Structures and conformations of trifluoromethanesulfonic anhydride, (CF3SO2)2O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF3SO2)2CF2

The geometric structures and conformational properties of trifluoromethanesulfonic anhydride, (CF₃SO₂)₂O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF₃SO₂)₂CF₂ have been studied by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*). The calculations predict for both systems two stable conformers with C₂ symmetry and one with C₁ symmetry. In both compounds structures with C₂ symmetry and dihedral angles SOSC ≈ 100° ((CF₃SO₂)₂O) and SCSC≈ 150° ((CF₃SO₂)₂CF₂ are lowest in energy. According to the GED analyses the dominant conformer of (CF₃SO₂)₂O₂ possesses C₂ symmetry with SOSC dihedral angles of 99.1(14)°. The presence of up to 30% of the two other conformers cannot be excluded; for (CF₃SO₂)₂CF₂ only one conformer with C₂ symmetry and SCSC dihedral angles of 143(2)° is observed. A complete set of geometric parameters is given.     

Structures and conformations of trifluoromethanesulfonic anhydride, (CF3SO2)2O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF3SO2)2CF2

The geometric structures and conformational properties of trifluoromethanesulfonic anhydride, (CF₃SO₂)₂O, and bis(trifluoromethylsulfonyl)difluoromethane, (CF₃SO₂)₂CF₂ have been studied by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*). The calculations predict for both systems two stable conformers with C₂ symmetry and one with C₁ symmetry. In both compounds structures with C₂ symmetry and dihedral angles SOSC ≈ 100° ((CF₃SO₂)₂O) and SCSC ≈ 150° ((CF₃SO₂)₂CF₂) are lowest in energy. According to the GED analyses the dominant conformer of (CF₃SO₂)₂O possesses C₂ symmetry with SOSC dihedral angles of 99.1(14)°. The presence of up to 30% of the two other conformers cannot be excluded; for (CF₃SO₂)₂CF₂ only one conformer with C₂ symmetry and SCSC dihedral angles of 143(2)° is observed. A complete set of geometric parameters is given.     

Structure and bonding in a series of cyano complexes: RuCp(PPh3) 2CN, [RuCp(PPh3) 2(CNH)]CF3SO3, and H-bridged [Ru2(Cp) 2(PPh3) 4CNHNC]CF3SO3

The three title cyanoruthenium complexes have been characterized by means of X-ray diffraction analysis, IR and NMR solution spectroscopies, as well as extended Hückel molecular orbital calculations examining the properties of the cyanide fragment changing with complexation and with the co-ligands Cp and PPh₃. Explanations are given for crystallographic results of the C-N bond shortening upon complexation, the supershort (2.573 Å) bond length of N(H) N in the bridged complex, as well as the Ru-C-N and C-N-H-N-C bendings. Although the crystallographically found asymmetry of coordinated Cp is not significant, the MO calculations suggest a distorted endocyclic bond-length pattern indicative of the relative importance of σ and π bonding in the metalcyclopentadienyl interactions.     

Comparaison des effects electroniques des ligands a deux electronx CX (X = O, S, Se) dans des complexes organometalliques du type CH3CO2(C6H5)Cr(CO)2(CX)

Structural and spectroscopic (IR, Raman) results concerning the organometallic complexes, CH₃CO₂(C₆H₅)Cr(CO)₂(CX) (X = O, S, Se) and theoretical calculations allow the comparison of electronic effects of CO, CS and CSe ligands. The strenght of the ligand---metal bond and the overall electron-with- drawing ability are higher for Se than for S and O, the largest variation being between S and O. This overall effect results in better σ-electron-repelling and π-electron-withdrawing abilities for Se than for S and O. Consequences of substituting one CO by CS or CSe in CH₃CO₂(C₆H₅)Cr(CO)₃ are analyzedin terms of molecular coordination. In particular Cr(CO)₂(CS) deformations and Cr---C (ring) bond variation are discussed. Some comparisons are made with phosphinechromium complexes.     

Octahedral tilting in ACu3Ru4O12 (A=Na, Ca, Sr, La, Nd)

The perovskite-like compounds ACu₃Ru₄O₁₂ (A=Na, Ca, Sr, La, Nd) are studied by means of density functional theory based electronic structure calculations using the augmented spherical wave (ASW) method. The electronic properties are strongly influenced by covalent-type bonding between transition metal d and oxygen p states. The characteristic tilting of the RuO₆ octahedra arises mainly from the Cu–O bonding, allowing for optimal bond lengths between these two atoms. Our results provide a deeper understanding of octahedral tilting as a universal mechanism, applicable to a large variety of multinary compounds.     

