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.     

Synthetic and structural studies on some 1,3-diselena- and 1,3-dithia-[3]ferrocenophanes of germanium and tin. crystal and molecular structure of 1,3-diselena-2,2- dichlorogermyl-[3]ferrocenophane

A series of [3]ferrocenophanes of general formula Fe(C₅H₄X)₂YCl₂ and the spiro compounds [Fe(C₅H₄X)₂]₂Ge (X = S, Se; Y = Ge, Sn) have been prepared by the reaction of ferrocene 1,1′-dithiol and ferrocene 1,1′-diselenol with tetrahalides of germanium and tin. Spectroscopic properties of the compounds are reported. In solution, the compounds are fluxional by a bridge reversal process. The crystal structure of 1,3-diselena-2,2-dichlorogermyl-[3]ferrocenophane at 163 K. has been determined by X-ray diffraction methods. At that temperature, crystals have space group P2₁/n with a 6.222(3), b 16.156(13), c 12.968(4) Å, β 97.53(1)° and Z = 4. Least-squares refinement gave R = 0.033 for 2834 unique significant reflections whose intensities were measured by counter diffractometry. The two SeGe bond lengths are 2.323 and 2.325(1) Å, with GeCl 2.148 and 2.161(1) Å. The SeGeSe bond angle is 118.2(1)°, ClGeCl 104.7(1)°, and SeGeCl angles range from 106.2 to 109.8(1)°. The SeC bond lengths are 1.901 and 1.904(5) Å, with CSeGe angles of 95.8 and 96.5(2)°. The cyclopentadienyl rings are in an eclipsed conformation with a mean twist angle of 2.7°, and are inclined to one another at 6.1°. The Se atoms are displaced from the ring planes by 0.17 and 0.20 Å yielding a non-bonded intramolecular Se…Se contact of 3.99 Å.     

1,2,4-Triazincs XIII. The bond lengths and bond angles of a 1,2,4-triazine

The bond distances and bond angles of 5-(p-chlorophenyl)-1,2,4-triazine determined by three dimensional X-ray crystallographic analysis are reported. The pertinent bond lengths are N₁? N₂, 1.335Å, N₂-C₃, 1.314Å, C₃? N₄, 1.339; N₄-C₅, 1.317; C₅-C₆, 1.401; C₆? N₁, 1.317Å. A comparison of these bond distances with those of similar polyazabenzenes shows that the canonical structure of 1,2,4-triazine with a N₁? N₂ single bond more closely represents the ground state of this ring system, than the one with a N₁? N₂ double bond.     

Ab initio studies of structural features not easily amenable to experiment. 22. Structural aspects of a long-chain hydrocarbon (n-nonane) and a study of the transferability of electronic effects through C?C single bonds

The molecular structure of the stretched form of n-nonane, as a typical long-chain hydrocarbon, was refined by geometrically unconstrained ab initio force relaxation on the 4-21G level. The C? C bonds and C? H bond distances in the interior of the hydrocarbon chain are found to be longer (by about 0.001 Å and 0.002 Å, respectively) than those near the end of the chain. Similarly, interior C? C? C bond angles are 0.4° larger than the terminal angles. The variation of structural parameters with distance from the molecular ends levels off after the second carbon atom, and the geometry of methylene is practically constant from C₃ on. However, if one end of the system is perturbed by moving the inplane methyl hydrogen away from equilibrium, the resulting destabilizing electronic effects are transmitted through the C? C bond distance chain in such a way that significant perturbations are still experienced at C₅. Molecular mechanics (MM 2) gives a structure in which the small changes in bond lengths and angles with chain location are well reproduced.     

The Solitary Isomer of C60H18 Is Proven to Have a C3v Crown Shape: Crystal Structure Determination and Synthesis of Its Triruthenium Cluster Complex

