Bifluoride Research Articles

Fluoride processing of non-bauxite ores

Integrated processing of non-bauxite ores using ammonium hydrogen difluoride was studied. The kinetics of sintering of the raw material, sublimation of ammonium hexafluorosilicate, and formation of aluminum fluoride and alumina were described. The rate constants and activation energies of the reactions were determined.

Temperature-induced displacement of the proton site in strong F–H–F hydrogen bond and mechanism of phase transition in 1,4 diazabicyclo[2.2.2]octane dihydrogen difluoride

The crystal of [C6H13N2] +[HF2] − is built of ionic pairs tied by strong N–H···F hydrogen bonds. A very strong F–H···F hydrogen bond linking the anion is symmetric at higher temperatures, while upon cooling the H-atom shifts continuously to a clearly non-centred site. This first observation of the thermally induced proton migration in the strongest known hydrogen bond is explained by the potential-energy fluctuations due to the large-amplitude motions of the fluorine atoms. The crystal undergoes a continuous phase transition at 150.6 K, accompanied by the symmetry change from Cmc2 1 to P1. The transition mechanism involves an order–disorder contribution related to the behaviour of the hydrogen difluoride anion.

Epoxide Opening with Tetrabutylammonium Fluoride (TBAF)

Positron emission tomography (PET) has been used to assess the fundamental and neurochemical parameters in normal and diseased human organisms. Measuring these parameters with PET requires the preparation of specific molecular imaging probes labeled with positron-emitting radioisotopes. Labeling pharmaceuticals with [F]fluorine often enables the fluorine-substituted analogue to be used to trace biochemical processes while maintaining favorable interaction with the target. Thus, a rapid and effective method for the introduction of F is a great concern in organofluorine and radiopharmaceutical chemistry. The typical method for introduction of a fluorine atom in an aliphatic molecule is the nucleophilic substitution of the corresponding sulfonates or halides by a fluoride ion. For example, the reaction of 2-(3-methanesulfonyloxypropoxy)naphthalene with CsF in t-BuOH gave 2-(3-fluoropropoxy)naphthalene in 92% yield along with the corresponding ether. Epoxide opening with a fluoride ion has been widely used in the preparation of fluorohydrins, which were often found in a certain bioactive molecules such as steroids, amino acids, carbohydrates, and prostaglandins. Anhydrous hydrogen fluoride is a good reagent for cleavage of the epoxide ring, but it is not easy to handle due to its toxicity and corrosiveness. To avoid this problem, some reagents have been developed; HF-amine complex, potassium hydrogen difluoride, silicon tetrafluoride, tetrabutylammonium dihydrogen trifluoride, and so on. Although these reagents gave successful results to some extent, most cases require heating at high temperature for a long period. In consequences, byproducts were often resulted from elimination, rearrangements or polymerization. Metal fluoride[F] or tetrabutylammonium fluoride[F] (TBAF) is a good source of the fluorinating agent to prepare radiopharmaceuticals containing F, but they were rarely used in the epoxide ring opening reaction. In this report, we examined epoxide opening reactions with metal fluoride or TBAF for introducing [F]fluorine to fluorohydrins.

Hydrogen‐Bonded Self‐Assembly of Pyridinium and Anilinium Bisphenols Mediated by the Hydrogen Difluoride Ion: Towards Control of CH⋅⋅⋅π (Aromatic) Interactions

The role of C-H...pi and C-H...O interactions in HF(2)(-)-assisted self-assembly of nitrogen-containing bisphenols are investigated. Unusual control on the end-face and edge-face geometries of aromatic C-H...pi interactions by a water molecule in the 4-[(4-hydroxy-3,5-dimethylphenyl)methyl]pyridinium difluoride lattice is observed. The bis(4-hydroxy-3,5-dimethylphenyl)(4-ammoniophenyl)methane.HF(2)(-) self-assembles through the formation of hydrogen-bonded cyclic hexamers.

