as C-X…X dihalogen and C-X…O halogen bonds have been investigated in halomethanol dimers (bromomethanol dimer, iodomethanol dimer, difluorobromomethanol…bromomethanol complex and difluoroiodomethanol…iodomethanol complex). Structures of all complexes were optimized at the counterpoise-corrected MP2/cc-pVTZ level and single-point energies were calculated at the CCSD(T)/aug-cc-pVTZ level. Energy decomposition for the bromomethanol dimer complex was performed using the DFT-SAPT method based on the aug-cc-pVTZ basis set. OH…O and OH…X H-bonds are systematically the strongest in all complexes investigated, with the former being the strongest bond. Halogen and dihalogen bonds, being of comparable strength, are weaker than both H-bonds but are still significant. The strongest bonds were found in the difluoroiodomethanol…iodomethanol complex, where the O-H…O H-bond exceeds 7 kcal mol-1, and the halogen and dihalogen bonds exceed 2.5 and 2.3 kcal mol-1, respectively. Electrostatic energy is dominant for H-bonded structures, in halogen bonded structures electrostatic and dispersion energies are comparable, and, finally, for dihalogen structures the dispersion energy is clearly dominant.
Figure
Competition of hydrogen, halogen, and dihalogen bonding in the bromomethanol dimer are investigated 相似文献
In the present paper, a new type of Lewis acid–base complex BX3???Li@Calix[4]pyrrole (X = H and F) was designed and assembled based on electride molecule Li@calix[4]pyrrole (as a Lewis base) and the electron deficient molecule BX3 (as a Lewis acid) by employing quantum mechanical calculation. The new Lewis acid–base complex offers an interesting push-excess electron-pull (P-e-P) framework to enhance the stability and nonlinear optical (NLO) response. To measure the nonlinear optical response, static first hyperpolarizabilities (β0) are exhibited. Significantly, point-face assembled Lewis acid–base complex BF3???Li@Calix[4]pyrrole (II) has considerable first hyperpolarizabilities (β0) value (1.4?×?106 a.u.), which is about 117 times larger than reported 11,721 a.u. of electride Li@Calix[4]pyrrole. Further investigations show that, in BX3???Li@Calix[4]pyrrole with P-e-P framework, a strong charge-transfer transition from the ground state to the excited state contributes to the enhancement of first hyperpolarizability. Theory calculation of enthalpies of reaction (ΔrH0) at 298 K demonstrates that it is feasible to synthetize the complexes BX3???Li@Calix[4]pyrrole. In addition, compared with Li@Calix[4]pyrrole, the vertical ionization potential (VIP) and HOMO–LUMO gap of BX3???Li@Calix[4]pyrrole have obviously increased, due to the introduction of the Lewis acid molecule BX3. The novel Lewis acid–base NLO complex possesses not only a large nonlinear optical response but also higher stability.
Figure
A novel Lewis acid–base complex is first proposed by the combination of usual Lewis acid and an electride. It offers an interesting push-excess electron-pull framework to enhance the stability and nonlinear optical response. 相似文献
MP2(full)/6-311++G(3df,3pd) calculations were carried out on complexes linked through various non-covalent Lewis acid – Lewis base interactions. These are: hydrogen bond, dihydrogen bond, hydride bond and halogen bond. The quantum theory of ´atoms in molecules´ (QTAIM) as well as the natural bond orbitals (NBO) method were applied to analyze properties of these interactions. It was found that for the A-H…B hydrogen bond as well as for the A-X…B halogen bond (X designates halogen) the complex formation leads to the increase of s-character in the A-atom hybrid orbital aimed toward the H or X atom. In opposite, for the A…H-B hydride bond, where the H-atom possesses negative charge, the decrease of s-character in the B-atom orbital is observed. All these changes connected with the redistribution of the electron charge being the effect of the complex formation are in line with Bent´s rule. The numerous correlations between energetic, geometrical, NBO and QTAIM parameters were also found.
Figure
QTAIM atomic radii for NH4+…HMgH and Na+…HBeH 相似文献
In the present study we have characterized the halogen bonding in selected molecules H3N–ICF3 (1-NH3), (PH3)2C–ICF3 (1-CPH3), C3H7Br–(IN2H2C3)2C6H4 (2-Br), H2–(IN2H2C3)2C6H4 (2-H2) and Cl–(IC6F5)2C7H10N2O5 (3-Cl), containing from one halogen bond (1-NH3, 1-CPH3) up to four connections in 3-Cl (the two Cl–HN and two Cl–I), based on recently proposed ETS-NOCV analysis. It was found based on the NOCV-deformation density components that the halogen bonding C–X…B (X-halogen atom, B-Lewis base), contains a large degree of covalent contribution (the charge transfer to X…B inter-atomic region) supported further by the electron donation from base atom B to the empty σ*(C–X) orbital. Such charge transfers can be of similar importance compared to the electrostatic stabilization. Further, the covalent part of halogen bonding is due to the presence of σ-hole at outer part of halogen atom (X). ETS-NOCV approach allowed to visualize formation of the σ-hole at iodine atom of CF3I molecule. It has also been demonstrated that strongly electrophilic halogen bond donor, [C6H4(C3H2N2I)2][OTf]2, can activate chemically inert isopropyl bromide (2-Br) moiety via formation of Br–I bonding and bind the hydrogen molecule (2-H2). Finally, ETS-NOCV analysis performed for 3-Cl leads to the conclusion that, in terms of the orbital-interaction component, the strength of halogen (Cl–I) bond is roughly three times more important than the hydrogen bonding (Cl–HN).
