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1.
Density functional B3LYP method with 6-31++G** basis set is applied to optimize the geometries of the luteolin, water and luteolin–(H2O)n complexes. The vibrational frequencies are also studied at the same level to analyze these complexes. We obtained four steady luteolin–H2O, nine steady luteolin–(H2O)2 and ten steady luteolin–(H2O)3, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) are used to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are within −13.7 to −82.5 kJ/mol. The strong hydrogen bonding mainly contribute to the interaction energies, Natural bond orbital analysis is performed to reveal the origin of the interaction. All calculations also indicate that there are strong hydrogen bonding interactions in luteolin–(H2O)n complexes. The OH stretching modes of complexes are red-shifted relative to those of the monomer.  相似文献   

2.
The hydrogen-bonding ability of five-membered heteroaromatic molecules containing one chalcogen and two heteroatoms with nitrogen in addition to chalcogen, respectively, have been analyzed using density functional and molecular orbital methods through adduct formation with water. The stabilization energies for all the adducts are established at B3LYP/6-31+G* and MP2/6-31+G* levels after correcting for the basis set superposition error by using the counterpoise method and also corrected for zero-point vibrational energies. A natural bond orbital analysis at B3LYP/6-31+G* level and natural energy decomposition analysis at HF/6-31+G* using MP2/6-31+G* geometries have been carried out to understand the nature of hydrogen-bonding interaction in monohydrated heterocyclic adducts. Nucleus-independent chemical shift have been evaluated to understand the correlation between hydrogen bond formation and aromaticity.  相似文献   

3.
The molecular structure of phenylsilane has been determined accurately by gas-phase electron diffraction and ab initio MO calculations at the MP2(f.c.)/6-31G* level. The calculations indicate that the perpendicular conformation of the molecule, with a Si–H bond in a plane orthogonal to the plane of the benzene ring, is the potential energy minimum. The coplanar conformation, with a Si–H bond in the plane of the ring, corresponds to a rotational transition state. However, the difference in energy is very small, 0.13 kJ mol−1, implying free rotation of the substituent at the temperature of the electron diffraction experiment (301 K). Important bond lengths from electron diffraction are: <rg(C–C)>=1.403±0.003 Å, rg(Si–C)=1.870±0.004 Å, and rg(Si–H)=1.497±0.007 Å. The calculations indicate that the Cipso–Cortho bonds are 0.010 Å longer than the other C–C bonds. The internal ring angle at the ipso position is 118.1±0.2° from electron diffraction and 118.0° from calculations. This confirms the more than 40-year old suggestion of a possible angular deformation of the ring in phenylsilane, in an early electron diffraction study by F.A. Keidel, S.H. Bauer, J. Chem. Phys. 25 (1956) 1218.  相似文献   

4.
As a continuation of our systematic investigation of the effect of substituents on the ring geometry and dynamics in silacyclobutanes and in order to explore the role of the silicon atom as a mediator for electronic interactions between the attached fragments, we studied the molecular structure of 1,1-diethynylsilacyclobutane (DESCB) by means of gas-phase electron diffraction and ab initio calculations. The structural refinement of the electron diffraction data yielded the following bond lengths (ra) and bond angles (uncertainties are 3σ): r(Si–C)=1.874(2) Å, r(Si–C)=1.817(1) Å, (C–Si–C)=79.2(6)°, (C–Si–C)=106.5(6)°. The geminal Si–CC moieties were found to be bent outwards by 3.1(15)° and the puckering angle was determined to be 30.0(15)°. The evidently short Si–C bond length, which was also reproduced by the ab initio calculations, could be rationalized as being the consequence of the electronic interaction between the outer π charges of the triple bond and the 3pπ orbitals at the silicon atom. It is also likely that the conjugation of the geminal ethynyl groups leads to an enhancement of this bond contraction. Electrostatic interactions and the subsequent reduction of the covalent radius of the silicon atom may also contribute to this bond shortening. It has been found that the endocyclic Si–C bond length fits nicely within a scheme describing a monotonous decrease of the Si–C bond length with the increase of the electronegativity of the substituent in various geminally substituted silacyclobutanes.A series of related silacyclobutanes and acyclic diethynylsilanes have been studied by applying various ab initio methods and their optimized structures were compared to the structure of DESCB. Among these compounds are 1,1-dicyanosilacyclobutane (DCYSCB), which is isoelectronic to DESCB, 1,1-diethynylcyclobutane (DECB) which is isovalent to DESCB, monoethynylsilacyclobutane (MESCB) and monocyanosilacyclobutane (MCYSCB). Searching for reasonable support for the explanation of the structural results of DESCB we performed detailed natural population analysis as well as Mulliken population analysis (MPA) on DESCB and other related molecules. In contrast to the Mulliken charges, the natural atomic charges provided helpful information concerning the bonding properties in DESCB and the corresponding compounds. By varying the size of some basis sets, we could demonstrate the validity of the repeatedly discussed dependency of the Mulliken MPA on the basis set.For the performance of the quantum mechanical calculations we employed the following methods and basis sets: HF/6-31G(d,p), DFT/B3PW91/6-31G(d), DFT/B3PW91/6-311++G(d,p), MP2/6-31G(d,p) and MP2/6-311++G(d,p).  相似文献   

