Bridging Fluorine Atoms Research Articles

Syntheses and X-ray Crystal Structures of α- and β-[XeO2F][SbF6], [XeO2F][AsF6], [FO2XeFXeO2F][AsF6], and [XeF5][SbF6]·XeOF4and Computational Studies of the XeO2F+and FO2XeFXeO2F+Cations and Related Species

Reactions of XeO2F2 with the strong fluoride ion acceptors, AsF5 and SbF5, in anhydrous HF solvent give rise to alpha- and beta-[XeO2F][SbF6], [XeO2F][AsF6], and [FO2XeFXeO2F][AsF6]. The crystal structures of alpha-[XeO2F][SbF6] and [XeO2F][AsF6] consist of trigonal-pyramidal XeO2F+ cations, which are consistent with an AXY2E VSEPR arrangement, and distorted octahedral MF6- (M = As, Sb) anions. The beta-phase of [XeO2F][SbF6] is a tetramer in which the xenon atoms of four XeO2F+ cations and the antimony atoms of four SbF6- anions are positioned at alternate corners of a cube. The FO2XeFXeO2F+ cations of [FO(2)XeFXeO2F][AsF6] are comprised of two XeO2F units that are bridged by a fluorine atom, providing a bent Xe- - -F- - -Xe arrangement. The angle subtended by the bridging fluorine atom, a xenon atom, and the terminal fluorine atom of the XeO2F group is bent toward the valence electron lone-pair domain on xenon, so that each F- - -XeO2F moiety resembles the AX(2)Y(2)E arrangement and geometry of the parent XeO2F2 molecule. Reaction of XeF6 with [H3O][SbF6] in a 1:2 molar ratio in anhydrous HF predominantly yielded [XeF5][SbF6].XeOF4 as well as [XeO2F][Sb2F11]. The crystal structure of the former salt was also determined. The energy-minimized, gas-phase MP2 geometries for the XeO2F+ and FO2XeFXeO2F+ cations are compared with the experimental and calculated geometries of the related species IO2F, TeO2F-, XeO2(OTeF5)+, XeO2F2, and XeO2(OTeF5)2. The bonding in these species has been described by natural bond orbital and electron localization function analyses. The standard enthalpies and Gibbs free energies for reactions leading to XeO2F+ and FO2XeFXeO2F+ salts from MF5 (M = As, Sb) and XeO2F2 were obtained from Born-Haber cycles and are mildly exothermic and positive, respectively. When the reactions are carried out in anhydrous HF at low temperatures, the salts are readily formed and crystallized from the reaction medium. With the exception of [XeO2F][AsF6], the XeO2F+ and FO2XeFXeO2F+ salts are kinetically stable toward dissociation to XeO2F2 and MF5 at room temperature. The salt, [XeO2F][AsF6], readily dissociates to [FO2XeFXeO2F][AsF6] and AsF5 under dynamic vacuum at 0 degree C. The decompositions of XeO2F+ salts to the corresponding XeF+ salts and O2 are exothermic and spontaneous but slow at room temperature.

Re‐evaluation of the X‐ray Crystal Structure of [Ta4F20] and the Synthesis and Characterization of a Series of Mixed‐Metal Pentafluorides of Niobium and Tantalum

AbstractThe direct fluorination of intimately mixed niobium and tantalum powders gives a range of mixed‐metal pentafluorides [NbxTa4‐xF20] (x = 1 2, 2 3, 3 4) as discreet species isostructural with tantalum pentafluoride (x = 0 1). The crystal structures of 1–4 are indistinguishable by X‐ray crystallography. Complex 1 crystallizes in the monoclinic space group C2/m with a = 9.5462(13), b = 14.3578(19), c = 5.0174(7) Å, β = 97.086(2)°, Z = 2. The geometry about the tantalum atom is distorted octahedral with 2 short and 2 slightly longer Ta‐Fterminal, and 2 Ta‐Fbridging distances. The angles at the bridging fluorine atoms are 172.9(5)°.

