Do halogen and methyl substituents have electronic effects on the structures of simple disilanes? An experimental and theoretical study of the molecular structures of the series X3SiSiMe3 (X = H, F, Cl and Br)

The gas-phase molecular structures of a series of halogen-substituted disilanes [X₃SiSiMe₃ (X = H, F, Cl and Br)], 1,1,1-trimethyldisilane (H₃SiSiMe₃), 1,1,1-trifluoro-2,2,2-trimethyldisilane (F₃SiSiMe₃), 1,1,1-trichloro-2,2,2-trimethyldisilane (Cl₃SiSiMe₃) and 1,1,1-tribromo-2,2,2-trimethyldisilane (Br₃SiSiMe₃), have been determined in the gas phase by electron diffraction. Ab initio calculations at the HF and MP2 level were used to support the experimental investigation using the SARACEN method. All of the investigated structures were determined to adopt a staggered structure with C _3v symmetry. The effect of substitution on the Si–Si bond and the Si–Si–X bond angle was investigated and these results were compared to results obtained from a recent study of halogen-substituted disilanes [X₃SiSiXMe₂ (X = F, Cl, Br and I)] to consider the effect of the methyl groups on the substituted disilanes.     

Electron diffraction study on the molecular structure of methyltrimethoxysilane

The electron diffraction data for methyltrimethoxysilane are consistent with a C₃ symmetry model, the predominant forms of which have rotational angle(s) between 100 and 155° around the SiO bond (the anti conformation of the CSiOC chain would respond to 0°). There is probably large amplitude motion around the SiO bonds. The following bond lengths and bond angles were determined: r_a(CH) 1.093 ± 0.005, r_a(SiC) 1.842 ± 0.013, r_a(SiO) 1.632 ± 0.004, r_a(OC) 1.425 ± 0.004 », ∠CSiO 109.6 ± 0.5°. and ∠SiOC 123.6 ± 0.5°.     

The gas-phase molecular structure of methyl formate,determined by electron diffraction

The structure of methyl formate in the gas phase has been reinvestigated by electron diffraction. The results confirm that the molecular skeleton is cis-planar, with bond lengths and angles in close agreement with those found by microwave techniques. Principal parameters (r_a) are: r(CO) 120.2(2) pm, r(C-O) 134.0(2), and 143.5(3) pm; ∠ (OC-O) 125.4(5)°, and ∠ (C-O-C) 115.9(5)°.     

Die Kristallstruktur von Ph3PNBr · Br2

Crystal Structure of Ph₃PNBr · Br₂ Ph₃PNBr · Br₂ ( 1 ) has been prepared besides of other products from the reaction of Ph₃PNH with bromine, forming orange‐yellow single crystals which are characterized by IR‐spectroscopy and by a crystal structure determination. Space group P2₁/n, Z = 4, lattice dimensions at 20 °C: a = 916.76(10), b = 1351.42(8), c = 1494.9(2) pm, β = 96.191(5)°, R₁ = 0.0538. 1 has a molecular structure in which the Br₂ molecule is coordinated at the nitrogen atom of the N‐bromine‐phosphoraneimine Ph₃PNBr in a linear arrangement N–Br–Br with bond lengths N–Br of 224.5(6) pm and Br–Br of 248.4(1) pm. The nitrogen atom of 1 is ψ‐tetrahedrally coordinated in addition by the phosphorus atom with a P–N distance of 165.3(6) pm and by the covalently bonded bromine atom with a bond length of 188.9(6) pm.     

An electron diffraction investigation of the molecular structure of dichloromaleic anhydride

The molecular structure of gaseous dichloromaleic anhydride has been investigated by electron diffraction at a nozzle-tip temperature of 164–170°C. The molecule is planar to within experimental error, but small deviations from planarity corresponding to torsion up to about 10° around the carbon-carbon single bonds cannot be ruled out. Values of the more important r_α distances and angles with estimated 2σ uncertainties are r(CO) = 1.188(2) Å, r(CC) = 1.332(5) Å, r(C-O) = 1.389(3) Å, r(C—C) = 1.495(3) Å, r(C—Cl) = 1.685(2) Å, ∠CC-Cl = 129.4(2)°, ∠C-CO = 128.5(4)° and ∠CC—C = 107.9(2)°. The shortening of the carbonyl bond relative to that in maleic anhydride itself is discussed in terms of a possible general effect of vicinal substitution.     

