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1.
杨颙  张为俊  高晓明 《中国化学》2006,24(7):887-893
A theoretical study on the blue-shifted H-bond N-H…O and red-shifted H-bond O-H…O in the complexHNO…H_2O_2 was conducted by employment of both standard and counterpoise-corrected methods to calculate thegeometric structures and vibrational frequencies at the MP2/6-31G(d),MP2/6-31 G(d,p),MP2/6-311 q G(d,p),B3LYP/6-31G(d),B3LYP/6-31 G(d,p) and B3LYP/6-311 G(d,p) levels.In the H-bond N-H…O,the calcu-lated blue shift of N-H stretching frequency is in the vicinity of 120 cm~(-1) and this is indeed the largest theoreticalestimate of a blue shift in the X-H…Y H-bond ever reported in the literature.From the natural bond orbital analy-sis,the red-shifted H-bond O-H…O can be explained on the basis of the dominant role of the hyperconjugation.For the blue-shifted H-bond N-H…O,the hyperconjugation was inhibited due to the existence of significant elec-tron density redistribution effect,and the large blue shift of the N-H stretching frequency was prominently due tothe rehybridization of sp~n N-H hybrid orbital.  相似文献   

2.
On the basis of a comparison of chemical shifts and wavenumbers of several secondary thioamides and amides having monocationic substituents attached to thiocarbamoyl or carbamoyl groups by a polymethylene chain, new intramolecular unconventional N···H+···N hydrogen bonding effects were discovered. It is argued that the CH2—N rotation is hindered and two +H···NHCH3 non‐equivalent protons occur in a proton spectrum of hydrochloride 1a (at 10.68 and 2.77 ppm, respectively) instead of two +NH2CH3 protons. Presumably, the above steric factors inhibit the acidic hydrolysis of 1a (stabilized by strong intramolecular N···H+···N hydrogen bonds) to an amide and prevent intramolecular cyclization of 2a (stabilized by strong intramolecular neutral–neutral N···HN hydrogen bonds) to a cyclic amidine. Postulation of additional dihydrogen bond formation is helpful in understanding the spectroscopic differences of 4 and 5 . The above new bonding is also compared with intramolecular N···H—N+ hydrogen bonds in primary amine salts 7 and 8 . In contrast to 3 , a cooperative hydrogen bonded system is observed in 9 and 10 . The weak hydrogen bonds in 7 – 10 facilitate the hydrolysis and cyclization reactions of secondary thioamides. The spectroscopic data for secondary (thio)amides are especially useful for characterizing the electronic situation at the (thio)carbamoyl nitrogen atoms and they are perfectly correlated with the reactivity. Examples of chelation of protons by thioamides ( 11 and 12 ), which contain strongly electron‐donating pyrimidine groups, are presented to show the contribution of dihydrogen bonding in the protonation reaction similar to 1 and 4 . Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

3.
Noncovalent interactions involving aromatic rings, such as π···π stacking, CH···π are very essential for supramolecular carbon nanostructures. Graphite is a typical homogenous carbon matter based on π···π stacking of graphene sheets. Even in systems not involving aromatic groups, the stability of diamondoid dimer and layer‐layer graphane dimer originates from C − H···H − C noncovalent interaction. In this article, the structures and properties of novel heterogeneous layer‐layer carbon‐nanostructures involving π···H‐C‐C‐H···π···H‐C‐C‐H stacking based on [n ]‐graphane and [n ]‐graphene and their derivatives are theoretically investigated for n = 16–54 using dispersion corrected density functional theory B3LYP‐D3 method. Energy decomposition analysis shows that dispersion interaction is the most important for the stabilization of both double‐ and multi‐layer‐layer [n ]‐graphane@graphene. Binding energy between graphane and graphene sheets shows that there is a distinct additive nature of CH···π interaction. For comparison and simplicity, the concept of H‐H bond energy equivalent number of carbon atoms (noted as NHEQ), is used to describe the strength of these noncovalent interactions. The NHEQ of the graphene dimers, graphane dimers, and double‐layered graphane@graphene are 103, 143, and 110, indicating that the strength of C‐H···π interaction is close to that of π···π and much stronger than that of C‐H···H‐C in large size systems. Additionally, frontier molecular orbital, electron density difference and visualized noncovalent interaction regions are discussed for deeply understanding the nature of the C‐H···π stacking interaction in construction of heterogeneous layer‐layer graphane@graphene structures. We hope that the present study would be helpful for creations of new functional supramolecular materials based on graphane and graphene carbon nano‐structures. © 2017 Wiley Periodicals, Inc.  相似文献   