Chemical Bonding in the Complexes XeF 5 + XF 6 − (X = P, As, Sb, and Bi)

Ab initio quantum-chemical calculations of the complexes XeF 5 + XF 6 − (X = P, As, Sb, and Bi) were performed with the use of relativistic pseudopotentials for heavy atoms and full-electron basis sets. The chemical bonds were characterized by the parameters of critical points (electron density, its Laplacian, total electron energy, and its kinetic and potential components). It was demonstrated that the interaction between the XeF 5 + cation and the XF 6 − anion in XeF 5 + XF 6 − follows a key-lock scheme involving directed interactions of bridging fluorine atoms Fb → Xe and that the structuring function of the lone electron pair of the Xe atom is to compensate the destabilizing electrostatic interaction between the Xe and X atoms bearing excess positive charges.

The Crystal Structures of Rubidium and 4-Amino-1,2,4-Triazolium Tetrafluoroantimonates(III)

The crystal structures of complex antimony(III) fluorides RbSbF4 (I) and (C2N4H5)SbF4 (II) were determined. The crystals of I and II are monoclinic; for I: a = 4.628(1) A, b = 6.167(1) A, c = 7.922(1) A, β = 100.582(3)°, V = 222.24(7) A3, Z = 2, ρ(calcd.) = 4.23 g/cm3, ρ(exp.) = 4.25 g/cm3, F(000) = 248, space group P21/m, R = 0.0395; for II: a = 4.678(1) A, b = 7.339(4) A, c = 10.185(1) A, β = 90.88(2)°, V = 349.6(2) A3, Z = 2, ρ(calcd.) = 2.69 g/cm3, ρ(exp.) = 2.70 g/cm3, F(000) = 264, space group P21. The structure of I is formed by Rb+ cations and [SbF4]n−n anionic chains composed of SbF5E octahedra with two bridging fluorine atoms. The structure of IIis formed by (C2N4H5)+ cations and isolated [SbF4]− anions in which the antimony polyhedra are SbF4E trigonal bipyramids. The relationship between the crystal structures and electrophysical and biological properties of single-charged cation tetrafluoroantimonates(III) was studied.

Fluorination of [Os3(CO)12] and [Ir4(CO)12

Fluorination of [Os(3)CO(12)] in HF/SbF(5) affords [Os(CO)(4)(FSbF(5))(2)]. According to its crystal structure (orthorhombic, Pna2(1), a = 1590.3(3), b = 1036.6(1), c = 878.2(2) pm, Z = 4), the two SbF(6) units occupy cis positions in the octahedral environment around the Os atom. Fluorination of [Ir(4)(CO)(12)] in HF/SbF(5) produced three different compounds: (1) [Ir(4)(CO)(8)(mu-F)(2)(Sb(2)F(11))(2)] (tetragonal, P4n2, a = 1285.2(2), c = 952.9(1) pm, Z = 2). Here, two of the six edges of the Ir(4) tetrahedron in [Ir(4)CO(12)] are replaced by bridging fluorine atoms. (2) [fac-Ir(CO)(3)(FSbF(5))(2)HF]SbF(6).HF (orthorhombic, Pnma, a = 1250.6(1), b = 1340.7(2), c = 1092.6(2) ppm, Z = 4). The Ir(4) tetrahedron in Ir(4)(CO)(12) is completely broken down, but the facial Ir(CO)(3) configuration is retained. (3) [mer-Ir(CO)(3)F(FSbF(5))(2)] (triclinic, P1, a = 834.9(1), b = 86 4.9(1), c = 1060.0(1) pm, alpha = 69.173(4) degrees, beta = 77.139(4) degrees, gamma = 88.856(4) degrees, Z = 2).

Syntheses and crystal structures of [Mg(HF) 2](SbF 6) 2 and [Ca(HF) 2](SbF 6) 2: new examples of HF acting as a ligand to metal centres

