Molecular structure, spectroscopy and matrix photochemistry of fluorocarbonyl iodide, FC(O)I.

The molecular structure of FC(O)I has been determined by gas electron diffraction. High-level ab initio methods, including coupled-cluster and the new correlation-consistent basis sets for fourth row elements, have been used to calculate the structure of FC(O)I. A comprehensive vibrational spectroscopic study (both IR and Raman) complemented by high-level calculations has also been performed. Furthermore, UV, mass, and NMR spectra have been recorded for FC(O)I. The matrix photochemistry of FC(O)I has been studied with a low-pressure mercury lamp and with a high-pressure xenon lamp in combination with interference and cut-off filters. UV photolysis revealed the formation of the OC. IF and OC.FI complexes and further photolysis of these complexes at lambda>320 nm resulted in a re-formation of FC(O)I. The structural conformation of the complexes has been characterized by comparing shifts in their CO and IF vibrational modes with respect to those of the free species. The structures, vibrational properties, and stability of the complexes were analyzed with the aid of coupled-cluster ab initio calculations.

Tetramethylphosphonium fluoride: "naked" fluoride and phosphorane.

Me(4)PF was investigated in the solid state, in the gas phase, and in solutions. Vibrational spectra of the solid and a single-crystal structure show an ionic tetramethylphosphonium fluoride. The compound crystallizes in the space group Pbca with a = 1016.0(1), b = 1018.0(1), c = 1205.8(4) pm, and Z = 8. The fluoride ion is nearly trigonal planar surrounded by three Me(4)P+ cations forming six H...F contacts between 218 and 240 pm. The compound is stable below 120 degrees C and sublimes in a vacuum. It possesses a phosphorane structure in the gas phase that was studied by electron diffraction and vibrational spectra, and additionally by theoretical calculations. The Me(4)PF molecule has a trigonal bipyramidal structure with one methyl group and the fluorine atom in axial positions and bond lengths of d(PC(eq)) = 182.6(4) pm, d(PC(ax)) = 188.4(8) pm, and d(PF) = 175.3(6) pm. The compound is remarkably soluble in acetonitrile, water, and alcohols, and slightly soluble in benzene, dimethyl ether, and diethyl ether. The solutions were studied by (1)H, (13)C, (19)F, and (31)P NMR spectroscopy. The hygroscopic Me(4)PF forms a tetrahydrate which crystallizes in the space group I4(1)/a with a = 1106.1(1) pm, c = 816.3(1) pm, and Z = 4. The fluoride ion in Me(4)PF.4 H(2)O is surrounded by four water molecules. These units form a three-dimensional network in which the Me(4)P+ cations are embedded without any contacts.

Trifluoroacetylsulfenyl trifluoroacetate, CF(3)C(O)-S-O-C(O)CF(3), a novel compound with a symmetrically substituted S-O bond: synthesis, spectroscopic characterization, and quantum chemical calculations.

The new compound trifluoroacetylsulfenyl trifluoroacetate, CF(3)C(O)SOC(O)CF(3), which possesses two identical carbonyl substituents attached to the S-O bond, has been synthesized. The IR and UV spectra of the gas phase as well as the (13)C NMR spectrum of the solution in CDCl(3) were recorded and assigned. Quantum chemical calculations were performed with the ab initio methods HF and MP2 and the density functional approach B3LYP. The 6-31G basis set was chosen in all calculations. The molecule possesses a skew structure, and according to all computational methods, the syn-syn structure (C=O bonds of both C(O)CF(3) groups synperiplanar to S-O bond) represents the most stable conformer. In agreement with the quantum chemical calculations, the presence of small amounts (< or =5%) of a second conformer (anti-syn) cannot be excluded on the basis of the IR spectrum. The calculated values for the torsional angle around the S-O bond (delta(C-S-O-C)) of the syn-syn form are smaller than 80 degrees (72-78 degrees). Comparison with theoretical results for the corresponding disulfide CF(3)C(O)SSC(O)CF(3) and peroxide CF(3)C(O)OOC(O)CF(3) indicates that the structural properties of sulfenyl compounds are more similar to those of disulfides than to those of peroxides.