4.
According to the 1H, 13C and 15N NMR spectroscopic data and DFT calculations, the E‐isomer of 1‐vinylpyrrole‐2‐carbaldehyde adopts preferable conformation with the anti‐orientation of the vinyl group relative to the carbaldehyde oxime group and with the syn‐arrangement of the carbaldehyde oxime group with reference to the pyrrole ring. This conformation is stabilized by the C? H···N intramolecular hydrogen bond between the α‐hydrogen of the vinyl group and the oxime group nitrogen, which causes a pronounced high‐frequency shift of the α‐hydrogen signal in 1H NMR (~0.5 ppm) and an increase in the corresponding one‐bond 13C–1H coupling constant (ca 4 Hz). In the Z‐isomer, the carbaldehyde oxime group turns to the anti‐position with respect to the pyrrole ring. The C? H···O intramolecular hydrogen bond between the H‐3 hydrogen of the pyrrole ring and the oxime group oxygen is realized in this case. Due to such hydrogen bonding, the H‐3 hydrogen resonance is shifted to a higher frequency by about 1 ppm and the one‐bond 13C–1H coupling constant for this proton increases by ~5 Hz. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

5.
The occurrence of bifurcate H‐bonds CAr–H···O=C in the structure of (diaryl)‐tetrahydrofuranones was experimentally demonstrated using different methods and techniques. The consistent increasing spin–spin coupling constants 1J(C,H) of the ortho‐H‐atoms and low‐field shift of vC=O in IR spectra of 2,2‐(diaryl)tetrahydrofuran‐3(2H)‐ones relative to their 5,5‐diaryl counterparts, as well as pronounced dependence of the ortho‐C–H H‐atoms chemical shifts on the temperature and solvent polarity along with X‐ray diffraction analysis data unambiguously point to the existence of weak CAr–H···O=C H‐bonds in these molecules.  相似文献   

6.
Linear hydrogen bonding formed between the nitrogen end of cyanogen‐N‐oxide (ONCCN) and hydrogen halides HX (X = F, Cl, Br) has been observed in their ground Σ states. The order of agreement of energetic stabilities between the correlated functionals used in this calculation is: B3LYP < PBE0 < PBE < PW91 in conjunction with the 6–311++G(3df,3pd) basis set. Analysis of various parameters describing the existence of H‐bonds in these dimers follows the conventional trend: ONCCN···HF > ONCCN···HCl > ONCCN···HBr in the series, except H‐bond lengths and static dipole polarizabilities which are in reverse order. The atomic charges obtained from the Mulliken and natural population analysis is used to assess the charge transfer effects that accompany the dimer formation. It is found from the investigation that the dimers having highest binding energy are accompanied by the highest transfer of charge. The 14N nuclear quadrupole coupling constants of the monomer ON1CCN2 are found to be decreased upon complection and in the series it increases from F through Br. We observed enhancements in the values of the dimer dipole moment and intrinsic dipole polarizabilities compared with the sum of the monomer values by intermolecular electrical interaction. Investigation reveals vibrational spectral shifts of HX and CN stretching modes similar to the conventional red‐shifted H‐bonded dimers; for the former case, the infrared band intensity increases significantly. Finally, the new vibrational modes originated from the intermolecular interaction are outlined. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007  相似文献   

