Phase Electron Diffraction Data Research Articles

Chloromethyl phenyl ether in the gas phase, studied by electron diffraction, infrared spectroscopy and ab initio calculations

The molecular structure of chloromethyl phenyl ether (CMPE) is investigated from gas phase electron diffraction data and IR frequencies in CS 2 solution, complemented with geometry relaxed ab initio calculations on the HF/4-21G/3-3-31G level. The anomeric effect greatly affects the geometrical parameters, among other things making the C(sp 3)O bond shorter than the C(sp 2)O bond. Furthermore, the anomeric interaction significantly shifts the equilibrium between an e rotameric form (OC(sp 3) in-plane with phenyl ring) and an o rotameric (OC(sp 3) approximately perpendicular to phenyl ring) towards the o form. In fact CMPE appears as a mixture of about equal amounts of ( e, sc) and ( o, sc) conformations. The IR spectral frequencies are reassigned and analogous geometrical trends with anisole rotamers are discussed.

Molecular structures of tris(methylcyclopentadienyl) -scandium and -ytterbium as studied by gas phase electron diffraction and molecular mechanics calculations: the scandium atom is too small to accommodate three pentahapto cyclopentadienyl rings

The syntheses and spectroscopic properties (IR and 1H and 13C NMR spectra) of tris(methylcyclopentadienyl)-scandium and -ytterbium are described. The vapour pressure of Yb(MeCP) 3 has been determined over the range 70–90°C. The gas phase electron diffraction data for M(MeCP) 3 (M  Sc or Yb) have been recorded with nozzle temperatures of about 160°C. The data for M  Yb are consistent with a model containing three pentahapto cyclopentadienyl rings; Yb(η 5-MeCp) 3, a mean Yb to ring-centre distance of YbZ = 236.6(6) pm, and a mean YbC bond distance of 265.5(7) pm. The gas phase electron diffraction data for M  Sc are incompatible with models containing three η 5-MeCp rings, but consistent with models containing two η 5 rings and one ring with a hapticity of 2 or 3; η 2/3-MeCp. The distance from Sc to the centres of the two η 5-MeCp rings is 222.3(6) pm, corresponding to a mean Sc C(η 5) bond distance of 253.0(6) pm. The third ring is at a greater distance from the Sc atom, SCZ(η 2/3) = 252(5) pm, but is tilted, the angle between the ScZ(μ 2/3) vector and the ring normal being 22(4)°. As a result two or three carbon atoms of the ring are in a position to form strong bonds to the metal atom. Molecular mechanics calculations indicate that interligand interactions in M(η 5-C 5H 4) 3 or M(η 5-MeCP) 3 molecules are strongly repulsive when MZ(η 5) is less than 225 pm, and that the strain is eliminated on rearrangement to M(η 5-C 5H 5) 2(η 2/3-C 5H 5) or M(η 5-MeCP) 2(η 2/3-MeCp) configurations.

Structure of zinc phthalocyanine by gas phase electron diffraction

Gas phase electron diffraction data have been successfully recorded for zinc phthalocyanine. Molecular structure parameters have been determined by least square fitting a geometrically consistent model of C4v symmetry to the data. The results agree well with previous x-ray diffraction studies of crystals. However, the zinc atom was found to be slightly out the plane of the molecule in contrast with the x-ray results.

Molecular geometries, vibrational frequencies, force fields and mean-square amplitudes of silicon dihalides determined from ab initio calculations

Ab initio studies and force field calculations are reported for the molecules SiF 2, SiCl 2 and SiBr 2; structural, vibrational and energetic features of the dimers Si 2F 4 and Si 2Cl 4 are also determined. The molecules have been optimized at the SCF level of theory employing split valence basis sets; geometries and vibrational frequencies of the molecules SiF 2 and SiCl 2 have been obtained at the MP2/DZP level. The computed structural parameters and properties have been compared with the experimental ones. General valence force fields are used to calculate force constants. The mean square amplitudes are calculated and compared with the gas phase electron diffraction data. Theoretical calculations are also reported for SiH 2, SiHF, SiHCl and SiFCl.

