Electron diffraction study of molecular structure of mebicar

The structure of the mebicar molecule has been studied by gas-phase electron-diffractometry using quantum chemical calculations. An eclipsed conformation along the C-C bond (torsion angle ?(H-C-C-H) = 10°) and flattened semi-chair conformations of cyclic fragments have been found. The bond lengths (r _g ) and angles (∠α) show the following average values: r(C-C) 1.576(3) Å, r(C-N) 1.460(3) Å, r(C(O)-N) 1.390(4) Å, r(C=O) 1.211(5) Å, r(C-H) 1.090(5) Å, ∠CCN 103.0(5)°, ∠CNC(O) 112.2(1)°, ∠CNC 122.4(1)°. The dihedral angle between the cyclic fragments is 116.6°.     

Molecular structure of propargylgermane (2-propynylgermane) determined by gas-phase electron diffraction and quantum chemical calculations

The molecular structure of propargylgermane, HCCCH₂GeH₃, has been determined by gas-phase electron diffraction. The electron-diffraction investigation has been supported by density functional theory and ab initio calculations. The r_a value of the bond lengths (pm) are: r(C–Ge)=197.2(1); r(C–C)=143.9(2); r(CC)=123.1(1); r(H–C_acetylene)=108.5(3); r(C–H)=111.6(3) and r(Ge–H_average)=153.7(2). The Ge–C–C angle is 111.7(1)° and the C–CC angle is 178.3(4)°. The uncertainties are one standard deviation from the least-squares refinement.     

Crystal and molecular structure of (hexafluoroacetylacetonato) (pivaloylacetonato)copper(II)

The crystal structure of (hexafluoroacetylacetonato)(pivaloylacetonato)copper(II) has been determined. Crystal data for CuO₄C₁₃H₁₄F₆: a = 8.288(2) Å, b = 8.682(2) Å, c = 12.307(2) Å; α = 90.75(3)°, β = 94.29(3)°, γ = 106.60(3)°; V = 845.7(3) ų, space group \(P\overline 1 \), Z = 2, d_calc = 1.617 g/cm³. The coordination polyhedron of the copper atom is formed by four oxygen atoms of two different β-diketonate ligands with Cu-O distances within 1.874–1.946 Å; the O-Cu-O bond angles are 94.8° and 90.6°. The complexes are united into centrosymmetrical “dimers” with Cu...Cu distances of 4.365 Å.     

Gas phase electron diffraction study of tetraphenyltin,Sn(C6H5)4

The geometrical parameters of the tetraphenyltin molecule have been determined by gas phase electron diffraction at about 310°. The S₄ and “open” D_2d molecular models with the tetrahedral bond configuration at tin were chosen for the structure analysis. The former gave the better fit. The thermal average bond lengths (r_g, in Å) are as follows:

The benzene ring geometry appears to be almost unaffected by bonding to tin. However, tin causes an increase in the endocyclic valence angle at the ipso-carbon atom to 121.0(0.9)° rather than a decrease of that angle as might be expected, tin being a σ-electron donor. The ring plane and the plane containing the

bond and S₄ axis make an angle, ?, of 34.1(2.1)°. The

bond length in tetraphenyltin is longer than not only the

bond in tetravinyltin (r_g = 2.117(4) Å) but also the

bond in tetramethyltin (r_g = 2.144(7) A).     

Synthesis and molecular structure of salicylaldehydeS-methyl-isothiosemicarbazone,C9H11N3OS

The crystal structure of salicylaldehyde S-methylisothiosemicarbazone together with the synthesis applied are reported: C₉H₁₁N₃OS, monoclinic, P2₁/n,a=5.169(4),b=16.853 (10),c=11.367(5)Å, β=92.48(1)°,V=989.3(18)ų,Z=4,d _x =1.405g cm^?3. The structure was solved by the heavy atom method and refined anisotropically to a residualR=0.046. The molecule is practically co-planar. There is only one basic difference between the title compound H₂ L and its deprotonated and complexed forms reported hitherto: the nearly 180° difference in rotation about the formal double bond C1—N2. The molecules form hydrogen bonded dimers around \(\bar 1\) .     