[Mg(HF) 2](SbF 6) 2 and [Ca(HF) 2](SbF 6) 2 monocrystals were grown from the corresponding hexafluoroantimonates(V) dissolved in anhydrous hydrogen fluoride. [Mg(HF) 2](SbF 6) 2 crystallizes in the space group Pnma (no. 62) with a=1249.1(4) pm, b=1230.2(4) pm, c=699.1(2) pm, V=1.0742(6) nm 3, Z=4. Magnesium is octahedrally coordinated by six fluorine atoms from which two belong to two HF molecules. The structure can be represented by alternating rows of magnesium and antimony atoms running parallel to the c-axis. Magnesium atoms are connected by cis bridging Sb(2)F 6 units along the a-axis and by trans bridging Sb(1)F 6 units along the b-axis. In this way a three-dimensional network is formed. [Ca(HF) 2](SbF 6) 2 crystallizes in the space group P2 1/ n (no. 14) with a=935.2(3) pm, b=1088.7(3) pm, c=1104.8(3) pm, β=106.697(5)°, V=1.0774(5) nm 3, Z=4. The coordination sphere around the calcium atom consists of eight fluorine atoms which define the vertices of an Archimedean antiprism. The two HF molecules directly coordinate the calcium atom and their fluorine atoms are placed in the corners of different square faces of the Archimedean antiprism. The Ca–F(HF) distances are shorter than the Ca–F(Sb) distances. The Sb(1)F 6 and Sb(2)F 6 groups have four equatorial bridging fluorine atoms, while the Sb(3)F 6 groups have only two bridging trans F ligands. The Ca atoms in the [−1,0,1] plane are connected by equatorial F ligands of Sb(1)F 6 and Sb(2)F 6 units, forming a [Ca(SbF 6) +] n layer. These layers are connected by trans bridging Sb(3)F 6 groups. HF molecules occupy the space between these layers and additionally contribute to the connection between the layers by hydrogen bonding.

Single-Crystal Growth and Classification of EuAlF5 and Solid Solutions M(II)1−xEuxAlF5 (M=Ca, Sr, Ba) within the Structural Family of Tetragonal M(II)M(III)F5 Compounds

The compound EuAlF5, as well as the solid solutions Ca0.19(1)Eu0.81(1)AlF5, Sr0.15(1)Eu0.85(1)AlF5, Sr0.55(1)Eu0.45(1)AlF5, Sr0.77(1)Eu0.23(1)AlF5, and Ba0.62(1)Eu0.38(1)AlF5, crystallize in colorless tetragonal columns. These have been prepared by solid state reactions at 900°C, starting from mixtures of the binary fluorides. According to Vegard's rule the solid solution Sr1−xEuxAlF5 shows a linear dependence of the crystal volume on the molar ratio Eu/Sr. All crystal structures have been refined from single-crystal diffractometer data. EuAlF5 and the M1−xEuxAlF5 (M=Ca, Sr) compounds obtained are isotypic with β-SrAlF5. They crystallize in a superstructure in space group I41/a (no. 88) with 64 formula units and lattice parameters a≈19.9 Å, c≈14.3 Å. The structure is characterized by chains of trans-corner-sharing [AlF4/2F2/1] and branched [AlF5/1F1/2] octahedra forming a channel structure. Inside the channels isolated ordered dimeric units [AlF4/1F2/2]2 are located. The divalent metal atoms show coordination numbers 8 and 9; they connect the [AlF6] octahedra into a three-dimensional structure. Ba0.62(1)Eu0.38(1)AlF5 is isotypic with the corresponding Sr compound Ba0.43(1)Sr0.57(1)AlF5, and it crystallizes with 16 formula units and lattice parameters a=14.3860(7) Å, c=7.2778(3) Å in space group I4/m (no. 87). The network structure is identical with that of EuAlF5. Instead of the dimeric units, infinite chains [AlF4/1F2/2]∞ of trans-corner-sharing [AlF6] octahedra extending along the c- axis are located inside the channels. The bridging fluorine atoms of this chain show large anisotropic displacement parameters, but no superstructure reflections have been observed for this compound.

Crystal structure and vibrational spectra of hydrazinium(2+) aquatetrafluoroindate(III), N2H6(InF4H2O)2

The crystal structure of hydrazinium(2+) aquatetrafluoroindate(III), N2H6(InF4H2O)2, has been determined by X-ray diffraction. The compound crystallizes in the triclinic space group $$P\bar 1$$ (C i 1) with a = 6.759(2) A, b = 6.228(1) A, c = 5.7854(7) A, α = 80.28(2)°, β = 88.79(1)°, γ = 69.96(2)°, V = 225.3(1) A3, and Z = 1. The structure comprises hydrazinium(2+) cations and InF2F4/2O− anions in which In appears to be seven-coordinated in the form of a pentagonal bipyramid by four bridging fluorine atoms, two terminal fluorine atoms, and one oxygen atom. Pentagonal bipyramids are interconnected and form chains along a axis. Bands in vibrational spectra were assigned to the vibrations in N2H6 2+ cations and anionic InF2F4/2O− entities. The rather intensive band appearing at 1042 cm−1 in Raman spectrum, which is absent from infrared, is characteristic of the N2H6 2+ cation, in line with the predictions of the unit-cell group analysis for the studied system.