Beryllocene, (C5H5)2Be. The He(I) photoelectron spectrum and ab initio molecular orbital calculations

Ab initio molecular orbital calculations with a double-ζ basis have been carrried out on five models of beryllocene, Cp₂Be, with fixed geometries. The lowest energies are obtained for the π-Cp, σ-Cp and D_5d models.

The He(I) photoelectron spectrum of Cp₂Be was recorded and the ionization potentials of the first bands were compared with the orbital energies obtained from the molecular orbital calculations. A satisfactory fit between experiment and calculations was obtained for a slip sandwich model of C_s symmetry. A model of C_5v symmetry is only compatible with the PE spectrum if the Jahn—Teller splitting of the lowest ²E₁ state of the molecular ion is exceptionally large, 1.0 eV.     

Infrared and Raman spectra of 2-chloro-2,2-difluoroacetamide (ClF2CC(O)NH2)

The infrared and Raman spectra of 2-chloro-2,2-difluoroacetamide (ClF₂CC(O)NH₂) have been recorded and analyzed with the complement of results derived from computational chemistry calculations. Thus, delocalization effects and stabilization energies have been computed for the title molecule and a complete assignment has been also proposed. ¹³C, ¹⁹F and ¹H NMR chemical shifts and coupling constants have been also measured for this substance.     

Ab initio SCF and DFT models of met-car adducts: Ti8C12(L)n (L = Cl, NH3, CO, C6H6; N = 4, 8)

The addition of Cl, NH₃, CO, C₆H₆ to Ti₈C₁₂ has been investigated by means of ab initio RHF and DFT calculations. The metallocarbohedrene (met-car) molecule has been modelled as a structure of a tetracapped tetrahedron with T_d symmetry and two distinct metal sites, found to be most stable from previous theoretical investigations. The addition of four molecules to the atoms of the external tetrahedron of metal atoms has been found to be exothermic for all ligands considered. The addition of four extra ligands leading to T₈C₁₂(L)₈ appears easy for L = Cl, and also for L = NH₃. It appears that π-bonding molecules, either non-polar like benzene or weakly polar like CO, have much less affinity for the inner tetrahedron of metal atoms, which makes adducts with eight ligands difficult or impossible to obtain in that case. Those results agree with the recently observed reactivity of met-cars.     

Direct dynamics studies on the hydrogen abstraction reactions CF3O+CH4(CD4)→CF3OH(CF3OD)+CH3(CD3)

The dynamics properties of the hydrogen abstraction reaction CF₃O+CH₄→CF₃OH+CH₃ are studied by dual-level direct dynamics method. Optimization calculations are preformed by B3LYP and MP2 with the 6-311G(d,p) basis set, and the single-point calculations are done at the multi-coefficient correction method based on quadratic configuration interaction with single and double excitations (MC-QCISD) method. The rate constants are evaluated by canonical variational transition-state theory with a small-curvature tunneling correction over a wide range of temperature 200–2000 K. The agreement between theoretical and experimental rate constants is good in the measured temperature range. The calculated results show that the variational effect is small and almost neglected over the whole temperature range, whereas, the tunneling correction plays a role in the lower temperature range. The kinetic isotope effect for the reaction is ‘normal’. The value of k_H/k_D is 2.38 at room temperature and it decreases with the temperature increasing.     

exo-closo-Rhodacarboranes: synthesis and characterisation of [{exo-(R3P)2Rh}(closo-CB11H12)] [R3P=P(OMe)3, PCy3, 1/2dppe]

Addition of H₂ to CH₂Cl₂ solutions of [(diene)Rh(L)₂][closo-CB₁₁H₁₂] (diene=norbornadiene, cyclooctadiene, L=PCy₃, P(OMe)₃, 1/2dppe) results in the formation of the exo-closo complexes [(PR₃)₂Rh(closo-CB₁₁H₁₂)]. These have been characterised in solution by ¹H- and ¹¹B-NMR spectroscopy, and for L=PCy₃ by a single crystal X-ray diffraction study. This suggests that the metal fragment is bound with the cage through the 7,8- and not the 7,12-{BH} vertices. DFT calculations on a model system where L=PMe₃ show that there is only a negligible energy difference between these two isomers (1 kcal mol⁻¹), suggesting that both represent stable structures. The salient spectroscopic markers that indicate an interaction of [closo-CB₁₁H₁₂]⁻ with a metal fragment are discussed and compared across a range of metal complexes. Large upfield shifts in the ¹¹B-NMR spectrum and a small downfield shift of the CH vertex in the ¹H-NMR spectrum are shown to the most reliable indicators of borane interaction in solution.     

