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1.
The interaction between lanthanum atom (La) and C74 (D 3h) was investigated by all-electron relativistic density function theory (DFT). With the aid of the representative patch of C74 (D 3h), we studied the interaction between C74 (D 3h) and La and obtained the interaction potential. Optimized structures show that there are three equivalent stable isomers, with La located about 1.7 Å off center. There is one transition state between every two stable isomers. According to the minimum energy pathway, the possible movement trajectory of La atoms in the C74 (D 3h) cage was explored. The calculated energy barrier for La atoms moving from the stable isomer to the transition state is 18.4 kcal mol?1. In addition, the dynamic NMR spectra of La@C74 according to the trajectory was calculated. Figure
Optimized structure of La@C74, the ring trajectory of La in C74, and the dynamic 13C NMR spectrum as investigated by all-electron relativistic density function theory 相似文献
2.
This study investigates the interaction between X (X = H and F) and graphene C54H18 (D6 h), and the potential energy surface of the graphene radical. The calculations on the structures and energies are further discussed thermodynamically and kinetically using the density function theory method at the B3LYP/6-31G (d) level. Our findings show that there are four distinct isomers of C54H18–X. C54H18–H2 and C54H18–F4 are the most stable isomers in their own systems. In addition, the transition states, as well as reaction pathways of H transferring between different key points on representative patch, are given to explore the possible reaction mechanism. Finally, the stability of C54H18–X2 is discussed through the density functional theory. 相似文献
3.
The stable structures and aromatic characters for three cationic X3+ (X = Sc, Y, and La) and three relevant neutral X3Cl (X = Sc, Y, La) clusters are investigated at the DFT and post HF level of theory. The calculated results show that the
X3+ cations each has two stable structures: the regular trigon (D3h) and the line (D¥h {{\hbox{D}}_{\infty {\rm{h}}}} ) with the regular trigon (D3h) being the ground state, while for three neutral X3Cl clusters, Sc3Cl has three stable isomers: the trigon-pyramidal (C3v), bidentate (C2v-1), and C2v-2 structures, Y3Cl and La3Cl each has only two stable isomers: the trigon-pyramidal (C3v) and bidentate (C2v-1) structures. The ground states for three X3Cl species are all the bidentate (C2v-1) isomers. The calculations of the resonance energy (RE) and NICS show that trigonal X3+ isomers exhibit higher degree of aromaticity. The detailed molecular orbital analyzes reveal that the isolated trigonal Sc3+ and Y3+ cations each has one delocalized π-type MO and shows single π-aromaticity, while the isolated trigonal La3+ cation has one delocalized σ-type MO and shows single σ-aromaticity. The single π- or σ-aromaticity for X3+ are attributed to the contributions mainly from the d AOs of the corresponding transition metal X atoms. However, when a
singly negatively charged counterion Cl- is added to Sc3+, Y3+, and La3+ cations respectively, the aromatic type for the two Sc3+, Y3+ units in the corresponding neutral Sc3Cl, Y3Cl complexes are changed from π-aromaticity into σ-aromaticity, whereas the σ-aromaticity of the La3+ units in the La3Cl complex keeps unchanged in this process. Thus three Sc3+, Y3+, La3+ units in the corresponding X3Cl complexes all have only one σ-type MO and exhibit single σ-aromaticity. 相似文献
4.