5.
Structural and IR-spectroscopic evidence is given that directed contacts from terminal alkynes to C=C double bonds possess the essential characteristics of weak hydrogen bonds. The contacts are directed at the center of the π-bond rather than at one of the individual C-atoms. The contact distances from H to the center of the C=C bond are typically 2.8 Å, with the shortest distances being 2.5 Å. The interaction is of pronounced long-range nature and can be detected in the infrared spectrum even with a long H…π distance of almost 3.0 Å. The sample used is mainly composed of ethynyl steroids belonging to the progestine family.  相似文献   

6.
The reaction of tris(2-hydroxyphenyl)amine with Ge(OEt)4 produced 1,1′-oxybis(1-germa-5-aza-2,8,9-trioxatribenzobicyclo[3.3.3]undeca-3,6,10-triene) (11). This reaction proceeded via 1-ethoxy-1-germa-5-aza-2,8,9-trioxatribenzobicyclo[3.3.3]undeca-3,6,10-triene (10a). In oxo-bridged germatrane dimer 11, the Ge---O---Ge moiety is bent at an angle of 131.2(4)°, and Ge---Obridge distances are 1.750(7) and 1.743(6) Å. The other Ge---O distances, by comparison, averaged 1.785(7) Å. The germanium centers in 11 are nearly trigonal bipyramidal by virtue of significant interaction with transannular nitrogen: the Ge---N distances are 2.235(8) and 2.247(7) Å. Ab initio calculations on 11 and H3Ge---O---GeH3 predict a linear Ge---O---Ge geometry when d-orbitals are omitted from the basis set, but correctly predict a bent geometry when d-orbitals are used.  相似文献   

7.
Three-dimensional X-ray crystal structure analysis shows that the organotelluronium salt, triphenyltelluronium cyanate-chloroform( ), exists as a tetramer in the solid state with both end-to-end and terminally bridging NCO groups. The oligomer is predominantly ionic with tellurium—nitrogen and tellurium—oxygen distances significantly shorter than respective van der Waals distances. Refinement of the structure, based on 3817 reflections collected by automatic diffractometry, converged to a conventional R factor of 4.9% and a weighted R factor of 4.2%. Crystal data for Ph3Te(NCO) · CHCl3 are as follows: a = 12.083(6)Å, b = 12.900(12)Å, c = 13.878(10)Å, α = 95.83(7)°, β = 103.47(7)°γ = 98.87(6)°, V = 1901Å3 (temperature = 23°C) and Z = 4.  相似文献   

8.
5,6-Dihydrouracil (DHU) is a rare pyrimidine base naturally occurring in tRNAs, it differs from the base uracil due to the saturation of the C5–C6 bond. This work presents the interaction energies of complexes formation involving DHU bound to the natural RNA bases adenine (A), uracil (U), guanine (G), and cytosine (C). Full geometry optimization has been performed for the studied complexes by B3LYP/6-31+G(d,p) and MP2/6-31+G(d,p) calculations. The interaction energies were corrected for the basis-set superposition error (BSSE), using the full Boys–Bernardi counterpoise correction scheme. We find that the stability order is DHU:G > DHU:A > DHU:C  DHU:U.  相似文献   

