首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
2.
In this study, we report substituent effect on aryl group migration in (para-C6H4X)Mn(CO)5 complexes using mpw1pw91 quantum chemical calculations. These calculations reveal good linear relationships between barrier energy (ΔE), activation energy (ΔH?), activation free energy (ΔG?) values and rate constants with Hammett constants of X-substituents. The occupancy values of Mn–COcis and Mn–C(O)-(para-C6H4X) bonds in reactant, transition state and product were calculated by Natural bond orbital (NBO) method.  相似文献   

3.
Barrelene, H–C(CH=CH)3C–H, is an unsaturated polycyclic hydrocarbon containing three isolated double bonds in a non-planar arrangement. We have studied the transmission of field effects through the barrelene framework by analyzing the small structural changes occurring in the phenyl group of many Ph–C(CH=CH)3C–X molecules, where X is a variable substituent. Molecular geometries have been determined by quantum chemical calculations at the HF/6-31G* and B3LYP/6-311++G** levels of theory. Comparison with the results obtained for the corresponding saturated molecules, the bicyclo[2.2.2]octane derivatives Ph–C(CH2–CH2)3C–X, reveals a small, but significant, field-induced π-polarization of the barrelene cage, especially when the remote substituent is a charged group. Additional evidence of π-polarization is obtained by comparing the electric dipole moments of the two sets of uncharged molecules. The structural variation of the barrelene cage caused by the variable substituent in Ph–C(CH=CH)3C–X molecules has also been investigated. It is much larger than that of the phenyl group and depends primarily on the electronegativity of the substituent. Particularly pronounced is the concerted variation of the non-bonded distance between the bridgehead carbons of the cage, r(C···C) 1 BARR , and the average of the three C–C–C angles at the cage carbon bonded to the variable substituent, α 1 BARR . A scattergram of r(C···C) 1 BARR versus the corresponding parameter for bicyclo[2.2.2]octane derivatives, r(C···C) 1 BCO , shows that the variation of r(C···C) 1 BARR becomes gradually less pronounced than that of r(C···C) 1 BCO as the electronegativity of the substituent increases.  相似文献   

4.
Two Mn(II) coordination polymers, {[Mn3 (Pfca)6(Phen)2] · 2DMF} n (I) and [Mn(Pfca)2(Phen)(H2O)] n (II) (HPfca = 4-fluorocinnamic acid, Phen = 1,10-phenanthroline), were synthesized and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, and singlecrystal X-ray diffraction (CIF files CCDC nos. 967513 (I), 1542972 (II)). Complex I crystallizes in the triclinic crystal system, space group Pī with a = 11.0821(11), b = 12.2632(12), c = 15.0288(15) Å, α = 87.3760(10)°, β = 88.4610(10)°, γ = 81.2220(10)°, V = 2016.0(3) Å3, ρc = 1.369 g/cm3, M r = 1662.25, Z = 1, F(000) = 853, μ = 0.543 mm–1, the final R = 0.0592 and wR = 0.1681 for 15498 observed reflections with I > 2σ(I). Complex II is of monoclinic system, space group P21/c with a = 18.0539(19), b = 8.5806(9), c = 18.758(2) Å, β = 116.5700(10)°, V = 2599.0(5) Å3, ρc = 1.491 g/cm3, M r = 583.44, Z = 4, F(000) = 1196, μ = 0.567 mm–1, the final R = 0.0337 and wR = 0.0853 for 18139 observed reflections with I > 2σ(I). Complex I features linear Mn(II)-trinuclear units, which form 1D chain structure through F···F weak interactions, and complex II is 1D polymeric Mn(II)-chains. Antiferromagnetic coupling interactions exist within Mn(II)- carboxylate trinuclear in I (J =–0.40 cm–1) and Mn(II)-carboxylate chain in II (J =–0.45 cm–1).  相似文献   