A series of N4X (X = O, S, Se) compounds have been examined with ab initio and density functional theory (DFT) methods. To our knowledge,
these compounds, except for the C2v ring and the C3v towerlike isomers of N4O, are first reported here. The ring structures are the most energetically favored for N4X (X = O and S) systems. For N4Se, the cagelike structure is the most energetically favored. Several decomposition and isomerization pathways for the N4X species have been investigated. The dissociation of C2v ring N4O and N4S structures via ring breaking and the barrier height are only 1.1 and −0.2 kcal mol−1 at the CCSD(T)/6-311+G*//MP2/6-311+G* level of theory. The dissociation of the cagelike N4X species is at a cost of 12.1–16.2 kcal mol−1. As for the towerlike and triangle bipyramidal isomers, their decomposition or isomerization barrier heights are all lower
than 10.0 kcal mol−1. Although the CS cagelike N4S isomer has a moderate isomerization barrier (18.3–29.1 kcal mol−1), the low dissociation barrier (−1.0 kcal mol−1) indicates that it will disappear when going to the higher CCSD(T) level.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
《Inorganica chimica acta》1986,121(2):161-166
Atomic Na, K and Cs were codeposited with CO2 in excess of matrix gas at the temperature of 12 K. The IR spectra revealed the presence of ionic aggregates corresponding to the molecules M(CO)2 and M2(CO2) (M=Na, K, Cs). Both molecular species have C2v symmetry; M(CO2) species have a planar ring structure while M2(CO2) have a W-shape structure. M2(CO2) molecules with Cs symmetry were also identified. The geometrical parameters of all the molecules were determined by 12C/13C and 16O/18O isotopic shifts. Raman spectra were also recorded and the results are reported in this study. The effect of photolysis on the structure of these molecules was examined. It was determined that photolysis promotes the formation of Na(CO2) and transforms the M2(CO2) molecules with C2v symmetry into Cs symmetry isomers. 相似文献
6.
Dušan N. Sredojević Predrag V. Petrović Goran V. Janjić Edward N. Brothers Michael B. Hall Snežana D. Zarić 《Journal of molecular modeling》2016,22(1):30
The strength of the stacking interactions in the bipy complexes of nickel, palladium, and platinum, [M(CN)2 bipy]2 (M?=?Ni, Pd, Pt), was calculated using the ωB97xD/def2-TZVP method. The results show that for all considered geometries, interactions are the strongest for platinum, and weakest for nickel complexes, as a result of higher dispersion contributions of platinum over the palladium and nickel complexes. It was also shown that strength of interactions considerably rises with an increase of the stacking overlap area. As a consequence of the favorable electrostatic term, the strength of interactions also rises when metal atom and cyano ligands are involved in the overlap with bipy ligand. The strongest interaction was calculated in the platinum complex, for the geometry that has overlap of metal and cyano ligands with bipy ligand with an energy of -39.80 kcal mol-1. The energies for similar geometries of palladium and nickel complexes are -34.60 and -32.45 kcal mol-1. These energies, remarkably, exceed the strength of the stacking interactions between organic aromatic molecules. These results can be of importance in all systems with stacking interactions, from materials to biomolecules. 相似文献
7.
《Inorganica chimica acta》1988,147(2):189-197
Complexes of the M(en)3Ag2(CN)4 (M = Ni, Zn, Cd) and M(en)2Ag2(CN)4 (M = Ni, Cu, Zn, Cd) type were prepared and identified by elemental analysis, infrared spectroscopy, measurement of magnetic susceptibility, and X-ray powder diffractometry. The crystal structures of Ni(en)3Ag2(CN)4 (I) and Zn(en)2Ag2(CN)4 (II) were determined by the method of monocrystal structure analysis. Complex I crystallizes in the space group C2/c, a = 1.2639(5), b = 1.3739(4), c = 1.2494(4) nm, β = 113.25(4)°, Dm = 1.86(1), Dc = 1.86 gcm−3 Z = 4, R = 0.0429. The crystal structure of I consists of complex cations [Ni(en)3]2+ and complex anions [Ag(CN)2]−. Complex II crystallizes in the space group I2/m, a = 0.9150(3), b = 1.3308(4), c = 0.6442(2) nm, β = 95.80(3)°, Dm = 2.14(1), Dc = 2.15 gcm−3, Z = 2, R = 0.0334. Its crystal structure consists of infinite, positively charged chains of the [-NCAgCNZn- (en)2]nn+ type and isolated [Ag(CN)2]− anions. The atoms of Ag are positioned parallely to the z axis and the AgAg distance is equal to 0.3221(2) nm. 相似文献
8.
An unusual phenomenon, the specific interaction between tris(hydroxymethyl)aminomethane (Tris) and lysozyme (LZM), was demonstrated for the first time by rapid screen analysis of interactions using a quartz crystal microbalance (QCM) biosensor. This phenomenon was also observed in a surface plasmon resonance (SPR) system. Further study using high-performance affinity chromatography (HPAC) confirmed this specific interaction between LZM and immobilized Tris with an apparent dissociation constant (KD) of 6.7 × 10−5 M. Molecular docking was carried out to identify possible modes of binding between LZM and Tris linked to a binding arm. The estimated binding free energy was −6.34 kcal mol−1, corresponding to a KD of 2.3 × 10−5 M, which correlated well with the experimental value. Based on the docking model, the three hydroxyl groups of Tris form intermolecular H bonds with Asp52, Glu35, and Ala107 in LZM. This study reinforces the importance of buffer selection in quantitative biochemical investigations. For a lysozyme ligand binding study, it is better to avoid using Tris when the ligands under study are weak binders. 相似文献
9.