7.
Concentrated aqueous solutions of magnesium chloride and calcium nitrate, respectively, allow on addition of the potassium salt of tetrathiosquarate, K2C4S4 · H2O, the isolation of the earth alkaline salts MgC4S4 · 6 H2O ( 1 ) and CaC4S4 · 4 H2O ( 2 ) as orange and red crystals. The crystal structure determinations ( 1 : monoclinic, C2/c, a = 17.2280(7), b = 5.9185(2), c = 13.1480(4) Å, β = 104.730(3)°, Z = 4; 2 : monoclinic, P21/m, a = 7.8515(3), b = 12.7705(5), c = 10.6010(4) Å, β = 93.228(2)°, Z = 4) show the presence of C4S42? ions with almost undistorted D4h symmetry having average C–C and C–S bond lengths of 1.451Å and 1.659Å for 1 and 1.451Å and 1.655Å for 2 . The structure of 1 contains discrete, octahedral [Mg(H2O)6]2+ complexes. Several O–H····O and O–H····S bridges with H····O and H····S distances of less than 2.50Å connect cations and anions. The structure of 2 is built of concatenated, edge‐sharing Ca(H2O)6S2 polyhedra. The Ca2+ ions have the coordination number eight, C4S42? act as a chelating ligands towards Ca2+ with Ca–S distances of 3.14Å. The infrared and Raman spectra show bands typical for the molecular building units of the two compounds.  相似文献   

8.
The X‐ray crystal structures of the polyfluorinated complexes [5,5′‐bis(HCF2CF2CF2CF2CH2OCH2)‐2,2′‐bpy]MI2 ( 55‐8F‐PtI 2 and 55‐8F‐PdI 2 where M = Pt and Pd, respectively) were obtained. These two structures are found to show not only two different types of intramolecular, six‐membered cyclic C–H···F–C interactions (F2C–H···F–C and HC–H···F–C) as important structural features but also alternating fluorinated and non‐fluorinated layers. The F2C–H···F–C interactions, which are close to the metal core, are much better structurally characterized in this type of complexes with fluorous ponytails at the 5,5′ positions than those previously reported at the 4,4′ positions. The molecular planes of (bpy)MI2 are extended by self‐matching, using two C–H···I hydrogen bonds and one C–H···F–C blue‐shifting hydrogen bond. The F2C–H···F–C hydrogen bonds interact at the supramolecular level such that one polyfluorinated ponytail of the title compounds is transoid without an intramolecular C–H···F–C interaction, while the other polyfluorinated ponytail is cisoid with an intramolecular C–H···F–C interaction. Why one ponytail is cisoidal while the other is transoidal will be explained. Furthermore, the second type of C–H···F–C interactions involving the methylene H atom has been identified for the first time. In addition, these two metal structures are studied by density functional theory (DFT).  相似文献   

9.
Melting reactions of copper, CuI, selenium, and Bi2Se3 yielded black, shiny needles of Cu4BiSe4I = Cu4BiSe2(Se2)I. The compound decomposes peritectically above 635(5) K and crystallizes in the orthorhombic space group Pnma with a = 960.1(1) pm, b = 413.16(3) pm, and c = 2274.7(2) pm (T = 293(2) K). In the crystal structure, strands ${1}\atop{{\infty}}$ [BiSeSe2/2(Se2)2/2]3– run along [010]. Therein, the bismuth(III) cation is coordinated by five selenium atoms, which form a square pyramid. The copper(I) cations are coordinated tetrahedrally by selenide, diselenide and iodide ions. Edge‐sharing of these tetrahedra results in zigzag chains of copper cations with short distances of 262.7(4) pm. Enhanced dispersion of the 3d bands, the Crystal Orbital Hamilton Populations (COHP), and disynaptic ELI‐D basins indicate weakly attractive d10···d10 interactions between the copper cations. The semiconducting properties and the calculated electronic band structure suggest an electron‐precise compound. In copper‐deficient Cu3.824(8)BiSe4I, the Cu···Cu distances are 5 pm shorter, and Raman spectroscopy indicates the presence of diselenide(1–) radical anions besides the diselenide(2–) groups. As a result, in Cu3.824(8)BiSe4I, selenium coexists in the oxidations states –II, –I, and –0.5.  相似文献   