Analytically pure C₆₀H₁₈ is obtained by a Ru₃ cluster complexation and decomplexation method. The crystal structure of C₆₀H₁₈ consists of one flattened hemisphere, to which all 18 hydrogen atoms are symmetrically bonded, and one curved hemisphere akin to C₆₀. A benzenoid ring in the flattened hemisphere is isolated from the residual π systems by a belt composed of sp³‐hybridized CH units. The average out‐of‐plane distances for carbon atoms attached to the benzenoid ring (0.14 Å) is substantially larger than that found in C₆₀F₁₈ (0.06 Å). Several long C(sp³)?C(sp³) single bond lengths [1.61(3)–1.65(3) Å] are observed for C₆₀H₁₈. The reaction of [Ru₃(CO)₁₂] and C₆₀H₁₈ produces [Ru₃(CO)₉(μ₃‐η²,η²,η²‐C₆₀H₁₈)] ( 1 ), where the Ru₃ triangle is regiospecifically linked to the hexagon opposite to the benzenoid ring. Compound 1 is the first transition metal complex of a polyhydrofullerene (fullerane). C₆₀H₁₈ and 1 have been characterized by ¹H and ¹³C NMR, UV/Vis, and mass spectroscopies. The HOMO–LUMO gap of C₆₀H₁₈ is evaluated to be 1.51 V by cyclic voltammetry.     

2,2′‐[2,3‐Di­hydro‐2‐(prop‐2‐enyl)‐1H‐isoindole‐1,3‐diyl­idene]bis(propane­di­nitrile)–tetra­thia­fulvalene (1/1), TCPI–TTF

The title complex, C₁₇H₉N₅·C₆H₄S₄, contains π‐deficient bis(di­nitrile) and TTF mol­ecules stacked alternately in columns along the a‐axis direction; the interplanar angle between the TTF molecule and the isoindolinyl C₄N[C(CN)₂]₂ moiety is 1.21 (4)°. The N‐allyl moiety in the TCPI mol­ecule is oriented at an angle of 87.10 (10)° with respect to the five‐membered C₄N ring, and the four C[triple‐bond]N bond lengths range from 1.134 (3) to 1.142 (3) Å, with C—C[triple‐bond]N angles in the range 174.3 (3)–176.9 (2)°. In the TTF system, the S—C bond lengths are 1.726 (3)–1.740 (3) and 1.751 (2)–1.763 (2) Å for the external S—C(H) and internal S—C(S) bonds, respectively.     

Computational modeling of the structure of large molecules: I. molecule C60H12 and cluster C852

Structural parameters of dodecahydro-Buckminster fullerene C₆₀H₁₂ and its derivative, the carbon cluster C₈₅₂ consisting of a central C₆₀ dodecaradical and twelve peripheral C₆₀ diradicals connected by eighteen-C≡C-C≡C-bridges, are calculated using a PM3 quantum-chemical method. The C₆₀H₁₂ molecule and the central fragment of the cluster each contain eight quasiaromatic six-membered rings with bond lengths of 1.38 and 1.43 Å. The calculations we performed using the GAMESS package and an original algorithm for diagonalization of dense symmetric matrices.     

On the equilibrium structures and the IR active bending vibrations of linear C13 and C15: results of large-scale coupled cluster calculations

Accurate equilibrium (r_e) structures (ca. 0.0005 Å accuracy in bond lengths) have been established for linear C₁₃ and C₁₅ by applying a uniform correction to the results of CCSD(T) calculations with the cc-pVQZ basis set. The equilibrium bond lengths cover a small range between 1.2690 and 1.2928 Å and are indicative of strong carbon–carbon double bonds. Equilibrium structures of still longer chains may be obtained by taking the recommended r_e structure for C₁₅ and inserting one or more C₂ links with R_e = 1.277 Å in the middle of the molecule. Both linear C₁₃ and C₁₅ exhibit no sign of floppiness and appear to behave like fairly normal semi-rigid molecules. Diagonal potentials for the IR active bending vibrations of both molecules have large correlation contributions between -33 and 47%, with MP2 strongly overshooting with respect to CCSD(T). Harmonic cis-bending vibrational wavenumbers and their absolute IR intensities are predicted. Since the latter are rather small, the chances of an interstellar detection of linear C₁₃ or C₁₅ in the far IR may be poor.     

Structures of polyfluoroaromatic compounds. Part IX [1]. Crystal structure of decafluorofluoranthene

Crystals of decafluorofluoranthene, C₁₆F₁₀, are monoclinic, space group C2/c with unit cell dimensions a = 18.92(1), b = 4.84(1), c = 29.01(2) Å, β = 105.34(5)°. The structure was refined to a conventional discrepancy factor R of 4.7% and weighted discrepancy factor R_w of 4.9% for 1841 observed counter amplitudes. Estimated standard deviations average 0.004 Å; for bond lengths and 0.3° for bond angles. The molecule is essentially planar. Detailed comparison with the parent hydrocarbon indicates that substitution of fluorine for hydrogen has brought about only quite small changes in molecular geometry.     

