Gas phase structure and conformational properties of trifluoroacetic anhydride, CF3C(O)OC(O)CF3

The geometric structure of trifluoroacetic anhydride, CF₃C(O)OC(O)CF₃, has been studied by gas electron diffraction (GED) and quantum chemical calculations (MP2 and B3LYP with 6-31G^* basis sets). The GED analysis results in a single conformer with synperiplanar orientation of the two CO bonds. This analysis, however, cannot discriminate between a planar equilibrium structure (C_2v symmetry) with large amplitude torsional motions around the OC bonds and a nonplanar equilibrium structure (C₂ symmetry) with a low barrier at the planar arrangement. An effective dihedral angle φ(COCO=18(4)° is obtained. Both quantum chemical methods predict a nonplanar equilibrium structure of C₂ symmetry and φ(COCO)=16.5° and 13.9°, respectively.     

Higher trifluoromethylated derivatives of C60, C60(CF3)16 and C60(CF3)18: Synthesis, structure, and theoretical study

Three isomers of C₆₀(CF₃)₁₆ and one isomer of C₆₀(CF₃)₁₈ have been isolated by HPLC from a mixture prepared by trifluoromethylation of C₆₀ with CF₃I in a glass ampoule at 380-400 °C. The molecular structures of the four new compounds have been determined by means of X-ray single crystal diffraction and discussed in terms of mechanistic pathways of their formation and relative stability according to the DFT calculations.     

Structure of 1,4,10,19,25,41-C70(CF3)6, isomer with unique arrangement of addends

A novel isomer of C₇₀(CF₃)₆ has been isolated by HPLC from a mixture prepared by trifluoromethylation of C₇₀ with CF₃COOAg. The X-ray structure revealed an unprecedented arrangement of CF₃ groups forming a p³mp ribbon. This result provides additional evidence of the preferable formation of trifluoromethylated fullerene molecules comprising a single continuous ribbon of edge-sharing para- and meta-C₆(CF₃)₂ hexagons.     

Structural and theoretical studies of Xe(OChF5)2 and [XeOChF5][AsF6] (Ch = Se, Te)

The XeOSeF₅⁺ cation has been synthesized for the first time and characterized in solution by ¹⁹F, ⁷⁷Se and ¹²⁹Xe NMR spectroscopy and in the solid state by X-ray crystallography and Raman spectroscopy with AsF₆⁻ as its counter anion. The X-ray crystal structures of the tellurium analogue and of the Xe(OChF₅)₂ derivatives have also been determined: [XeOChF₅][AsF₆] crystallize in tetragonal systems, P4/n, a=6.1356(1) Å, c=13.8232(2) Å, V=520.383(14) Å³, Z=2 and R₁=0.0453 at −60°C (Te) and a=6.1195(7) Å, c=13.0315(2) Å, V=488.01(8) Å³, Z=2 and R₁=0.0730 at −113°C (Se); Xe(OTeF₅)₂ crystallizes in a monoclinic system, P2₁/c, a=10.289(2) Å, b=9.605(2) Å, c=10.478(2) Å, β=106.599(4)°, V=992.3(3) Å³, Z=4 and R₁=0.0680 at −127°C; Xe(OSeF₅)₂ crystallizes in a triclinic system, , a=8.3859(6) Å, c=12.0355(13) Å, V=732.98(11) Å³, Z=3 and R₁=0.0504 at −45°C. The energy minimized geometries and vibrational frequencies of the XeOChF₅⁺ cations and Xe(OChF₅)₂ were calculated using density functional theory, allowing for definitive assignments of their experimental vibrational spectra.     

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).     

Synthesis, spectroscopic and structural properties of CF3SO2OCCl3

Trichloromethyl trifluoromethanesulphonate, CF₃SO₂OCCl₃, was prepared by quantitative reaction between Ag(CF₃SO₂O) and BrCCl₃. The conformational and structural properties of the gaseous molecule were studied by vibrational spectroscopy (IR (gas, liquid), Raman (liquid) and quantum chemical calculations (DFT and ab initio methods)).Theoretical and experimental vibrational results evidenced the presence of a single conformer with C₁ symmetry. This result is in agreement with the adopted geometry of covalent sulphonates. The conformational preference was studied using the total energy scheme and natural bond orbital partition scheme. Additionally, the total potential-energy has been deconvoluted using six fold decomposition in terms of a Fourier-type expansion.     

