Bridging Fluorine Atoms Research Articles

Syntheses of Dioxygenyl Salts by Photochemical Reactions in Liquid Anhydrous Hydrogen Fluoride: X-ray Crystal Structures of α- and β-O2Sn2F9, O2Sn2F9·0.9HF, O2GeF5·HF, and O2[Hg(HF)]4(SbF6)9.

By treating gaseous, liquid, or solid fluorides with UV-photolyzed O2/F2 mixtures and by treating solid oxides with UV-photolyzed F2 (or O2/F2 mixtures) in liquid anhydrous HF at ambient temperature, we investigated the possibility of the preparation of O2MIIIF4 (M = B, Fe, Co, Ag), O2MIVF5 (M = Ti, Sn, Pb), (O2)2MIVF6 (M = Ti, Ge, Sn, Pb, Pd, Ni, Mn), O2MIV2F9 (M = Sn), O2MVF6 (M = As, Sb, Au, Pt), O2MV2F11 (M = Pt), O2MVIF7 (M = Se), (O2)2MVIF8 (M = Mo, W), and O2MVIIF8 (M = I). The approach has been successful in the case of previously known O2BF4, O2MF6 (M = As, Sb, Au; Pt), O2GeF5, and (O2)2(Ti7F30). Novel compounds O2GeF5·HF, α-O2Sn2F9 (1-D), and the HF-solvated and nonsolvated forms of β-O2Sn2F9 (2-D) were synthesized and their crystal structures determined using single-crystal X-ray diffraction. The crystal structures of all of these materials arise from the condensation of octahedral MF6 (M = Ge, Sn) units. The anion in the crystal structure of O2GeF5·HF is comprised of infinite ([GeF5]−)∞ chains of GeF6 octahedra that share common vertices. The HF molecules and O2+ cations are located between the chains. The crystal structure of α-O2SnF9 (1-D) is constructed from [O2]+ cations and polymeric ([Sn2F9]−)∞ anions which appear as two parallel infinite chains comprised of SnF6 units, where each SnF6 unit of one chain is connected to a SnF6 unit of the second chain through a shared fluorine vertex. The single-crystal structure determination of [O2][Sn2F9]·0.9HF reveals that it is comprised of two-dimensional ([Sn2F9]−)∞ grids with [O2]+ cations and HF molecules located between them. The 2-D grids have a wavelike conformation. The ([Sn2F9]−)∞ layer contains both six- and seven-coordinated Sn(IV) atoms that are interconnected by bridging fluorine atoms. A new, more complex [O2]+ salt, O2[Hg(HF)]4[SbF6]9, was prepared. In its crystal structure, the Hg atoms bridge to SbF6 units to form a 3-D framework. The O2+ cations are located inside the voids while the HF molecules are bound to Hg atoms through the F atom. Attempts to prepare several chlorine analogues of O2+ fluorine salts (i.e., O2TiCl5 and O2MCl6 (M = Nb, Sb)) failed.

The Structure of Hydrated Sodium Fluorophosphatozirconates According to NMR Data

23Na, 31P, 19F, 1H NMR and MAS NMR methods are used to study compounds Na2Zr3F2(PO4)4×3H2O (I), NaZr2F6PO4·4H2O (II), and NaZrO0.5FPO4·4H2O (III). It is established that fluorine in these compounds is coordinated to zirconium and occupies terminal positions in fluorophosphatozirconates I and III. Compound II contains both bridging and terminal fluorine atoms. Hypotheses are proposed concerning the nature of fluorophosphatozirconate crystal structure. The presence of translational motions of water molecules and sodium ions in compounds II and III has been established. The activation energy for the mobility of sodium ions in compound III is 0.24 eV.

Crystal Structures of Photochemically Prepared (Xe2F11)2(MF6) (M = Sn, Pb) and (XeF5)4(Sn5F24) Containing Six‐ and Seven‐Coordinated Tin(IV)

Single crystals of [Xe2F11]2[SnF6], [Xe2F11]2[PbF6], and [XeF5]4[Sn5F24] were grown from saturated aHF solutions upon crystallizations. The crystal structures of isotypic [Xe2F11]2[SnF6] and [Xe2F11]2[PbF6] consist of [Xe2F11]+ cations and [MF6]2– anions (M = Sn, Pb) that interact by means of fluorine bridge contacts. The single crystal structure determination of [XeF5]4[Sn5F24] reveals that it is built of two‐dimensional ([Sn5F24]4–)∞ grids and [XeF5]+ cations located between them. The 2D grids have a wave‐like conformation. The ([Sn5F24]4–)∞ layer contains, both, six‐ and seven‐coordinated Sn(IV) interconnected by bridging fluorine atoms. The coordination of Sn(IV) by seven fluorine atoms is unprecedented. Attempts to synthesize and grow single crystals of the [XeF5][MF5] (M = Zr, Hf, Ni, Pd) compounds failed.