Matthias Hofmann 《Journal of biological inorganic chemistry》2007,12(7):989-1001
Molybdenum and tungsten complexes as models for the active sites of assimilatory or dissimilatory nitrate reductases (NR)
were computed at the CPCM-B98/SDDp//B3LYP/Lanl2DZp* plus zero point energy level of density functional theory. The ligands
were chosen on the basis of available experimental protein or small chemical model structures. A water molecule is found to
bind to assimilatory NR models [(Me2C2S2)MO(YMe)]− (−11.5 kcal mol−1 for M is Mo, Y is S) and may be replaced by nitrate (−4.5 kcal mol−1) (but a hydroxy group may not). Nature’s choice of M is Mo and Y is S for NR has the largest activation energy for protein-free
models (13.3 kcal mol−1) and the least exothermic reaction energy for the nitrate reduction (−14.9 kcal mol−1) compared with M is W and Y is O or Se alternatives. Water binding to dissimilatory NR model complexes [(Me2C2S2)2M(YR)]− is considerably endothermic (10.3 kcal mol−1); nitrate binding is only slightly so (1.5 kcal mol−1 for RY− is MeS−). The exchange of an oxo ligand (assimilatory NR) for a dithiolato ligand (dissimilatory NR model) reduces the exothermicity
(−8.6 kcal mol−1 relative to the fivefold-coordinate reduced complex) and raises the barrier for oxygen atom transfer (OAT) in the nitrate
complex (19.2 kcal mol−1). Not for the mono but only for the bisdithiolato complexes hydrogen bonding involving the coordinated substrate may significantly
lower the OAT barrier as shown by explicitly adding water molecules. Substitution of tungsten for molybdenum generally lowers
OAT activation energies and makes nitrate reduction reaction energies more negative. Bidentate carboxylato binding identified
in Escherichia coli NarGHI is the preferred binding mode also for an acetato model. However, one dithiolato ligand folds when the MoVI center is bare of a good π-donor ligand, e.g., an oxo group. Computations on [(mnt)2MoIV(YR)(PPh3)]− [mnt is (CN)2C2S2
2−] gave a smaller nitrate reduction activation energy for RY− is Cl−, compared with RY− is PhS−, although experimentally only the phenyl thiolato complex and not the chloro complex was found to be a functional NR model.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Alejandra?Monjaraz-Rodríguez Mariano?Rodriguez-Bautista Jorge?Garza Rafael?A.?Zubillaga Rubicelia?Vargas
The potential energy surface of [Cu(H2O)n]2+ clusters with n?=?12, 16, and 18 was explored by using a modified version of the simulated annealing method. Such exploration was carried out by using the PM7 semiempirical method to obtain around 100,000 isomers, which provide candidates to be optimized with PBE0-D3, M06-2X, and BHLYP exchange-correlation functionals coupled with the 6–311++G** basis set. These methods based on the Kohn-Sham approach delivered isomers with coordination numbers of 4, 5, and 6. The analysis used to obtain coordination numbers was based on geometrical parameters and the quantum theory of atoms in molecules (QTAIM) approach. Our methodology found only one isomer with fourfold coordination and its probabilities to appear in these clusters are quite small for high temperatures. The procedure used in this article predicts important populations of fivefold and sixfold coordination clusters, in fact, the fivefold coordination dominates for PBE0-D3 and BHLYP methods, although the sixfold coordination starts to be important when the number of water molecules is increased. The nature of axial and equatorial contacts is discussed in the context of the QTAIM and the noncovalent interaction index (NCI), which gives a clear classification of such orientations. Also, these methods suggest a partial covalent interaction between the Cu2+ and water molecules in both positions; equatorial and axial. 相似文献
11.