Malonatobenzhydrazidediaquacobalt(II) hydrate: Synthesis,crystal and molecular structures

The coordination compound [Co(L)(Mal)(H₂O)₂]H₂O (I) (L is benzhydrazide, H₂Mal is malonic acid) has been synthesized and studied by IR spectroscopy, thermogravimetry, and X-ray diffraction. Crystals are triclinic, a = 7.610(4) Å, b = 7.854(2) Å, c = 12.751(2) Å, α = 75.12(3)°, β = 88.01(3)°, γ = 80.26(3)°, Z = 2, space group \(P\bar 1\). The structure is molecular. The Co²⁺ atom has a distorted octahedral coordination. The Co-O and Co-N bond lengths are 2.031-2.129(4) and 2.157(5) Å, respectively. The endocyclic O1Co1N1 bond angles are 77.3(2)° and 90.0(2)° in the five- and six-membered chelate rings, respectively. Molecules of complex I are linked via a great number of hydrogen bonds. The C…C contacts between phenyl rings additionally strengthen the structure.     

The molecular structure of norbornene as determined by electron diffraction and microwave spectroscopy

The molecular structure of norbornene has been investigated in the gas phase by combining electron diffraction data with microwave spectroscopic rotational constants. The interatomic distances (r_g) and bond angles were obtained by applying a least squares program to the refined experimental molecular diffraction intensities. The CC bond length was found to be 1.336 ± 0.002 Å while the

) bond length was 1. 529 ± 0.007 Å. Other bond lengths and angles included (IUPAC numbering system was used for norbornene): C₁-C₆ = 1.550 ± 0.020 Å, C₁-C₇ = 1.566± 0.005 Å, C₅-C₆ = 1.556 ± 0.005 Å, C-H_ave. = 1.103 ± 0.003 Å, ∠C₁C₂C₄ = 95.3°. The dihedral angle between planes C₁C₂C₃C₄ and C₁C₆C₅C₄ is 110.8 ± 1.5° while that between C₁C₂C₃C₄ and C₁C₇C₄ is 122.3°. The moments of inertia calculated from ED structure are in good agreement with microwave spectroscopic values.     

Gas electron diffraction and quantum chemical studies of the molecular structure of 2-nitrobenzenesulfonic acid

A combined gas electron diffraction and quantum chemical (B3LYP/6-311+G**, B3LYP/cc-pVTZ) study of the molecular structure of 2-nitrobenzenesulfonic acid (2-NBSA) is performed. Quantum chemical calculations show that the 2-NBSA molecule has five conformers, and the Gibbs energy of one of them is lower by more than 4.5 kcal/mol than the energy of the other conformers. It is found experimentally that the saturated vapor of 2-NBSA at T = 394(5) K contains only the low-energy conformer that has an intramolecular hydrogen bond between the H atom of the hydroxyl group and one of the O atoms of the NO₂ group. The C-C-S-O(H) torsion angle determining the position of the S-O(H) bond is ?72(7)°, while the NO₂ group is substantially turned relative to the benzene ring plane (C1-C2-N-O = 40(5)°). The following experimental values of the internuclear distances are obtained for this conformer (Å): r _h1(C-H)_av = 1.07(2), r _h1(C-C)_av = 1.401(4), r _h1(C-S) = 1.767(6), r _h1(S=O)_av = 1.412(4), r _h1(S-O) = 1.560(6), r _h1(N-O)_av = 1.217(5), r _h1(C-N) = 1.461(8), r _h1(O-H) = 0.99(3).     

Crystal structure of the 1:3 thiourea-hexachloroethane inclusion compound at 295 K

The crystal structure of the 1:3 thiourea-hexachloroethane inclusion compound at 295 K has been determined. The parameters of the rhombohedral Bravais cell (space group R3ˉc) are a = 16.097(2) Å, c = 12.450(3) Å, V = 2793.6(8) ų, d _calc = 1.659 g/cm³, d _exp = 1.661±0.005 g/cm³, Z = 6 for C₅H₁₂Cl₆N₆S₃. The disordered guest molecules lie in the channels (parallel to the c axis) of the clathrate framework constructed from thiourea molecules linked by N-H...S hydrogen bonds. The mutual arrangement of the carbon and chlorine atoms is such that they define four orientations of the C-C bond relative to the channel of the host framework with nearly eclipsed conformations of hexachloroethane: one orientation along the triple bond axis (channel axis) and three equiprobable orientations at an angle of 74(2)° to the axis; for the coaxial orientation, there are two different configurations of the guest with slightly different geometries. The relative contributions of each of the five orientations were determined from the site occupancies of the guest atoms: 26.18 (coaxial orientations) and 3×19%. The resulting structure model is compared with the literature data about guest disordering in the structure of an adduct of the same composition determined at 233 K and with other similar structures. Original Russian Text Copyright ? 2007 by S. F. Solodovnikov, G. N. Chekhova, G. V. Romanenko, N. V. Podberezskaya, Z. A. Solodovnikova, D. V. Pinakov, and A. R. Semenov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 2, pp. 348–357, March–April, 2007.     