On the molecular structure of (CH3)2NSO2N(CH3)2 as studied by gas electron diffraction

The following bond lengths and bond angles have been deduced from a vapour phase electron diffraction study of (CH₃)₂NSO₂N(CH₃)₂: r(C-H) 1.114 ± 0.005 Å, r(S-O) 1.432 ± 0.010 Å, r(N-C) 1.475 ± 0.013 Å, r(S-N) 1.651 ± 0.003 Å, ∠N-C-H 109.3 ± 2.0°, ∠C-N-C 118.0 ± 302°, ∠S-N-C 115.2 ± 1.1°, ∠N-S-N 110.5±1.3° and ∠O-S-O 114.7±2.5°. The sulphur bond configuration and the prevailing conformation, which was identical to that in the crystal, are discussed in relation to analogous sulphide and sulphoxide derivatives.     

The molecular structure of diethyl(silyl)amine in the gas phase,determined by electron diffraction

The molecular structure of N(C₂H₅)₂(SiH₃) in the gas phase has been determined by electron diffraction. The SiNC₂ skeleton is a shallow pyramid, with angles CNC 114.5(12)° and SiNC 120.9(5)°, and the methyl groups lie so that one CC bond lies close to the CNC plane, but the other is almost perpendicular to it. Other important parameters (r_a) are: r(SiN) 171.5(3), r(CN) 145.6(4), r(CC) 154.3(8) pm, and ∠NCC 113.6(6)°.     

Electron diffraction and CNDO/2 investigation on the molecular structure of tetrafluoro-1,3-diselenetane (F2CSe)2

The molecular structure of tetrafluoro-1,3-diselenetane was determined in the gas phase by electron diffraction. A planar ring configuration with the following geometric parameters (r_g-values) was obtained:r(Se-C) = 1.968 ± 0.004 Å, r(C-F) = 1.353 ± 0.003 Å, ∠SeCSe = 98.5° ± 0.4°, ∠FCF = 106.3 ± 0.8°. SCF-MO calculations in the CNDO/2 approximation confirm the planarity of the four membered ring and give a plausible explanation for the remarkably short Se-C bond length in the ring which in spite of ring strain is shorter than in Se(CF₃)₂. There exists a strong bonding interaction between the diagonal selenium atoms which amounts to about one fourth of a normal single bond strength.     

Electron diffraction and quantum chemical study of the molecular structure of 4-methylbenzene sulfochloride

A combined electron diffraction and mass spectrometric study was carried out to investigate the molecular structure of 4-methylbenzene sulfochloride at 330(2) K. An analysis of the electron diffraction data was performed in terms of the r_α structure. Several models of geometrical structure having different orientations of the sulfochloride group relative to the plane of the benzene ring are treated. The following values of structural parameters were obtained: r_α(C-H)_meth= 1.104(41)Å, r_a(C-H)/_phen = 1.103(27)Å, r_a(C-C)_phen = 1.403(7) Å, r_a(C-C)_meth = 1.512(25) Å, r_a(C-S) =1.758(6) Å, r_a(S = O) = 1.419(3) Å,r _a(S-Cl) = 2.049(5) Å, ∠CCH_meth = 106.9(47)?, ∠CSO = 110.5(6)?, ∠CSCl = 101.3(6)°, ∠OSO = 120.5(9)°. The angle between the plane of the benzene ring and the plane of the S-Cl bond was found to be 83°. Ab initio and semiempirical quantum chemical calculations were accomplished to estimate the geometrical and energy parameters and compare them with electron diffraction data.     

Molecular structure and conformational composition of gaseous 1,1-dichloro-2-bromomethyl-cyclopropane and 1,1-dichloro-2-cyanomethyl-cyclopropane as determined by electron diffraction

The molecular structure of the title compounds have been investigated by gas-phase electron diffraction. Both molecules exist as about equal amounts of the two gauche conformers. There is no evidence for the presence of a syn conformer, but small amounts of this form cannot be excluded. Some of the important distance (r_a) and angle (∠_α) parameters for 1,1-dichloro-2-bromomethyl-cyclopropane are: r(CH) = 1.095(19) Å, r(C₁C₂) = 1.476(11) Å, r(C₂C₃) = 1.517(31) Å, r(CCH₂Br) = 1.543(32) Å, r(CCl) = 1.752(6) Å, r(CBr) = 1.950(13) Å, ∠CCBr = 110.5(1.9)°, ∠ClCCl = 111.9(6)°, ∠CCC = 117.5(1.3)°, σ₁ (CC torsion angle between CBr and the three-membered ring for gauche-1) = 116.2(5.6)°, σ₂ = −132.7(7.6). For 1,1-dichloro-2-cyanomethyl-cyclopropane the parameter values are: r(CH) = 1.101(16) Å, r(C₁C₂) = 1.498(9) Å, r(C₂C₃) = 1.544(21) Å, r(C₂C₄) = 1.497(33) Å, r(CCN) = 1.466(26) Å, r(CN) = 1.165(8) Å, r(CCl) = 1.754(5) Å, ∠CCCN = 113.7(2.0)°, ∠CCC = 122.8(1.6)°, ClCCl = 112.5(4)°, σ₁ = 113(13)°, σ₂ = −124(10)°.     