An ab initio MO Study of the Gas-Phase Reactions 2 SF2 → FS−SF3 → S=SF4 − Molecular Structures, Reaction Enthalpies and Activation Energies

High level ab initio MO calculations at the G3(MP2) level of theory were employed to study the molecular structures of SF2, FSSF3, and SSF4, as well as the dimerization of gaseous SF2 to FSSF3 and the isomerization of FSSF3 to SSF4. The dimerization of SF2 was calculated to be an exothermic process (ΔH°298 = −77 kJ·mol−1) with an activation enthalpy (ΔH≠298) of 65 kJ·mol−1. The transition state of the dimerization reaction is characterized by a bridging fluorine atom that undergoes a 1,2-shift, and a weak sulfur-sulfur single bond. The calculated lowest-energy structure of FSSF3 (2a) is in excellent agreement with the experimentally derived structure, with the −SF group in an equatorial position of the distorted pseudo-trigonal-bipyramid at the central sulfur atom. A significantly less stable FSSF3 conformer 2b, 76 kJ·mol−1 higher in energy, has the −SF group in an axial position. Unimolecular rearrangement of FSSF3 (2a) to the trigonal-bipyramidal SSF4 (3), by a 1,2-fluorine shift (TS2), is endothermic by 37 kJ·mol−1 and is inhibited by a large activation barrier of 267 kJ·mol−1. SSF4 is predicted to be an observable species in the gas phase. Calculated infrared spectra of 2a and 3 are also reported.

New alkaline earth aluminium fluorides with the formula (M, M′)AlF5 (M, M′ = Ca, Sr, Ba)

Abstract Two new modifications, α′-SrAlF5 and δ-BaAlF5, as well as two solid solutions, Ca0.08Sr0.92AlF5 and Ca0.33Sr0.67AlF5, have been synthesized in the system (M, M′)F2/AlF3 with M, M′ = Ca, Sr, Ba. The preparation of single crystals has been performed under hydrothermal conditions and solid state reactions, respectively. All crystal structures have been refined from single crystal diffractometer data. A common feature of the structures are the corner linked AlF6 octahedra forming chains [AlF4/1F2/2]. α′-SrAlF5 is the second well characterized modification known up until now having this composition. Its crystal structure (P21/n (No. 14), a=8.9574(5), b=7.4614(4), c=10.7212(6) A, β=94.158(1)°, Z=8,R[F2>2σ(F2)]=0.020, wR 2 (F 2 all )=0.045) is isotypic with α′-BaFeF5. Incorporation of small amounts of calcium into the structure leads to the solid solution Ca0.08Sr0.92AlF5 (P21/n (No. 14), a=8.9351(7), b=7.4387(6), c=10.6845(8) A, β=94.194(2)°, Z=8, R[F2>2σ(F2)]=0.025, wR 2 (F 2 all )=0.053) with slightly smaller lattice parameters. Increase of the calcium amount in the SrAlF5 host lattice stabilizes the second modification of SrAlF5 and the tetragonal superlattice structure of Ca0.33Sr0.67AlF5 (I41/a (No. 88), a=19.7345(3), c=14.1982(2) A, Z=64, R[F2>2σ(F2)]=0.039, wR 2 (F 2 all )=0.099) is obtained. δ-BaAlF5 is the fourth modification of BaAlF5 so far; it crystallizes in the triclinic system, P 1 (No. 2), a=5.2146(7), b=7.3933(10), c=14.946(2) A, α=79.365(2)°, β=88.525(2)°, γ=88.183(2)°, Z=6, R[F2>2σ(F2)]=0.033, wR 2 (F 2 all )=0.089 . The δ-BaAlF5 crystals show ferroelastic behaviour; no first order phase transition could be observed up to 580°C. The bridging fluorine atoms are disordered around one Al atom. The relations between different BaAlF5 polymorphs are briefly discussed.