Structural Studies of Vapour Phase Transport Reactions Using X-ray Absorption Spectroscopy and Matrix Isolation

The vapour above heated ferric chloride (Fe2Cl6) been isolated in nitrogen, argon and neon matrices. The XANES features are indicative of iron in a tetrahedral environment and the interatomic distances from the EXAFS data for the nearest neighbour shells are in good agreement with the vapour phase electron diffraction data. In the case of the nitrogen matrix isolated species the Fe...Fe distance has been determined, indicating the potential usefulness of matrix XAS for the study of vapour phase intermediates. The reasons for the non-observance of this shell in argon and neon matrices are considered.

Coordination structures and vibrational frequencies of Li and Na metaphosphates and nitrates. An ab initio SCF study

Ab initio quantum-mechanical calculations, at the HF SCF level of theory, were performed on the planar C 2v and pyramidal C 3v coordination structures of LiPO 3 and NaPO 3. Preference for bidentate binding is indicated for alkali-metal metaphosphates. Harmonic vibrational frequencies were computed for the free PO 3 − and all the C 2v and C 3v forms of LiPO 3 and NaPO 3. The 18 isotopic patterns predicted for bidentate and monodentate C 2v structures are discussed. SCF MO calculations are also reported for LiNO 3 and NaNO 3 molecules in order to extend previous ab initio studies. The theoretical results were compared with gas phase electron diffraction and IR spectroscopy data.

Electron diffraction analysis of XY 2 and XY 3 molecules with large amplitude motion : Part II. Survey of experimental studies

A survey is given on the application of the interpretational scheme formulated in Paper I of this series to the analysis of gas phase electron diffraction data on MnF 2, FeF 2, CoF 2, NiF 2, CrF 2 and ZnF 2 conjointly with spectroscopic or estimated vibrational frequencies available from the literature. The results of an analysis by a conventional scheme of interpretation in terms of thermally averaged internuclear distances and amplitudes of vibration are also described. The bending potentials of all the above molecules were found to be shallow. Dynamical behavior of these systems conforms to the pattern of a fairly felxible quasi-linear molecule exhibiting large amplitude bending motion. The bending frequencies estimated independently from electron diffraction data are presented and the results of a numerical calculation of bending vibration spectra are reported. The equilibrium MeF distances, bond angle mean-square displacements and best fit stretching frequencies have also been given. A similar analysis of diffraction data on CrF 3 and LaCl 3 is described. CrF 3 is shown to be a planar molecule exerting large amplitude out-of-plane motion. By contrast, LaCl 3 appears to be pyramidal enough with four lowest doubly degenerated levels located inside both wells of the inversion potential. The fifth level exhibits apparent inversion splitting associated with tunneling of the metal atom, whereas at higher levels of excitation nearly free inversion motion is likely to occur. The equilibrium CrF and LaCl distances and best fit skeletal frequencies optimized against electron diffraction data and spectroscopic or estimated vibrational frequencies available from the literature are presented. The inversion frequencies estimated independently from electron diffraction are also given. By taking CrF 2 as an example, confirmative evidence is given for the potentially fruitful application in diffraction analysis of nonrigid molecules of multidimensional classical and semiclassical distribution functions in cases where appropriate conditions for their adequate use are satisfied.

Structure and solvation of soluble [Fe(NO)2Lp] compounds - II

We are interested in extracting reliable structural information from the X-ray Absorption Spectra of solutions of iron dinitrosyl compounds. Evidence is produced showing that the structure of 1= [Fe(NO)2(CO)2] is different in solution from what it was expected from recent gas phase electron diffraction data. The paper next deals with ab initio simulations of higher order correlations (α3, ξ4hellip;) which are essential to interpret the spectra beyond the coordination shell. The intense ξ4 [Fe-N-O-N-Fe] correlations were found to interfer with the less intense ξ2 [Fe-O-Fe] and Ξ3 [Fe-N-O-N-Fe] signatures. These calculations were not accurate enough yet to yield absolute determination of the Fe-N-O bond angle but they can be used, at least, to probe qualitatively whether the nitrosyl ligands are bent or not.

Calculations of structures of biphenyl and alkylbiphenyls by molecular mechanics

MM2′ parameters for “mechanical” calculation of biphenyl are revised on the basis of Bastiansen's gas phase electron diffraction data. These parameters well reproduce the structures of energy minimum conformer of biphenyl and of alkylbiphenyls.