Room‐Temperature Nucleophilic Aromatic Fluorination: Experimental and Theoretical Studies

Room‐Temperature Nucleophilic Aromatic Fluorination: Experimental and Theoretical Studies

Trapped Bifluoride

Trapped Bifluoride

Trapped Bifluoride

Trapped Bifluoride

Gold Nanoparticle-Modified Etched Capillaries for Open-Tubular Capillary Electrochromatography

The use of gold nanoparticles in conjunction with etched capillary-based open-tubular capillary electrochromatography (OTCEC) to improve the efficiency of separation and the selectivity between selected solutes is described. The fused-silica capillaries (50-microm i.d.) were etched with ammonium hydrogen difluoride, followed by prederivatization of the new surface with (3-mercaptopropyl)trimethoxysilane (MPTMS) for the immobilization of dodecanethiol gold nanoparticles, for OTCEC. The electrochromatography of a "reversed-phase" test mixture and of selected polycylic aromatic hydrocarbons was investigated, and efficient separations and high theoretical plate numbers per meter were obtained. The electroosmotic flow characteristics of the etched gold nanoparticle capillary, unetched gold nanoparticle capillary, bare capillary, and etched bare capillary were studied by varying the percentage of organic modifier in buffer, buffer pH, and separation voltage. Optical microscopy and scanning electron microscopy were used to examine the process of etching and modification and the surface features of the etched gold nanoparticle capillary. The results confirm that dodecanethiol gold nanoparticles bonded on the etched inner wall of the fused-silica capillary can provide sufficient solute-bonded phase interactions to obtain OTCEC separations with reproducible retention, as well as characteristic reversed-phase behavior, even with the inner diameter of the capillary of 50 microm.

Routes to unique palladium A-frame complexes with a bridging fluoro-ligand

Treatment of a toluene solution of [PdMe(2)(Cy(2)PCH(2)PCy(2))](1) with pentafluoropyridine in the presence of traces of water affords the generation of the A-frame complexes [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][SiMeF(4)]() and [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][OC(5)NF(4)](2b). If the reaction is performed in an NMR tube equipped with a PFA inliner, complex 2b is produced, only. Treatment of 1 with pentafluoropyridine in the presence of an excess water yields the pyridyloxy complex [PdMe(OC(5)NF(4))(Cy(2)PCH(2)PCy(2))](3). Compound [(PdMe)(2){mu-kappa(2)(P,P)Cy(2)PCH(2)PCy(2)}(2)(mu-F)][FHF](2c) bearing a bifluoride anion instead of SiMeF(4)(-) or OC(5)NF(4)(-) can be generated by reaction of 1 with substoichiometric amounts of Et(3)N.3HF. The analogous complex [(PdMe)(2){mu-kappa(2)(P,P)Ph(2)PCH(2)PPh(2)}(2)(mu-F)][FHF] (5c) has been synthesized by addition of Ph(2)PCH(2)PPh(2) to a solution of [PdMe(2)(Me(2)NCH(2)CH(2)NMe(2))](4) in THF and subsequent treatment of the reaction mixture with Et(3)N.3HF. The structure of the A-frame complex 5c has been determined by X-ray crystallography.

Synthesis, vibrational and NMR spectroscopic characterization of [N(CH 3) 4][IO 2F 2] and X-ray crystal structure of [N(CH 3) 4] 2[IO 2F 2][HF 2

The salt, [N(CH 3) 4][IO 2F 2], was prepared from [N(CH 3) 4][IO 3] and 49% aqueous HF, and characterized by Raman, infrared, and 19F NMR spectroscopy. Crystals of [N(CH 3) 4] 2[IO 2F 2][HF 2] were obtained by reduction of [N(CH 3) 4][ cis-IO 2F 4] in the presence of [N(CH 3) 4][F] in CH 3CN solvent and were characterized by Raman spectroscopy and single-crystal X-ray diffraction: C2/ m, a = 14.6765(2) Å, b = 8.60490(10) Å, c = 13.9572(2) Å, β = 120.2040(10)°, V = 1523.35(3) Å 3, Z = 4 and R = 0.0192 at 210 K. The crystal structure consists of two I O 2 F 2 − anions that are symmetrically bridged by two H F 2 − anions, forming a [F 2O 2I(FHF) 2IO 2F 2] 4− dimer. The symmetric bridging coordination for the H F 2 − anion in this structure represents a new bonding modality for the bifluoride anion.