Characterization of <Emphasis Type="Italic">σ</Emphasis>-hole interactions in 1:1 and 1:2 complexes of YOF<Subscript>2</Subscript>X (X = F,Cl, Br,I; Y = P,As) with ammonia: competition between halogen and pnicogen bonds

Ab initio calculations at the MP2/aug-cc-pVTZ level of theory are performed to examine 1:1 and 1:2 complexes of YOF₂X (X = F, Cl, Br, I; Y = P, As) with ammonia. The YOF₂X:NH₃ complexes are formed through the interaction of the lone pair of the ammonia with the σ-hole region associated with the X or Y atom of YOF₂X molecule. The calculated interaction energies of halogen-bonded complexes are between ?1.06 kcal/mol in the POF₃···NH₃ and ?6.21 kcal/mol in the AsOF₂I···NH₃ one. For a given Y atom, the largest pnicogen bond interaction energy is found for the YOF₃, while the smallest for the YOF₂I one. Almost a strong linear relationship is evident between the interaction energies and the magnitudes of the positive electrostatic potentials on the X and Y atoms. The results indicate that the interaction energies of halogen and pnicogen bonds in the ternary H₃N:YOF₂X:NH₃ systems are less negative relative to the respective binary systems. The interaction energy of Y···N bond is decreased by 1–22 %, whereas that of X···N bond by about 5–61 %. That is, both Y···N and X···N interactions exhibit anticooperativity or diminutive effects in the ternary complexes.     

The molecular structure of difluorophosphine selenide,determined using a combination of gas electron diffraction and liquid-crystal NMR data

The molecular structure of difluorophosphine selenide has been determined by a combined analysis of gas-phase electron diffraction data and dipolar couplings obtained for a solution in a nematic phase. Geometrical parameters (r_a) are: _r(PSe) 202.6(4), r(P-F) 155.7(3), r(P-H) 142.2(7) pm, ∠SePF 116.8(3), ∠FPF 98.1(7), ∠SePH 118.6(7)°.     

Electron diffraction and vibrational spectroscopic investigation of the molecular structure of (chloromethyl)trichlorosilane

An electron diffraction analysis of the molecular structure of the title compound has been carried out, and related vibrational spectroscopic measurements and calculations have been made. The main bond lengths (r_g and bond angles r_α) are as follows: SiCl, 202.8(2); SiC, 185.1(10); CCl, 179.4(11); CH, 111.2(18) pm; SiCCl, 111.7(4);l ClSiC, 109.95(21)°. The conformation of the molecule is staggered. The barrier to internal rotation is estimated to be around 10 kJ mol^?1.     

Molecular structure of WO2Br2

Molecular structure of WO₂Br₂ has been studied by electron diffractometry. Structural parameters for the molecule with C_2v symmetry are: r_α(W=O)=1.710(6) Å, r_α(W?Br)=2.398(5) Å, r_α(O?O)=2.815(30) Å, r_α(Br?Br)=4.021(16) Å, r_α(O?Br)=3.347(10) Å. The OWO and BrWBr bond angles are close to tetrahedral:L _αOWO=110.8(2.0)°, L_αBrWBr=113.9(1.0)°. The W=O bond was found to be characteristic in the series of tungsten dioxyhalides.     

Internal Rotation and Equilibrium Structure of the Bromonitromethane Molecule According to Gas Electron Diffraction Data and Quantum Chemical Calculations

The structure and internal rotation of the bromonitromethane molecule are studied using electron diffraction analysis and quantum chemical calculations. The electron diffraction data are analyzed within the models of a general intramolecular anharmonic force field and quantum chemical pseudoconformers to account for the adiabatic separation of a large amplitude motion associated with the internal rotation of the NO₂ group. The following experimental bond lengths and valence angles are obtained for the equilibrium orthogonal configuration of the molecule with C_s symmetry: r_e(N=O) = 1.217(5) Å, r_e(C–N) = 1.48(2) Å, r_e(C–Br) = 1.919(5) Å, ∠_еBr–C–N = 109.6(9)°, ∠_еO=N=O = 125.9(9)°. The equilibrium geometry parameters are in good agreement with CCSD(T)/cc-pVTZ calculations. Thermally averaged parameters are calculated using the equilibrium geometry and quadratic and cubic quantum chemical force constants. The barrier to internal rotation cannot be determined reliably based on the electron diffraction data used in this work. There is a 82% probability that the equilibrium configuration with orthogonal C–Br and N=O bonds is most preferable, and internal rotation barrier does not exceed 280 cm^-1, which agrees with CCSD(T)/cc-pVTZ calculations.     