Electron diffraction and quantum-chemical studies of the molecular structure of 2-methylbenzenesulfochloride

A combined electron diffraction and quantum-chemical (MP2/6-31G**) study of the molecular structure of 2-methylbenzenesulfochloride at 336(5) K was carried out. It was found that the gas phase contained only one conformer, C ₁. The following structural parameters were obtained: r _h1(C-H)_av = 1.095(8) Å, r _h1(C-C)_Ph = 1.402(4) Å, r _h1(C_Ph-C_meth) = 1.507(13) Å, r _h1(C_Ph-S) = 1.763(6) Å, r _h1(S=O) = 1.418(4) Å, r _h1(S-Cl) = 2.048(5) Å, ∠(H-C-H)_meth/av = 107.3(96)°, ∠(Cl-S-O)_av = 106.4(3)°, ∠C_Ph-S-Cl = 100.8(9), ∠O=S=O = 120.8(10)°. The C_C-C_S-S-Cl torsion angle that defines the position of the S-Cl bond relative to the plane of the benzene ring is 75.6(20)°. The B3LYP/6-311+G** calculated barriers of internal rotation of the methyl and sulfochloride groups are 1.2 kcal/mol and V ₀₁ = 10.2 (V ₀₂ = 4.1) kcal/mol, respectively.     

The influence of carbon nanotubes on the relative stability of diborane molecular forms

Relative stability of three molecular forms of diborane in the model single-walled carbon nanotubes has been studied by means of the PBE/3ζ hybrid DFT method. The influence of the force field of the nanotube results in the decrease of the В–В bond length, decrease of the energy difference between the orthogonal and the planar forms, and appearance of high negative charge at the В₂Н₄ molecule. The strengthening of these effects is not related to the length and geometry [(n,n) or (n,0)] of the nanotube, but is determined only by the nanotube diameter.     

Crystal and molecular structure of nitraminotetrazoles and nitramino-1,2,4-triazoles. V. 5-nitraminotetrazole methylammonium salt

An X-ray study was performed to investigate the structure of 5-nitraminotetrazole methylammonium salt. Monoclinic crystals, space group P2₁/n; a = 6.541(2) Å, b = 19.157(4) Å, c = 10.726(2) Å; β = 96.24(2)°; V = 1336.07(1) ų; Z = 8, ρ_calc = 1.602 g/cm³. The crystal structure has anions and cations of two independent types with close geometrical parameters. The anions are planar and have a nitrimine structure with an intramolecular hydrogen bond. All hydrogen atoms of the cationic amino groups form hydrogen bonds to the oxygen and nitrogen atoms of the anions. The negative charge is delocalized to different extents in the anions.     

The molecular structure of fumaric acid and the deformation of carboxyl group geometry on crystallization

The molecular structure of fumaric acid was studied by means of gas electron diffraction at 260° C. The molecular parameters and their standard deviations obtained for a C_2h model are (r_a distances in Å, angles in degrees): CO: 1.202(0.002), C-O: 1.341(0.006), C-C: 1.486(0.004), CC: 1.356(0.016). C-C-O: 112.1(1.0), C-CO: 124.4(1.1), C-CC: 121.8(1.2). From the available data on carboxylic acids the weighted average deformation of the structure of a carboxylic group on crystallization was determined; a significant expansion of the O-H bond (0.040 Å ), the CO bond (0.010 Å ) and the C-C-O bond angle (1.5° ) and a shrinkage of the C-O bond (0.041 Å ), the C_α-C bond (0.012 Å ) and the C-CO bond angle (2.0° ) was found. The energy for these deformations was estimated to be 1.8 kcal mol^?1.     

Molecular Structure of Triphenylamine in the Gas Phase

The molecular structure of triphenylamine was studied by gas-phase electron diffraction in combination with ab initio calculations. It is found that in the gas phase at 160°C the molecule possesses C₃ symmetry. The principal geometric parameters are as follows (r _a structure): N-C 1.421(4), C-C_mean 1.399(1), C-H 1.123(2) Å, bond angles NCC 123.6(10)° and 117.2(7)°, and CNC 119.9(2)°. Torsion angles around C-N bonds are ?39° and ?45°. Phenyl groups are rotated by 48° from the position in which the C₃ axis lies in the phenyl ring plane.     

