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1.
The molecular structure of 1,1,2,2-tetrabromodisilane has been investigated using gas-phase electron diffraction data obtained at 110°C. At this temperature the molecules exist as a mixture of about equal parts ( X = 0.5 ±0.2) of the two conformers with the H---Si---Si---H torsion angle equal to 180° ( anti) or 60° ( gauche). Assuming that the two conformers differ in their geometries only in the torsion angle φ, some of the important distance ( ra) and angle ( ) parameters are: r(Si---Si) = 2.349(19) Å, r(Si---Br) = 2.205(5) Å, r(Si---H) = 1.485 Å (assumed), Br---Si---Br = 110.1(1.6)°, Si---Si---Br = 107.1(1.2)° Si---Si---H = 108.6° (assumed). The error limits are 2σ. The observed conformational composition ( Xanti = 0.5(0.2)) corresponds to an energy difference between the conformers of Δ E = E( gauche) — E( anti) = 0.5 ± 0.6 kcal mol −1, assuming Δ S = Rln2. 相似文献
2.
The molecular structure of gaseous epichlorohydrin has been investigated using electron diffraction data obtained at 67°C. The conformational composition at this temperature is such that the molecules exist predominantly in a gauche-2 conformer (where the C---Cl bond is 160° away from the C---O) bond). Refinements showed that 33% (σ = 4) of the molecule exist in the gauche-1 form. The important distances ( rg) and angle () with the associated uncertainties are r(C---H) = 1.095(5) Å, r(C---O) = 1.442(3) Å, r(C---C) = 1.475(8) Å, r(C---C M) = 1.523(7) Å, r(C---Cl) = 1.788(2) Å, CCO = 114° (1), CCC M = 119°(1), ClCC = 108.9° (7), and Tau(ClCCO) = −150°(10) ( gauche-2) and Tau(ClCCO) = 78° (10) ( gauche-1). 相似文献
3.
Gaseous 3-chloro-1-butene has been studied experimentally by electron diffraction (ED) at 20 and 180°C, and at these temperatures, 76(10)% and 62(10)%, respectively, of the most stable conformer i.e. the one having a hydrogen atom eclipsing the double bond, were found. The conformer with the chlorine atom eclipsing the C=C bond was also present. However, from the experimental data it was not possible to establish conclusive evidence for the conformer with an eclipsed CH 3 group. Molecular mechanics (MM) calculations and ab initio calculations using a 4-21 basis set were carried out with complete geometry optimization, and calculated parameters from each of the methods were used in combination with the ED data. Such calculations indicated the existence of all three conformers mentioned above. Least-squares analysis including constraints from the ab initio calculation gave as a result the following molecular structure ( ra distances and ??? angles) for the predominant conformer: r(C=C) = 1.337(6) Å, r(=C---C) = 1.503(4) Å, r(C---CH 3) = 1.522 Å, R(C---Cl) = 1.813(4) Å, < r(C---H)> = 1.089(18) Å, ???C=C---C = 122.9(2.1)°, ???C---C---C = 112.6(2.2)°, ???=C---C---Cl = 109.9(0.2)°, ???Cl---C---CH 3 = 109.3°. ?? C=C---H> = 121.9° and ?? C---C---H> = 110.0(1.3)°. The torsional angles were then τ(C=C---C---Cl> = −119.4° and τ(C=C---C---CH 3) = 120.3(2.1)°. Error limits are 2σ (σ includes estimates of systematic errors and correlations), parameters without quoted uncertainties are dependent or were constrained relative to another parameter. Combining the ED data with MM results yielded parameters consistent with those given above. 相似文献
4.
Dichlorotetramethyldisiloxane is studied by gas-phase electron diffraction at room temperature. The least-squares values of the bond distances ( rg) and bond angles ( ) are: r(C---H)=1.084(5) Å, r(Si---O) = 1.624(2) Å, r(Si---C) = 1.852(2) Å, r(Si---Cl) = 2.067(2) Å, SiOSi = 154.0° (1.5), ClSiO = 110.2° (0.8), ClSiC = 109.6°(0.7), HCSi = 111.7°(1.5), OSiC = 110.0°(0.8), τ 1 (zero corresponds to the Si---Cl bond trans to the Si---O---Si linkage) = 78°(6) and τ 2 = 141°(19). A two-conformer model cannot be ruled out. 相似文献
5.