Tautomeric and conformational properties of dimethyl malonate, CH3OC(O)-CH2-C(O)OCH3: electron diffraction and quantum chemical study

The geometric structure of dimethyl malonate, CH₃OC(O)-CH₂-C(O)OCH₃, was studied by gas electron diffraction (GED) and quantum chemical methods. We conclude that only diketo conformers exist in the gas phase. According to the GED refinement, a mixture of two diketo conformers is present: 69(10)% (ac,ac) conformer with C₂ symmetry (both CO bonds anticlinal relative to the opposite C-C bond) and 31(10)% (sp,ac) conformer with C₁ symmetry (one CO bond with synperiplanar, the other CO bond with anticlinal orientation). Ab initio calculations, however, predict a preference of the (sp,ac) conformer rather than the (ac,ac) form.     

Theoretical studies of the oxidative addition of PhBr to Pd(PX3)2 and Pd(X2PCH2CH2PX2) (X = Me, H, Cl)

The density functional theory calculations were used to study the influence of the substituent at P on the oxidative addition of PhBr to Pd(PX₃)₂ and Pd(X₂PCH₂CH₂PX₂) where X = Me, H, Cl. It was shown that the C_ipso-Br activation energy by Pd(PX₃)₂ correlates well with the rigidity of the X₃P-Pd-PX₃ angle and increases via the trend X = Cl < H < Me. The more rigid the X₃P-Pd-PX₃ angle is, the higher the oxidative addition barrier is. The exothermicity of this reaction also increases via the same sequence X = Cl < H < Me. The trend in the exothermicity is a result of the Pd(II)-PX₃ bond strength increasing faster than the Pd(0)-PX₃ bond strength upon going from X = Cl to Me. Contrary to the trend in the barrier to the oxidative addition of PhBr to Pd(PX₃)₂, the C_ipso-Br activation energy by Pd(X₂PCH₂CH₂PX₂) decreases in the following order X = Cl > H > Me. This trend correlates well with the filled d_π orbital energy of the metal center. For a given X, the oxidative addition reaction energy was found to be more exothermic for the case of X₂PCH₂CH₂PX₂ than for the case of PX₃. This effect is especially more important for the strong electron donating phosphine ligands (X = Me) than for the weak electron donating phosphine ligands (X = Cl).     

Density functional theory study on structural isomers and bonding of model complexes M(CO)5(BH3 · PH3) (M = Cr, Mo, W) and W(CO)5(BH3 · AH3) (A = N, P, As, Sb)

The influence of group 15 various substituents and effect of metal centers on metal-borane interactions and structural isomers of transition metal-borane complexes W(CO)₅(BH₃ · AH₃) and M(CO)₅(BH₃ · PH₃) (A = N, P, As, and Sb; M = Cr, Mo, and W), were investigated by pure density functional theory at BP86 level. The following results were observed: (a) the ground state is monodentate, η¹, with C₁ point group; (b) in all complexes, the η¹ isomer with C_S symmetry on potential energy surface is the transition state for oscillating borane; (c) the η² isomer is the transition state for the hydrogens interchange mechanism; (d) in W(CO)₅(BH₃ · AH₃), the degree of pyramidalization at boron, interaction energy as well as charge transfer between metal and boron moieties, energy barrier for interchanging hydrogens, and diffuseness of A increase along the series A = Sb < As < P < N; (e) in M(CO)₅(BH₃ · PH₃), interaction energy is ordered as M = W > Cr > Mo, while energy barrier for interchanging hydrogens decreases in the order of M = Cr > W > Mo.     

Influence of coordination on N-H X hydrogen bonds. Part II. Zn(NH3)2Br2 and Ni(NH3)2X2 (X is Cl and Br)

Microcrystalline samples of Zn(NH₃)₂Br₂ and Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻) have been investigated from 100 to 293 K using X-ray diffraction and IR spectroscopy measurements (range 400–4000 cm⁻) performed with isotopically dilute (5% deuterated) samples. Values of Δν(ND)/ΔT for all compounds hint at the existence of hydrogen bonds. Zn(NH₃)₂Br₂ shows The dynamics of ammonia molecules even at 100 K, and no indications are apparent that dynamic disorder of ammonia molecules takes place in Ni(NH₃)₂X₂ (X is Cl⁻ and Br⁻). A comparison between octahedrally coordinated ammoniates [Ni(NH₃)₆]Br₂, Ni(NH₃)₂Br₂ and [Zn(NH₃)₆]Br₂ with tetrahedrally coordinated ones [Zn(NH₃)₂Br₂] leads to the conclusion that the lower coordination number increases the strength of the hydrogen bonds. Because this effect is small, it is not possible to separate the influence of the type of coordinating ions for one coordination number from the influence of the coordination number itself.     