Combined Approach for the Structural Characterization of Alkali Fluoroscandates: Solid-State NMR, Powder X-ray Diffraction, and Density Functional Theory Calculations.

The structures of several fluoroscandate compounds are presented here using a characterization approach combining powder X-ray diffraction and solid-state NMR. The structure of K5Sc3F14 was fully determined from Rietveld refinement performed on powder X-ray diffraction data. Moreover, the local structures of NaScF4, Li3ScF6, KSc2F7, and Na3ScF6 compounds were studied in detail from solid-state 19F and 45Sc NMR experiments. The 45Sc chemical shift ranges for six- and seven-coordinated scandium environments were defined. The 19F chemical shift ranges for bridging and terminal fluorine atoms were also determined. First-principles calculations of the 19F and 45Sc NMR parameters were carried out using plane-wave basis sets and periodic boundary conditions (CASTEP), and the results were compared with the experimental data. A good agreement between the calculated shielding constants and experimental chemical shifts was obtained. This demonstrates the good potential of computational methods in spectroscopic assignments of solid-state 45Sc NMR spectroscopy.

Crystal structure and 121,123Sb NQR parameters of ammonium tridecafluorotetraantimonate(III) NH4Sb4F13

(NH4)Sb4F13 crystals (I) are synthesized and their crystal structure (tetragonal crystal system: a = 9.6431(2) A, c = 6.5503(2) A, V = 609.11(3) A3, Z = 2, d calc = 4.100 g/cm3, F(000) = 664, space group I4) is determined. The main structural units of I are tetranuclear anionic [Sb4F13]− complexes and [NH4]+ cations. The anionic complexes are built of four SbF3 groups linked together by tetrahedral bridging fluorine atom. At room temperature the (NH4)Sb4F13 crystals are isostructural to previously studied МSb4F13 (М = K, Rb, Cs, and Tl). The study of 121,123Sb NQR spectra of compound I is performed in a range of 77-370 K, which shows that when the temperature decreases (<250 K) the substance exhibits piezoelectric properties, as do other compounds of this group, but with a violation of their isostructurality.

K+···Cπ and K+···F Non-Covalent Interactions in π-Functionalized Potassium Fluoroalkoxides

Secondary interactions stabilize coordinatively demanding complexes of s-block metals [...]

Investigation on fluoroacidity of molten fluorides solutions in relation with mass transport

Equilibria between species in solution and its corresponding gaseous species were investigated in various molten fluorides mixtures. From the measurements of boron and silicon kinetic constant of gas release, a relative fluoroacidity scale of solvents was proposed. Due to very high kinetic rates of SiF4(g) and BF3(g) release for the most acidic melts, another approach to evaluate fluoroacidity based on mass transport was considered. Relationships between bridging fluorine atoms, viscosity and fluoroacidity was demonstrated. Diffusion coefficients of Si(IV) and B(III) ions were measured and correlated to the viscosity through the Schmidt number (Sc) defined as the ratio between solvent viscosity and solute diffusivity. These results confirmed the fluoroacidity scale previously obtained, validating the original approach developed on mass transport.

X-ray photoelectron spectroscopy as detection tool for coordinated or uncoordinated fluorine atoms demonstrated on fluoride systems NaF, K2TaF7, K3TaF8, K2ZrF6, Na7Zr6F31 and K3ZrF7

While systems K3TaF8 and K3ZrF7 were prepared by modified molten salt method modified wet pathway was used for reproducible preparation of Na7Zr6F31. Its congruently melting character was demonstrated on simultaneous TG/DSC measurements and XRD patterns. X-ray photoelectron spectroscopy was applied for identification of differently bonded fluorine atoms in series of compounds NaF, K2TaF7, K3TaF8, K2ZrF6, Na7Zr6F31 and K3ZrF7. Three different types of fluorine atoms were described qualitatively and quantitatively. Uncoordinated fluorine atoms (F−) provide signals at lowest binding energies, followed by signals from terminally coordinated fluorine atoms (M–F) and then bridging fluorine atoms (M–F–M) at highest energy. Based on XPS F 1s signals assigned to fluorine atoms in compounds with correctly determined structure it was suggested that fluorine atoms in K3ZrF7 have partially bridging character.