5.
We investigate the tandem mass spectrometry of regiospecifically labeled, deprotonated sucrose analytes. We utilize density functional theory calculations to model the pertinent gas-phase fragmentation chemistry of the prevalent glycosidic bond cleavages (B1-Y1 and C1-Z1 reactions) and compare these predictions to infrared spectroscopy experiments on the resulting B1 and C1 product anions. For the C1 anions, barriers to interconversion of the pyranose [α-glucose-H]?, C1 anions to entropically favorable ring-open aldehyde-terminated forms were modest (41 kJ mol?1) consistent with the observation of a band assigned to a carbonyl stretch at ~?1680–1720 cm?1. For the B1 anions, our transition structure calculations predict the presence of both deprotonated 1,6-anhydroglucose and carbon 2-ketone ((4S,5S,6R)-4,5-dihydroxy-6-(hydroxymethyl)dihydro-2H-pyran-3(4H)-one) anion structures, with the latter predominating. This hypothesis is supported by our spectroscopic data which show diagnostic bands at 1600, 1674, and 1699 cm?1 (deprotonated carbon 2-ketone structures), and at ~?1541 cm?1 (both types of structure) and RRKM rate calculations. The deprotonated carbon 2-ketone structures are also the lowest energy product B1 anions.
Graphical Abstract ?
  相似文献   

6.
Fourier transform infrared (FTIR) spectroscopy studies were performed to confirm and to provide information on the identity and binding characteristics of the chemical groups responsible for the binding of elements using Aspergillus niger (A. niger) wild-type strains. Two absorption bands in the 3690–3615 and 2970–2895 cm?1 regions can characterize stretching vibrations OH and CH groups in fatty acids, respectively, and intensive bands around of 1600 cm?1 and by 1048 cm?1 correspond to stretching vibrations of C=O groups of amides (amide I) or stretching vibrations ν(C–N). The FTIR results confirmed that no extra differences between IR spectra of A. niger in raw biomass and in solid rest after extraction with chloroform were observed. The small differences were observed in IR spectra of A. niger in chloroform after extraction.  相似文献   

7.
The UV absorption spectrum of methacryloyl fluoride molecule in the gas phase is obtained in the wavenumber range of 32300–35900 cm?1. The resolved vibrational structure of this spectrum consists of 153 absorption bands. The assignment of all bands has been made for the first time. Values ν00trans = 35670.0 сm?1 and ν00cis = 35371.1 cm?1 are determined. The fundamental frequencies for isomers in the S0 and S1 states are found. Several Deslandres Tables (DTs) are constructed for the torsional vibration of the s-trans- and s-cis-isomers of the investigated molecule using the NONIUS program. The origins in these DTs correspond to bands attributed to ν00, and to the fundamental frequencies of each isomer in states S0 and S1. These DTs are used to determine harmonic frequencies ωe, anharmonicity coefficients х11, and the frequencies of torsional vibration 0–v transitions up to high values of vibrational quantum number v for s-trans- and s-cis-isomers in both electronic states. The frequencies of torsional vibrations for the s-trans-isomer and the s-cis-isomer in the S0 state are ν″1 = 80.9 сm?1 and ν″1 = 59.8 сm?1, respectively. The frequencies for the s-trans- isomer and the s-cis-isomer in the S1 state are ν′1 = 134.1 сm?1 and ν′1 = 103.6 cm?1, respectively.  相似文献   

8.
A silver(I) complex of saccharinate (sac) with pyrazine (pyz), [Ag(sac)(pyz)] n , has been synthesized and characterized by elemental analysis, IR, thermal analysis, and single-crystal X-ray diffractometry. The complex crystallizes orthorhombic space group Pnma with unit cell parameters of a = 13.0073(9) Å, b = 6.4907(6) Å, c = 13.4007(9) Å, V = 1131.37(15) Å3, and Z = 4. [Ag(sac)(pyz)] n is a one-dimensional coordination polymer, in which the sac ligand acts as a monodentate ligand through the N atom and the trigonal silver centers are linked by the bridging pyz ligands. The individual chains are connected into two-dimensional supramolemular network by aromatic π(sac)···π(pyz) stacking interactions. The FTIR spectrum of [Ag(sac)(pyz)] n has been recorded in the region and 4,000–400 cm?1. The optimized geometry, frequency, and intensity of the vibrational bands of [Ag(sac)(pyz)] n were obtained by density functional theory (DFT) at the B3LYP level. The vibrational frequencies were calculated and the scaled values have been compared with the experimental FTIR data. The observed and calculated frequencies are found to be in good agreement.  相似文献   