A density functional theory (DFT) investigation into the structures and bonding characteristics of [(B3O3H3)nM]+(n?=?1, 2;M?=?Cu, Ag, Au) complexes was performed. DFT calculations and natural bond orbital (NBO) analyses indicate that the ΙB metal complexes of boroxine exhibit intriguing bonding characteristics, different from the typical cation–π interactions between ΙB metal-cations and benzene. The complexes of [B3O3H3M]+ and [(B3O3H3)2?M]+ (M?=?Cu, Ag, and Au) favor the conformation of perfectly planar structures with the C2v and D2h symmetry along one of the threefold molecular axes of boroxine, respectively. Detailed natural resonance theory (NRT) and canonical molecular orbitals (CMOs) analyses show that interaction between the metal cation and the boroxine in [B3O3H3M]+ (M?=?Cu, Ag, and Au) is mainly ionic, while the ΙB metal-cations←π donation effect is responsible for the binding site. In these complexes, boroxine serves as terminals η1-B3O3H3 with one O atom of the B3O3 ring. The infra-red (IR) spectra of [B3O3H3M]+ were simulated to facilitate their future experimental characterization. The complexes all give two IR active modes at about 1,300 and 2,700 cm?1, which are inactive in pure boroxine. Simultaneously, the B–H stretching modes of the complexes are red-shifted due to the interaction between the metal-cation and boroxine. To explore the possibility of the structural pattern developed in this work forming mesoporous materials, complexes [(B3O3H3M)6]6+ (M?=?Cu, Ag, and Au) were also studied, which appear to be unique and particular interesting: they are all true minima with D6h symmetries and pore sizes ranging from 12.04 Å to 13.65 Å.
A density functional theory investigation on the structures and bonding characteristics of [(B3O3H3)nM]+(n?=?1, 2;M?=?Cu, Ag, Au) complexes has been performed. Detailed natural resonance theory (NRT) and canonical molecular orbitals (CMOs) analyses show that the interactions between the metal cation and the boroxine in [B3O3H3M]+ (M?=?Cu, Ag, and Au) are mainly ionic, while the IB metal-cations?←?π donation effect is responsible for the binding site. The [(B3O3H3M)6]6+ (M?=?Cu, Ag, and Au) appear to be unique and are particular interesting: they are all true minima with D6h symmetries and pore sizes ranging from 12.04 Å to 13.65 Å and may be extended to form mesoporous materials. 相似文献
12.
Dipankar Sutradhar Therese Zeegers-Huyskens Asit K. Chandra 《Journal of molecular modeling》2013,19(11):5045-5052
The conformation and the interaction of CHF2OCF2CHF2 (desflurane II) with one water molecule is investigated theoretically using the ab initio MP2/aug-cc-pvdz and DFT-based M062X/6-311++G(d,p) methods. The calculations include the optimized geometries, the harmonic frequencies of relevant vibrational modes along with a natural bond orbital (NBO) analysis including the NBO charges, the hybridization of the C atom and the intra- and intermolecular hyperconjugation energies. In the two most stable conformers, the CH bond of the F2HCO- group occupies the gauche position. The hyperconjugation energies are about the same for both conformers and the conformational preference depends on the interaction between the non-bonded F and H atoms. The deprotonation enthalpies of the CH bonds are about the same for both conformers, the proton affinity of the less stable conformer being 3 kcal mol?1 higher. Both conformers of desflurane II interact with water forming cyclic complexes characterized by CH…O and OH…F hydrogen bonds. The binding energies are moderate, ranging from ?2.4 to ?3.2 kcal mol?1 at the MP2 level. The origin of the blue shifts of the ν(CH) vibrations is analyzed. In three of the complexes, the water molecule acts as an electron donor. Interestingly, in these cases a charge transfer is also directed to the non bonded OH group of the water molecule. This effect seems to be a property of polyfluorinated ethers. 相似文献
13.
《Inorganica chimica acta》1988,142(2):329-331
The complex (C5D5)2Yb(dme) (dme = 1,2- dimethoxyethane) has been prepared by reaction of Tl(C5D5) with ytterbium metal in dme and is isostructural with (C5H5)2Yb(dme). Thermal desolvation under vacuum yields (C5D5)2Yb, for which essentially identical high resolution neutron powder diffraction data were obtained at 294 K and 77 K, but the structure could not be determined. 相似文献
14.