Cu(en)2SiF6 and [Cu(dmen)2(H2O)]SiF6 (en = 1,2-diaminoethane; dmen = N,N-dimethyl-1,2-diaminoethane): Preparations, crystal structures, spectroscopic properties and hydrogen bonding mediated magnetism

Crystals of Cu(en)2SiF6 (en=1,2-diaminoethane) (1) and [Cu(dmen)2(H2O)]SiF6 (dmen=N,N-dimethyl-1,2-diaminoethane) (2) were isolated from aqueous–ethanolic systems Cu2+-en or dmen-SiF62−. The chain-like crystal structure of 1 is built up of [Cu(en)2]2+ complex cations linked by bridging μ2-SiF62− anions with trans positions of the bridging fluorine atoms. Copper ion exhibits usual distorted octahedral coordination; there are two chelate coordinated en ligands in the equatorial plane with CuN1 bonds of 1.9994(14)Å (4x), while the axial positions are occupied by fluorine atoms from SiF62− anions with CuF2 bond of 2.6065(14)Å (2x). The individual chains are linked by NH···F type hydrogen bonds. In 2 the coordination polyhedron of the Cu(II) atom can be described as slightly deformed square pyramid (τ=13.0%) with four N atoms from two chelate dmen ligands placed in the basal plane (CuN bonds are from the range 2.0164–2.0599Å) while the apical position is occupied by an aqua ligand at CuO distance is 2.293(2)Å. The structure of 2 is stabilized by OH···F and NH···F hydrogen bonds between complex cations and the hexafluoridosilicate anions. The EPR spectra show the rhombic anisotropy of g-factor in both complexes. Magnetic measurements indicate the presence of two-dimensional antiferromagnetic structure in both complexes. A weak exchange coupling J/kB=−0.85K was found in 1. Much stronger exchange coupling J/kB=−3.69K present in 2 allowed us to identify spatial anisotropy of the exchange coupling, α=0.2, and to describe 2 by rectangular antiferromagnetic lattice model.

Structural Studies on Ba2SrMg4F14 and Ba2MM´Mg4F14 (M= Ca, Sr, Ba)

The new barium strontium magnesium fluoride Ba2SrMg4F14 has been prepared as an almost single-phase colorless powder by precipitating amorphous precursors and heating them at 650 °C. The compound crystallizes in the space group P42/mnm (no. 136) with a = 12.45514(4), c = 7.46092(3) Å, V = 1157.42(1) Å3 and Z = 4. It is isostructural with the previously known Ca analog, Ba2.2Ca0.8Mg4F14. The structure is built up from a channel-forming network of tetrahedral (MgF6)4 units linked by bridging fluorine atoms. The channels contain the Ba2+ ions (CN = 11) and Sr2+ ions (CN = 8, CaF2 type-related environment). Solid solutions with composition Ba2(Sr1−xCax)Mg4F14 with x = 0.13(1), 0.36(1) and 0.51(1) as well as Ba2(Sr0.83(1)Ba0.17(1))Mg4F14 were synthesized and characterized by powder X-ray diffraction.