9.
The crystal structure of a new oxide, La2RuO5, was determined ab initio using conventional laboratory X-ray powder diffraction. Combining X-ray and electron diffraction techniques, we found that the new phase crystallized in the monoclinic system with the space group P21/c (SG no.14) and the cell parameters a=9.1878(2) Å, b=5.8313(2) Å, c=7.9575(2) Å and β=100.773(2)° (V=418.8 Å3, Z=4). The structural determination with the Patterson method and Fourier difference syntheses and the final Rietveld refinement were performed by means of the JANA2000 program. The structure is built up from the regular stacking of a two octahedra thick [LaRuO4] zigzag perovskite slab and an original 3.4 Å thick [LaO] slab which constitutes the key feature of this new structure.  相似文献   

10.
The crystal structure of the title compound was determined (crystal data at 143 K: triclinic, space group P−1, Z=4, a=9.538(2) Å, b=11.638(2) Å, c=14.473(2) Å, α=88.647(3)°, β=89.875(3)°, γ=83.835(3)°, V=1596.9(4) Å3). In the crystal there exist two kinds of tetrameric O–HO hydrogen-bond (H-bond) systems that are quite similar to each other. The oxygen atoms accept also intermolecular C–HO H-bonds. The two types of the H-bonds connect the molecules to an infinite two-dimensional supramolecular unit, the stacking of which is aided by an intermolecular C–Hπ H-bond. A phase transition with ΔHt=4.4±0.1 kJ/mol was found at around 420 K.  相似文献   

11.
The crystal and molecular structure of trimethyltin(IV) chloride has been determined by the heavy-atom technique, and refined to a final R value of 0.041 for 1375 independent reflections (2θ < 53°; Mo-Ka radiation I > 2σ(I)) recorded at 138 ± 2 K on a Nonius CAD-4 counter diffractometer. The crystals are monoclinic with space group I2/c; a 12.541(8), b 9.618(11), c 11.015(11) Å, β 92.62(7)°, Z = 8, Dcalcd 1.994 g cm−3. The needle crystals are composed of polymeric chains of chlorine atoms bridging non-planar trimethyltin(IV) units at unequal (2.430(2) and 3.269(2) Å) distances. The zig-zag chains are bent at chlorine (angle Sn---Cl Sn 150.30(9)°), but nearly linear at tin (angle Cl---Sn Cl 176.85(6)°) to describe a distorted trigonal bipyramidal geometry at tin with the trimethyltin groups eclipsed. The interchain d(Sn Cl) distances are greater than 4.1 Å. The angles carbon—tin—carbon (mean 117.1(3)°) are larger than tetrahedral, while the angles carbon—tin—chlorine (mean 99.9(2) Å) are smaller, in accord with isovalent hybridization principles, but more severely distorted than in the gas-phase, monomeric structure. The tin—chlorine distance of 2.430(2) Å is also longer than in the gas phase monomer, and the intermolecular contact of 3.269 Å is shorter than in other organotin chloride bridged systems (sum of Van der Waals radii 3.85 Å).  相似文献   

12.
The R? CH2? HO…H? X (R = SCl, Cl, SH, NO2, OMe, CHO, CN, C2H5, CH3, H; X = F, Cl, Br) complexes are considered here as the interest sample for the consideration of different measures of H‐bond strength. The intermolecular interaction energies are predicted by using MP2/6‐31++G(d,p) and B3LYP/6‐31++G(d,p) methods with basis set superposition error and zero‐point energy corrections. The results showed that intermolecular hydrogen bonds for complexes with HF are stronger than such interactions in complexes with HCl and HBr. Quantum theory of “Atoms in Molecules” and natural bond orbitals method were applied to analyzed H‐bond interactions. The gas phase thermodynamic properties of complexes were predicted using quantum mechanical computations. The obtained results showed a strong influence of the R and X substituents on the thermodynamic properties of complexes. Numerous correlations between topological, geometrical, thermodynamic properties and energetic parameters were also found. © 2011 Wiley Periodicals, Inc.  相似文献   