9.
By means of DFT B3LYP/6-31G(d, p) calculations of 7-(heptaphenylcycloheptatrienyl) isothiocyanate, the dissociation–recombination mechanism for intramolecular migrations of the isothiocyanato group has been revealed, and the structure of the transition state preceding the formation of a tight ion pair has been found for the first time. According to calculations, the high activation barrier for displacements of the isothiocyanato group ΔEZPE = 21.3 kcal/mol is related to the stable conformation of the molecule with the equatorial–NCS group and the orthogonally located phenyl substituent in the axial position. The rearrangement of the molecule to the form favorable for migrations of the–NCS group involves the inversion of the seven-membered ring accompanied by rotation of the phenyl group.  相似文献   

10.
The molecular structure of 1,3-dimethyluracil (C6H8N2O2; 1,3-DMU) is studied theoretically and experimentally using Gaussian 98 calculations and different spectroscopic techniques. The vibrational spectrum for 1,3-DMU in the solid phase is recorded in the IR range 4000-400 cm–1. Initially, in order to get the most stable structure, twelve structures were proposed for the titled compound as a result of the internal rotation of CH3 around C–N bonds and keto-enol tautomerism. The single point energy and frequency calculations are obtained by MP2 (Full) and DFT/B3LYP methods with the 6-31G(d) basis set using the Gaussian 98 computation package. After the complete relaxation of twelve isolated isomers, the (diketo) tautomer was the only favored structure owing to its low energy relative to the other isomers and the prediction of real frequencies. This interpretation is supported by the recorded infrared spectrum that shows the presence of only the diketo tautomer. Aided by the normal coordinate analysis and potential energy distributions, a confident vibrational assignment of the fundamental frequencies is calculated. The results are discussed herein and compared with similar molecules whenever possible.  相似文献   

11.
The behavior of the [B12H12]2– anion in CH3CN, CF3COOH, and the CH3CN/CF3COOH system is studied by IR spectroscopy. Based on the IR spectroscopy data correlated with the data obtained when studying the protonation processes of boron cluster anions [B6H6]2– and [B10H10]2–, the possibility to prepare the protonated form of the closo-dodecaborate anion, namely monoanion [B12H13], is concluded in CF3COOH and the CH3CN/CF3COOH system. In the IR spectra of salts of the protonated forms of anions [BnHn]2– (n = 6, 10, 12) in solutions and Nujol mulls, a high-frequency shift of the ν(BH) absorption bands is observed as compared with the spectra of salts of non-protonated anions Cat2[BnHn] (Δν = 70–100 cm–1).  相似文献   

12.
This article presents the electronic spectral characteristics enhanced with the structural, IR and magnetic data of the copper(II) acetate complex with 3-methyl-4-nitropyridine-N-oxide. The complex of the formula, [Cu2(OAc)4(3-mnpn)2], belongs to the group of the ‘paddle wheel’ type species with a very short (2.58 Å) metal–metal distance. In the electronic spectra, new bands were found at 16,000 and 24,000 cm?1, which have been tentatively assigned to the metal–metal interactions and solid state effects, respectively. The complex show fast kinetic exchange of the apical ligand, i.e. 3-methyl-4-nitropyridine-N-oxide.  相似文献   