Die Kristallstruktur von (PPh4)2[Mo2(O2C?Ph)4Br2] · 2 CH2Br2

Crystal Structure of (PPh₄)₂[Mo₂(O₂C? Ph)₄Br₂] · 2 CH₂Br₂ The title compound, prepared by the reaction of Mo₂(O₂C? Ph)₄ with PPh₄Br and PPh₄N₃, respectively, under the assistance of CH₂Br₂, was characterized by an X-ray structure determination. Space group P2₁/n, Z = 2, R = 0.074 (5261 independent observed reflexions). The lattice dimensions are at ?70°C: a = 1562.9, b = 1406.2, c = 1662.1 pm, β = 94.11°. the compound consists of PPh₄^⊕ ions, CH₂Br₂ molecules, and centrosymmetric anions [Mo₂(O₂C? Ph)₄Br₂]^2?. The axis Br? Mo?Mo–Br is nearly linear (bond angle 175.6°) with bond lengths MoMo = 212.3 pm and Mo? Br = 303 pm, corresponding with a weak electrostatic Mo? Br bond. In the FIR spectrum the Mobr stretching vibration is found at 85 cm^?1, which corresponds with the low value of the force constant of 0.24 N · cm^?1.     

The molecular structure and conformation of acetamides in the vapour phase: Part III. Thioacetamide (ethanethioamide)

Thioacetamide has been studied by electron diffraction in the gas phase, utilizing a new nozzle construction and using a broad electron beam. The molecule has C_s symmetry, and one C-H bond eclipses the CS bond. The most important structural parameters are: r_g(C-N) = 135.6(3) pm, r_g(C—C) = 151.2(4) pm, r_g(CS) = 164.7(3) pm,∠_αCCS = 122.9(3)° and ∠_αCCN = 114.8(4)°. Parenthesized values are one standard deviation where correlation among data and uncertainty in the electron wavelength have been included. The methyl barrier, V₃, is found from the electron diffraction data to be 4.56 kJ mol^?1. This corresponds to a torsional frequency of 131 cm^?1.     

Structure determination of gaseous 1,3-dimethyl-2chloro-diazaboracyclopentane by electron diffraction

By means of gas phase electron diffraction it has been shown that the five-membered ring in 1,3-dimethyl-2-chloro-diazaboracyclopentane is essentially planar, while there seems to be a slight deviation from planarity about the N atoms. The most important bond lengths (r_a) and bond angles are (standard deviations in parentheses): r(B-N) = 1.413(3) Å; r(C-N)_av = 1.455(2) Å; r(B-Cl) = 1.770(4) Å; ∠NBN = 110.8(3)°; ∠B2N3C4 = 108.6(3)°; ∠N3C4C5 = 105.7(3)°.     

The gas phase molecular structure of silyl formate,determined by electron diffraction

The structure of silyi formate, HCOOSiH₃, in the gas phase is determined by electron diffraction. The principal bond lengths and angles (r_a) are r(Si-O) = 169.5 ± 0.3 pm, r(C-O) = 135.1 ± 0.6 pm, r(C  O) = 120.9 ± 0.7 pm, ∠(C-O-Si) = 116.8 ± 0.5°, ∠(OC-O) = 123.5 ± 0.5°. The silyi group is twisted by 21° away from the planar cis conformation but there is nevertheless a very short (286.5 ±1.0 pm) non-bonded Si ·O contact.     

Molecular structure and conformation of gaseous vinyldimethylchlorosilane as determined by electron diffraction

The molecular structure of vinyldimethylchlorosilane has been determined by gas phase electron diffraction at room temperature. The least squares values of the bond lengths (r_g) and bond angles (∠_α) are : r(CH) = 1.086(6) Å, r(CC) = 1.347(5) Å, r(SiC=) = 1.838(6) Å, r(SiC) = 1.876(3) Å, r(SiCl) = 2.078(2) Å, ∠CCSi = 127.8° (1.2) and ∠=CSiCl = 107° (1). Models with pure syn form and a mixture of syn and gauche gave equally good agreement with the diffraction data.