The force constants in the isoelectronic series CF3SO2X (X=F, OH, NH2, CH3): a study based on DFT calculations and experimental data

Density functional theory calculations at the B3LYP/6-31G(d,p) level of theory were performed on the members of the isoelectronic series CF₃SO₂X (X=F, OH, NH₂, CH₃), in order to obtain the optimized geometric parameters and conformations for the four molecules, as well as the wavenumbers corresponding to the normal modes of vibration and the associated force constants. The original force field was transformed to local symmetry coordinates and scaled to reproduce the experimental wavenumbers. The trends observed in geometrical parameters and force constants along the isoelectronic series could be explained making use of the calculated atomic charges.     

A NMR, X-ray, and DFT combined study on the regio-chemistry of nucleophilic addition to platinum(II) coordinated terminal olefins

The series of platinum complexes [PtCl(η²-CH₂CH-C₆H₄-X)(tmeda)](ClO₄) (X = H, 1b; 4-OMe, 1c; 3-OMe, 1d; 4-CF₃, 1e; 3-CF₃, 1f; 3-NO₂, 1g; tmeda = N,N,N′,N′-tetramethyl-1,2-ethanediamine) has been considered. In the styrene complex (1b) both solution (NMR) and solid state (X-ray) data indicate a significant difference in the Pt-C bond lengths (the longer bond being that involving the olefin carbon atom carrying the phenyl ring). Such a difference increases when X is an electron donor group (EDG, 1c) and decreases when X is an electron withdrawing group (EWG, 1d-g). The attack of a nucleophile (MeO⁻) to the substituted carbon (Markovnikov type, M) is by far the most favoured in the case of unsubstituted (1b) or EDG-substituted (1c) styrenes. The presence of an EWG (compounds 1d-g) levels off the probability of M and anti-M type of attack. DFT calculations on 1b,c and 1e were also performed. The NLMO analysis reveals the crucial role of the interaction between the filled π orbital of the olefin and the empty d orbital of platinum; the carbon with greater electron density becoming less susceptible of nucleophilic attack.     

Trends in the Structural and Vibrational Properties of the Disulfanes S2X2 (X = H,Halogen, CH3, CF3)

The geometrical parameters and associated force constants for the molecules XSSX (X = H, halogen, CH₃, CF₃) were studied using DFT quantum chemistry calculations. The study showed rather monotonic trends in these properties related to the SS bonds, although an anomalous behavior is noted when the substituent is CF₃. The calculated vibrational frequencies allowed a confirmation of published band assignments, but corrections were necessary for S₂F₂ and S₂H₂.     

Synthesis and properties of novel guanidine bases. N,N′,N″-Tris(3-dimethylaminopropyl)-guanidine

The synthesis of novel N,N′,N″-tris(3-dimethylaminopropyl)-guanidine 1 is described and X-ray structure of its hexafluorophosphate salt measured (1H·PF₆). The hydrogen bonding in protonated 1 and in 1H·PF₆ is also discussed.     

Novel ammonium hexafluoroarsenate salts from reaction of (CF3)2NH,CF3N(OCF3)H,CF3N[OCF(CF3)2]H,CF3NHF and SF5NHF with the strong acid HF/ASF5.

Reactions of the fluorinated amines (CF₃)₂NH, CF₃N(OCF₃)H, CF₃N[OCF(CF₃)₂]H, CF₃NHF and SF₅NHF with the strong acid HF/AsF₅ form the corresponding ammonium salts R_f¹R_f²NH₂⁺AsF₆^? and R_fNFH₂⁺ AsF₆^? in high yield. [R_f¹=CF₃, R_f²=CF₃, CF₃O, (CF₃)₂CFO; R_f=CF₃, SF₅] The colorless crystalline solids are stable for prolonged periods at 22°C in sealed FEP containers. They have dissociation pressures at 22°C ranging from ～5 torr (R_fNFH₂⁺ AsF₆^?) to ～50 torr [CF₃N(OCF₃)H₂⁺AsF₆^?]. ¹⁹F NMR and Raman spectroscopy were used to identify the compounds.     

(Trifluoromethyl)sulfanyl sulfinylimine, CF3SNSO. Structure and conformation in the electronic ground and excited states

The molecular structure of (trifluoromethyl)sulfanyl sulfinylimine, CF₃---S---N=S=O, was determined by gas electron diffraction (GED) and ab initio calculations (HF/3–21G*, HF/6–31+G* and MP2/6–31+G*). Experimental and theoretical methods result in a structure with planar C---S---N=S=O skeleton (C_s symmetry), anti orientation of the S---C bond relative to the N=S bond and syn orientation of the S---N bond relative to the S=O double bond (anti-syn structure). The following skeletal parameters (r_a values with 3σ uncertainties) were derived in the GED analysis: S---C, 1.831(4) Å; S---N, 1.684(5) Å; N=S, 1.538(6) Å; S=O, 1.453(6) Å; C---S---N, 94.6(8)°; S---N=S, 120.6(6)°; N=S=O: 116.5(8)°. A normal coordinate analysis based on FTIR (gas), FTIR (matrix) and Raman (liquid) spectra was performed. The UV (gas) spectrum was recorded and interpretation of the resonance Raman effect leads to the conclusion that the molecular symmetry (C_s) is retained upon electronic excitation.     