Reactions of Oxides of Some 3d Elements with Ammonium Hydrogen Difluoride

Reactions of iron, manganese(II), manganese(IV), copper, and zinc oxides with ammonium hydrogen difluoride were studied by thermogravimetry, X-ray phase analysis, IR spectrometry, and chemical analysis.

Henri Arthur Levy

Henri Arthur Levy, a pioneer in neutron crystallography at Oak Ridge National Laboratory (ORNL), died of congestive heart failure on 25 March 2003 at his home in Oak Ridge, Tennessee.Henri (who pronounced his name “Henry”) was born in Oxnard, California, on 12 September 1913. He attended Caltech, where he received his BA in chemistry in 1935 and his PhD in physical chemistry in 1938. His thesis included a section on second-order polarization energies in atoms, a theoretical topic proposed by Linus Pauling. Another section described electron diffraction studies done in cooperation with Lawrence Brockway. After receiving his degree, Henri stayed on at Caltech to work on x-ray crystallography. In 1943, Henri joined Clinton Laboratories, the predecessor to ORNL, where he became an expert in the new field of radiochemistry. He extracted radioactive lanthanum from fission products to produce an intense radiation source needed at Los Alamos for testing the implosion bomb during World War II. That work formed the basis of articles he subsequently published on designing laboratories to handle radioactive materials. As the war work wound down, Ernest Wollan and Clifford Shull began using a neutron beam from ORNL’s Graphite Reactor for diffraction studies on various crystalline powders. Henri quickly followed their example and set up a neutron diffraction instrument for chemical studies. In 1949, Selmer Peterson joined ORNL to work with Henri on a study of potassium hydrogen fluoride, which was of interest because the bifluoride ion would eventually prove to have a strong centered hydrogen bond between the fluorine atoms. Because their initial powder experiments were inconclusive, they proceeded with one of the first single-crystal neutron diffraction studies and produced a precise analysis of potassium hydrogen fluoride.Henri and Peterson made other studies of hydrogen-bonded materials, including a detailed study of several phases of the ammonium halides. Their single-crystal study of heavy ice showed conclusively that Pauling’s postulate of disordered hydrogen bonding was correct. As a result, the Antarctic Place-names Commission later honored Levy and Peterson, along with others who had worked on water and ice, by naming islands in Antarctica’s Crystal Sound after them. Henri also made important studies of liquids by both x-ray and neutron diffraction, many of them in collaboration with Alfred Narten, also of ORNL. Notable was their 1967 x-ray study of water over the temperature range from 4 to 200°C.Henri and his coworkers developed automatic data-collection equipment and computer programs to control experiments and analyze results. For the early single-crystal neutron diffraction work, he designed a mechanical device that permitted the experimenter to preset angles for rotation of the sample about one axis so that the intensities of 20 reflections could be measured automatically.When one of the early electronic computers became available at ORNL in 1954, Henri’s group quickly put it to use for various crystallographic calculations. When the Oak Ridge Research Reactor came on line, Henri and his coworkers developed a three-circle diffractometer controlled by punched paper tape from the computer. The resulting data counts were punched on tape for automatic processing. When minicomputers became available in 1965, Henri’s group programmed the PDP-5 computer to control a four-circle Picker diffractometer, first as an x-ray instrument and then for neutron crystallography at ORNL’s High Flux Isotope Reactor Facility.Henri and I developed and distributed a full-matrix, least-squares structure refinement program that was modified so often that the 1979 version listed nine authors. By 1981, that program had been cited more than 3000 times. A companion program permitted the calculation of various molecular parameters with their standard errors. We also created a method for correcting observed bond distances for the thermal motion of the atoms involved.In 1978, Henri retired at the then mandatory age of 65. However, he continued to develop methods for combining electron microscope images to produce three-dimensional information.Henri served as an officer of the American Crystallographic Association, first as secretary (1961–63), then as president-elect (1964), president (1965), and past president (1966). He was also a member of the US National Committee for Crystallography. Henri joined the Smoky Mountains Hiking Club in 1945 and maintained his membership for the rest of his life. While hiking with this group, he met his future wife, Bettie Juresco. He later proposed to her on the Appalachian Trail.Undoubtedly, Henri’s work has had a profound influence on our knowledge of the atomic and molecular structure of matter. Techniques that he pioneered are still being used to advance this knowledge. Henri Arthur Levy OAK RIDGE NATIONAL LABORATORYPPT|High resolution© 2004 American Institute of Physics.

