M. Leblanc

Crystal structure of the metastable form of aluminum trifluoride β-AlF3 and the gallium and indium homologs

Abstract The crystal structure of the metastable phase β-AlF3, which is related to the hexagonal tungsten bronze structure, has been solved by X-ray powder and single-crystal diffraction methods. The crystal habit is pseudo-hexagonal with systematic twinning (rotation of 120° around the c axis), but the true symmetry is orthorhombic with space group Cmcm, Z = 12, a = 6.931(3), b = 12.002(6), c = 7.134(2), A (R = 0.044 and Rw = 0.051) from 929 independent reflections). The network is built from very regular AlF6 octahedra rotated by approximately 7.2° from the positions of the ideal HTB structure. A similar network, with the same propagation of the tilting, was observed in the compound (H2O)0.33FeF3 and in the metastable polymorphs of CrF3 and of VF3. Our reinvestigation of the structures of β-GaF3 and β-InF3 using powder data shows that they are isotypic with the aluminum compound, with a = 7.210(1), b = 12.398(2), c = 7.333(1) and a = 7.875(2), b = 13.499(4), c = 7.956(2), A, respectively.

Hexagonal tungsten bronze-type FeIII fluoride: (H2O)0.33FeF3; crystal structure, magnetic properties, dehydration to a new form of iron trifluoride

(H2O)0.33FeF3, grown by hydrothermal synthesis, crystallizes in the orthorhombic system with cell dimensions a = 7.423(3) A, b = 12.730(4) A, c = 7.526(3)A, and space group Cmcm, Z = 12. The structure, derived from single crystal X-ray diffraction data (605 independent reflections) is refined to R = 0.019 (Rω = 0.021). The framework of the FeIIIF6 octahedra is related to that of hexagonal tungsten bronze (HTB) Rb0.29WO3. At 122°C, zeolithic water is evolved from hexagonal tunnels without any noticeable change of the fluorine skeleton. The related anhydrous compound represents a new form of iron trifluoride which is denoted HTBFeF3; at 525°C, it transforms into the cubic form of ReO3-type. (H2O)0.33FeF3 and HTBFeF3 are antiferromagnetic, with Neel temperatures of TN = 128°7 ± 0.5 K and TN = 97 ± 2 K, respectively.

Crystal chemistry and selected physical properties of inorganic fluorides and oxide-fluorides.

importance in the development of many new technologies, and are impacting various key points of modern life, that is, energy production and storage, microelectronics and photonics, catalysis, automotive, building, etc. Many research fields and applications are indeed concerned by a better knowledge of the relationships occurring between the structure of such compounds and some pertinent physical properties. This Review deals with the structural chemistry of solid-state inorganic fluorides and oxide-fluorides, mostly transition metal-based, including rare-earth elements. Such a Review has not been published for a long time.1 Articles that recently appeared on inorganic fluorinated compounds were mostly focused on material science characteristics: morphology, surface functionalization, nanostructuration of the materials and applications, rather than on the description of characteristic structural features.2−5 Detailed reviews focused on rare earthbased inorganic fluorides have also appeared some years ago...

Structural chemistry of organically-templated metal fluorides

We present a systematic survey of the structural chemistry of crystalline hybrid fluorides. About a hundred different metal fluoride building units are represented in these systems, predominantly as anionic moieties, ranging from simple tetrahedral or octahedral dimers to larger oligomeric species, complex chains, layers and, ultimately, three-dimensional frameworks. Although a few compositional spaces have been moderately well explored and certain key features of their chemistries are understood, the underlying message is that this is an area still in its infancy, ripe for further and wider exploration, rich in new crystal-chemical characteristics and, perhaps, with great potential for the development of new physical and chemical functionalities.