Structural And Energetic Changes of Si (100) Surface With Fluorine in Presence of Water – A Density Functional Study

We report density functional electronic structure calculations to monitor the change in the surface characteristics of the Si (100)-2x1 surface after fluorination followed by interaction with water. Embedded finite silicon clusters are used to model an extended Si (100)-2x1 surface. Two high symmetry pathways and subsequent adsorption sites were examined: (i) adsorption of an fluorine atom directing onto a silicon dangling bond to form a monocoordinated fluorine atom (ii) adsorption of a fluorine atom directing on top of silicon dimer to form a bridging dicoordinated fluorine atom. However, in the later case we find that no barrier exists for the bridging fluorine atom to slide towards silicon dimer dangling bond to form more stable mono coordinated Si-F bond. We calculated activation barriers and equilibrium surface configuration as a function of fluorine coverage upto 2.0 ML. We compared the stability of the fluorinated surface. The results were compared with existing experimental and theoretical results. The reaction of water with HF treated Si surface is monitored. It produces, as a first step, the exchange of Si-F with water to form Si-OH groups reducing the concentration of the fluorine on the surface, followed by a rapture of Si-Si bonds and finally the Si-O-Si bridge formation in the lattice.

Syntheses and structures of the first examples of zinc compounds with bridging fluorine and hydrogen atoms

The first examples of zinc compounds with bridging fluorine and hydrogen atoms [{HC(CMeNAr)2}Zn(μ-X)]2 (Ar = 2,6-Me2C6H3, X = F, 8; X = H, 9) have been synthesised and structurally characterised.

Adsorption and Structural Energetics of Chemisorbed F Atom on Si(100)-a Density Functional Theory (DFT) Study

We report density functional electronic structure calculations related to the initial fluorination of the Si(100)-2×1 surface. Embedded finite silicon clusters are used to model an extended Si(100)-2×1 surface. Two high symmetry pathways and subsequent adsorption sites were examined: (i) adsorption of an fluorine atom directing onto a silicon dangling bond to form a monocoordinated fluorine atom (ii) adsorption of a fluorine atom directing on top of silicon dimer to form a bridging dicoordinated fluorine atom. However, in the later case we find that no barrier exists for the bridging fluorine atom to slide towards silicon dimer dangling bond to form more stable mono coordinated Si–F bond. We calculated activation barriers and equilibrium surface configuration as a function of fluorine coverage upto 2.0 ML. We report the harmonic vibrational frequency for surface fluorosilyl species. We compared the stability of the fluorinated surface. We finally propose a plausible mechanism of the initial stage of fluorine etching.

Fluoride ion donor properties of TcO2F3 and ReO2F3: X-ray crystal structures of MO2F3.SbF5 (M = Tc, Re) and TcO2F3.XeO2F2 and Raman and NMR spectroscopic characterization of MO2F3.PnF5 (Pn = As, Sb), [ReO2F2(CH3CN)2][SbF6], and [Re2O4F5][Sb2F11