The molecular structure of 3-methylthiophene
has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G* level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: rg(S---C2) = 1.719(2) Å, rg(C2=C3) = 1.370(3) Å, rg(C3---C6) = 1.497(6) Å, rg(C2---H) = 1.101(5) Å, CSC = 91.6(2)°, SC2C3 = 113.3(5)°, SC5C4 = 111.3(3)°, C2C3C6 = 123.2(11)° and C3C6H = 112(2)°. The values of r(S---C2) − r(S---C5) and r(C2=C3) − r(C4=C5) were fixed at the 3–21G* value of 0.002Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit. 相似文献
6.
The molecular structure of 3-methylthiophene
has been determined by gas electron diffraction (GED) combined with microwave (MW) spectroscopic data. Ab initio calculations at the HF/3–21G* level were carried out and used as structural constraints in the data analysis. The torsional vibration of the methyl group was treated as a large-amplitude motion. The structural parameters were determined to be: rg(S---C2) = 1.719(2) Å, rg(C2=C3) = 1.370(3) Å, rg(C3---C6) = 1.497(6) Å, rg(C2---H) = 1.101(5) Å, CSC = 91.6(2)°, SC 2C 3 = 113.3(5)°, SC 5C 4 = 111.3(3)°, C 2C 3C 6 = 123.2(11)° and C 3C 6H = 112(2)°. The values of r(S---C 2) - r(S=C 5) and r(C 2=C 3)- r(C 4 =C 5) were fixed at the 3–21G* value of 0.002 Å. Parenthesized values are the estimated limits of error (3σ) referring to the last significant digit. 相似文献
7.
The molecular structure of 2-furoyl chloride has been investigated by gas-phase electron diffraction at 86°C. Two distinct conformers were identified, a more stable planar form with the furan oxygen and the carbonyl oxygen syn and a less stable planar (or nearly planar) anti form. Assuming that the two forms differ in their geometries only in the O=C---C---O torsion angles and assuming the furan ring to have C 2v symmetry, the results for some of the distances ( ra) and angles ( a) are: r(C---H) = 1.110(20) Å, r(C=O) = 1.207(6) Å, r(C---O) = 1.378(10) Å, r(C??? = 1.465(13) A, ( r(C---C)) (average carbon—carbon distance in the furan ring) = 1.392(8) A Δ r(C---C) (difference between single and double carbon—carbon distances in the furan ring) = 0.069 A (assumed), r(C---Cl) = 1.787(6) A, C=C---COCl = 131.6(9)°, C=C---O = 110.9(4)°, C=C---H = 127.7(13.4)°, C---C=O = 125.8(8)° and C---C---Cl = 111.8(6)°. At 359 K the observed amount of the conformer with the oxygen atoms syn was 69.8(14.2)%. 相似文献
8.
The gas phase molecular structure of methyl vinyl ether at room temperature has been studied by joint analysis of electron diffraction and microwave data. Constraints on geometrical and thermal parameters were derived from the geometry and force field of the s-cis form, obtained by ab-initio calculations (4–21 G basis set) after complete geometry relaxation. A range of models was investigated that fits all available data (infrared, microwave and electron diffraction). The following rg/ r-parameters were obtained: C=C: 1.337 Å, C( sp2)---O: 1.359 Å, C( sp3)---O: 1.427 Å, : 1.102 Å C=C---O : 127.3° and COC: 116.8°. Experimental rg---re (ab initio) corrections are given for C=C, C(sp2)---O and Csp3)---O.This investigation demonstrates that molecular orbital constrained electron diffraction is sufficiently reliable and in such a manner that it can be applied to more complicated problems. 相似文献
9.
Microwave spectra of allylsilane and its 13C and deuterium substituted species have been measured and assigned for the skew isomer. The rs structure was determined with the aid of several assumptions. Some of the parameters determined are; r(C=C) = 1.328 ± 0.007 Å, r(C---C) = 1.492 ± 0.008 Å, (CCC) = 126.7 ± 0.8°, (CCSi) = 111.6 ± 0.5° and τ(CCCSi) = 106.8 ± 1.1°. Dipole moments and their components were also determined for the CH 2 = CHCH 2SiH 3 and CH 2=CHCH 2SiD 3 species. Hyperconjugation between the C=C π bond and the C---Si σ bond is discussed. 相似文献
10.
