Evidence of New Fluorinated Coordination Compounds in the

Article pubs.acs.org/crystal

Evidence of New Fluorinated Coordination Compounds in the Composition Space Diagram of FeF3/ZnF2−Hamtetraz-HFaq System Vanessa Pimenta, Jérôme Lhoste,* Annie Hémon-Ribaud, Marc Leblanc, Jean-Marc Grenèche, Laurent Jouffret,† Arnaud Martel, Gilles Dujardin, and Vincent Maisonneuve IMMM-UMR 6283 CNRS, LUNAM, Faculté des Sciences et Techniques, Université du Maine, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France S Supporting Information *

ABSTRACT: The exploration of the composition space diagram of the FeF3/ZnF2−Hamtetraz-HFaq system (Hamtetraz = 5aminotetrazole) by solvothermal synthesis at 160 °C for 72 h in dimethylformamide (DMF) has evidenced five new hybrid fluorides (1−5); the structures are characterized from single crystal X-ray diffraction data. [Hdma]·(ZnFeIII(H2O)4F6) (1) and [Hdma]·[Hgua]2·(FeIIIF6) (2) contain anionic inorganic chains (1) or isolated octahedra (2) weakly hydrogen bonded (Class I hybrids) to dimethylammonium (Hdma) and/or guanidinium (Hgua) cations which are produced from the tetrazole ligand and solvent decomposition. [Hdma]2·[Hgua]·[NH4]· [ZnFe III F 5 (amtetraz) 2 ] 2 (3), [Hdma] 2 ·[Zn 1.6 Fe II 0.4 Fe III F 6 (amtetraz) 3] (4), and [Hdma]·[Zn4F 5(amtetraz) 4] (5) are considered as Class II hybrids in which the (amtetraz)− anions are strongly linked to divalent metal cations via N−M bonds. In 3, ∞{[NH4]·[ZnFeIIIF5(amtetraz)2]2} layers are separated by [Hdma]+ and [Hgua]+ cations. 4 and 5 exhibit three-dimensional (3D) hybrid networks that contain small cavities where [Hdma]+ cations are inserted. A porous 3D metal−organic framework intermediate is evidenced from the thermogravimetric analysis and X-ray thermodiffraction of 5.

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INTRODUCTION The search for new coordination polymers or metal organic frameworks (MOFs) has been very intense during the last two decades. The number of MOFs may be considered as limitless owing to the diversity of organic molecules, metal cations, and counterions. The modification of these different precursors allows tuning of the structural dimensionality and the pore sizes of the resulting hybrid materials. This versatility contributes to their broad range of promising properties in particular for gas and bioactive molecule storage, catalysis, and magnetic and optical properties.1−5 The most frequently used organic molecules, containing donor groups to establish covalent or iono-covalent bonds with the metal, are carboxylates, azolates, polypyridyls, sulfonates, or phosphates.6−9 The metal complexes with azoles as organic ligands are called metal azolate frameworks (MAFs).10−12 Azoles are five-membered aromatic heterocycles containing at least one nitrogen atom to form N−M bond(s). 1,2,4-Triazole (Htaz) and 5-aminotetrazole (Hamtetraz) are interesting azoles because the azole ring may contain respectively three and four electron-donating N atoms. Aminotetrazole displays nine different coordination modes (Scheme 1) and, consequently, is largely applied in the design of novel coordination polymers.13 The valence and the coordination geometry of the metallic centers provide the possibility to build diverse architectures which will have an impact on the expected © 2015 American Chemical Society

properties. As an example, to increase the gas storage capacity of framework materials, a significant effort is currently focused on obtaining accessible coordinatively unsaturated metal sites.14 The metallic cations of 3d-block, which are able to accept nitrogen atoms in their coordination sphere, are more commonly used and especially the divalent cations (M2+ = Cu, Zn, Co, Ni, Fe). Finally, the metal cations may adopt various types of coordination geometry as a function of the counterion nature. Zubieta et al. reported six structures obtained in Cd(II)-1,2,4 triazole systems with different anionic counterions (F−, Cl−, Br−, I−, SO42−, and NO3−); the coordination polyhedra are trigonal bipyramids or octahedra.15 Numerous other metal complexes containing azolate ligands are described in the literature, but their number becomes more restricted when the counterion is a fluorine atom. Twenty-one fluorinated MAFs were found with 3d-block elements (Co2+,16,17 Cu2+,18 Zn2+,19−21) in which the metal cations commonly adopt the octahedral coordination geometry or other coordination types. Eight mixed metal phases combine trivalent (Fe3+, Al3+, Ga3+) with divalent cations (Fe2+, Zn2+, Cu2+): most of these compounds, obtained with triazolate Received: April 17, 2015 Revised: July 17, 2015 Published: July 29, 2015 4248