Interpretation of Hydrogen/Deuterium Isotope Effects on NMR Chemical Shifts of [FHF]− Ion Based on Calculations of Nuclear Magnetic Shielding Tensor Surface

Abstract Using ab initio calculations of 1H, 19F magnetic shielding tensors of hydrogen difluoride ion as the functions of three coordinates of symmetry, an attempt is made to estimate the contributions of different vibrational isotope effects to H/D NMR isotope shifts referred in the literature. It is shown that the contributions of the amplitudes of proton stretching and bending vibrations dominate whereas the contribution of the totally symmetric vibration can be neglected. Different signs of the H/D isotope effects on hydron and fluorine chemical shifts are caused by very strong angle dependence of the fluorine magnetic shielding. The agreement of the calculated and measured values is nearly quantitative. An unusually strong paramagnetic deshielding of hydrogen for the equilibrium geometry of the [FHF]− ion is noted.

Low-temperature NMR studies of the structure and dynamics of a novel series of acid-base complexes of HF with collidine exhibiting scalar couplings across hydrogen bonds.

The low-temperature (1)H, (19)F, and (15)N NMR spectra of mixtures of collidine-(15)N (2,4,6-trimethylpyridine-(15)N, Col) with HF have been measured using CDF(3)/CDF(2)Cl as a solvent in the temperature range 94-170 K. Below 140 K, the slow proton and hydrogen bond exchange regime is reached where four hydrogen-bonded complexes between collidine and HF with the compositions 1:1, 2:3, 1:2, and 1:3 could be observed and assigned. For these complexes, chemical shifts and scalar coupling constants across the (19)F(1)H(19)F and (19)F(1)H(15)N hydrogen bridges have been measured which allowed us to determine the chemical composition of the complexes. The simplest complex, collidine hydrofluoride ColHF, is characterized at low temperatures by a structure intermediate between a molecular and a zwitterionic complex. Its NMR parameters depend strongly on temperature and the polarity of the solvent. The 2:3 complex [ColHFHCol](+)[FHF](-) is a contact ion pair. Collidinium hydrogen difluoride [ColH](+)[FHF](-) is an ionic salt exhibiting a strong hydrogen bond between collidinium and the [FHF](-) anion. In this complex, the anion [FHF](-) is subject to a fast reorientation rendering both fluorine atoms equivalent in the NMR time scale with an activation energy of about 5 kcal mol(-)(1) for the reorientation. Finally, collidinium dihydrogen trifluoride [ColH](+)[F(HF)(2)](-) is an ionic pair exhibiting one FHN and two FHF hydrogen bonds. Together with the [F(HF)(n)()](-) clusters studied previously (Shenderovich et al., Phys. Chem. Chem. Phys. 2002, 4, 5488), the new complexes represent an interesting model system where the evolution of scalar couplings between the heavy atoms and between the proton and the heavy atoms of hydrogen bonds can be studied. As in the related FHF case, we observe also for the FHN case a sign change of the coupling constant (1)J(FH) when the F.H distance is increased and the proton shifted to nitrogen. When the sign change occurs, that is, (1)J(FH) = 0, the heavy atom coupling constant (2)J(FN) remains very large, of the order of 95 Hz. Using the valence bond order model and hydrogen bond correlations, we describe the dependence of the hydrogen bond coupling constants, of hydrogen bond chemical shifts, and of some H/D isotope effects on the latter as a function of the hydrogen bond geometries.