2D zirconium fluorides: Synthesis, structure and NMR spectroscopy

Two new zirconium (IV) fluorides, [H 2 dap]·(Zr 2F 10)·H 2O ( I) and [H meam] 2·(Zr 2F 10)·H 2O ( II), are synthesized and characterized by X-ray diffraction, thermal techniques and NMR spectroscopy. I is triclinic ( P 1 ¯ ) with a = 6.805 (1) Å, b = 8.361(1) Å, and c = 11.853 (2) Å, α = 94.54(1)°, β = 105.44(1)°, γ = 108.75(1)°. II is monoclinic ( C2 /m) with a = 10.340(6) Å, b = 6.624(4) Å, c = 8.758(6) Å and β = 110.57(3)°. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R/R w reliability factors 0.041/0.113 for I and 0.057/0.177 for II. The structures are built up from ZrF 7 and ZrF 8 units in I and only ZrF 8 units in II. The polyhedra share common edges in order to form two different ZrF 5 layers that are also found in [H 2 C 2 H 10 N 2]·(Zr 2F 10)·H 2O and (H 3O) 2·(Zr 2F 10)·H 2O. On heating at 145 °C, [H 2 dap]·(Zr 2F 10)·H 2O decomposes to give the anhydrous form [H 2 dap]·(Zr 2F 10) that undergoes two successive phase transformations at 220 °C and 290 °C. 19F NMR spectroscopy confirms the structural features of [H 2 dap]·(Zr 2F 10)·H 2O ( I): two sets of three lines with a relative intensity 1:2:2 are attributed to five bridging fluorine atoms and to five nonbridging fluorine atoms. This spectroscopy demonstrates that a noticeable substitution of F − anions by hydroxyl OH − groups is excluded, together with the eventual substitution of H 2O by HF molecules.

ChemInform Abstract: 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 [Re2O4F

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.

Organometallic polymers MF3(4,4′-Bipy) with M = Ga and In

Organometallic polymers MF3(4,4′-Bipy) with M = Ga and In are synthesized by the hydrothermal method. According to X-ray diffraction data, in a metal atom in the polymeric structure is octahedrally coordinated by four fluorine atoms and two nitrogen atoms. Bridging fluorine atoms and bidentate-bridging 4,4′-Bipy molecules join the complexes into layers.

Fluoride ion donor properties of group 13 trifluorides (MF3, M = Al, Ga, In, Tl) and crystal structures of InF3·3SbF5, TlF3·3SbF5 and TlF3·AsF5·2HF

Reactions between strong Lewis acids (i.e. AsF5, SbF5) and MF3 (M = Al, Ga, In, Tl) in anhydrous hydrogen fluoride at ambient temperature proceeded only in three cases, yielding InF3·3SbF5, TlF3·3SbF5, TlF3·AsF5·2HF and TlF3·AsF5. Crystal structure of InF3·3SbF5 consists from infinite chains of In atoms connected by three SbF6 units, with two bridging fluorine atoms (Fb) in cis-position. Due to the strong interaction of SbF6 units with In3+, the Sb–Fb bonds are significantly elongated (200.7(4) pm). Such long Sb–Fb bonds have been observed in the crystal structure of SbF5. The crystal structure of TlF3·3SbF5 is built from slabs where thallium atoms are connected by SbF6 units. The thallium is nine-fold coordinated by fluorine atoms in the shape of a tricapped trigonal prism. In the crystal structure of TlF3·AsF5·2HF there are puckered layers, composed of rectangular rings made of Tl and F atoms. The seven-fold coordination around each Tl is completed by three axial fluorine atoms, provided by one HF molecule and two AsF6 units arranged below and above the puckered layers forming infinite slabs on that way. The second molecule of HF is placed between the slabs. Vibrational spectra of isolated InF3·3SbF5, TlF3·3SbF5, and TlF3·AsF5 are consistent with the presence of highly deformed SbF6/AsF6 octahedra.

Fluoride Ion Donor Properties of cis-OsO2F4: Synthesis, Raman Spectroscopic Study, and X-ray Crystal Structure of [OsO2F3][Sb2F11