The molecular structure of trichloronitromethane has been studied in the gas phase using electron diffraction data. The molecules are found to undergo low barrier rotation about the CN bond with a planar CNO 2 moiety in agreement with HF/MP2/B3LYP/6-311G(d,p) calculations. The experimental data are consistent with a dynamic model using a potential function for the torsion of V = ( V6/2)(1 − cos 6 τ). The major geometrical parameters ( rg and ) for the eclipsed form, obtained from least squares analysis of the data are as follows: r(NO 3) = r(NO 4) = 1.213(2) Å, r(CN) = 1.592(6) Å, r(CCl) av = 1.749(1) Å, Cl 5CN/Cl 6CN = 109. 6°/106.3°(2), O 3NC/O 4NC = 117. 6°/114.1°(4), τCl 5C 1N 2O 3 = 0.0°, and V6 = 0.20(25) kcal/mol. 相似文献
11.
Using gas-phase electron diffraction it has been demonstrated that a composition of known isomer mixtures can be determined with error limits of about 5%, all relevant structural parameters being refined simultaneously by the least-squares method. If, however, corresponding bond distances and valence angles have erroneously been assigned equal values in the two isomers, a large increase in the least-squares error limits from 5% to 12% is noticed. Apparently innocent assumptions about some of the parameters can lead to incorrect isomer composition and to too small error limits as estimated by the least-squares formulae. From the reinvestigation of pure cis-1,2-dichloroethene the following bond distances (ra) and valence angles () were determined: r(C---H) = 1.090(29) Å, r(C=C) = 1.345(6) Å, r(C---Cl) = 1.716(4) Å, C=C---Cl = 123.8(2)°, C=C---H = 119.4(26)°. Error limits are 2σ. 相似文献
12.
The XeOSeF 5+ cation has been synthesized for the first time and characterized in solution by 19F, 77Se and 129Xe NMR spectroscopy and in the solid state by X-ray crystallography and Raman spectroscopy with AsF 6− as its counter anion. The X-ray crystal structures of the tellurium analogue and of the Xe(OChF 5) 2 derivatives have also been determined: [XeOChF 5][AsF 6] crystallize in tetragonal systems, P4/ n, a=6.1356(1) Å, c=13.8232(2) Å, V=520.383(14) Å 3, Z=2 and R1=0.0453 at −60°C (Te) and a=6.1195(7) Å, c=13.0315(2) Å, V=488.01(8) Å 3, Z=2 and R1=0.0730 at −113°C (Se); Xe(OTeF 5) 2 crystallizes in a monoclinic system, P2 1/ c, a=10.289(2) Å, b=9.605(2) Å, c=10.478(2) Å, β=106.599(4)°, V=992.3(3) Å 3, Z=4 and R1=0.0680 at −127°C; Xe(OSeF 5) 2 crystallizes in a triclinic system,
, a=8.3859(6) Å, c=12.0355(13) Å, V=732.98(11) Å 3, Z=3 and R1=0.0504 at −45°C. The energy minimized geometries and vibrational frequencies of the XeOChF 5+ cations and Xe(OChF 5) 2 were calculated using density functional theory, allowing for definitive assignments of their experimental vibrational spectra. 相似文献
13.