Syntheses and characterization of ANi(AsF6)3 (A = H3O, O2, NO, NH4, K, Rb, and Cs) compounds

ANi(AsF₆)₃ (A = O₂⁺, NO⁺, NH₄⁺) compounds could be prepared by reaction between corresponding AAsF₆ salts and Ni(AsF₆)₂. When mixtures of AF (A = Li, Na, K, Rb, Cs) and NiF₂ are dissolved in aHF acidified with an excess of AsF₅ the corresponding AAsF₆ and Ni(AsF₆)₂ were formed in situ. For A = Li and Na only mixtures of AAsF₆ and Ni(AsF₆)₂ were obtained, while for A = K, Rb and Cs, the final products were ANi(AsF₆)₃ (A = K-Cs) compounds contaminated with AAsF₆ (A = K-Cs) and Ni(AsF₆)₂.ANi(AsF₆)₃ (A = H₃O⁺, O₂⁺, NO⁺, NH₄⁺ and K⁺) compounds are structurally related to previously known H₃OCo(AsF₆)₃. The main features of the structure of these compounds are rings of NiF₆ octahedra sharing apexes with AsF₆ octahedra connected into infinite tri-dimensional network. In this arrangement cavities are formed where single charged cations are placed.In O₂Ni(AsF₆)₃ the vibrational band belonging to O₂⁺ vibration is found at 1866 cm⁻¹, which is according to the literature data one of the highest known values, and it is only 10 cm⁻¹ lower than the value for free O₂⁺.     

Syntheses, structures, and vibrational spectroscopy of the two-dimensional iodates Ln(IO3)3 and Ln(IO3)3(H2O) (LnYb, Lu)

The reaction of Lu³⁺ or Yb³⁺ and H₅IO₆ in aqueous media at 180 °C leads to the formation of Yb(IO₃)₃(H₂O) or Lu(IO₃)₃(H₂O), respectively, while the reaction of Yb metal with H₅IO₆ under similar reaction conditions gives rise to the anhydrous iodate, Yb(IO₃)₃. Under supercritical conditions Lu³⁺ reacts with HIO₃ and KIO₄ to yield the isostructural Lu(IO₃)₃. The structures have been determined by single-crystal X-ray diffraction. Crystallographic data are (MoKα, λ=0.71073 Å): Yb(IO₃)₃, monoclinic, space group P2₁/n, a=8.6664(9) Å, b=5.9904(6) Å, c=14.8826(15) Å, β=96.931(2)°, V=766.99(13), Z=4, R(F)=4.23% for 114 parameters with 1880 reflections with I>2σ(I); Lu(IO₃)₃, monoclinic, space group P2₁/n, a=8.6410(9), b=5.9961(6), c=14.8782(16) Å, β=97.028(2)°, V=765.08(14), Z=4, R(F)=2.65% for 119 parameters with 1756 reflections with I>2σ(I); Yb(IO₃)₃(H₂O), monoclinic, space group C2/c, a=27.2476(15), b=5.6296(3), c=12.0157(7) Å, β=98.636(1)°, V=1822.2(2), Z=8, R(F)=1.51% for 128 parameters with 2250 reflections with I>2σ(I); Lu(IO₃)₃(H₂O), monoclinic, space group C2/c, a=27.258(4), b=5.6251(7), c=12.0006(16) Å, β=98.704(2)°, V=1818.8(4), Z=8, R(F)=1.98% for 128 parameters with 2242 reflections with I>2σ(I). The f elements in all of the compounds are found in seven-coordinate environments and bridged with monodentate, bidentate, or tridentate iodate anions. Both Lu(IO₃)₃(H₂O) and Yb(IO₃)₃(H₂O) display distinctively different vibrational profiles from their respective anhydrous analogs. Hence, the Raman profile can be used as a complementary diagnostic tool to discern the different structural motifs of the compounds.     

The first synthesis, isolation and X-ray structure of a phosphonium phosphide, (Ph3PMe){[C6H2(CF3)3-2,4,6]2P}

The synthesis of a bulky secondary phosphine, Ar₂PH [Ar=C₆H₂(CF₃)₃-2,4,6], and its use in the first synthesis and isolation of a phosphonium phosphide, (Ph₃PMe)+(Ar₂P)⁻, via the deprotonation of Ar₂PH with a nonstabilised phosphorus ylide, Ph₃P=CH₂, are reported. An X-ray structure of this salt reveals that cations and anions are weakly associated in the solid state through C–HP interactions.