Darstellung und Charakterisierung der Fulleren-Kokristallisate C60 · 12 C6H12, C70 · 12 C6H12, C60 · 12 CCl4, C60 · 2 CHBr3, C60 · 2 CHCl3, C60 · 2 H2CCl2

Synthesis and Characterization of the Fullerene Co-Crystals C₆₀ · 12 C₆H₁₂, C₇₀ · 12 C₆H₁₂, C₆₀ · 12 CCl₄, C₆₀ · 2CHBr₃, C₆₀ · 2CHCl₃, C₆₀ · 2H₂CCl₂ By crystallization of fullerenes from non-polar solvents (C₆H₁₂, CCl₄, CHBr₃, CHCl₃, H₂CCl₂) compounds of the following compositions were obtained: C₆₀ · 12C₆H₁₂, C₇₀ · 12C₆H₁₂, C₆₀ · 12CCl₄, C₆₀ · 2CHCl₃, C₆₀ · 2CHBr₃ and C₆₀ · 2H₂CCl₂. Lattice parameters have been determined by X-ray diffraction of powder samples; according to single-crystal examinations on C₆₀ · 12C₆H₁₂, C₆₀ · 12CCl₄ and C₆₀ · 2CHBr₃ the fullerene is orientationally disordered. C₆₀ · 12C₆H₁₂, cubic, a = 28.167(1) Å; C₇₀ · 12C₆H₁₂, cubic, a = 28.608(2) Å; C₆₀ · 12CCl₄, cubic, a = 27.42(1) Å; C₆₀ · 2CHBr₃, hexagonal, a = 10.212(1), c = 10.209(1) Å; C₆₀ · 2CHCl₃, hexagonal, a = 10.08(1), c = 10.11(2) Å; C₆₀ · 2H₂CCl₂, tetragonal, a = 16.400(1) Å, c = 11.645(7) Å.     

Structural properties of 3-dimensional carbon clusters

Structural properties of 3d carbon clusters were calculated employing recently developed model potential energy functions for carbon. Primarily, spherical shell structures were included in the present investigation. Configurations corresponding to local energy minima were calculated for various shells of an icosahedron containing different number of C atoms. For C₆₀, the two low-lying isomers, the buckminsterfullerene and truncated dodecahedron, were found to be almost isoenergetic. It was also found that fully relaxed structures of C₉₀ and C₁₂₀ have energies very comparable to that of C₆₀. Furthermore, a systematic analysis carried out in this study for carbon clusters with varying dimensionalities, revealed an interesting relationship between the bond lengths and the distribution of bond angles. In all cases, shorter bond distances were found to be associated with larger bond angles.     

On the geometrical structure and UV spectrum of the truncated icosahedral C60, molecule

The PPP CI molecular-orbital theory for three-dimensional systems has been applied to study the UV spectrum of the truncated icosahedral C₆₀ molecule. We have found that only the one-electron transitions to T_1u symmetry (4.2270,4.7498 and 6.5182 eV) have oscillator strengths different from zero. Using a bond-order-bond-length relation in SCF iteration connected to the PPP method, we have obtained two kinds of bond lengths r₁ = 1.439 Å and r₂ = 1.398 Å, which correspond to the edges of the regular pentagon and the edge of a hexagon not lying on a pentagon.     

The structure of tetramethyl μ-monothiopyrophosphate

The compound tetramethyl μ-monothiopyrophosphate (C₄H₁₂O₆P₂S) crystallizes in the monoclinic space group C 2/c, with (at -130°C) a = 10.322 Å, b = 8.229 Å, c = 12.062 Å, β = 98.44°, and D_calc = 1.639 g/mL³ and Z = 4. The crystal structure has been determined by single crystal X-ray diffraction to give a final R value of 0.0329 for 614 independent observed reflections [F_˚ > 2.5σ(F_˚)]. The sulfur atom resides on a crystallographic two-fold axis. The P S P bond angle is 105.4° and the P S bond lengths are 2.093 Å. The bond angles around phosphorus range from 99.1° to 118.2°. The terminal PO bond is 1.465 Å, and the methoxyl P O bond is about 1.556 Å. The H₃C O P bond angle is about 119.5°. Many structural features are interpreted in terms of π-bonding to phosphorus. Comparisons with the structures of pyrophosphate and related compounds indicate that the combined effects of increased acuteness of the P S P bond and the increased length of the P—S bonds lead to an increase of about 0.4 Å in the separation of phosphorus atoms in the sulfur-bridging compound. These facts, together with the weakness of the P S bond, must be taken into account in the interpretation of kinetic data for enzymatic reactions of phosphorothiolates as substrates in place of phosphates.     