Figure
ETS-NOCV reprezentation of σ-hole at iodine together with the molecular electrostatic potential picture 相似文献
Detailed electrostatic potential (ESP) analyses were performed to compare the directionality of halogen bonds with those of hydrogen bonds and lithium bonds. To do this, the interactions of HOOOH with the molecules XF (X?=?Cl, Br, H, Li) were investigated. For each molecule, the percentage of the van der Waals (vdW) molecular surface that intersected with the ESP surface was used to roughly quantify the directionality of the halogen/hydrogen/lithium bond associated with the molecule. The size of the region of intersection was found to increase in the following order: ClF?<?BrF?<?HF?<?LiF. The maximum ESP in the region of intersection, VS, max, was observed to become more positive according to the sequence ClF?<?BrF?<?HF?<?LiF. For ClF and BrF, the positive electrostatic potential was concentrated in a very small region of the vdW molecular surface. On the other hand, for HF and LiF, the positive electrostatic potential was more diffusely scattered across the vdW surface than for ClF and BrF. Also, the optimized geometries of the dipolymers HOOOH···?XF (X?=?Cl, Br, H, Li) indicated that halogen bonds are more directional than hydrogen bonds and lithium bonds, consistent with the results of ESP analyses.
The electronic structure of the two most stable isomers of squaric acid and their complexes with BeH2 were investigated at the B3LYP/6-311?+?G(3df,2p)// B3LYP/6-31?+?G(d,p) level of theory. Squaric acid forms rather strong beryllium bonds with BeH2, with binding energies of the order of 60 kJ?mol?1. The preferential sites for BeH2 attachment are the carbonyl oxygen atoms, but the global minima of the potential energy surfaces of both EZ and ZZ isomers are extra-stabilized through the formation of a BeH···HO dihydrogen bond. More importantly, analysis of the electron density of these complexes shows the existence of significant cooperative effects between the beryllium bond and the dihydrogen bond, with both becoming significantly reinforced. The charge transfer involved in the formation of the beryllium bond induces a significant electron density redistribution within the squaric acid subunit, affecting not only the carbonyl group interacting with the BeH2 moiety but significantly increasing the electron delocalization within the four membered ring. Accordingly the intrinsic properties of squaric acid become perturbed, as reflected in its ability to self-associate.
Figure
The ability of squaric acid to self-associate is significantly enhanced when this molecule forms beryllium bonds with BeH2相似文献
The ternary complexes ML???PyZX2???NH3 (ML?=?CuCl, CuCN, AgCN, and AuCN; Z?=?P, As, and Sb; X?=?H and F) have been investigated with quantum chemical calculations. The results showed that the existence of coordination interaction has a prominent enhancing effect on the strength of pnicogen bonding. Even in ML???PySbH2???NH3, ML???PyAsF2???NH3, and ML???PySbF2???NH3, the pnicogen bond varies from a purely closed-shell interaction to a partially covalent interaction. The coordination interaction results in the enlargement of the σ-hole on the pnicogen atom and thus the enhancement of pnicogen bonding. In addition, the contribution of orbital interaction is also important.
This study aimed at better characterising background nitrous oxide (N2O) emissions (BNE) in agricultural and natural lands.
Methods
We compiled and analysed field-measured data for annual background N2O emission in agricultural (BNEA) and natural (BNEN) lands from 600 and 307 independent experimental studies, respectively.
Results
There were no significant differences between BNEA (median: 0.70 & mean: 1.52 kg N2O???N ha?1 yr?1) and BNEN (median:0.31 & mean:1.75 kg N2O???N ha?1 yr?1) (P?>?0.05). A simultaneous comparison across all BNEA and BNEN indicated that BNEs from riparian, vegetable crop fields and intentional fallow areas were significantly higher than from boreal forests (P?<?0.05). Correlation and regression analyses supported the underlying associations of soil organic carbon (C), nitrogen (N), pH, bulk density (BD),and/or air temperature (AT) with BNEs to a varying degree as a function of land-use or ecosystem type (Ps?<?0.05).