Crystal structure of the ordered pyrochlore NH4FeIIFeIIIF6 structural correlations with Fe2F5 · 2H2O and its dehydration product Fe2F5 · H2O

Abstract Crystal structure of NH4FeIIFeIIIF6 is studied in order to explain further its peculiar antiferromagnetic behavior compared to the spin glass one of the pyrochlore family. NH4FeIIFeIIIF6 is orthorhombic, space group Pnma with a = 7.045 (4) A , b = 7.454 (4) A , c = 10.116 (6) A , Z = 4. Diffraction data on single crystals obtained by hydrothermal synthesis, collected on an automatic four circle diffractometer, have been refined by full matrix least-squares calculations to a weighted value of 0.029 (unweighted R = 0.024) for 798 observed reflections. This structure is derived from the pyrochlore structure, with a cationic order between Fe2+ and Fe3+ ions. (FeIIF6)4− octahedra form infinite trans chains along [100] by sharing corners although similar chains of (FeIIIF6)3−) octahedra lie along [010]. This type of FeIIFeIII order is related to a similar one existing in Fe2F5 · 2H2O, the dehydration of which leads to the pyrochlore Fe2F5 · H2O. A mechanism is proposed to explain the formation of this compound.

From Isolated Polyanions to 1-D Structure: Synthesis and Crystal Structure of Hybrid Fluorides {[(C2H4NH3)3NH]4+}2 · (H3O)+ · [Al7F30]9– and {[(C2H4NH3)3NH]4+}2 · [Al7F29]8– · (H2O)2

Two new hybrid fluorides, {[(C2H4NH3)3NH]4+}2 · (H3O)+ · [Al7F30]9– (I) and {[(C2H4NH3)3NH]4+}2 · [Al7F29]8– · (H2O)2 (II), are synthesized by solvothermal method. The structure determinations are performed by single crystal technique. The symmetry of both crystals is triclinic, sp. gr. P 1, I: a = 9.1111(6) A, b = 10.2652(8) A, c = 11.3302(8) A, α = 110.746(7)°, β = 102.02(1)°, γ = 103.035(4)°, V = 915.9(3) A3, Z = 1, R = 0.0489, Rw = 0.0654 for 2659 reflections, II: a = 8.438(2) A, b = 10.125(2) A, c = 10.853(4) A, α = 106.56(2)°, β = 96.48(4)°, γ = 94.02(2)°, V = 877.9(9) A3, Z = 1, R = 0.0327, Rw = 0.0411 for 3185 reflections. In I, seven corner-sharing AlF6 octahedra form a [Al7F30]9– anion with pseudo 3 symmetry; such units are found in the pyrochlore structure. The aluminum atoms lie at the corners of two tetrahedra, linked by a common vertex. In II, similar heptamers are linked in order to build infinite (Al7F29)n8– chains oriented along a axis. In both compounds, organic moieties are tetra protonated and establish a system of hydrogen bonds N–H…F with four Al7F309– heptamers in I and with three inorganic chains in II. Von Isolierten Polyanionen zur 1-D-Struktur: Synthese und Kristallstruktur der Hybridfluoride {[(C2H4NH3)3NH]4+}2 · (H3O)+ · [Al7F30]9– und {[(C2H4NH3)3NH]4+}2 · [Al7F29]8– · (H2O)2 Zwei neue Hybridfluoride {[(C2H4NH3)3NH]4+}2 · (H3O)+ · [Al7F30]9– (I) und {[(C2H4NH3)3NH]4+}2 · [Al7F29]8– · (H2O)2 (II) wurden durch Hydrothermalsynthese dargestellt. Die Kristallstrukturen wurden mittels Rontgenbeugung an Einkristallen bestimmt. Beide Verbindungen kristallisieren triklin in der zentrosymmetrischen Raumgruppe P 1. I: a = 9,1111(6) A, b = 10,2652(8) A, c = 11,3302(8) A, α = 110,746(7)°, β = 102,02(1)°, γ = 103,035(4)°, V = 915,9(3) A3, Z = 1, R = 0.0489, Rw = 0.0654 fur 2659 beobachtete Reflexe, II: a = 8,438(2) A, b = 10,125(2) A, c = 10,853(4) A, α = 106,56(2)°, β = 96,48(4)°, γ = 94,02(2)°, V = 877,9(9) A3, Z = 1, R = 0.0327, Rw = 0.0411 fur 3185 beobachtete Reflexe. Die Kristallstruktur von I enthalt [Al7F30]9–-Anionen mit Pseudosymmetrie 3 aus sieben eckenverknupften AlF6-Oktaedern; solche Einheiten werden in der Pyrochlor-Struktur gefunden. In der Kristallstruktur von II bilden ahnliche heptamere Anionen unendliche (Al7F29)n8–-Ketten entlang der kristallographischen a-Achse. In beiden Verbindungen bestehen durch vierfach protonierte organische Kationen zusatzliche Verknupfungen uber Wasserstoffbruckenbindungen. In der Struktur I ist der organische Teil mit vier [Al7F30]9–-Anionen, in der Struktur II mit drei anorganischen Ketten verbunden.