10.
The effect of substitution on the strength and nature of CH···N hydrogen bond in XCCH···NH3 (X = F, Cl, Br, OH, H, Me) and NCH···NH3 complexes were investigated by quantum chemical calculations. Ab initio calculations were performed using MP2 method with a wide range of basis sets. With tacking into account the BSSE and ZPVE, the values of BEs decrease. Replacement of the nonparticipatory hydrogen atom of HCCH by the electronegative atoms (F, Cl, and Br), lead to the BEs increases. The BE corresponding to the replacement of the nonparticipatory hydrogen atom of HCCH by the OH and CH3 groups decreases. A far greater enhancement of the interaction energy arises from replacement of HCCH by the more acidic HCN. The natural bond orbital analysis and the Bader's quantum theory of atoms in molecules were also used to elucidate the interaction characteristics of these complexes. The electrostatic nature of H‐bond interactions is predicted from QTAIM analysis. In addition, the relationship between the isotropic and anisotropic chemical shifts of the bridging hydrogen and binding energy of complexes as well as electron density at N···H BCPs were investigated. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011  相似文献   

11.
In the series of diaminoenones, large high‐frequency shifts of the 1H NMR of the N? H group in the cis‐position relative to the carbonyl group suggests strong N? H···O intramolecular hydrogen bonding comprising a six‐membered chelate ring. The N? H···O hydrogen bond causes an increase of the 1J(N,H) coupling constant by 2–4 Hz and high‐frequency shift of the 15N signal by 9–10 ppm despite of the lengthening of the relevant N? H bond. These experimental trends are substantiated by gauge‐independent atomic orbital and density functional theory calculations of the shielding and coupling constants in the 3,3‐bis(isopropylamino)‐1‐(aryl)prop‐2‐en‐1‐one (12) for conformations with the Z‐ and E‐orientations of the carbonyl group relative to the N? H group. The effects of the N? H···O hydrogen‐bond on the NMR parameters are analyzed with the atoms‐in‐molecules (AIM) and natural bond orbital (NBO) methods. The AIM method indicates a weakening of the N? H···O hydrogen bond as compared with that of 1,1‐di(pyrrol‐2‐yl)‐2‐formylethene (13) where N? H···O hydrogen bridge establishes a seven‐membered chelate ring, and the corresponding 1J(N,H) coupling constant decreases. The NBO method reveals that the LP(O) →σ*N? H hyperconjugative interaction is weakened on going from the six‐membered chelate ring to the seven‐membered one due to a more bent hydrogen bond in the former case. A dominating effect of the N? H bond rehybridization, owing to an electrostatic term in the hydrogen bonding, seems to provide an increase of the 1J(N,H) value as a consequence of the N? H···O hydrogen bonding in the studied diaminoenones. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

12.
Structures of Ionic Di(arenesulfonyl)amides. 8. Sodium Bis[di(4‐fluorobenzenesulfonyl)amido‐N]argentate: A Heterobimetallic Complex Exhibiting a Lamellar Layer Structure and Short C–H···F–C Interlayer Contacts Na[Ag{N(SO2–C6H4–4‐F)2}2] (monoclinic, C2/c, Z′ = 1/2) is the first heterobimetallic representative in a well‐documented class of layered inorgano‐organic solids where the inorganic component is comprised of metal cations and coordinating N(SO2)2 groups and the outer regions are formed by the aromatic rings of the di(arenesulfonyl)amide entities, which adopt a folded conformation approximating to mirror symmetry. The inversion‐symmetric bis(amido)argentate unit of the novel compound displays an exactly linear N–Ag–N core and short Ag–N bonds of 217.55(17) pm (at ?140 °C); the coordination number of the silver ion is extended to 2 + 6 by four internal and two external Ag···O secondary interactions. The polar lamella is constructed from rows of Na+ ions located on twofold axes, alternating with bis(amido)argentate strands reinforced by Ag···O interactions and weak C–H···O hydrogen bonds; Na+ is embedded in an O6 environment. Adjacent layers are cross‐linked via short C–H···F–C contacts suggestive of weak hydrogen bonding enhanced by cooperativity.  相似文献   