13.
The present study reports the shell thickness dependence fluorescence resonance energy transfer between Rhodamine 6G dye and Au@SnO2 core–shell nanoparticles. There is a pronounced effect on the PL quenching and shortening of the lifetime of the dye in presence of Au@SnO2 core–shell nanoparticles. The calculated energy transfer efficiencies from dye to Au@SnO2 are 64.4% and 78.3% for 1.5 nm and 2.5 nm thickness of shell, respectively. Considering the interactions of single acceptor and multiple donors, the calculated average distances (rn) are 75.8 and 71.5 Å for 1.5 nm and 2.5 nm thick core–shell Au@SnO2 nanoparticles, respectively.  相似文献   

14.
The structures of two complexes, [Ph3PCH2Ph]+[Bu3SnCl2] and [Ph3AsCH2COPh]+[Ph3SnCl2], have been determined by X-ray diffraction. Both materials are monoclinic, space group P21/c. Unit cell data for [Ph3PCH2Ph]+−[Bu3SnCl2] are a 9.8521(6), b 16.9142(4), c 22.3517(7) Å, β 91.4235(9)°; and for [Ph3AsCH2COPh]+[Ph3SnCl2] a 34.9760(3), b 11.1290(5), c 24.2410(2) Å, β 108.56(2)°, and both consist of the component ionic species. The organotin anions each have trigonal bipyramidal geometry with equatorial organic groups and axial halogens. In the [Ph3SnCl2] anion the two Sn---Cl bond distances are the same (2.58(1) and 2.60(1) Å), but in [Bu3SnCl2], as in [Me3SnCl2], they are substantially different (2.573(7) and 2.689(6) Å). The Sn---C bond distances also vary: [Ph3SnCl2] 2.15(4), 2.16(3) and 2.25(5); [Bu3SnCl2] 2.21(1), 2.20(2) and 2.29(2) Å. Tin-119 Mössbauer data for these and several other similar complexes are also reported.  相似文献   

15.
Molecules of the series ClAsX2 [X = C2H5, N(CH3)2, OCH3] were studied by RHF/6-31G(d) and MP2/6-31G(d) calculations. Their 35Cl NQR frequencies were calculated from the populations of the 3p constituents of the chlorine valence p orbitals. The features of interaction of the geminal atoms in the molecules and the effect of this interaction on the electron distribution in them were analyzed.  相似文献   

16.
Ab initio calculations at second-order Møller-Plesset perturbation theory with the 6-31 + G(d,p) basis set have been performed to determine the equilibrium structures and energies of a series of negative-ion hydrogen-bonded complexes with H2O, H2S, HCN, and HCl as proton donors and OH, SH, CN, and Cl as proton acceptors. The computed stabilization enthalpies of these complexes are in agreement to within the experimental error of 1 kcal mol–1 with the gas-phase hydrogen bond enthalpies, except for HOHOH, in which case the difference is 1.8 kcal mol–1. The structures of these complexes exhibit linear hydrogen bonds and directed lone pairs of electrons except for complexes with H2O as the proton donor, in which cases the hydrogen bonds deviate slightly from linearity. All of the complexes have equilibrium structures in which the hydrogen-bonded proton is nonsymmetrically bound, although the symmetric structures of HOHOH and ClHCl are only slightly less bound than the equilibrium structures. MP2/6-31 + G(d,p) hydrogen bond energies calculated at optimized MP2/B-31 + G(d,p) and at optimized HF/6-31G(d) geometries are similar. Using HF/6-31G(d) frequencies to evaluate zero-point and thermal vibrational energies does not introduce significant error into the computed hydrogen bond enthalpies of these complexes provided that the hydrogen-bonded proton is definitely nonsymmetrically bound at both Hartree-Fock and MP2.  相似文献   