Vibrational studies of sulfamoil chloride (ClSO2NH2)

The infrared spectrum of sulfamoil chloride in the liquid phase was reinvestigated; the infrared and Raman spectra of the solid phase have also been obtained. A complete assignment of the observed bands is proposed. A subsequent normal coordinate analysis was performed. The experimental data are compared to results of ab initio and DFT (density functional theory) calculations. According to the experimental and theoretical results the main conformer of ClSO₂NH₂ possesses an anti conformation (C_s symmetry, S---Cl single bond in anti position with respect to the nitrogen lone pair).     

Electronically excited states of disulphur dinitride (S2N2) and its conversion to the metallic polymer (SN)x

Ab initio configuration interaction calculations with a double zeta basis augmented by polarisation functions have been carried out for all the lowest singlet and triplet states of S₂N₂ and (SN)₂) - a unit of the polymer (SN)_x. The results satisfactory account for the UV-absorption spectrum of S₂N₂ which is probably dominated by ¹B_2u. There are low-lying singlet and triplet states for (SN)₂, and one of these a σσ* triplet seems likely to be the polymerisation precursor.     

The molecular structure of N-sulfinyl trimethylsilanamine, (CH3)3SiNSO

The geometric structure of (CH₃)₃Si---NSO in the vapour phase has been determined by gas electron diffraction. The molecule possesses a planar Si---N=S=O skeleton with syn conformation. The Si(CH₃)₃ group staggers the N=S double bond. The following skeletal parameters (r_a distances and angles with 3σ errors limits) were obtained: Si---N 1.750(6)Å, N=S 1.508(5)Å, S=O 1.444(4)Å, Si---N=S 133.9(9)°, N=S=O 122.5(10)°. Ab initio calculations (HF/3−21G*) were performed for H₃Si---NSO and confirm the planar syn structure for sulfinyl silanamines.     

Experimental and theoretical investigations on the electric field gradient at the Br site in Sr(BrO3)2 · H2O and Ba(BrO3)2 · H2O

Single-crystal Zeeman effect studies have been done using ⁷⁹Br NQR in Sr(BrO₃)₂ · H₂O and Ba(BrO₃)₂ · H₂O and the electric field gradient (EFG) parameters at the Br site have been determined. The point-charge model for the evaluation of EFG at the Br site, when applied to these systems, has not yielded satisfactory results. In another model, the total EFG is obtained as the sum of the covalent contribution and the inter-ionic contribution. To obtain the covalent contribution CNDO/2 MO calculations have been done for the (BrO₃)⁻ ions of these systems. There is excellent agreement with the experimental values in the case of Sr(BrO₃)₂ · H₂O, while the results on Ba(BrO₃)₂ · H₂O indicate that the structural data on this crystal need refinement.     

Synthesis,characterization, and phase transition of an inorganic-organic hybrid compound,[(3-nitroanilinium+) (18-crown-6)] [IO4-](CH3OH)

A novel inorganic-organic hybrid supramolecular compound,[(3-nitroanilinium~+)(18-crown-6)][IO_4](CH_3OH)(1),was discovered as phase-transition materials displaying dielectric anomalous behaviors.The yellow block crystal formed by N-H…O hydrogen bonding that made contact through the cavity of 18-crown-6 was characterized by single-crystal X-ray diffraction,elemental analysis,infrared analysis,thermogravimetric analysis,differential scanning calorimetry,and potential-energy calculations.Differential scanning calorimetry measurements indicate that the compound experiences a reversible phase transition at around 220 K.Temperature-dependent dielectric measurements further confirm the phase transitions.Potential-energy calculations demonstrate that the phase transition occurs due to the molecular order-disorder rotation of CH_3OH,whereas the space grouping of the crystal remains unchanged.     