Conclusions
Although overall BNEN tended to be lower than BNEA on median basis, results in general suggest that land-use shifts between natural and managed production systems would not result in consistent changes in BNE. 相似文献
Increase of the atmospheric concentration of halogenated organic compounds is partially responsible for a change of the global climate. In this work we have investigated the interaction between halogenated ether and water, which is one of the most important constituent of the atmosphere. The structures of the complexes formed by the two most stable conformers of enflurane (a volatile anaesthetic) with one and two water molecules were calculated by means of the counterpoise CP-corrected gradient optimization at the MP2/6–311++G(d,p) level. In these complexes the CH…Ow hydrogen bonds are formed, with the H…Ow distances varying between 2.23 and 2.32 Å. A small contraction of the CH bonds and the blue shifts of the ν(CH) stretching vibrations are predicted. There is also a weak interaction between one of the F atoms and the H atom of water, with the Hw…F distances between 2.41 and 2.87 Å. The CCSD(T)/CBS calculated stabilization energies in these complexes are between ?5.89 and ?4.66 kcal?mol?1, while the enthalpies of formation are between ?4.35 and ?3.22 kcal?mol?1. The Cl halogen bonding between enflurane and water has been found in two complexes. The intermolecular (Cl···O) distance is smaller than the sum of the corresponding van der Waals radii. The CCSD(T)/CBS stabilization energies for these complexes are about ?2 kcal?mol?1.
Figure
Complex between enflurane and water molecules 相似文献
The halogen bonding interactions between C6F5I and a series of transition metal monohalides trans-[M(X)(2-C5NF4)-(PR3)2] (M = Ni, Pd, Pt; X = F, Cl, Br; R = Me, Cy) have been studied with quantum chemical calculations. Optimized geometries of the halogen bonding complexes indicate that angles C1-I···X are basically linear (178–180°) and angles I···X-M mainly range from 90 to 150°. The strength of these metal-influenced halogen bonds alters with different metal centers, metal-bound halogen atoms and the substitutes on phosphine ligands. Electrostatic potential and natural bond orbital analysis show that both of the electrostatic and orbital interactions make a contribution to the formation of halogen bonds, while the electrostatic term plays a dominant role. AIM analysis suggests that, for trans-[M(F)(2-C5NF4)-(PR3)2] (M = Ni, Pd, Pt) monomers, the formed halogen bonding complexes are stabilized by local concentration of the charge of intermediate character, while for the metal monomers containing chlorine and bromine, a typical closed-shell interaction exist. These results prove that the structures and geometries of these halogen bonding complexes can be tuned by changing the halogen atoms and metal centers, which may provide useful information for the design and synthesis of new functional materials.
Figure
The properties and structural characteristics of a series of metal-influenced halogen-bonding complexes have been studied by using density functional theory (DFT) method. The calculation results indicate that metal centers and metal-bound halogen atoms have significant influence on the geometries and strength of halogen bonds 相似文献
Quantum chemical calculations were performed for LiNH2–HMgX (X?=?H, F, Cl, Br, CH3, OH, and NH2) complexes to propose a new interaction mechanism between them. This theoretical survey showed that the complexes are stabilized through the combinative interaction of magnesium and lithium bonds. The binding energies are in the range of 63.2–66.5 kcal mol?1, i.e., much larger than that of the lithium bond. Upon complexation, both Mg–H and Li–N bonds are lengthened. Substituents increase Mg-H bond elongation and at the same time decrease Li-N bond elongation. These cyclic complexes were characterized with the presence of a ring critical point and natural population analysis charges.
Figure
A new interaction mechanism has been suggested for the LiNH2-HMgH complex. It was found that the combinative interaction of magnesium and lithium bonds is responsible for the stability of the complex. The effect of subsitutents on its stability has also been investigated 相似文献
To understand the chemical behavior of uranyl complexes in water, a bis-uranyl [(phen)(UO2)(μ2–F)(F)]2 (A; phen?=?phenanthroline, μ2?=?doubly bridged) and its hydrated form A?·?(H2O)n (n?=?2, 4 and 6) were examined using scalar relativistic density functional theory. The addition of water caused the phen ligands to deviate slightly from the U2(μ2–F)2 plane, and red-shifts the U–F-terminal and U?=?O stretching vibrations. Four types of hydrogen bonds are present in the optimized hydrated A?·?(H2O)n complexes; their energies were calculated to fall within the range 4.37–6.77 kcal mol-1, comparable to the typical values of 5.0 kcal mol-1 reported for hydrogen bonds. An aqueous environment simulated by explicit and/or implicit models lowers and re-arranges the orbitals of the bis-uranyl complex.
Figure
A bis(uranyl) complex [(phen)(UO2)(μ2–F)(F)]2 (A) and its solvated form A?·?(H2O)n were examined using scalar relativistic density functional theory. Hydrogen bonds cause the phen ligand to slightly deviate from the equatorial plane of the uranyl ion, resulting in a pronounced red-shift of the U–F-terminal and U?=?O asymmetric stretching vibrations. The calculated energies fall within 4.4?–6.8 kcal/mol. Explicit and/or implicit aqueous solvation re-arranges the molecular orbitals of the complex 相似文献