Plasma fluorination of organosilicon polymeric films for gas separation applications

SF₆ plasma treatment using an RF discharge was carried out for the surface fluorination of polytrimethylsilylpropyne (PTMSP) and polyvinyltrimethylsilane (PVTMS) films. Gas permeation of the fluorinated and untreated films for O₂, N₂, He, H₂, CH₄ and CO₂ gases has been measured. Plasma fluorination increases the ideal selectivities of the PTMSP films decreasing their permeances for all the gases measured, and does not affect the permeances and selectivities of the PVTMS films. The composition and chemical structure of the fluorinated polymer surface were investigated using X-ray photoelectron spectroscopy (XPS) and ¹⁹F nuclear magnetic resonance (NMR) spectroscopy. Within the range of the treatment parameters studied, permselectivity and surface composition of the fluorinated PTMSP films depend slightly on the treatment time and the density of the fluorine atom flux on the modified surface. The trimethylsilyl substituents are detached and carbon atoms are partially fluorinated during modification. The structure of the fluorinated layer contains crosslinks and unsaturated bonds.     

29Si and 13C NMR spectra of chloro- and fluoro-substituted linear permethylpolysilanes

²⁹Si and ¹³C NMR spectra are reported for the three halopolysilane series Me(SiMe₂)_nCl, Cl(SiMe₂)_nCl and F(SiMe₂)_nF, where n = 2 to 6. Except for the dihalodisilanes (XSiMe₂)₂, data for all of the compounds fit linear relationships based on substituent constants for chlorine or fluorine atoms in the α, β and γ positions. The effects of halogen substitution on ²⁹Si and ¹³C chemical shifts are rapidly attenuated along the polysilane chain, becoming negligible four atoms away from the halogen. The NMR data provide no evidence for long-range electronic transmission from chlorine or fluorine in halopermethylpolysilanes of the type suggested by other workers [1].     

Quantum-chemical calculations of NMR chemical shifts of organic molecules: XII. Calculation of the 13C NMR chemical shifts of fluoromethanes at the DFT level

Calculation was carried out of chemical shifts in ¹³C NMR spectra for a series of fluoromethanes CH _n F_4?n (n = 0–4) by the methods of the electron density functional theory GIAO-DFT taking in consideration the solvent effect in the framework of the polarizable continuum model Tomasi IEF-PCM. The best results were obtained at the use of Keal-Tozer KT3 functional combined with Pople standard basis sets 6-311G(d,p) and 6-311++G(d,p), and also with Jensen special set pcS-2 containing tight p-functions. The optimum reference in the calculation of chemical shifts in ¹³C NMR spectra for the fluoromethanes series is TMS.     

19F DOSY NMR analysis for spin systems with nJFF couplings

NMR is a powerful method for identification and quantification of drug components and contaminations. These problems present themselves as mixtures, and here, one of the most powerful tools is DOSY. DOSY works best when there is no spectral overlap between components, so drugs containing fluorine substituents are well‐suited for DOSY analysis as ¹⁹F spectra are typically very sparse. Here, we demonstrate the use of a modified ¹⁹F DOSY experiment (on the basis of the Oneshot sequences) for various fluorinated benzenes. For compounds with significant ⁿJ_FF coupling constants, as is common, the undesirable J‐modulation can be efficiently suppressed using the Oneshot45 pulse sequence. This investigation highlights ¹⁹F DOSY as a valuable and robust method for analysis of molecular systems containing fluorine atoms even where there are large fluorine–fluorine couplings. Copyright © 2014 John Wiley & Sons, Ltd.     

Counterintuitive deshielding on the 13C NMR chemical shift for the trifluoromethyl anion

The trifluoromethyl anion (CF₃⁻) displays ¹³C NMR chemical shift (175.0 ppm) surprisingly larger than neutral (CHF₃, 122.2 ppm) and cation (CF₃⁺, 150.7 ppm) compounds. This unexpected deshielding effect for a carbanion is investigated by density functional theory calculations and decomposition analyses of the ¹³C shielding tensor into localized molecular orbital contributions. The present work determines the shielding mechanisms involved in the observed behaviour of the fluorinated anion species, shedding light on the experimental NMR data and demystify the classical correlation between electron density and NMR chemical shift. The presence of fluorine atoms induces the carbon lone pair to create a paramagnetic shielding on the carbon nucleus.     