The salt, [OsO(2)F(3)][Sb(2)F(11)], has been synthesized by dissolution of cis-OsO(2)F(4) in liquid SbF(5), followed by removal of excess SbF(5) at 0 degrees C to yield orange, crystalline [OsO(2)F(3)][Sb(2)F(11)]. The X-ray crystal structure (-173 degrees C) consists of an OsO(2)F(3)(+) cation fluorine bridged to an Sb(2)F(11)(-) anion. The light atoms of OsO(2)F(3)(+) and the bridging fluorine atom form a distorted octahedron around osmium in which the osmium atom is displaced from its center toward an oxygen atom and away from the trans-fluorine bridge atom. As in other transition metal dioxofluorides, the oxygen ligands are cis to one another and the fluorine bridge atom is trans to an oxygen ligand and cis to the remaining oxygen ligand. The Raman spectrum (-150 degrees C) of solid [OsO(2)F(3)][Sb(2)F(11)] was assigned on the basis of the ion pair observed in the low-temperature crystal structure. Under dynamic vacuum, [OsO(2)F(3)][Sb(2)F(11)] loses SbF(5), yielding the known [mu-F(OsO(2)F(3))(2)][Sb(2)F(11)] salt with no evidence for [OsO(2)F(3)][SbF(6)] formation. Attempts to synthesize [OsO(2)F(3)][SbF(6)] by the reaction of [OsO(2)F(3)][Sb(2)F(11)] with an equimolar amount of cis-OsO(2)F(4) or by a 1:1 stoichiometric reaction of cis-OsO(2)F(4) with SbF(5) in anhydrous HF yielded only [mu-F(OsO(2)F(3))(2)][Sb(2)F(11)]. Quantum-chemical calculations at the SVWN and B3LYP levels of theory and natural bond orbital analyses were used to calculate the gas-phase geometries, vibrational frequencies, natural population analysis charges, bond orders, and valencies of OsO(2)F(3)(+), [OsO(2)F(3)][Sb(2)F(11)], [OsO(2)F(3)][SbF(6)], and Sb(2)F(11)(-). The relative thermochemical stabilities of [OsO(2)F(3)][SbF(6)], [OsO(2)F(3)][Sb(2)F(11)], [OsO(2)F(3)][AsF(6)], [mu-F(OsO(2)F(3))(2)][SbF(6)], [mu-F(OsO(2)F(3))(2)][Sb(2)F(11)], and [mu-F(OsO(2)F(3))(2)][AsF(6)] were assessed using the appropriate Born-Haber cycles to account for the preference for [mu-F(OsO(2)F(3))(2)][Sb(2)F(11)] formation over [OsO(2)F(3)][SbF(6)] formation and for the inability to synthesize [OsO(2)F(3)][SbF(6)].

Synthesis, structure characterization and fluorescence property of a new fluoride borate crystal, CdZn 2KB 2O 6F

A new fluoride borate crystal, CdZn 2KB 2O 6F, has been synthesized by flux-supported solid-state reaction. The crystal structure has been determined by single-crystal X-ray diffraction. It crystallizes in the trigonal space group P 3 ¯ c 1 with a=5.0381(6) Å, b=5.0381(6) Å, c=15.1550(19) Å, α=90.00°, β=90.00°, γ=120.00°, Z=2. The crystal represents a new structure type in which ZnBO 3 layers are connected through bridging fluorine and cadmium atoms alternately along the c-axis. K + cations are filled in the intralayer open channels to balance charge. IR and Raman spectra further confirm the crystal structure. Photoluminescent measurement reveals that CdZn 2KB 2O 6F exhibits blue fluorescence at room temperature in the solid-state.

Synthesis, Raman Spectra and Crystal Structures of [Cu(XeF2)n](SbF6)2 (n = 2, 4)

Pure [Cu(XeF2)2](SbF6)2 was prepared by the reaction of Cu(SbF 6) 2 with a stoichiometric amount of XeF2 in anhydrous hydrogen fluoride (aHF) at ambient temperature. The reaction between Cu(SbF6)2 and XeF2 (1:4 molar ratio) in aHF yielded [Cu(XeF2)4](SbF6)2 contaminated with traces of Xe 2F 3SbF6 and CuF2. The 6-fold coordination of Cu(2+) in [Cu(XeF2)2](SbF6)2 includes two fluorine atoms from two XeF2 ligands and four fluorine atoms provided by four [SbF6](-) anions. The neighboring [Cu(XeF 2)2](2+) moieties are connected via two [SbF6] units, with the bridging fluorine atoms in cis positions, into infinite [Cu(eta(1)-XeF2)2](cis-eta(2)-SbF 6)2[Cu(eta(1)-XeF 2)2] chains. Because of the high electron affinity of Cu(2+), coordinated XeF2 shows the highest distortion (Xe-Fb=210.2(5) pm, Xe-Ft=190.6(5) pm) observed so far among all known [M(x+)(XeF2)n](A)x (A=BF4, PF6, etc.) complexes. The four equatorial coordination sites of the Cu(2+) ion in [Cu(XeF 2) 4](SbF6)2 are occupied by four XeF 2 ligands. Two fluorine atoms belonging to two [SbF6] units complete the Cu (2+) coordination environment. The neighboring [Cu(XeF2)4](2+) species are linked via one [SbF6] unit, with bridging fluorine atoms in trans positions, into linear infinite [Cu(eta(1)-XeF2)4](trans-eta(2)-SbF6)[Cu(eta(1)-XeF2)4] chains. To compensate for the remaining positive charge, crystallographically independent [SbF6](-) anions are located between the chains and are fixed in the crystal space by weak Xe...F(Sb) interactions.