Bound and continuum vibrational states of the bifluoride anion

The energies of the bound vibrational states and energy density spectra of the continuum vibrational states of FHF − are calculated, ‘exactly’ and ‘adiabatically’, using a new ab initio (CCSD(T)) potential energy surface. Statistical properties of the bound states are probed in terms of the density of states and nearest neighbor level spacing distributions (NNSD). Importantly, the approximate ‘adiabatic’ densities coincide nearly quantitatively with their ‘exact’ counterparts. A quantitative fitting of the NNSDs is achieved with a new empirical modification of the Wigner distribution.

Coordinated bifluoride ions in the first thiofluoride molybdenum triangular cluster complex: synthesis and crystal structure of K5[Mo3S4F7(FHF)2]·2H2O

The first triangular thiofluoride cluster complex of molybdenum K5[Mo3S4F7(FHF)2]·2H2O with unexpected coordination of bifluoride ions has been synthesized by the reaction of Mo3S7Br4 with molten KHF2. The compound was characterized by single crystal X-ray diffraction. The compound crystallizes in the orthorhombic space group Cmc21 with four formulas in unit cell of dimensions a=15.1060(20)Å,b=8.7820(9)Å,c=14.3358(13)Å,V=1901.8(4)Å3.

Structural and Spectral Properties of Aqueous Hydrogen Fluoride Studied Using ab Initio Molecular Dynamics

Aqueous solutions of deuterated hydrofluoric acid (DF) have been studied at three concentrations using ab initio molecular dynamics (AIMD). At low concentration, DF was found to form a strongly bound complex, dynamically fluctuating between F−D···D2O and F-···D3O+ structures. The coordination number of molecular DF is as low as 2. The fluctuation behavior was observed also at higher concentrations, although in that case 40% of the DFs can be considered as dissociated into F- ions rather than being a part of F-···D3O+ complexes. No FDF- ions formed spontaenously at ambient temperature. One such complex was built, and it was stable for the whole simulation time (6 ps). The increasing acidity as a function of concentration is suggested to derive partly from the increasing stabilization of F- when its surroundings become more ionic. The F- ion can be also stabilized by HF molecule, which results in a bifluoride ion. The high DF concentration also lowers all coordination numbers and compresses the first solvat...

Stabilization of molecular LiF and LiFHF inside metallamacrocyclic hosts.

Complexes of molecular LiF and LiFHF were synthesized using the metallamacrocyclic receptors [(cymene)Ru(C(5)H(3)NO(2))](3) (1), [CpRh(C(5)H(3)NO(2))](3) (2), and [CpIr(C(5)H(3)NO(2))](3) (3). LiBF(4) complexes of 1-3 were prepared and subsequently treated with F(-) or FHF(-) to give the desired products in an anion-exchange reaction. All complexes were characterized by multinuclear NMR spectroscopy ((1)H, (13)C, (19)F, (7)Li). Strong scalar coupling between (7)Li and (19)F is observed for the LiF and the LiFHF complexes ((1)J(LiF) = 91-103 Hz). The LiFHF adduct of 1 displays fluxional behavior with fast exchange of the two fluorine atoms. The structures of the complexes 1.LiBF(4), 2.LiBF(4), 1.LiF, 2.LiF, 1.LiFHF, and 3.LiFHF were determined by single-crystal X-ray analysis. Li-F bond lengths between 1.77 and 1.81 A were found. The LiFHF complexes show a hydrogen difluoride anion coordinated in a bent fashion via one fluorine atom to the lithium ion.