The fluoride ion donor properties of TcO2F3 and ReO2F3 toward AsF5, SbF5, and XeO2F2 have been investigated, leading to the formation of TcO2F3.PnF5 and ReO2F3.PnF5 (Pn = As, Sb) and TcO2F3.XeO2F2, which were characterized in the solid state by Raman spectroscopy and X-ray crystallography. TcO2F3.SbF5 crystallizes in the monoclinic system P2(1)/n, with a = 7.366(2) A, b = 10.441(2) A, c = 9.398(2) A, beta = 93.32(3) degrees, V = 721.6(3) A3, and Z = 4 at 24 degrees C, R1 = 0.0649, and wR2 = 0.1112. ReO2F3.SbF5 crystallizes in the monoclinic system P2(1)/c, with a = 5.479(1) A, b = 10.040(2) A, c = 12.426(2) A, beta = 99.01(3) degrees, V = 675.1(2) A3, and Z = 4 at -50 degrees C, R1 = 0.0533, and wR2 = 0.1158. TcO2F3.XeO2F2 crystallizes in the orthorhombic system Cmc2(1), with a = 7.895(2) A, b = 16.204(3) A, c = 5.198(1) A, beta = 90 degrees, V = 665.0(2) A3, and Z = 4 at 24 degrees C, R1 = 0.0402, and wR2 = 0.0822. The structures of TcO2F3.SbF5 and ReO2F3.SbF5 consist of infinite chains of alternating MO2F4 and SbF6 units in which the bridging fluorine atoms on the antimony are trans to each other. The structure of TcO2F3.XeO2F2 comprises two distinct fluorine-bridged chains, one of TcO2F3 and the other of XeO2F2 bridged by long Tc-F...Xe contacts. The oxygen atoms of the group 7 metals in the three structures are cis to each other and to two terminal fluorine atoms and trans to the bridging fluorine atoms. The 19F NMR and Raman spectra of TcO2F3.PnF5 and ReO2F3.PnF5 in SbF5 and PnF5-acidified HF solvents are consistent with dissociation of the adducts into cis-MO2F2(HF)2+ cations and PnF6- anions. The energy-minimized geometries of the free MO2F2+ cations and their HF adducts, cis-MO2F2(HF)2+, have been calculated by local density functional theory (LDFT), and the calculated vibrational frequencies have been used as an aid in the assignment of the Raman spectra of the solid MO2F3.PnF5 adducts and their PnF5-acidified HF solutions. In contrast, ReO2F3.SbF5 ionizes in SO2ClF solvent to give the novel Re2O4F5+ cation and Sb2F11- anion. The 19F NMR spectrum of the cation is consistent with two ReO2F2 units joined by a fluorine bridge in which the oxygen atoms are assumed to lie in the equatorial plane. The [ReO2F2(CH3CN)2][SbF6] salt was formed upon dissolution of ReO2F3.SbF5 in CH3CN and was characterized by 1H, 13C, and 19F NMR and Raman spectroscopies. The ReO2F2(CH3CN)2+ cation is a pseudooctahedral cis-dioxo arrangement in which the CH3CN ligands are trans to the oxygens and the fluorines are trans to each other.

Isomerism in OBe3F3 + cation: anab initio study

Ab initio MP2/6-31G*//HF/6-31G*+ZPE(HF/6-31G*) calculations of the potential energy surface in the vicinity of stationary points and the pathways of intramolecular rearrangements between low-lying structures of the OBe3F3+ cation detected in the mass spectra of μ4-Be4O(CF3COO)6 were carried out. Ten stable isomers with di- and tricoordinate oxygen atoms were localized. The relative energies of six structures lie in the range 0–8 kcal mol−1 and those of the remaining four structures lie in the range 20–40 kcal mol−1. Two most favorable isomers, aC2v isomer with a dicoordinate oxygen atom, planar six-membered cycle, and one terminal fluorine atom and a pyramidalC3v isomer with a tricoordinate oxygen atom and three bridging fluorine atoms, are almost degenerate in energy. The barriers to rearrangements with the breaking of one fluorine bridge are no higher than 4 kcal mol−1, except for the pyramidalC3v isomer (∼16 kcal mol−1). On the contrary, rearrangements with the breaking of the O−Be bond occur with overcoming of a high energy barrier (∼24 kcal mol−1). A planarD3h isomer with a tricoordinate oxygen atom and linear O−Be−H fragments was found to be the most favorable for the OBe3H3+ cation, a hydride analog of the OBe3F3+ ion; the energies of the remaining five isomers are more than 25 kcal mol−1 higher.