13.
Low-temperature photolysis of 2-and 4-(4′-azidostyryl)quinolines and azidohemicyanine dye, 1-methyl-4-(4′-azidostyryl)quinolinium iodide, was studied in an ether-ethanol matrix at 77 K and a methyltetrahydrofuran matrix at 5 K by means of electronic absorption spectroscopy and ESR technique. The formation of corresponding triplet nitrenes with absorption bands at 380–440 nm and zero-field splitting parameters of |D/h cl = 0.781–0.790 cm?1 and E = 0 was detected. It was found that the introduction of the positive charge into the azidostyrylquinoline molecule resulted in a bathochromic shift of the nitrene absorption band by ~40 nm and a decrease in the D by 0.005 cm?1 due to charge transfer from the nitrene center to the quinoline moiety.  相似文献   

14.
The frequencies for the IR spectra of M(Acac)3 (M = Sc, Ti, V, Cr, Fe, Mn, and Co) were qualitatively calculated by the Hartree-Fock-Roothaan method with the MIDI basis set including p and d polarization functions. It was demonstrated that the coordination entity of the manganese complex is deformed more strongly than that of the vanadium complex. A correlation diagram for the IR bands in the 200–1600 cm?1 range is presented for the complexes in the condensed state. A correlation was found between the experimental frequency of the M-O vibrations and the corresponding force constants.  相似文献   

15.
16.
Three novel carboxylate complexes were synthesized: dimethylgold(III) trifluoroacetate [Me2Au(Tfa)]2 (I), trimethylacetate (pivalate) [Me2Au(Piv)]2 (II), and benzoate [Me2Au(OBz)]2 (III). The starting reagent was [Me2AuI]2. The procedure of its synthesis provides 60% product yield. Dimethylgold(III) carboxylates were identified from the IR and 1H NMR data. The title compounds were studied by X-ray diffraction. The unit cell parameters for I, C8H12Au2F6O4: a = 15.5522(13), b = 12.9398(11), c = 15.6555(14) Å, β = 104.308(2)°, Z = 8, ρ(calcd.) = 2.959 g/cm3, space group C2/c, R = 0.0779; for II, C14H30Au2O4: a = 10.3025(3), b = 15.5952(4), c = 12.6819(3) Å, β = 105.8270(10)°, Z = 4, ρ(calcd.) = 2.224 g/cm3, space group P21/c, R = 0.0229; for III, C18H22Au2O4: a = 12.8050(2), b = 19.7886(3), c = 7.60300(10) Å, Z = 4, ρ(calcd.) = 2.401 g/cm3, space group Pnma, R = 0.0144. Compounds I–III have the molecular structures; the structural units are the [(CH3)2Au(OOCR)]2 dimers (Au…Au 2.984–3.080 Å), R = CF3, tert-Bu, Ph. The gold atoms have the square coordination with two carbon atoms and two oxygen atoms (Au-O 2.120–2.173 Å). The molecules in compounds I–III are united into infinite unidimensional chains connected by van der Waals interactions.  相似文献   

17.
The molecular and crystal structures of the title compound, C16H18N2O, were characterized and determined by single crystal X-ray diffraction method in addition to spectroscopic means such as IR, UV–VIS and 1H NMR. The compound crystallizes in orthorhombic space group P bca, with a = 9.3350(5) Å, b = 23.4878(13) Å, c = 26.5871(12) Å, Z = 16, D calc. = 1.1591(1) g/cm3, μ (MoKα) = 0.073 mm?1. Monomers of the compound in the crystal structure are linked into C(7) and C(8) chains generated by translation along the [1 0 0] direction with the aid of O–H···N type H-bonds which serve to the stabilization of periodic organization of the molecules beside major and minor component in the disordered azo fragment. In order to describe conformational flexibility and the crystal packing effects on the molecular conformation, potential barriers regarding the rotation along both Ar–N bonds were calculated by varying the related torsional degrees of freedom in every 10° ranging from ?180° to +180° via quantum chemical calculations at DFT/B3LYP level.  相似文献   