The crystal and molecular structure of 1,2-diphenyl-1,2-diphospholane-1,2-disulphide

The crystal and molecular structure of 1,2-diphenyl-1,2-diphospholane-1, 2-disulphide has been determined from three dimensional X-ray diffraction data

by Patterson and Fourier techniques. The structure has been refined by full matrix least squares methods to a final R value of 0.055 based on 1733 observed reflexions. The unit cell is orthorhombic, space group P2₁2₁2₁, with dimensions a = 13.867 Å, b = 12.379 Å and c = 9.312 Å (all ± 0.003 Å), and contains 4 molecules. The PP bond length of 2.253 ± 0.002 Å is similar to that in several diphosphine disulphides and phosphorus sulphides, and indicates the absence of any π bonding in the PP bond.     

Structure,infrared and Raman spectroscopic studies of newly synthetic AII(SbV0.50FeIII0.50)(PO4)2 (ABa,Sr, Pb) phosphates with yavapaiite structure

The synthesis and structural study of three new A^II(Sb^V_0.5Fe^III_0.5)(PO₄)₂ (ABa, Sr, Pb) phosphates belonging to the ASbFePO system were reported here for the first time. Structures of [Ba], [Sr] and [Pb] compounds, obtained by solid state reaction in air atmosphere, were determined at room temperature from X-ray powder diffraction using the Rietveld method. Ba^II(Sb^V_0.5Fe^III_0.5)(PO₄)₂ features the yavapaiite-type structure, with space group C2/m, Z = 2 and a = 8.1568(4) Å; b = 5.1996(3) Å c = 7.8290(4) Å; β = 94.53(1)°. A^II(Sb^V_0.5Fe^III_0.5)(PO₄)₂ (ASr, Pb) compounds have a distorted yavapaiite structure with space group C2/c, Z = 4 and a = 16.5215(2) Å; b = 5.1891(1) Å c = 8.0489(1) Å; β = 115.70(1)° for [Sr]; a = 16.6925(2) Å; b = 5.1832(1) Å c = 8.1215(1) Å; β = 115.03(1)° for [Pb]. Raman and Infrared spectroscopic study was used to obtain further structural information about the nature of bonding in selected compositions.     

A phase-analytical study of the TlCuSe system

High-temperature silica-tube syntheses and room-temperature copper extraction experiments of the single phases found with the former technique have established five new ternary phases in the TlCuSe system. The compositions were determined by microprobe analysis. The new phases have been crystallographically characterized by means of single-crystal and powder diffraction: TlCu₃Se₂ (CsAg₃S₂ type),a = 15.2128(7)Å,b = 4.0115(2)Å,c = 8.3944(4)Å, β = 111.700°(4); Tl₅Cu₁₄Se₁₀ (new type),C2/m?)a = 18.097(2)Å,b = 3.9582(2)Å,c = 18.118(2)Å, β = 116.089°(7); TlCu₅Se₃ (new type,P4¯n2?),a = 12.9023(2)Å,c = 3.9905(1)Å; TlCu_5−xSe₃ (new type,Pnn2?),a = 12.43(1)Å,b = 12.80(1)Å,c = 3.93(1)Å; TlCu₇Se₄ (NH₄Cu₇S₄ type),a = 10.4524(2)Å,c = 3.9736(1)Å. The latter phase may be considered as stoichiometric crookesite.     

Molecular structure of caffeine as determined by gas electron diffraction aided by theoretical calculations

The molecular structure of caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) was determined by means of gas electron diffraction. The nozzle temperature was 185 °C. The results of MP2 and B3LYP calculations with the 6-31G⁷ basis set were used as supporting information. These calculations predicted that caffeine has only one conformer and some of the methyl groups perform low frequency internal rotation. The electron diffraction data were analyzed on this basis. The determined structural parameters (r_g and ∠_α) of caffeine are as follows: <r(NC)_ring> = 1.382(3) Å; r(CC) = 1.382(←) Å; r(CC) = 1.446(18) Å; r(CN) = 1.297(11) Å; <r(NC_methyl)> = 1.459(13) Å; <r(CO)> = 1.206(5) Å; <r(CH)> = 1.085(11) Å; ∠N₁C₂N₃ = 116.5(11)°; ∠N₃C₄C₅ = 121. 5(13)°; ∠C₄C₅C₆ = 122.9(10)°; ∠C₄C₅N₇ = 104.7(14)°; ∠N₉–C₄=C₅ = 111.6(10)°; <∠NCH_methyl> = 108.5(28)°. Angle brackets denote average values; parenthesized values are the estimated limits of error (3σ) referring to the last significant digit; left arrow in parentheses means that this parameter is bound to the preceding one.