Synthesis and structural characterization of sulfonates, phosphinates and carboxylates of organometallic Group 4 metal fluorides

Reaction of [Cp *TiF 3] (Cp *=( η 5-C 5Me 5)) with Me 3SiOSO 2- p-C 6H 4CH 3, Me 3SiOPOPh 2 and 1,2-(Me 3SiOCO) 2C 6H 4 yields the dinuclear complexes [{Cp *TiF( μ-F)( μ-OSO 2- p-C 6H 4CH 3)} 2] ( 1), [{Cp *TiF( μ-F)( μ-OPOPh 2)} 2] ( 2) and [{Cp *TiF( μ-F)( μ-OCO- o-C 6H 4CO 2SiMe 3)} 2] ( 3). The molecular structures of 1 and 2 have been determined by single-crystal X-ray analysis. In complexes 1– 3, the two titanium atoms are connected by bridging fluorine atoms as well as bridging sulfonate, phosphinate and carboxylate groups respectively. Each titanium atom is also bonded to a terminal fluorine atom. Reaction of [Cp * 2ZrF 2] with 1,2-(Me 3SiOCO) 2C 6H 4 leads to the mononuclear pentacoordinate 18-electron species [Cp * 2ZrF( μ-OCO- o-C 6H 4CO 2SiMe 3)] ( 4) and its structure was determined by X-ray crystallographic methods.

Internal Fluorocarbon Coordination as a Tool for the Protection of Active Catalytic Sites: Experimental Characterization of the Zr···F−C Interaction in the Group 4 Metallocene(butadiene)/B(C6F5)3 Betaine Ziegler Catalyst Systems

The Lewis acid tris(pentafluorophenyl)borane adds to the (butadiene)group 4 metallocenes 1a−d (metallocene = Cp2Zr, Cp2Hf, (MeCp)2Zr, (Me3CCp)2Zr) to give the metallocene−(μ-C4H6)−borate−betaine complexes 2a−d. (Isoprene)zirconocene (1e) and (2-phenylbutadiene)zirconocene (1f) add the B(C6F5)3 reagent regioselectively at the carbon atom C-4 to give the complexes 2e and 2f, respectively. The complexes 2 all show a pronounced M···F−C interaction with one of the six ortho-B(C6F5)3 fluorine atoms. The resulting metallacyclic structures were characterized by X-ray diffraction of the complexes 2c and 2e (Zr···F ≈ 2.40 Å, angle Zr−F−C ≈ 140°). The bridging fluorine atom of the complexes in solution is characterized by an extreme upfield shift of its 19F NMR resonance (δ ≈ −210 to −220 ppm) relative to the signals of the remaining five o-F resonances of the B(C6F5)3 moiety (average δ ≈ −135 ppm). The 19F NMR spectra of the complexes 2 are dynamic even in the noncoordinating solvent toluene-d8. All six o-fluorine signals equilibrate with coalescence temperatures around 240 K at 564 MHz to give a single resonance signal at high temperature. This fluorine equilibration process of the −B(C6F5)3 end of the metallocene−borate−betaine complexes 2 is very likely to proceed via a rate determining cleavage of the coordinative M···F−C interaction. From the activation barrier of this process, obtained from the dynamic fluorine NMR spectra, Zr···F bond dissociation energies of ca. 8.5 kcal/mol were estimated for the complexes 2. This magnitude of the M···F−C bond dissociation energy makes the internal fluorocarbon coordination a very suitable tool for protecting active electrophilic metal catalyst centers. The Zr···F−C bond of the complexes 2 is cleaved by the addition of the donor solvent THF with formation of acyclic 1,2-η2-allyl metallocene complexes.

Synthesis and characterization of a fluorinated anionic aluminophosphate framework UT-6, and its high-temperature dehydrofluorination to AlPO4-CHA

The structure of an anionic aluminophosphate molecular sieve UT-6 has been determined by single-crystal X-ray diffraction and 19 F MAS NMR, 31 P CP MAS NMR and 27 Al MQ MAS spectroscopy. Large crystals were grown in a non-aqueous synthesis system when hydrogen fluoride was used in trace amounts. The title compound, [Al 3 P 3 O 12 F] - [C 5 H 5 NH] + ·0.15H 2 O, crystallizes in the triclinic space group P (no. 2), with Z=2, a=9.118(1), b=9.161(1), c=9.335(1) A, α=85.98(1), β=77.45(1), γ=89.01(1)°, V=759.25(14) A 3 , R 1 =0.0280 and wR 2 =0.0830. UT-6 is a small pore material that has a three-dimensional network of channels running through the structure. The structure is closely related to that of chabazite. In addition to alternating tetrahedral phosphorus and aluminium atoms connected by bridging oxygens, there are also isolated pairs of octahedral aluminiums in the four-membered rings of the UT-6 framework that share two bridging fluorine atoms. The resulting negative charge on the framework is balanced by pyridinium cations that reside in the chabazite cages. Upon thermal treatment of UT-6, pyridine molecules and HF are removed from the structure and the material transforms into rhombohedral AlPO 4 -CHA, as evidenced by in situ high-temperature powder X-ray diffraction, thermogravimetry and mass spectrometry. This represents the first solid-state transformation of an anionic aluminophosphate molecular sieve framework to an entirely neutral one.