Structure and conformation of 1,3-dithlane: an electron diffraction study

A gas-phase electron diffraction study of 1,3-dithiane, carried out at 100° C, has found no statistically significant evidence for the presence of any conformer in the vapor other than the chair, within an estimated uncertainty of 10%. An index of the degree of ring puckering in 1,3-dithiane is the average torsional angle which was found to be 61.3°, appreciably greater than that in cyclohexane, but somewhat less than that in 1,4-dithiane and 1,3,5-trithianc. The C-C-C, C-C-S and S-C-S valency angles, 113.6(33)°, 114.9(4)° and 115.0(3)° respectively, were all larger than the C-C-C valency angles in cyclohexane. The C-S-C valency angle, 98.1(7)°, was slightly smaller than that of dimethyl sulfide. Observed bond lengths were r_g(C-H) = 1.116(10) Å, r_g(C-H) = 1.533(5)Å, and r_g(C-S) = 1. 812(3)Å and mean amplitudes of vibration were l_g(C-H) = 0.081(12)Å, l_g(C-C) = 0.052(6)Å and l_g(C-S) = 0.052(4) Å (parenthesized quantities correspond to 3σ). Curiously, nonbonded distances between the axial hydrogen atoms in 1,3-dithiane are virtually identical to those in cyclohexane, even though these molecules have greatly different bond lengths, valency angles, and torsional angles.     

The crystal and molecular structures of bis (pentafluorophenyl)disulphide and bis(pentafluorophenyl)diselenide

The structures of (C₆F₅)₂S₂ and (C₆F₅)₂Se₂ have been determined by single crystal, X-ray diffraction techniques. The compounds are isostructural although the molecules are packed differently in the crystal in comparison with their phenyl analogues. Important bond lengths and angles are: SS, 2.059(4)Å; SeSe, 2.319(4)Å; SC, 1.770Å; SeC, 1.910(15)Å; SSC, 101.3(3)°; SeSeC, 98.8(1)°.     

A low‐temperature modification of hexa‐tert‐butyldisilane and a new polymorph of 1,1,2,2‐tetra‐tert‐butyl‐1,2‐diphenyldisilane

Crystals of hexa‐tert‐butyldisilane, C₂₄H₅₄Si₂, undergo a reversible phase transition at 179 (2) K. The space group changes from Ibca (high temperature) to Pbca (low temperature), but the lattice constants a, b and c do not change significantly during the phase transition. The crystallographic twofold axis of the molecule in the high‐temperature phase is replaced by a noncrystallographic twofold axis in the low‐temperature phase. The angle between the two axes is 2.36 (4)°. The centre of the molecule undergoes a translation of 0.123 (1) Å during the phase transition, but the conformation angles of the molecule remain unchanged. Between the two tri‐tert‐butylsilyl subunits there are six short repulsive intramolecular C—H...H—C contacts, with H...H distances between 2.02 and 2.04 Å, resulting in a significant lengthening of the Si—Si and Si—C bonds. The Si—Si bond length is 2.6863 (5) Å and the Si—C bond lengths are between 1.9860 (14) and 1.9933 (14) Å. Torsion angles about the Si—Si and Si—C bonds deviate by approximately 15° from the values expected for staggered conformations due to intramolecular steric H...H repulsions. A new polymorph is reported for the crystal structure of 1,1,2,2‐tetra‐tert‐butyl‐1,2‐diphenyldisilane, C₂₈H₄₆Si₂. It has two independent molecules with rather similar conformations. The Si—Si bond lengths are 2.4869 (8) and 2.4944 (8) Å. The C—Si—Si—C torsion angles deviate by between −3.4 (1) and −18.5 (1)° from the values expected for a staggered conformation. These deviations result from steric interactions. Four Si—C(t‐Bu) bonds are almost staggered, while the other four Si—C(t‐Bu) bonds are intermediate between a staggered and an eclipsed conformation. The latter Si—C(t‐Bu) bonds are about 0.019 (2) Å longer than the staggered Si—C(t‐Bu) bonds.     