Oxovanadium(V) and cobalt(III) complexes of dithiocarbazate-based Schiff base ligands: formation of a thiadiazole ring by vanadium-induced cyclization of the coordinated ligand.

S-Methyl 3-((2-hydroxyphenyl)methyl)dithiocarbazate (H(2)L(1)) and its bromo derivative (H(2)L(2)), which are traditionally biprotic tridentate (ONS) ligands, behave in an unprecedented manner when allowed to react with [VO(acac)(2)] under an oxidative environment in acetonitrile-water medium containing a catalytic amount of alkali metal ion. The products obtained are oxovanadium(V) compounds [VOL(L(cyclic))] (L = L(1), 1a, and L(2), 1b) that contain one molecule of ligand which undergoes metal-induced cyclization to form a thiadiazole ring. Compound 1a crystallizes in the triclinic space group P(-)1 with a = 9.1830(9) A, b = 9.4165(12) A, c = 12.700(2) A, alpha = 100.988(8)(o), beta = 100.195(7)(o), gamma = 78.774(8)(o), V = 1046.3(2) A(3), and Z = 2. With cobalt(III), however, the products [CoL(HL)].H(2)O (L = L(1), 2a, and L(2), 2b) have hydrogen-bonded dimeric structures with each ligand virtually carrying 1.5 units of negative charge as confirmed by X-ray crystal structure analysis of 2a. It also crystallizes in triclinic space group P(-)1 with a = 12.0842(8) A, b = 13.5251(9) A, c = 14.1960(10) A, alpha = 78.122(6)(o), beta = 73.888(6)(o), gamma = 78.255(6)(o), V = 2154.7(3) A(3), and Z = 4. In solution, 2a is a symmetric molecule as indicated by (1)H NMR, involving a characteristic hydrogen-bonded O-H-O broad feature in the downfield (at 14.5 ppm) connecting both monoprotonated (LH(-)) and deprotonated (L(2-)) forms of the ligand--a situation somewhat analogous to the classic H-F-H case as observed in bifluoride ion.

Electron correlation and basis set effects on strong hydrogen bond behavior: a case study of the hydrogen difluoride anion

A strong hydrogen bond between hydrogen fluoride and fluoride anions forms an anionic chemical species, i.e. a hydrogen difluoride anion. This paper describes the result of ab initio investigations on hydrogen bond behavior of the hydrogen difluoride anion, whose geometry and energy were evaluated at various computational levels of theory, from Hartree–Fock to QCISD(T) calculations using basis sets from cc-pVDZ to aug-cc-pV5Z. The MP4(SDQ) or QCISD level of calculations using aug-cc-pVTZ or a larger basis set suggested an almost constant value (2.27 Å) for the atom distance between two fluorine atoms. The larger basis set was utilized, the more negative (the larger) hydrogen bond energy was suggested. But when aug-cc-pVTZ or a larger basis set was utilized, the fluctuation of the calculated values for hydrogen bond energy was less than 1 kcal/mol. Accurate estimation of the hydrogen bond energy requires MP4(SDQ) geometry optimization and subsequent QCISD(T) energy estimation. But the difference in the geometry and energy between the MP2 and QCISD results was small and, thus, the MP2 results are considered reliable despite the low computational costs. The change in the potential energy was also examined for dissociation of the hydrogen difluoride anion into hydrogen fluoride and fluoride anions. The potential energy curve obtained from the computational level of QCISD(T)/aug-cc-pVTZ//MP4(SDQ)/aug-cc-pVTZ was in good agreement with that obtained from the calculation of QCISD(T)/aug-cc-pV5Z//MP4(SDQ)/aug-cc-pVTZ.