17.
The cooperative enhancement of water binding to the antiparallel β‐sheet models has been studied by quantum chemical calculations at the MP2/6‐311++G**//MP2/6‐31G* level. The binding energies of the two antiparallel β‐sheet models consisting of two strands of diglypeptide are calculated by supermolecular approach. Then water molecules are gradually bonded to the diglypeptide by N? H···OH2 and C?O···HOH hydrogen bonds. Our calculation results indicated that the hydrogen bond length and the atom charge distribution are affected by the addition of H2O molecules. The binding energy of antiparallel diglypeptide β‐sheet models has a great improvement by the increasing of the hydrogen bond cooperativity and the more H2O molecules added the more cooperativity enhancement can be found. The orbital interactions are calculated by natural bond orbital analysis, and the results indicate that the cooperative enhancement is closely related to the orbital interaction. © 2012 Wiley Periodicals, Inc.  相似文献   

18.
Benzamidinium d-glucuronate (1) crystallizes in the orthorhombic space group P212121 and exhibits a 3 D network with molecules linked by moderate intermolecular hydrogen bonds (HNH…O(solvent) 2.993 Å, HNH…OCO 2.894 Å, HNH…O(cycle) 2.844 Å, OH…NH2 2.931 Å, OH…O(solvent) 2.894, 2.924 and 2.715 Å (stronger)) with participation of cations, anions and solvent molecules. The IR-band assignment of carbohydrate moieties is elucidated by a comparison between the types and bond lengths of intermolecular interactions with participation of OH groups in d-glucuronate and linear polarized IR-(IR-LD) spectroscopic data. Experimental results are supported by theoretical ab initio calculations of benzamidinium cation and d-glucuronate anion.  相似文献   

19.
Treatment of the vanadium(II) tetrahydroborate complex trans-V(η1-BH4)2(dmpe)2 with (trimethylsilyl) methyllithium gives the new vanadium(II) alkyl cis-V(CH2SiMe3)2(dmpe)2, where dmpe is the chelating diphosphine 1,2-bis(dimethylphosphino)ethane. Interestingly, this complex could not be prepared from the chloride starting material VCl2(dmpe)2. The CH2SiMe3 complex has a magnetic moment of 3.8 μB, and has been characterized by 1H NMR and EPR spectroscopy. The cis geometry of the CH2SiMe3 complex is somewhat unexpected, but in fact the structure can be rationalized on steric grounds. The X-ray crystal structure of cis-V(CH2SiMe3)2(dmpe)2 is described along with that of the related vanadium(II) alkyl complex trans-VMe2(dmpe)2. Comparisons of the bond distances and angles for VMe2(dmpe) 2, V---C = 2.310(5) Å, V---P = 2.455(5) Å, and P---V---P = 83.5(2)° with those of V(CH2SiMe3)2(dmpe)2, V---C = 2.253(3) Å, V---P = 2.551(1) Å, and P ---V---P = 79.37(3)° show differences due to the differing trans influences of alkyl and phosphine ligands, and due to steric crowding in latter molecule. The V---P bond distances also suggest that metal-phosphorus π-back bonding is important in these early transition metal systems. Crystal data for VMe2(dmpe)2 at 25°C: space group P21/n, with a = 9.041(1) Å, b = 12.815(2) Å, c = 9.905(2) Å, β = 93.20(1)°, V = 1145.8(5) Å3, Z = 2, RF = 0.106, and RwF =0.127 for 74 variables and 728 data for which I 2.58 σ(I); crystal data for V(CH2SiMe3)2(dmpe)2 at −75°C: space group C2/c, with a = 9.652(4) Å, b = 17.958(5) Å, c = 18.524(4) Å, β = 102.07(3)°, V= 3140(3) Å3, Z = 4, RF = 0.033, and RwF = 0.032 for 231 variables and 1946 data for which I 2.58 σ(I).  相似文献   

20.
The C–HN hydrogen bond in the methane–ammonia complex is studied by determining its bond dissociation energy (BDE) and the n(N)→σ*(C–H) interaction. At the MP2(Full)/6-311++G(3df,2p) level of theory with basis set superposition error (BSSE) correction, the BDE was determined to be 2.5 kJ mol−1. The n(N)→σ*(C–H) interaction at this level of theory was found to be 3.7 kJ mol−1 by natural bond orbital (NBO) analysis. It was also found that the NBO values are in general higher than the BDE values with BSSE correction when they are compared at the same level of theory.  相似文献   

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