Pavlo O. Dral 《Journal of molecular modeling》2014,20(3):1-5
I have performed quantum chemical calculations for the CF3X (X = Cl, Br) ???Aun (n?=?2, 3, and 4) complexes at M05-2X/aug-cc-pVDZ(PP) level. Two types of optimized structures were obtained. Type I complexes are stabilized by the coordination force between the negative electrostatic potential of halogen atom and the gold atom, and type II complexes contain halogen bonds formed between the σ-hole of the halogen atoms and the negative electrostatic potential of Aun. Results of the interaction energy indicate that type I complexes are more stable than type II complexes. AIM analysis reveals that type II complexes are a closed shell interaction and there is a partially covalent nature for type I complexes. 相似文献
15.
We have studied the influence of hydrogenation on the relative stability of the low-lying isomers of the anionic B7− cluster, computationally. It is known that the pure-boron B7− cluster has a doubly (σ- and π-) aromatic C6v (3A1) quasi-planar wheel-type triplet global minimum (structure 1), a low-lying σ-aromatic and π-antiaromatic quasi-planar singlet C2v (1A1) isomer 2 (0.7 kcal mol−1 above the global minimum), and a planar doubly (σ- and π-) antiaromatic C2v (1A1) isomer 3 (7.8 kcal mol−1 above the global minimum). However, upon hydrogenation, an inversion in the stability of the species occurs. The planar B7H2− (C2v, 1A1) isomer 4, originated from the addition of two hydrogen atoms to the doubly antiaromatic B7− isomer 3, becomes the global minimum structure. The second most stable B7H2− isomer 5, originated from the quasi-planar triplet wheel isomer 1 of B7−, was found to be 27 kcal mol−1 higher in energy. The inversion in stability occurs due to the loss of the doubly aromatic character in the wheel-type global minimum isomer (C6v, 3A1) of B7− upon H2−addition. In contrast, the planar isomer of B7− (C2v, 1A1) gains aromatic character upon addition of two hydrogen atoms, which makes it more stable.
Figure The B7H2-global minimum structure and its σ-aromatic and π-antiaromatic MOs
Dedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday. 相似文献
16.
Tarun K. Panda 《Inorganica chimica acta》2006,359(15):4765-4768
Bis(diphosphanylamido) complexes of calcium and ytterbium, [{(Ph2P)2N}2M(THF)3] (M = Ca (1), Yb (2)), have been prepared by reaction of [K(THF)nN(PPh2)2] (n = 1.25, 1.5) and MI2. The single crystal X-ray structures of compounds 1 and 2 always show a η2-coordination of the ligand via the nitrogen and one phosphorus atom. In solution a dynamic behavior of the ligand is observed, which is caused by the rapid exchange of the two different phosphorus atoms. 相似文献
17.
G.A. dos Santos C.H. Thomé G.A. Ferreira J.S. Yoneda K.R.P. Daghastanli H.L. Gimenes-Teixeira M.G. Constantino V.M. Faça L.J. Greene E.M. Rego P. Ciancaglini 《生物化学与生物物理学报:生物膜》2010,1798(9):1714-1723
10-(Octyloxy) decyl-2-(trimethylammonium) ethyl phosphate (ODPC) is an alkylphospholipid that can interact with cell membranes because of its amphiphilic character. We describe here the interaction of ODPC with liposomes and its toxicity to leukemic cells with an ED-50 of 5.4, 5.6 and 2.9 μM for 72 h of treatment for inhibition of proliferation of NB4, U937 and K562 cell lines, respectively, and lack of toxicity to normal hematopoietic progenitor cells at concentrations up to 25 μM. The ED-50 for the non-malignant HEK-293 and primary human umbilical vein endothelial cells (HUVEC) was 63.4 and 60.7 μM, respectively. The critical micellar concentration (CMC) of ODPC was 200 μM. Dynamic light scattering indicated that dipalmitoylphosphatidylcholine (DPPC) liposome size was affected only above the CMC of ODPC. Differential calorimetric scanning (DCS) of liposomes indicated a critical transition temperature (Tc) of 41.5 °C and an enthalpy (?H) variation of 7.3 kcal mol−1. The presence of 25 μM ODPC decreased Tc and ?H to 39.3 °C and 4.7 kcal mol−1, respectively. ODPC at 250 μM destabilized the liposomes (36.3 °C, 0.46 kcal mol−1). Kinetics of 5(6)-carboxyfluorescein (CF) leakage from different liposome systems indicated that the rate and extent of CF release depended on liposome composition and ODPC concentration and that above the CMC it was instantaneous. Overall, the data indicate that ODPC acts on in vitro membrane systems and leukemia cell lines at concentrations below its CMC, suggesting that it does not act as a detergent and that this effect is dependent on membrane composition. 相似文献
18.