ZnAlF5·[TAZ]: an Al fluorinated MOF of MIL-53(Al) topology with cationic {Zn(1,2,4 triazole)}2+ linkers

ZnAlF5·[TAZ], the first aluminium fluorinated metal–organic framework with cationic {Zn(1,2,4 triazole)}2+ linkers has been synthesized. The structure is accurately determined by coupling direct space methods on laboratory powder X-ray diffraction data with solid-state nuclear magnetic resonance experiments and ab initio calculations, and is found to be analogous to that of MIL-53(Al).

Idle spin behavior of the shifted hexagonal tungsten bronze type compounds FeIIFeIII2F8(H2O)2 and MnFe2F8(H2O)2

Abstract FeIIFeIII2F8(H2O)2 and MnFe2F8(H2O)2, grown by hydrothermal synthesis ( P ⋍ 200 MPa , T = 450 or 380° C ), crystallize in the monoclinic system with cell dimensions (A): a = 7.609(5), b = 7.514(6), c = 7.453(4), β = 118.21(3)°; and a = 7.589(6), b = 7.503(8), c = 7.449(5), β = 118.06(3)°, and space group C2 m , Z = 2 . The structure is related to that of WO 3 · 1 3 H 2 O . It is described in terms of perovskite type layers of Fe3+ octahedra separated by Fe2+ or Mn2+ octahedra, or in terms of shifted hexagonal bronze type layers. Both compounds present a weak ferromagnetism below TN (157 and 156 K, respectively). Mossbauer spectroscopy points to an “idle spin” behavior for FeIIFeIII2F8(H2O)2: only Fe3+ spins order at TN, while the Fe2+ spins remain paramagnetic between 157 and 35 K. Below 35 K, the hyperfine magnetic field at the Fe2+ nuclei is very weak: Hhf = 47 kOe at T = 4.2 K. For MnFe2F8(H2O)2, Mn2+ spin disorder is expected at 4.2 K. This “idle spin” behavior is due to magnetic frustration.

Ordered magnetic frustration — V. Antiferromagnetic structure of the hexagonal bronzoid HTBFeF3; Comparison with the non frustrated rhombohedral form

Abstract A new antiferromagnetic compound HTBFeF3 is obtained from the flash evaporation of a solution of iron trifluoride in 49% HF. The nuclear (at 293 and 4.2 K) and the magnetic (at 4.2 K) structures are studied by neutron powder diffraction. The nuclear structure is related to that of the ideal hexagonal tungsten bronze. The symmetry is hexagonal above and below T N = 97 K (293 K : α = 7.413(2) A , c = 3.7949(5) A , SGP6/mmm, RN = 0.048, RP = 0.115, Rexp = 0.057; 4.2K: a = 7.402(1) A , c = 7.5690(3) A , SGP63/m, RN = 0.048, RM = 0.075, RP = 0.113, Rexp = 0.051). The magnetic moments (μ = 4.07(8)μB) lie in the basal (001) plane at 120° one from each other; the interactions between successive Fe3+ cations along c are strictly antiferromagnetic. HTBFeF3 experiments magnetic frustration in the (001) planes, related to the existence of triangles of corner sharing Fe3+ octahedra in the structure. For sake of comparison, the non frustrated RFeF3 is studied, in the temperature range 4.2–406 K, by neutron diffractometry.

Crystal structure and magnetic properties of Ba2Ni3F10

Ba2Ni3F10 is monoclinic (space group C2m), a = 18.542(7) A, b = 5.958(2) A, c = 7.821(3) A, β = 111°92(10). Ba2Co3F10 and Ba2Zn3F10 are isostructural. The structure has been refined from 995 reflections by full-matrix least-squares refinement to a weighted R value of 0.048 (unweighted R, 0.047). The three-dimensional network can be described either by complex chains connected to each other by octahedra sharing corners or with an 18L dense-packing sequence. The basic unit (Ni3F10)4− is discussed and compared to the different unit existing in Cs4Mg3F10. Antiferromagnetic properties of Ba2Ni3F10 (TN = 50 K are described.