IR Emission Spectra of Carbonate-Chloride Melts 2CsCl-NaCl-Cs2CO3 Containing Lithium and Beryllium Ions

The IR emission spectra of the molten systems NaCl-CsCl-Cs₂CO₃-MCl _n (M = Li, Be) have been obtained. Spectral data shows that, at a definite limiting molar ratio n _lim = [CO₃]/[Mⁿ⁺] characteristic for each Mⁿ⁺, carbonate-chloride melts based on the NaCl-CsCl eutectic contain carbonate complexes [Li(CO₃)₃]^5? and [Be(CO₃)₃]^4? and, if n < n _lim, carbonato chloro complexes [M(CO₃) _m Cl_4?m ], where m = 1–2.     

Solid-state NMR and EPR study of fluorinated carbon nanofibers

Carbon nanofibers were fluorinated in two manners, in pure fluorine gas (direct fluorination) and with a fluorinating agent (TbF₄ during the so-called controlled fluorination). The resulting fluorinated nanofibers have been investigated by solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). This underlines that the fluorination mechanisms differ since a (CF)_n structural type is obtained, whatever the temperature, with the controlled reaction, whereas, during the direct process, a (C₂F)_n type is formed over a wide temperature range. Through a careful characterization of the products, i.e. density of dangling bonds (as internal paramagnetic centers), structural type (acting on molecular motion) and specific surface area (related to the amount of physisorbed O₂), the effect of atmospheric oxygen molecules on the spin-lattice nuclear relaxation has been underlined.     

Revisiting Aromaticity and Chemical Bonding of Fluorinated Benzene Derivatives

The electron delocalization of benzene (C₆H₆) and hexafluorobenzene (C₆F₆) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Å above the ring center correlates well (R²>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C₆ skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C₆H_(6−n)F_n, where n=1–5).     

Synthesis and properties of fluorinated telechelic macromolecular diols prepared by radical grafting of fluorinated thiols onto hydroxyl-terminated polybutadienes

The radical grafting of C_nF_{2n +1} CH₂CH₂SH (n = 6,8) onto the double bonds of hydroxyl-terminated liquid polybutadienes (HTPBD) was studied. Various methods for investigating the amount of grafting (titration of residual thiol and fluorine analysis) were used and compared. The nature and the amount of the initiator, the quantity of thiol, the temperature and the time of the reaction. the solvent, and the microstructure of HTPBD were optimized. The kinetic aspect showed that the thiol disappeared according to a first-norder law. A method using up to 100% of grafting fluorinated mercaptan was described and standards were set up with fluorine contents of 5–59% to evaluate the physicochemical properties of these thioether group-containing polymers: solubility, refractive index, intrinsic and dynamic viscosities, and thermal characteristics (glass transition and decomposition temperatures). Finally, the surface properties of these standards showed improvements of surface energy as low as 9 mN m^?1 for a totally saturated fluorinated HTPBD. © 1993 John Wiley & Sons, Inc.     

Surface fluorination of the cathode active materials for lithium secondary battery

LiMn₂O₄ was treated with F₂ at room temperature (RT), 373 and 473 K under 1.3, 6.6 and 13.2 kPa-F₂. XPS data indicate that two kinds of fluorine species may exist on the sample surface and the ratio of these fluorines is affected by choosing the reaction condition. The peak indicating Mnⁿ⁺ bonded to fluorine appeared in the XPS spectra of Mn2p3/2 electron. From the results of the charge/discharge measurements, the efficiency of charge/discharge process for the sample fluorinated under 1.3, 6.6 and 13.2 kPa-F₂ below 373 K was larger than that of untreated one. The discharge capacity of the fluorinated sample was also larger than that of untreated one. The discharge capacity, the loss of discharge capacity during 50 charge/discharge cycles, F/O ratio measured from XPS data and the intensity of the peak indicating Mnⁿ⁺ bonded to fluorine in the XPS spectra were closely related to each other. The optimal fluorination condition was under 1.3 kPa-F₂ at RT for 1 h.     

A quantum chemical NMR study of branched and unbranched fluoropolymers

The work demonstrates the results of quantum chemical calculations of ¹⁹F and ¹³C NMR spectra of model fluorocarbon C _n F_2n+2 molecules with various configurations and hydrocarbon chain molecules. The possibilities to determine the chain length, formation of branches, identification of fluorine substitution for hydrogen during the fluorination of hydrocarbon paraffins and polymers are discussed.     