Synthesis and Crystal Structure of Ulm-16, A New Open Framework Fluorinated Gallium Phosphate with 16-Ring Channels

AbstractThe synthesis and characterization of ULM-16, a new fluorinated gallophosphate Ga4(PO4)F2• 1.5 NC6H14• 0.5 H2O • 0.5 H3O, is described. This material is hydrothermally prepared at 180°C using cyclohexylamine as the structuring agent. It cristallizes in the orthorhombic space group Pbcn (n° 60) with a = 27.329(4) Å, b = 17.377(2) Å, c = 10.2124(5) Å, V = 4849.6 (9) Å3and Z = 8. The structure is built up from vertex-linked GaO4and PO4tetrahedra, GaO4F trigonal bipyramids and GaO4F2octahedra forming hexameric units and infinite double crankshaft chains (calledccor UUDD). The hexameric unit is similar to that found in ULM-3, ULM-4, ULM-5 and ULM-8. The two types of building units are fully connected by vertex-sharing with respect to a strict Ga-P alternation. The 3-D framework consists of cylindrical tunnels delimited by sixteen and six polyhedra running along [001]. The cyclohexylamine molecules are trapped in the wider pores and interact with the bridging fluorine atoms and hydration water through hydrogen bonds. The ULM-16 topology is closely related to that of ULM-5 where, in ULM-16, the infinite crankshaft chains replace the isolated D4R cages of ULM-5. TGA curve (under argon) indicates that the ULM-16 structure is intact up to 800°C. Structural relationships will be stated explicitly for the different structures of the ULM-n series containing the hexameric units.

Organometallic Fluorides of Zirconium and Hafnium in the Synthesis of Carboxylate Complexes: Molecular Structures of [{(eta(5)-C(5)Me(5))ZrF(OCOCF(3))(2)}(2)] and [(eta(5)-C(5)Me(5))(2)Zr(OCOCF(3))(2)

The reaction of [(eta(5)-C(5)Me(5))ZrF(3)] and [(eta(5)-C(5)Me(5))HfF(3)] with Me(3)SiOCOCF(3) yields the dinuclear complexes [{(eta(5)-C(5)Me(5))ZrF(OCOCF(3))(2)}(2)] (1) and [{(eta(5)-C(5)Me(5))HfF(OCOCF(3))(2)}(2)] (2), regardless of the molar ratio employed. [(eta(5)-C(5)Me(5))(2)ZrF(2)] reacts with 1 and 2 equiv of Me(3)SiOCOCF(3) to form the mononuclear compounds [(eta(5)-C(5)Me(5))(2)Zr(OCOCF(3))(2)] (3) and [(eta(5)-C(5)Me(5))(2)ZrF(OCOCF(3))] (4), respectively. The molecular structures of 1 and 3 have been determined by single-crystal X-ray analysis: 1, triclinic, P&onemacr;, a = 9.508(3) Å, b = 11.002(4) Å, c = 17.528(3) Å, alpha = 78.55(4), beta = 76.80(2), gamma = 87.51(2) degrees, V = 1750(1) Å(3), Z = 2, R = 0.0378; 3, monoclinic, C2/c, a = 18.553(4) Å, b = 9.110(2) Å, c = 16.323(3) Å, beta = 114.88(3) degrees, V = 2503(1) Å(3), Z = 4, R = 0.0457. Compound 1 shows bridging bidentate and chelating carboxylate ligands as well as bridging fluorine atoms. The zirconium atoms are seven coordinated and have an 18-electron configuration. X-ray studies of 3 reveal two structural components where the carboxylate ligands coordinate in a monodentate (major component) and a chelating manner (minor component).