Wen Guo Xu Yuan Chun Zhang Shi Xiang Lu Rui Chun Zhang 《Journal of molecular modeling》2009,15(11):1329-1336
The equilibrium geometries, total energies, and vibrational frequencies of anions X2Y2
− (X = C, Si, Ge and Y = N, P, As) are theoretically investigated with density functional theory (DFT) method. Our calculation
shows that for C2N2
− species, the D
2h
isomer is the most stable four-membered structure, and for other species the C
2v
isomer in which two X atoms are contrapuntal is the most stable structure at the B3LYP/6-311 +G* level. Wiberg bond index (WBI) and negative nucleus-independent chemical shift (NICS) value indicate the existence of delocalization
in stable X2Y2
− structures. A detailed molecular orbital (MO) analysis further reveals that stable isomers of these species have strongly
aromatic character, which strengthens the structural stability and makes them closely connected with the concept of aromaticity. 相似文献
19.
L. Forlani C. Ioppolo E. Antonini C.J. Martin M.A. Marini 《Journal of inorganic biochemistry》1984,20(2):147-155
Calorimetric studies of the reduction of free oxygen in solution by sodium dithionite are in agreement with a stoichiometry of 2 moles Na2S2O4 per mole of oxygen. The reaction is biphasic with ΔHt - 118±7 kcal mol?1 (?494 ± 29 kJ mol?1). The initial phase of the reaction proceeds with an enthalpy change of ca ?20 kcal (?84 kJ) and occurs when 0.5 moles of dithionite have been added per mole dioxygen present. This could be interpreted as the enthalpy change for the addition of a single electron to form the superoxide anion. Further reduction of the oxygen to water by one or more additional steps is accompanied by an enthalpy change of ca ?100 kcal (?418. 5 kJ). Neither of these reductive phases is consistent with the formation of hydrogen peroxide as an intermediate. The reduction of hydrogen peroxide by dithionite in 0.1 M phosphate buffer, pH 7.15, is a much slower process and with an enthalpy change of ca ? 74 kcal mol?1 (?314 kJ mol?1). Dissociation of oxyhemoglobin induced by the reduction of free oxygen tension with dithionite also shows a stoichiometry of 2 moles dithionite per mole oxygen present and an enthalpy change of ca. ?101 ±9 kcal mol?1 (?423± 38 kJ mol?1). The difference in the observed enthalpies (reduction of dioxygen vs. oxyhemoglobin) has been attributed to the dissociation of oxyhemoglobin, which is 17 kcal mol?1 (71 kJ mol?1). 相似文献
20.
Calculation predicted the interacting forms of halopentafluorobenzene C6F5X (X=F, Cl, Br, I) with triethylphosphine oxide which is biologically interested and easily detected by 31P NMR. The interaction energy and geometric parameters of resultant halogen or π-hole bonding complexes were estimated and compared. Moreover, the bonding constants were determined by 31P NMR. Both theory and experiments indicated the C6F6 and C6F5Cl interact with triethylphosphine oxide by π-hole bonding pattern, while C6F5I by halogen/σ-hole bonding form. For C6F5Br, two interactions are comparative and should coexist competitively. The calculated interaction energies of σ-hole bonding complexes, ?5.07 kcal mol?1 for C6F5Br?O=P and ?8.25 kcal mol?1 for C6F5I?O=P, and π-hole bonding complexes, ?7.29 kcal mol?1 for C6F6?O=P and ?7.24 kcal mol?1 for C6F5Cl?O=P, are consistent with the changing tendency of bonding constants measured by 31P NMR, 4.37, 19.7, 2.42 and 2.23 M?1, respectively. Figure
The competitive σ-hole···O=P and π-hole···O=P bonds between C6F5X (X=F, Cl, Br, I) and O=PEt3 相似文献