13.
The following MX · MgX2 · 6H2O compounds (double salt hexahydrates) were synthesized by variation of the M+ and X? ions: CsCl · MgCl2 · 6 H2O, Li(H2O)Cl · MgCl2 · 6H2O, NH4Br · MgBr2 · 6 H2O, RbBr · MgBr2 · 6 H2O, CsBr. MgBr2 · 6 H2O, KI · MgI2 · 6 H2O, NH4I. Mgl2 · 6 H2O and RbI · MgI2 · 6H2O. By X-ray analysis of powder samples the lattice parameters and the space group were determined. On the basis of the results thus obtained, an identification with structural types was carried out. In accordance with the findings, the structure is made up of (M+)X6?octahedra which are linked into perovskite type units by sharing vertices. Their interstices are occupied by the Mg(H2O)62+ octahedra. A “tolerance factor” t which has been calculated on the basis of the proportion of radii and which attains values between 1.045 and 1.061 is a criterion for the upper limit of the area of existence of this structure. Carnallite has a higher to value and, therefore, a different structure.  相似文献   

14.
On the Compound BaO · Al2O3 · 7 H2O On the basis of investigations using 27Al, 1H NMR, IR and thermoanalytical methods for the compound BaO · Al2O3 · 7 H2O a constitution as Ban[Al2(OH)8]n · 3n H2O with condensed AlO6 groups, sharing edges, is proposed. Relations between the Ba/Al ratio and the constitution of anions of barium aluminate hydrates are discussed.  相似文献   

15.
A new zinc phosphonate Zn(H2O)PO3–C13H9 · H2O with a columnar structure was synthesized in hydrothermal conditions. This compound crystallizes in space group P21/c [a = 15.832(4) Å, b = 5.1915(10) Å, c = 17.519(4) Å and β = 114.479(6)°]. Its inorganic framework consists of isolated chains of corner‐sharing ZnO3(H2O) and PO3C tetrahedra. These chains are linked to fluorene cycles, forming hybrid columns, interconnected through C–H ··· π bonds. The photoluminescence properties of this hybrid material show that its emission bands are red shifted with respect to those of the mother phosphonic acid. This effect is explained on the basis of the structural constraints imposed by the inorganic Zn‐phosphonate chains.  相似文献   

16.
The molecular cations of 1,3,5-cyclooctatriene (COT) and bicyclo[4.2.0]octa-2,4-diene (BCO) can be observed intact in γ-irradiated Freon glasses, as opposed to Ar matrices where ionization is accompanied by extensive rearrangements. This proves the superiority of the Freon-glass method for the generation of metastable primary cations. The electronic absorption (EA) spectra reveal a) that a previous analysis of the BCO electronic structure on the basis of the ultraviolet photoelectron (UP( spectrum of BCO was incomplete, and b) that COT undergoes planarization upon ionization, in accord with qualitative expectations and MNDO calculations. A previously proposed LCBO model was used to assess the influence of the above geometry change on the electronic structure of COT.  相似文献   

17.
The title complex {[Co(dimb)2(H2O)2]·(NO3)2·(H2O)2}n ( 1 ) (dimb = 1,3‐di(imidazol‐1‐ylmethyl)‐5‐methylbenzene) has been hydrothermally synthesized by the reaction of dimb with Co(NO3)2·6H2O in aqueous solution. The cobalt(II) atoms are linked by bridging dimb ligands to form 2D corrugated and wavy networks containing Co4(dimb)4 macrocyclic motifs. Two neighboring independent layers interlinked each other in a parallel fashion to construct three‐dimensional structure by O–H···O, N–H···O and C–H···O hydrogen bonds. Magnetic measurement shows the weak antiferromagnetic interaction with a one‐dimensional chain model in the range of 5–300 K, with J of –0.68 cm−1.  相似文献   