Structure and conformational properties of diacetyl sulfide in the gaseous and condensed phases explored by gas electron diffraction, single-crystal X-ray diffraction, vibrational spectroscopy, and quantum chemical calculations.

On the evidence of the electron diffraction pattern of the vapor, of the IR spectrum of the matrix-isolated molecule, and of quantum chemical calculations, the diacetyl sulfide molecule, CH3C(O)SC(O)CH3, adopts a planar heavy-atom skeleton with the [sp,ap] conformation. Other conformations contribute little (<1%) to the population of the gaseous molecules at normal temperatures. Salient structural parameters (r(a) structure, distances (in A), angles (in deg), and 3sigma uncertainties in parentheses) were as follows: r(C=O) 1.198(2)/1.196(2), r(C-S) 1.787(3)/1.808(3), r(C-C) 1.483(4)/1.472(4), angleC-S-C 108.8(9), angleS-C=O 125.7(6)/115.1(6), and angleS-C-C 121.1(7)/111.2(7). The structure of a single crystal at 150 K [monoclinic, P2(1)/n, a = 4.2230(7) A, b = 11.2105(17) A, c = 12.332(2) A, beta = 94.544(16) degrees] also reveals planar molecules with the same conformation and dimensions close to those of the gaseous molecule. Changes in the vibrational spectra of the compound accompanying the transition from the vapor to the condensed phases are attributed not to the presence of more than one conformer but to differences in the local environment of the two carbonyl groups. The properties deduced are compared with those of other compounds of the type CH3C(O)XC(O)CH3 (X = CH2, NH, or O).

Tetrameric fluorophosphazene, (NPF(2))(4), planar or puckered?

The results obtained in a comprehensive experimental study on the redetermination of the structure of N(4)P(4)F(8) with single-crystal X-ray diffraction, gas electron diffraction (GED), and differential scanning calorimetry (DSC) establish clearly that, in contrast to the previous report, the eight-membered heterocycle is not planar. Above the phase transition temperature of -74 degrees C, the ring appears pseudoplanar. However, the N(4)P(4) ring is disordered and is puckered above the phase transition when the disorder is modeled correctly. Below the phase transition the ring clearly resembles that of the saddle (K form) of N(4)P(4)Cl(8). The unit cell of the low-temperature phase is derived from that of the higher temperature phase by doubling the c-axis and removing one-half of the symmetry elements. Full structure optimizations were performed at the HF/6-31G and B3LYP/6-31G levels and fully support the experimental diffraction data.

Vibrational spectra and gas phase structure of N-cyanoimidosulfurous difluoride, NCN=SF2.

The vibrational spectra, IR (gas) and Raman (liquid) of N-cyanoimidosulfurous difluoride, NCN=SF2, were recorded, and the molecular structure was determined by gas electron diffraction. The spectra were assigned by comparing the vibrational frequencies with those in related molecules and with calculated (HF, MP2, B3LYP with 6-31G(d) basis sets) values, and a normal coordinate analysis was performed. The molecule possesses a syn conformation (Ctriple bondN syn with respect to the bisector of the SF2 angle). This has been rationalized by orbital interactions of the electron lone pairs of sulfur and nitrogen with the N-C and S-F bonds, respectively, which are antiperiplanar or anticlinal to these lone pairs (anomeric effects). Quantum chemical calculations with the B3LYP and MP2 methods reproduce the experimental structure reasonably well if large basis sets (6-311G(2d,f)) are used.

Effect of fluorination: gas-phase structures of N,N-dimethylvinylamine and perfluoro-N,N-dimethylvinylamine.