18.
New crystal structure of Eu(DMF)4(H2O)3Co(CN)6·H2O (DMF = N,N′-dimethylformamide) (Eu-Co) has been determined to be monoclinic, P2(1)/n, a = 19.796(12) Å, b = 8.862(11) Å, c = 17.525(10) Å, β = 96.26(5)°, V = 3056(5) Å3, Z = 4. The Eu(III) ion adopts an antiprismatic eight-coordination and forms a cyano bridge with r(Eu-N) = 2.496(7) Å and Θ(Eu-N-C) = 165.7(7)° to the Co(III) ion. The complex exhibits some common features with the Eu-Fe complex. Diffuse reflectance electronic spectra and magnetic susceptibility of Eu-Cr, Eu-Mn, Eu-Fe, and Eu-Co complexes were compared. By substituting the metal ions, both electronic and structural features affected the charge transfer bands and superexchange interactions concerning cyanide ligands. In addition, only Eu-Co exhibited 5 D 07 F 2 and 5 D 07 F 1 luminescence bands at 16300 cm?1 and 16900 cm?1, respectively at 298 K (λex = 360 nm (27000 cm?1)), because quenching by cyano-bridged ions did not prevent Eu(III) ion from exhibiting emission. Thus, only Eu-Co may be suitable for verification of an assumption of mechanism concerning drastic photoinduced magnetic changes for Nd-Fe. Merely small decrease of magnetization was observed for Eu-Co after UV light irradiation at 2.0 K. This result was attributed to slight structural changes around cyano bridges without transitions of spin states.  相似文献   

19.
Copper(II) binuclear complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid in which the coordination polyhedra are connected by polymethylene chains of different length (1 to 5 units) were synthesized and studied by chemical and thermogravimetric analysis, IR spectroscopy, and EPR. The structure of binuclear copper(II) complex with succinic acid acyldihydrazone [Cu2L · 4Py] · 2Py was determined by X-ray diffraction. The crystals are monoclinic: a = 14.3795(6), b = 8.8736(4), c = 15.9147(7) Å, β = 101.062(3)°, space group P21/c, Z = 2. The number of independent reflections with I > 2σ(I) = 2804, R = 0.042, R w = 0.087. The copper atoms are spaced by a chain of seven σ bonds at 8.922 Å. The coordination polyhedron can be described as a tetragonal pyramid highly distorted toward a trigonal bipyramid. The EPR spectra of solutions of complexes based on malonic, succinic, glutaric, and adipinic acids exhibit a poorly resolved signal of seven HFS lines with a constant of (26.3–27.0) × 10?4 cm?1, which attests to the presence of weak exchange interactions between paramagnetic centers. An increase in the length of the polymethylene spaur suppresses exchange interactions, and the EPR spectrum of the complex based on pimelic acid acyldihydrazone shows a signal of four HFS lines with a constant of 43.8 × 10?4 cm?1 typical of monomeric copper(II) complexes.  相似文献   

20.
A new coordination polymer, {[Cd(bbmb)(bdc)]} n (bbmb = 1,1′-(1,4-butanediyl)bis-(2-methylbenzimidazole), H2bdc = 1,3-benzenedicarboxylic acid) was synthesized under hydrothermal conditions. The complex was structurally characterized by single crystal X-ray diffraction analyses, infrared spectroscopy (IR), elemental analyses. The compound crystallizes in the monoclinic system, space group P21/c with a = 10.860(6) Å, b = 13.115(7) Å, c = 21.009(9) Å, β = 120.94(2)°, V = 2567(2) Å3, Z = 4, C28H26CdN4O4, M r = 594.93, D c = 1.540 g/cm3, μ = 0.893 mm–1. Each cadmium center is six coordinated with four O atoms from two bdc2– anions, and two N atoms of two bbmb ligands. The complex features a 4-connected 2D (4, 4) sheet with a point symbol {42.62}. Fluorescence properties of the title complex were investigated.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号