18.
·OH Radicals generated by short electron-beam pulses were allowed to attack histone octamer complexes (extracted from calf-thymus chromatin) in N2O-saturated dilute solution (0.5–1.3 g/l, [NaClO4] = 1 – 2M , pH 9). They induced a volume contraction due to intra-complex cross-linking. In this process, essentially non-tyrosine moieties of the proteins were involved. Phenol coupling via tyrosyl radicals occurred mainly as an intramolecular reaction, i.e., it was restricted to single histone moelecules. Furthermore, it turned out that only about 55% of the tyrosine moieties were accessible to attacking ·OH and/or ·N3 radicals. When ·N3 radicals were generated via continuous irradiation of N2O-saturated octamer solutions containing NaN3 with 60Co-γ-rays, dimers, trimers, and tetramers were detected by SDS gel electrophoresis, in contrast to pulse radiolysis where only dimers were found. These results were explained in terms of denaturation being induced by small chemical changes and causing partial or complete dissociation of the complexes thus permitting, in the course of the γ-irradiation, the attack and conversion of amino-acid moieties non-accessible in the native octamer complexes. Removal of steric restrictions for the combination of tyrosyl radicals may also play a role. By time-resolved absorption measurements, it was shown that, upon the attack of intact octamer complexes by ·OH radicals, tyrosyl radicals were formed which were converted to dityrosine groups according to two modes with half-lives of several 100 m?s and 1–2 ms, respectively. Cross-linking of histone molecules occurred with a definitely lower rate (1st half-life: 50 100 ms). This process was detectable both by optical absorption measurements at λ = 300 400 nm and by light-scattering measurements.  相似文献   

19.
The Crystal Structures of [Cu2Cl2(AA · H+)2](NO3)2 and [AA · H+]Picr? (AA · H+ = Allylammonium; Picr? = Picrat) By an alternating current electro synthesis the crystal-line π-complex [Cu2Cl2(AA · H+)2](NO3)2 has been obtained from CuCl2 · 2H2O, allylamine (AA), and HNO3 in ethanolic solution. X-ray structure analysis revealed that the compound crystallized in the monoclinic system, space group P21/a, a = 7.229(3), b = 7.824(3), c = 26.098(6) Å, γ = 94.46(5)°, Z = 4, R = 0.025 for 2 023 reflections. The crystal structure is built up of CunCln chains which are connected by π-bonding bidentate AA · H+ …? ON(O)O …? H+ · AA units. For comparision with the above complex the structure of [AA · H+]Picr? (Picr? = picrate anion) is also reported.  相似文献   

20.
Two new hybrid fluorides, {[(C2H4NH3)3NH]4+}2 · (H3O)+ · [Al7F30]9– ( I ) and {[(C2H4NH3)3NH]4+}2 · [Al7F29]8– · (H2O)2 ( II ), are synthesized by solvothermal method. The structure determinations are performed by single crystal technique. The symmetry of both crystals is triclinic, sp. gr. P 1, I : a = 9.1111(6) Å, b = 10.2652(8) Å, c = 11.3302(8) Å, α = 110.746(7)°, β = 102.02(1)°, γ = 103.035(4)°, V = 915.9(3) Å3, Z = 1, R = 0.0489, Rw = 0.0654 for 2659 reflections, II : a = 8.438(2) Å, b = 10.125(2) Å, c = 10.853(4) Å, α = 106.56(2)°, β = 96.48(4)°, γ = 94.02(2)°, V = 877.9(9) Å3, Z = 1, R = 0.0327, Rw = 0.0411 for 3185 reflections. In I , seven corner‐sharing AlF6 octahedra form a [Al7F30]9– anion with pseudo 3 symmetry; such units are found in the pyrochlore structure. The aluminum atoms lie at the corners of two tetrahedra, linked by a common vertex. In II , similar heptamers are linked in order to build infinite (Al7F29)n8– chains oriented along a axis. In both compounds, organic moieties are tetra protonated and establish a system of hydrogen bonds N–H…F with four Al7F309– heptamers in I and with three inorganic chains in II .  相似文献   

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