Structure of gaseous methyl acetate as determined by joint analysis of electron diffraction, microwave and infrared spectroscopy, supplemented by a valence force field and constraints from geometry relaxed ab initio calculations

The structure of methyl acetate was studied by joint analysis of gas phase electron diffraction, microwave and IR data, using constraints taken from relaxed 4-21G gradient geometry and force field calculations. All data are in accord with a planar heavy-atom skeleton in the syn conformation. The geometry of methyl acetate in the gas phase is essentially equal to that in the crystal. Some r g— r e corrections have been evaluated. Subject to the ab initio constraints the following internal coordinates ( r 0 αstructure) have been found: CO = 1.206 Å, H 3CO = 1.438 Å, CO = 1.357 Å, CC = 1.496 Å, 〈CH〉 = 1.078 Å, ∠COC = 116.4°, ∠;OCO = 123.0°.

ChemInform Abstract: GAS‐PHASE ELECTRON‐DIFFRACTION STUDY OF 1‐CHLORO‐2,4‐DIMETHYL‐1,2‐DIHYDRO‐1,5,2,3‐PHOSPHAOXADIAZOLE

Abstract Earlier gas phase electron diffraction data on 1-chloro-2,4-dimethyl-1,2-dihydro-1,5,2,3-phosphaoxadiazole (I) obtained by these authors are treated using up-to-date developments in structure analysis and the conclusion of a considerable elongation of the P-Cl bond in chlorinated aminophosphines is subst anti ated. This bond length ( r a ) is found to be 2.168(4) A in I, i.e. far larger than the sum of the covalent radii (2.09 A). The r a parameters of the oxadiazaphospholene ring containing the NC double bond refine to the following values (bond lengths in A, angles in degrees): 1.699(6); PO, 1.628(5); weighted average , 1.403(9); NC, 1.277(8); NPO, 91.1(0.6); PNN, 108.7(1.0); POC, 109.3(1.0); NNC, 112.0(1.8); NCO, 114.0(2.0). The ring has an envelope-like nonplanar conformation with the P atom in the flap position. The dihedral angle between the NPO plane and the least-squares plane of the O-CN-N fragment is 20.0(2.5)°. The P–Cl bond is in the axial position. The amine nitrogen linked with phosphorus has a practically planar bond configuration (the sum of the valence angles at N is 357.7°).

Gas phase electron diffraction study of 1-chloro-2,4-dimethyl-1,2-dihydro-1,5,2,3-phosphaoxadiazole,

Earlier gas phase electron diffraction data on 1-chloro-2,4-dimethyl-1,2-dihydro-1,5,2,3-phosphaoxadiazole (I) obtained by these authors are treated using up-to-date developments in structure analysis and the conclusion of a considerable elongation of the P-Cl bond in chlorinated aminophosphines is subst antiated. This bond length ( r a) is found to be 2.168(4) Å in I, i.e. far larger than the sum of the covalent radii (2.09 Å). The r a parameters of the oxadiazaphospholene ring containing the NC double bond refine to the following values (bond lengths in Å, angles in degrees): ▪1.699(6); PO, 1.628(5); weighted average ▪, 1.403(9); NC, 1.277(8); NPO, 91.1(0.6); PNN, 108.7(1.0); POC, 109.3(1.0); NNC, 112.0(1.8); NCO, 114.0(2.0). The ring has an envelope-like nonplanar conformation with the P atom in the flap position. The dihedral angle between the NPO plane and the least-squares plane of the O-CN-N fragment is 20.0(2.5)°. The P–Cl bond is in the axial position. The amine nitrogen linked with phosphorus has a practically planar bond configuration (the sum of the valence angles at N is 357.7°).