Organolanthanide chloride complexes [(CH 3OCH 2CH 2C 5H 4) 2Ln(μ-Cl)] 2 (Ln = La, Pr, Ho and Y) react with excess NaH in THF at 45°C to give the dimeric hydride complexes [(CH 3OCH 2CH 2C 5H 4) 2Ln(μ-H)] 2, which have been characterized by IR, 1H NMR, MS and XPS spectroscopy, elemental analyses and X-ray crystallography. [(CH 3OCH 2CH 2C 5H 4) 2Y(μ-H)] 2 crystallizes from THF/n-hexane at −30°C, in the triclinic space group P1 with a = 8.795(2) Å, b = 11.040(1) Å, c = 16.602(2) Å, = 93.73(1)°, β = 91.82(1)°, γ = 94.21(1)°, Dc = 1.393 gcm −3 for Z = 2 dimers. However, crystals of [(CH 3OCH 2CH 2C 5H 4) 2Ho(μ-OH)] 2 were obtained by recrystallization of holmium hydride in THF/n-hexane at −30°C, in the orthorhombic space group Pbca with a = 11.217(2) Å, b = 15.865(7) Å, c = 17.608(4) Å, Dc = 1.816 gcm −3 for Z = 4 dimers. In the complexes of yttrium and holmium, each Ln atom of the dimers is coordinated by two substituted cyclopentadienyl ligands, one oxygen atom and two hydrogen atoms (for the Y atom) or two hydroxyl groups (for the Ho atom) to form a distorted trigonal bipyramid if the C(η 5)-bonded cyclopentadienyl is regarded as occupying a single polyhedral vertex. 相似文献
14.
The geometric structure of (CF 3S) 2C=C(SCF 3) 2 in the vapour phase was determined by electron diffraction. The molecule possesses D2 symmetry with the S---CF 3 bonds oriented perpendicular to the ethene plane, in alternating directions up-down-up-down. The following skeletal geometric parameters were obtained ( ra distances and angles, experimental uncertainties are 3σ values): C=C = 1.34Å (ass.), C(sp 2---S = 1.761(5)Å, S---C(sp 3) = 1.832(5)Å, S---C---C = 119.6(4)°, C---S---C = 100.6(13)°, and ø(C=C---S---C) = 90.9(11)°. The gas phase conformation differs considerably from the crystal structure, where the molecule possesses Ci symmetry and the CF 3 groups, which are bonded to cis-standing sulfur atoms, lie on the same side of the ethene plane with dihedral angles ø(C=C---S---C) of 117° and 127°. 相似文献
15.
The crystal structures of propionaldehyde complex ( RS, SR)-(η 5-C 5H 5)Re(NO)(PPh 3)(η 2-O=CHCH 2CH 3)] + PF 6− (1b + PF 6s−; monoclinic, P2 1/ c (No. 14), a = 10.166 (1) Å, b = 18.316(1) Å, c = 14.872(2) Å, β = 100.51(1)°, Z = 4) and butyraldehyde complex ( RS, SR)-[(η 5-C 5H 5)Re(NO)(PPh 3)(η 2-O=CHCH 2CH 2CH 3)] + PF 6− (1c +PF 6−; monoclinic, P2 1/ a (No. 14), a = 14.851(1) Å, b = 18.623(3) Å, c = 10.026(2) Å, β = 102.95(1)°, Z = 4) have been determined at 22°C and −125°C, respectively. These exhibit C
O bond lengths (1.35(1), 1.338(5) Å) that are intermediate between those of propionaldehyde (1.209(4) Å) and 1-propanol (1.41 Å). Other geometric features are analyzed. Reaction of [(η 5-C 5H 5)Re(NO)(PPh 3)(ClCH 2Cl)] + BF 4− and pivalaldehyde gives [(η 5-C 5H 5)Re(NO)(PPh 3)(η 2-O=CHC(CH 3) 3)] +BF 4− (81%), the spectroscopic properties of which establish a π C
O binding mode. 相似文献
16.
Propynyl isocyanide, CH 3C 2NC, has been prepared by vacuum pyrolysis of pentacarbonyl-(1,2-dichloropropenyl isocyanide) chromium, (CO) 5Cr–CN–C(Cl)=C(Cl)CH 3, and its ground state millimeter and microwave spectrum has been observed for the first time. rs structural parameters of this molecule with a C3v symmetry could be obtained from the rotational constants of several isotopomers: r(C1–C2)=1.456(2) Å, r(C2–C3)=1.206(2) Å, r(C3–N)= 1.316(2) Å, r(N–C4)= 1.175(2) Å, r(H–C1)= 1.090(1) Å, >HCC=110.7(4)°. The nitrogen quadrupole coupling constant has been determined to be 878(2) kHz and measurements of the Stark effect allowed to obtain an electric dipole moment of 4.19(3) Debye. The results fit well into a series of related compounds and are in good agreement with data from ab initio calculations. 相似文献
17.