The gas-phase structures of N,N-dimethylvinylamine, (CH(3))(2)NC(H)=CH(2) (1), and perfluoro-N,N-dimethylvinylamine, (CF(3))(2)NC(F)=CF(2) (2), were determined by gas electron diffraction and quantum chemical methods (B3LYP and MP2 with 6-31G basis sets). The configuration around nitrogen is slightly pyramidal in both compounds, with the sum of the nitrogen bond angles 351.2(12) degrees and 354.8(6) degrees in 1 and 2, respectively. In the parent compound 1, the (CH(3))(2)N group lies nearly in the plane of the vinyl group, and the nitrogen lone pair (lp) is almost perpendicular to this plane (Phi(C=C-N-lp) = 98(6) degrees). In the perfluorinated species 2, however, the (CF(3))(2)N group is oriented perpendicular to the vinyl plane, and the lone pair is parallel to the C=C bond (Phi(C=C-N-lp) = 2(5) degrees). A natural bond orbital analysis provides a qualitative explanation for this conformational change upon fluorination. The sterically unfavorable in-plane orientation of the dimethylamino group in 1 is stabilized by conjugation between the nitrogen lone pair and the C=C pi-bond. The anomeric effect between the lone pair and the C(alpha)-F sigma-bond in addition to steric effects favors the perpendicular orientation of the (CF(3))(2)N group in 2. Both quantum chemical methods reproduce the experimental structures satisfactorily.

Structures and conformations of trifluoromethyl fluoroformate and perfluorodimethyl carbonate.

The conformational properties and geometric structures of trifluoromethyl fluoroformate, CF(3)OC(O)F (1), and perfluorodimethyl carbonate, (CF(3)O)(2)CO (2), have been studied by matrix IR spectroscopy, gas electron diffraction (GED), and quantum chemical calculations (MP2 and B3LYP with 6-311G basis sets). In both compounds the synperiplanar orientation of the O-CF(3) groups relative to the C=O double bond is preferred. If heated Ar/1 and Ar/2 mixtures are deposited as a matrix at 14 K, new bands appear in the matrix IR spectra which are assigned to the anti form of 1 and to the syn/anti form of 2. At room temperature the contribution of the anti rotamer of 1 is 4% (DeltaH degrees = H degrees (anti) - H degrees (syn) = 1.97(5) kcal/mol), and the contribution of the syn/anti conformer of 2 is estimated to be less than 1%. These high-energy conformers are not observed in the GED experiment. The quantum chemical calculations reproduce the structural and conformational properties of both compounds satisfactorily.

Bis(trifluoroacetyl) peroxide, CF(3)C(O)OOC(O)CF(3).

Pure, highly explosive CF(3)C(O)OOC(O)CF(3) is prepared for the first time by low-temperature reaction between CF(3)C(O)Cl and Na(2)O(2). At room temperature CF(3)C(O)OOC(O)CF(3) is stable for days in the liquid or gaseous state. The melting point is -37.5 degrees C, and the boiling point is extrapolated to 44 degrees C from the vapor pressure curve log p = -1875/T + 8.92 (p/mbar, T/K). Above room temperature the first-order unimolecular decay into C(2)F(6) + CO(2) occurs with an activation energy of 129 kJ mol(-1). CF(3)C(O)OOC(O)CF(3) is a clean source for CF(3) radicals as demonstrated by matrix-isolation experiments. The pure compound is characterized by NMR, vibrational, and UV spectroscopy. The geometric structure is determined by gas electron diffraction and quantum chemical calculations (HF, B3PW91, B3LYP, and MP2 with 6-31G basis sets). The molecule possesses syn-syn conformation (both C=O bonds synperiplanar to the O-O bond) with O-O = 1.426(10) A and dihedral angle phi(C-O-O-C) = 86.5(32) degrees. The density functional calculations reproduce the experimental structure very well.

Gas-phase structures of acetyl peroxynitrate and trifluoroacetyl peroxynitrate.