15N and 17O NMR spectra of some nitrogen- and oxygen-containing polyfluoroaromatic compounds

The effect of substitution of hydrogen by fluorine on the ¹⁵N and ¹⁷O NMR chemical shifts in N-sulphinylarylamines, azoxy- benzenes, C,N-diarylnitrones and aromatic azomethines has been studied. Changes in nitrogen screening are controlled mainly by the radial factor <r^?3>_2p(N), which depends on the electron density on nitrogen, those in oxygen screening — by the two factors, the excitation energy ΔE^?1 and the radial factor <r^?3>_2p(0), which may operate in the same or opposite directions. The ¹⁵N and ¹⁷O NMR spectra of the above compounds did not show any specific effects of perfluorination.     

Chemical bonding and molecular dynamics in inclusion compounds of fluorinated graphite according to 19F NMR spectroscopy data

In Inclusion compounds of fluorinated graphite with chlorine trifluoride C₂. xClF₃ and hexafluoro-benzene C₂F. xC₆F₆ , the guest molecules are characterized by rotational mobility and weak bonds with the host matrix. ¹⁹F NMR chemical shift tensors are determined for the fluorine nuclei of the matrix and the guest molecules, including the structurally nonequivalent fluorine atoms ofClFj molecules [δ (Fl) = −700, δ(F1) = −280; δ|| (F2) = −440, δ±(F₂) = −220ppm relative to F2]. It is shown that C-F bonds in the host matrix are close to those in aromatic fluorocarbons. Translated from Zhumal Stmktumoi Khimii, Vol. 41, No. 1, pp. 80-85, January–February, 2000.     

Synthesis and properties of gemini-type hydrocarbon-fluorocarbon hybrid surfactants

Gemini-type hybrid surfactants with two fluorocarbon chains connected through a hydrocarbon spacer, F(CF₂)_m(CH₂)₂CH(OSO₃Na)(CH₂)_nCH(OSO₃Na)(CH₂)₂(CF₂)_mF [Fm(Hn)FmOS, m = 4, 6; n = 5, 6, 7, 8)], were synthesized and their surface chemical properties were examined with the aim to have highly functional and highly water-soluble fluorinated surfactants when compared with the conventional fluorinated surfactants. Comparisons of the surface chemical properties of the synthesized gemini-type hybrid surfactants with those of monounit-type hybrid surfactants, F(CF₂)_m(CH₂)₂CH(OSO₃Na)(CH₂)_nH [FmEHnOS, m = 4, 6; n = 3, 5)], revealed that gemination causes a remarkable lowering (about 1/100) in cmc value while it produces little changes in Krafft point (below 0 °C) and surface tension at cmc (γ_cmc).     

The thiolate anion as a nucleophile Part III. Reactions with various fluorobenzenes

The reactions of the fluorobenzenes, C₆F₅H, o-C₆H₂F₄, m-C₆H₂F₄, p-C₆H₂F₄, 1,3,5-C₆F₃H₃, 1,2,4-C₆F₃H₃, o-C₆F₂H₄, m-C₆F₂H₄, p-C₆F₂H₄ and C₆F₅H with thiolate anion nucleophiles RS^? (primarily MeS^?), have been studied in ethylene glycol/pyridine mixtures as a solvent. Multiple replacement of fluorine atoms was observed in the more highly fluorinated compounds, but in all cases two aromatic fluorine atoms were not replaced. Difluorobenzene and fluorobenzene did not react. The product orientations have been deduced from their NMR spectra. The mass spectra of the isomeric products C₆F₂H₃(SMe), C₆F₃H₂(SMe) and C₆F₂H₂(SMe)₂ have been examined.     

Etude RMN du 13C de composes fluoroaliphatiques et de tensioactifs non ioniques perfluoroalkyles

Carbon-13 chemical shifts, spin-lattice relaxation times and nuclear Overhauser enhancement factors at 28°C are reported for a series of polyfluoroaliphatic compounds :

, and perfluoroalkyl nonionic surfactants C_mF_2m+1CH₂(OC₂H₄)_nOH with m = 6, 7 and n = 3, 4, 5, 6 and C₆F₁₃CH₂CH₂CONH(C₂H₄O)_nH with n = 3, 4. The influence of the perfluoroalkyl group on the ¹³C chemtcal shifts of the neighbouring hydrogenated carbons is discussed in terms of hyperconjugative type interactions between lone electron pairs on fluorine and the neighbouring CC or CO bond. Relaxation data show similar flexibilities of the fluorinated chains in the different molecules investigated. Nonionic surfactants exhibit segmental motions in both the hydrophobic perfluoroalkyl and the hydrophilic polyoxyethylene chains ; these motions appear to be similar to those of the analogous hydrogenated surfactants.     