The reaction of Ru(CO) 4(C 2H 4) or Ru(CO) 5 with 1,5-Ph 4P 2N 4S 2 in CH 2Cl 2/hexane at 23°C produces the dimer [Ru(CO) 2(Ph 4 P 2N 4S 2)] 2 (2), which was shown by X-ray crystallography to have a centrosymmetric structure in which the P 2N 4S 2 ring is attached to one ruthenium atom through two (geminal) nitrogen atoms and the remote sulfur atom and serves as a bridge to the other ruthenium atom via the second sulfur atom. Crystals of 2 ·2(CH 2Cl 2) are triclinic, space group P
(No. 2), a = 12.901(1) Å, b = 13.072(1) Å, c = 10.123(1) Å, = 100.88(1)°, β = 98.90(1)°, γ = 67.50(1)°, V = 1542.4(3) Å, Z = 1 with final R and Rw values of 0.040 and 0.027, respectively. 相似文献
18.
The X-ray structures of the complexes Eu(NO 3)(Ph 3PO) 3(acetone) 2 (A) (Ph 3PO = triphenylphosphine oxide) and Eu(NO 3) 3(Ph 3PO) 2(ethanol) (B) have been solved by the heavy-atom method, by using the three-dimensional Patterson-Fourier synthesis. The crystals are both monoclinic and belong to the space group P2 1/ n, with Z = 4. The cell dimensions are: a = 27.825(4) Å, b = 19.422(4) Å, c = 11.238(2) Å, β = 94.9(3)° for A; and a = 22.193(4) Å, b = 10.866(2) Å, c = 17.101(3) Å, β = 105.6(3)° for B. In both complexes the europium(III) ion is ennea-coordinated to three chelate nitrate groups and three oxygens of the Ph 3PO ligands for A and two of the Ph 3PO and one of the ethanol for B. The acetone molecules of A are outside the coordination sphere of the metal and disordered. 相似文献
19.
The Schiff base compound, N- N′-bis(4-methoxybenzylidene)ethylenediamine (C 18H 20N 2O 2) has been synthesized and its crystal structure has been investigated by X-ray analysis and PM3 method. The compound crystallizes in monoclinic space group P2 1/ n with a=10.190(1), b=7.954(1), c=10.636(1) Å, β=111.68(1)°, V=801.1(1) Å 3, Z=2 and Dcal=1.229 Mgm −3. The title structure was solved by direct methods and refined to R=0.056 for 2414 reflections [ I>3.0σ( I)] by full-matrix anisotropic least-squares methods. The energy profile of the compound was calculated by PM3 method as a function of θ[N1′–C9′–C9–N1]. The most stable molecular structure of the title compound is the anti conformation, which is different in energy by 5.0 and 1.0 kcal mol −1 from the eclipsed conformation I and gauche conformations, (III and V), respectively. 相似文献
20.
The pentaamminecobalt(III) complex with the 3-cyano-2,4-pentanedionate anion coordinated through the nitrile nitrogen has been characterized by X-ray crystallography. The crystals of [(NH 3) 5CoNCacac](Cl)(ClO 4)·2H 2O are triclinic, space group P
, a = 10.245(2) Å, b = 14.071(4) Å, c = 6.971(2) Å, = 90.03(3)°, β = 109.86(2)°, γ = 108.91(2)°, V= 887.1 Å 3, Z = 2, Dc = 1.64 g cm −3, F(000) = 456, Mo- K radiation, λ = 0.71069 Å, μ(Mo- K) = 12.7 cm −1. The structure was determined by the heavy-atom method, and refined by block-diagonal least-squares calculations, R = 0.0537, Rw = 0.0607, for 2499 observed reflections. Principal dimensions are: Co---N(NH 3) trans to NCacac − 1.940(5), other Co---N(NH 3) 1.967(2), Co---N(NCacac −) 1.911(5) Å. The pendant acac moiety is best described in terms of a delocalized bond network with, for example, C---C distances in the range 1.44–1.52(1) Å. Several reactions involving this free acac group are also described including the preparation and characterization of the dimeric species pentaamminecobalt(III) - μ - (3 - cyano - 2,4 - pentanedionato) - bis(propylenediamine) cobalt(III) perchlorate. 相似文献
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