Localversusaverage structure: a study of neighborite (NaMgF3) utilizing the pair distribution function method for structure determination

The temperature-dependent local structure (&lt; 2 nm) of neighborite (NaMgF3) is probed through least-squares refinement of structure models fit to the pair distribution function [G(r)] derived from the total high-energy X-ray scattering of sample powders. In contrast to previous temperature-dependent structure models obtained through Rietveld refinement and statistical modelling of powder diffraction data, it is found that the average Mg—F bond length, corresponding to a ∼2 Å peak in theG(r), increases between 323 and 1123 K. At each temperature, asymmetry in this peak is consistent with an orthorhombic (Pbnm) perovskite local structure, allowing three unique Mg—F values and deformation of MgF6octahedra. Defined by the three orthogonal Mg—Mg distances, the pseudo-cubic unit cell of local structure models becomes metrically tetragonal and cubic at temperatures greater than ∼623 and 1038 K, respectively. A discontinuity in the temperature dependence of the fluorine atomic displacement parameters at 1038 K suggests thermal activation of new vibrational modes in NaMgF3at high temperature, consistent with transverse vibration of the bridging fluorine atoms (Mg—F—Mg).

The Structure of Tris(trifluoromethyl)tellurium Fluoride Dimethylformamide, $\rm [Te(CF_{3})_{3} \times DMF(\mu-F)]{\infty}$

Abstract$\rm [Te(CF_{3})_{3} \times DMF(\mu-F)]{\infty}$ represents the first structurally characterized example of a trifluoromethyl main group element compound with more than 8‐N (where N is the main group number) perfluoroalkyl groups and also the first fluoro(triorgano)tellurium derivative. Its polymeric nature is caused by asymmetric bridging fluorine atoms forming infinite chains.

Interaction of TiF 4 with the donor solvents SO 2, PhCN, and MeCN : Isolation and structural characterization of the first trimeric fluorine bridged donor–acceptor adduct {TiF 4(PhCN)} 3

There has been speculations on the structures of TiF 4 polymeric complexes {TiF 4L} n (L = molecular donor) for several decades, however no structurally characterized examples have been reported. In this work the complex {TiF 4(PhCN)} 3 was isolated from a solution of TiF 4 in PhCN (donor number DN = 11.9 kcal mol −1) as well as from the mixtures PhCN/CH 2Cl 2 and PhCN/toluene and characterized by X-ray, IR, NMR, EI-MS. The structure of the complex {TiF 4(PhCN)} 3 can be regarded as formed by combining three face-TiF 3(PhCN)( μ-F) units, containing octahedrally coordinated titanium centers surrounded by three terminal fluorine atoms on the face of the octahedron and the bridging fluorine atoms in cis-positions with respect to each other. The structure of {TiF 4(PhCN)} 3 represents the first example of a trimeric pseudo pentahalide MX 4L (M = Ti, Zr, X = halogen, D = ligand), a class of potentially interesting Lewis acids. The characterization of {TiF 4(PhCN)} 3 by 19F NMR revealed that in solution it dissociated to a mixture of [TiF 3(PhCN) 3] +, TiF 4(PhCN) 2 and oligomers including [Ti 4F 18] 2− and {TiF 4(PhCN)} n . The existence of oligomeric complexes containing face-{TiF 3(PhCN) 3− n ( μ-F) n } ( n = 1–3) fragments was established by one- and two-dimensional variable temperature 19F NMR. In contrast, TiF 4 has a low solubility in SO 2, because the donor strength of SO 2 (DN = 6.5 ± 2.2 kcal mol −1) is too weak to fully convert polymeric TiF 4 into soluble TiF 4–SO 2 donor–acceptor adducts. TiF 4 and MeCN (DN = 14.1 kcal mol −1) formed only the molecular complex TiF 4(MeCN) 2, characterized by preliminary X-ray structure, IR and EI-MS. Thus mononuclear donor–acceptor complexes TiF 4L 2 can only be isolated from MeCN and stronger basic solvents.