Univalent metal uranyl carbonates

Optimal procedures were developed for the synthesis of A _4?m ^I B _m ^I [UO₂(CO₃)₃]·nH₂O (A^I = Li, Na, K, Rb, Cs, NH₄, Ag, Tl; B^I = Na; m = 0?1; n = 0?6) compounds. The structure and thermal decomposition of these compounds were studied by X-ray diffraction, precision IR spectroscopy, and thermal analysis. The IR bands were assigned using mathematical simulation based on small-vibration theory. The standard enthalpies of formation of the compounds at 298.15 K were determined for the first time by reaction calorimetry.     

Tuning of Microenvironment in Covalent Organic Framework via Fluorination Strategy promotes Selective CO2 Capture

Herein, we have designed and synthesized two heteroatom (N, O) rich covalent organic frameworks (COF), PD-COF and TF-COF , respectively, to demonstrate their relative effect on CO₂ adsorption capacity and also CO₂/N₂ selectivity. Compared to the non-fluorinated PD-COF (BET surface area 805 m² g⁻¹, total pore volume 0.3647 ccg⁻¹), a decrease in BET surface area and also pore volume have been observed for fluorinated TF-COF due to the incorporation of fluorine to the porous framework (BET surface area 451 m² g⁻¹, total pore volume 0.2978 ccg⁻¹). This fact leads to an enormous decrease in the CO₂ adsorption capacity and CO₂/N₂ selectivity of TF-COF , though it shows stronger affinity towards CO₂ with a Qst of 37.76 KJ/mol. The more CO₂ adsorption capacity by PD-COF can be attributed to the large specific surface area with considerable amount of micropore volume compared to the TF-COF . Further, PD-COF exhibited CO₂/N₂ selectivity of 16.8, higher than that of TF-COF (CO₂/N₂ selectivity 13.4).     

The solid state structure of arene-mercury(II) complexes from magic-angle spinning carbon-13 NMR and the solution carbon-13 NMR of some complexes of mercury(II) with arenes having bulky aliphatic substituents

The cross-polarization magic angle spinning ¹³C NMR spectra of Hg(SbF₆)₂ - 2 Arene (Arene = C₆HMe₅, 1,2,4,5-C₆H₂Me₄, 1,2,3,4-C₆H₂Me₄, or C₆H₆) have been measured. The spectra of the complexes of C₆HMe₅ and 1,2,4,5-C₆H₂Me₄ are consistent with static η¹-bonding of the mercury to the arene at an unsubstituted carbon atom, while the spectra of the 1,2,3,4-C₆H₂Me₄ and C₆H₆ complexes show the arene to have time-averaged C_s or C₂, and C₆ symmetry respectively, at the temperature of measurement (300 K).The reduced temperature ¹³C NMR spectra of Hg(Arene)_n²⁺ (n = 1 or 2; Arene = 1,3,5-C₆H₃R₃ (R = Me, i-Pr, or t-Bu)) in SO₂ solution are also reported and affirm that in these intramolecularly mobile species the mercury bonds in an η¹-manner, with unsubstituted aryl carbon atoms being the strongly preferred point of mercury attachment. This site preference is further demonstrated by the solution ¹³C NMR spectra of Hg(Arene)_n²⁺ (Arene = 1,2,3,4-C₆H₂-Me₄, n = 1 or 2; Arene = 1,4-C₆H₄R₂, R = Me or t-Bu, n = 1). The spectra of the 1,4-C₆H₄R₂ complexes and Hg(p-C₆H₄-t-BuMe)²⁺ provide clear evidence for steric influence of the binding site.Like Hg(C₆Me₆)₂²⁺, but unlike most of the complexes of substituted benzenes which have been studied, Hg(1,3,5-C₆H₃-i-Pr₃)₂²⁺ exchanges only slowly with excess free ligand.     

Excess molar volumes of (ethyl formate or ethyl acetate + an isomer of hexanol) at 298.15 K

Excess molar volumes V_m^E were determined over the entire composition range at 298.15 K for ethyl formate or ethyl acetate + hexan-1-ol, +2-methylpentan-1-ol, +3-methylpentan-2-ol, +2-methylpentan-3-ol, +3-methylpentan-3-ol, +2-methylpentan-2-ol, +4-methyl-pentan-2-ol, and +hexan-2-ol. Excess volumes were determined from density measurements made with a vibrating-tube densimeter. The V_m^E values were all positive, decreasing with the n value of the ester: C_n?1H_2n?1CO₂C₂H₅.