The molecular structures and conformational properties of acetyl peroxynitrate (PAN, CH3C(O)OONO2) and trifluoroacetyl peroxynitrate (FPAN, CF3C(O)OONO2) were investigated in the gas phase by electron diffraction (GED), microwave spectroscopy (MW), and quantum chemical methods (HF/3-21G, HF/6-31G*, MP2/6-31G*, B3PW91/6-31G*, and B3PW91/6-311+G*). All experimental and theoretical methods show the syn conformer (C=O bond of acetyl group syn to O-O bond) to be strongly predominant relative to the anti conformer. The O-NO2 bonds are extremely long, 1.492(7) A in PAN and 1.526(10) A in FPAN, which correlates with their low bond energy and the easy formation of CX3C(O)OO* and *NO2 radicals in the atmosphere. The O-O bonds (1.418(12) A in PAN and 1.408(8) A in FPAN) are shorter than that in hydrogen peroxide (1.464 A). In both compounds the C-O-O-N dihedral angle is close to 85 degrees.

((Fluoroformyl)imido)(trifluoromethyl)sulfur fluoride, FC(O)N = S(F)CF3: unexpected conformational properties.

The geometric structure and conformational properties of ((fluoroformyl)imido)(trifluoromethyl)sulfur fluoride, FC(O)N = S(F)CF3, are investigated by gas electron diffraction (GED) experiments, IR (gas) spectroscopy, and quantum chemical calculations (HF, MP2, and B3LYP with 6-31G* basis sets). The GED intensities are reproduced best with a mixture of 79(12)% trans-syn and 21(12)% cis-syn conformers. "Trans/cis" describes the orientation around the S=N double bond (FC(O) group relative to sulfur substituents), and "syn" refers to the orientation of the C=O bond relative to the S=N bond. From the intensities of the C=O bands in the IR (gas) spectrum, a composition of 86(8)%:14(8)% is derived. These ratios correspond to delta G0(GED) = 0.79(36) and delta G0(IR) = 1.09(35) kcal mol-1. The preference of a trans structure, around the S=N double bond is unexpected, since all imidosulfur compounds studied thus far possess a cis configuration. The conformational properties are reproduced qualitatively correctly by all theoretical calculations. The predicted energy differences delta E(HF) = 2.41, delta E(MP2) = 0.64, and delta E(B3LYP) = 0.28 kcal mol-1 are larger or slightly smaller than the experimental values. Additional theoretical calculations (B3LYP) for several imidosulfur compounds reveal that only FC(O)N=S(F)CF3, with mixed substitution at sulfur and the FC(O) group bonded to nitrogen, prefers the trans structure.

Reaction of (carbonylimido)sulfur(IV) derivatives with TAS-fluoride, (Me2N)3S+Me3SiF2-.

In the reaction of TAS-fluoride, (Me2N)3S+Me3SiF2-, with carbonyl sulfur difluoride imides RC(O)NSF2 (R = F, CF3), C-N bond, cleavage is observed, and TAS+RC(O)F2- and NSF are the final products. From TASF and RC(O)NS(CF3)F, the salts TAS+RC(O)NS(CF3)F2- (R = F (14), CF3 (15)), with psi-pentacoordinate sulfur centers in the anions, are formed. An X-ray structure investigation of 14 shows that the fluorine atoms occupy axial positions and CF3, NC(O)F, and the sulfur lone pair occupy equatorial positions of the trigonal bipyramid. The -C(O)F group lies in the equatorial plane with the CO bond synperiplanar to the SN bond. According to B3LYP calculations, this structure corresponds to a global minimum and the expected axial orientation of the -C(O)F group represents a transition state. Calculations for the unstable FC(O)NSF3- anion show a different geometry. The -C(O)F group deviates 40 degrees from axial orientation, and the equatorially bonded fluorine is, in contrast to the -CF3 group in 14, syn positioned.