Mean amplitudes of vibration of SF6 and intramolecular multiple scattering

Precise gas phase electron diffraction data for incident electron energies of 43 and 54 keV have been collected for SF6 by counting techniques with emphasis toward a determination of root-mean-squared amplitudes of vibration and as a case study for the necessity of correcting the scattering cross sections for intramolecular multiple scattering. At first, the amplitudes and shrinkage values were found to disagree with predicted values based on spectroscopic results. However, after corrections for the multiple scattering had been applied, the values changed significantly. The new structural parameters obtained are ra (S–F) = 1.5622(7) Å, l(S–F) = 0.0416(5) Å, ra(F–F) (cis) = 2.2094(8) Å, l(F–F) = 0.0604(4) Å, ra(F–F) (trans) = 3.1240(21) Å, and l(F–F) = 0.0551(17) Å. The shrinkage values for the F–F trans distance changed from −0.0003(2) to +0.0018(2) Å due to the corrections and are now in agreement with the spectroscopic values. The success of the modified Glauber approximation warrants an introduction of this formalism into routine structure determination in electron scattering.

ChemInform Abstract: THE MOLECULAR STRUCTURE OF VINYL BROMIDE FROM GAS PHASE ELECTRON DIFFRACTION AND MICROWAVE DATA

Chemischer InformationsdienstVolume 11, Issue 11 Physical Organic Chemistry ChemInform Abstract: THE MOLECULAR STRUCTURE OF VINYL BROMIDE FROM GAS PHASE ELECTRON DIFFRACTION AND MICROWAVE DATA P. A. G. HUISMAN, P. A. G. HUISMANSearch for more papers by this authorF. C. MIJLHOFF, F. C. MIJLHOFFSearch for more papers by this author P. A. G. HUISMAN, P. A. G. HUISMANSearch for more papers by this authorF. C. MIJLHOFF, F. C. MIJLHOFFSearch for more papers by this author First published: March 18, 1980 https://doi.org/10.1002/chin.198011057AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue11March 18, 1980 RelatedInformation

Molecular structure of cis-1,2-difluoroethene as determined from gas phase electron diffraction and microwave data

The structure of cis-1,2-difluoroethene was determined from gas phase electron diffraction data and the rotational constants of HFCCHF, DFCCHF and DFCCDF derived from a microwave study by Laurie and Pence. From a joint least squares analysis of the data the following r g bond distances and r z bond angles have been derived: r(CC) = 1.330 ± 0.011 Å, r(C-F) = 1.342 ± 0.005 Å, r(C-H) = 1.103 ± 0.006 Å, ∠C-C-F = 122.0 ± 0.2°, ∠C-C-H = 124.1 ± 0.4°. The uncertainties represent the limits of error (3σ).

Molecular structure of 1,1-difluoroethylene as determined by gas phase electron diffraction and microwave data

The structure of 1,1-difluoroethylene was determined, from gas phase electron diffraction data obtained independently in Leiden and Tokyo and the rotational constants of F 2CCH 2, F 2CCHD and F 2CCD 2 derived from the microwave study by Chauffoureaux. The two electron diffraction data agreed without significant discrepancy. From a joint least squares analysis of the diffraction and microwave data, the following r g bond distances and r z bond angles were derived: CC = 1.340 ± 0.006 Å, C-F = 1.315 ± 0.003 Å, C-H = 1.091 ± 0.010 Å, ∠C-C-F = 124.7 ± 0.3°, ∠C-C-H = 119.0 ± 0.4°, where the uncertainties represent estimated limits of error.

The gas phase structures of the isomers of benzene: IV. Hexafluoro-dewar-benzene

Gas phase electron diffraction data for HFDB were analyzed, following conventional procedures, and a structure was deduced for the perfluoro-bicyclo-[2.2.0]hexa-2,5-diene consistent with its C 2 v symmetry. A least squares analysis of the molecular scattering function gave the following r g values: [-C-C-] = 1.597 ± 0.006 Å, [C-C-] = 1.503 ± 0.002 Å, [-C-C-] = 1.356 ± 0.007 Å, [-C-F](bridge) = 1.331 ± 0.008 Å, [-C-F] (terminal) = 1.323 ± 0.004 Å. The flap angle between the rings is 115.3( ± .7)°. The terminal fluorines are in the planes of the corresponding rings. The most notable feature of the structure is the long C-C bridge bond, which was also observed in hexamethyl-Dewar-benzene. The geometrical features of HFDB are compared with corresponding ones in HMDB, and with perfluoro- cyclobutene as well as with theoretical estimates.