Structures of polyfluoroaromatic compounds. Part VI [1]. Crystal structure of 3H,3′H-4,4′-dinitrohexafluorodiphenyl sulphide

Crystals of the title compound are tetragonal, with unit cell dimensions a = b = 6.10(1), c = 37.16(2) Å, space group P4₁2₁2. The structure has been determined from 780 three-dimensional counter data and refined to a value of 4.5% for the conventional discrepancy factor R. Estimated standard deviations average 0.006 Å for bond lengths and 0.5° for bond angles. The molecule has C₂ symmetry. The symmetry-related aromatic rings are each inclined at an angle of 61° to the C-S-C plane. The length of the C-S bond, 1.771(4) Å, corresponds closely to that expected for a single bond between sulphur and sp²-hybridized carbon. The bond angle at sulphur is 99.7(3)°, some 4° smaller than the angle in unfluorinated diaryl sulphides.     

Theoretical studies of C60/C70 fullerene derivatives: C60O and C70O

A semiempirical (AM1) calculation on the structures and stabilities of isomers of the fullerene derivatives C₆₀O and C₇₀O is carried out. The ozonolysis reaction mechanism and the thermodynamics of the compounds are studied. The two isomers of C₆₀O (56 bond and 66 bond) formed by an oxygen atom bridging across a C-C bond have an epoxide-like or an annulene-like structure. According to the ozonolysis reaction mechanism and kinetic factor analysis, the possible products of this ozonolysis reaction are C₆₀O with oxygen bridging over the 66 bond (C_2v) as an epoxide-like isomer and that with oxygen bridging over the 56 bond (C_s) as an annulene-like isomer. Further, the sixteen isomers of C₇₀O (both epoxide-like and annulene-like structures) have been studied with respect to the same reaction mechanism. The most possible product in this ozonolysis reaction contains oxygen bridging across in the upper part (66 bond in C₇₀O-2 or C₇₀O-4) as an epoxide-like structure. The other possible product is C₇₀O-8 (annulene-like structure), in which oxygen bridges across an broken equatorial CC bond in C₇₀ (D_5h). The vibrational frequency analysis and the electronic structure of the selected C₆₀O and C₇₀O isomers are generated for experimental characterisation. The experimental results indicate that C₆₀O and C₇₀O may decompose into the odd number fullerenes C₅₉ and C₆₉. We therefore studied the structures of C₅₉ and C₆₉ also.     

An analysis of the structure of fullerene C70 by quantum-chemical methods

Hartree-Fock and density functional theory calculations showed that the B, C, D, and E fullerene C₇₀ cycles were not coplanar. The interrelation between acoplanarity and pyramidality of atoms was studied. The bond lengths, valence and torsion angles, and charges and chemical shifts of fullerene C₇₀ atoms were jointly analyzed. Most attention was given to the acoplanarity of hexagons E in the aromatic belt.     

Beiträge zur Chemie des Schwefels. 114. Kristall- und Molekülstrukturen vom Hexathiepan (S6CH2), Pentathian (S5CH2) und Dibenzylpentathian (S5C(CH2C6H5)2)

Contributions to the Chemistry of Sulfur. 114. Crystal and Molecular Structures of Hexathiepane (S₆CH₂), Pentathiane (S₅CH₂), and Dibenzylpentathiane (S₅C (CH₂C₆H₅)₂) The crystal and molecular structures of hexathiepane 1 , pentathiane 2 and dibenzylpentathiane 3 were determined by single crystal X-ray structure analyses. 1 : Monoclinic space group P2₁/c; a = 7.694(4), b = 7.668(4), c = 12.367(6) Å, β = 108.9(1)°; Z = 4, d_calc. = 1.986 g/cm₃. The seven-membered heterocycle exists in twist-conformation. 2 : Monoclinic space group C2/c; a = 10.990(5), b = 6.872(4), c = 15.507(6) Å, β = 94.1(1)°; Z = 8, d_calc. = 1.982 g/cm₃. The six-membered heterocycle exists in chair-conformation. 3 : Monoclinic space group P2₁/c; a = 12.907(8), b = 13.611(8), c = 9.408(6) Å, β = 98.9(1)°; Z = 4, d_calc. = 1.442 g/cm₃. 3 is analogous to 2 a six-membered heterocycle with chair-conformation. The benzylic groups are distorted to each other. Bond lengths, bond angles, and dihedral angles of the heterocyclic sulfur rings arc discussed, especially with regard to a comparison with cyclohexasulfur, cycloheptasulfur. and cyclooctasulfur.