Synthesis and structural behavior of the P-functional organotin chlorides [Ph2P(CH2)3]2SnCl2, Ph2P(CH2)3SnCl2Me, and Ph2P(CH2)nSnCl3 (n=2, 3)

The P-functional organotin dichloride [Ph₂P(CH₂)₃]₂SnCl₂ (3) is synthesized by reaction of Ph₂P(CH₂)₃MgCl with SnCl₄ independently of the molar ratio of the starting compounds. The corresponding organotin trichlorides Ph₂P(CH₂)_nSnCl₂R (4: n=2, R=Cl; 5: n=3, R=Cl; 6: n=3, R=Me) are formed in a cleavage reaction of Ph₂P(CH₂)_nSnCy₃ (n=2, 3) with SnCl₄ or MeSnCl₃, respectively. The main features of the crystal structures of 3–6 are both intra- and intermolecular PSn coordinations and the existence of intermolecular Sn---ClSn bridges. For further characterization of the title compounds, the adducts 4(Ph₃PO)₂ (7) and 5(Ph₃PO) (8), as well as the P-oxides and P-sulfides of 3–6 (9–15), are synthesized. The results of crystal structure analyses of 7, 11, 12, and 14 are reported. The structures of 9–15 are characterized by intramolecular P=XSn interactions (X=O, S). A first insight into the structural behavior of the compounds 3–15 in solution is discussed on the basis of multinuclear NMR data.     

Structure and conformational properties of carbonylbisimidosulfuryl fluoride, O=C(N=S(O)F2)2

The molecular structure and conformational properties of O=C(N=S(O)F₂)₂ (carbonylbisimidosulfuryl fluoride) were determined by gas electron diffraction (GED) and quantumchemical calculations (HF/3-21G* and B3LYP/6-31G*). The analysis of the GED intensities resulted in a mixture of 76(12)% syn–syn and 24(12)% syn–anti conformer (ΔH⁰=H⁰(syn–anti)−H⁰(syn–syn)=1.11(32) kcal mol⁻¹) which is in agreement with the interpretation of the IR spectra (68(5)% syn–syn and 32(5)% syn–anti, ΔH⁰=0.87(11) kcal mol⁻¹). syn and anti describe the orientation of the S=N bonds relative to the C=O bond. In both conformers the S=O bonds of the two N=S(O)F₂ groups are trans to the C–N bonds. According to the theoretical calculations, structures with cis orientation of an S=O bond with respect to a C–N bond do not correspond to minima on the energy hyperface. The HF/3-21G* approximation predicts preference of the syn–anti structure (ΔE=−0.11 kcal mol⁻¹) and the B3LYP/6-31G* method results in an energy difference (ΔE=1.85 kcal mol⁻¹) which is slightly larger than the experimental values. The following geometric parameters for the O=C(N=S)₂ skeleton were derived (r_a values with 3σ uncertainties): C=O 1.193 (9) Å, C–N 1.365 (9) Å, S=N 1.466 (5) Å, O=C–N 125.1 (6)° and C–N=S 125.3 (10)°. The geometric parameters are reproduced satisfactorily by the HF/3-21G* approximation, except for the C–N=S angle which is too large by ca. 6°. The B3LYP method predicts all bonds to be too long by 0.02–0.05 Å and the C–N=S angle to be too small by ca. 4°.     

9-BBN activation. Synthesis, crystal structure and theoretical characterization of the ruthenium complex Ru[(μ-H)2BC8H14]2(PCy3)

Reaction of the bis(dihydrogen) ruthenium complex RuH₂(H₂)₂(PCy₃)₂ (1) with an excess of 9-borabicyclononane yields Ru[(μ-H)₂BC₈H₁₄]₂(PCy₃) (6) and the phosphine adduct PCy₃·HBC₈H₁₄. The new complex is characterized by NMR spectroscopy and X-ray diffraction. New X-ray data on 9-BBN dimer, from a measurement at 180 K, are also reported. DFT calculations (B3LYP) on Ru[(μ-H)₂BC₈H₁₄]₂(PMe₃) (7), the PMe₃ analogue of 6, confirm the ruthenium (II) formulation with two dihydroborate ligands. The data obtained using PH₃ or PMe₃ as models for PCy₃ in PR₃·HBC₈H₁₄ are also discussed.