DOI: 10.1021/acs.cgd.5b00530 Cryst. Growth Des. 2015, 15, 4248−4255

Crystal Growth & Design

Article

Scheme 1. Potential Bridging Modes between Aminotetrazole and Metal

Table 1. Best Molar Proportions (mmol) of the Starting Materials for the Synthesis of Fluorinated Hybrids for 1 mL of DMF in a 2 mL Reactora

a

formulation

FeF3/ZnF2/HFaq/Hamtetraz

[Hdma]·(ZnFeIII(H2O)4F6) (1) [Hdma]·[Hgua]2·(FeIIIF6)·H2O (2) [Hdma]2·[Hgua]·[NH4]·[FeIIIZnF5(amtetraz)2]2 (3) [Hdma]2·[Zn1.6FeII0.4FeIIIF6(amtetraz)3] (4) [Hdma]·[Zn4F5(amtetraz)4] (5)

0.075/0.075/0.255/0.045 0.075/0.075/0.069/0.473 0.075/0.075/0.069/0.473 0.075/0.075/1.025/0.325 0.075/0.075/1.200/0.150

dimensionality, Class 1D 0D 2D 3D 3D

(chain), Class I (monomer), Class I (layer), Class II (network), Class II (network), Class II

1, 2, 3 are contaminated with significant amounts of (NH4)3·[FeIIIF6] or ZnF2.

Figure 1. Composition space diagram of the FeF3/ZnF2−HFaq-Hamtetraz system in dimethylformamide solvent at 160 °C for 72 h.

The composition space diagram of the FeF3/ZnF2− Hamtetraz-HF system in dimethylformamide (DMF) solvent is explored by solvothermal synthesis at 160 °C for 72 h; five new compounds identified from single crystal X-ray diffraction data are reported: [Hdma]·(ZnFeIII(H2O)4F6) (1), [Hdma]· [Hgua] 2 ·(Fe I II F 6 )·H 2 O (2), [Hdma] 2 ·[Hgua]·[NH 4 ]· [ZnFeIIIF 5(amtetraz) 2]2 (3), [Hdma]2·[Zn1.6 Fe II0.4Fe IIIF 6(amtetraz)3] (4), and [Hdma]·[Zn4F5(amtetraz)4] (5) (Hdma = dimethylammonium, Hgua = guanidinium). 4 and 5 exhibit original 3D frameworks; they are characterized by thermal experiments and 57Fe Mössbauer spectrometry.

ligands, are isostructural and exhibit a three-dimensional (3D) inorganic connectivity.22−24 In the present work, we focus on the synthesis of new fluorinated coordination polymers with iron(III) and zinc(II) cations associated with aminotetrazole (Hamtetraz). Zn2+ and Fe3+ cations were selected for their ability to vary their coordination number due to their facile hydration/deshydration. The resulting phases can be activated by dehydration leading to undercoordinated metal sites, convenient for molecular adsorption. Aminotetrazole was chosen for two reasons: its low pKa values of deprotonation that are well fitted with the pKa value (3.2) of HF/F− couple, the tetrazole ring can increase the affinity between gas molecules and the framework. Gas storage (H2),25 or gas separation properties (CH4/CO2),26−28 are strongly expected.

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EXPERIMENTAL SECTION

Synthesis. All phases were synthesized solvothermally from a mixture of ZnF2 (≥99.9%, Alfa Aesar), FeF3 (≥99.9%, Alfa Aesar), hydrofluoric acid solution 4% (prepared from 40% HF, Riedel De 4249



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Table 2. Summary of Crystallographic Data for the Structures 1−5 empirical formula FW (g mol−1) temperature (K) crystal system space group a (Å) b (Å) c (Å) β (deg) V (Å3) Z ρcalc (g·cm−3) μ (mm−1) Rint R1 [I > 2σ(I)] wR2

1

2

3

4

5

C2H16F6FeNO4Zn 353.38 296 orthorhombic Cmcm 10.3201(2) 7.41940(10) 15.0123(3)

C4H22F6FeN7O 354.10 296 orthorhombic Pbca 10.5434(7) 10.4551(7) 26.510(2)

1149.48(4) 4 2.042 3.425 0.0219 0.0185 0.0557

2922.3(4) 8 1.610 1.103 0.0580 0.0334 0.0943

C9H30F10Fe2N26Zn2 934.97 296 monoclinic C2/c 29.371(10) 6.645(2) 17.375(6) 105.644(11) 3265.3(18) 4 1.902 2.431 0.1978 0.1369 0.3881

C7H22F12Fe1.4N17Zn1.6 755.16 150 monoclinic P21 13.2928(6) 6.5700(3) 13.6461(9) 119.069(3) 1041.64(10) 2 2.044 2.880 0.0468 0.0399 0.1006

C6H8F5N21Zn4 730.82 150 monoclinic P2/m 6.5576(4) 9.7150(6) 8.6358(6) 90.579(4) 550.13(6) 1 2.206 4.396 0.0673 0.0557 0.1467

crystallographic sites, Zn(1) and Zn(2), are attributed to zinc atoms with octahedral and square based pyramidal environments, respectively. Consequently, the diffraction data were refined with a substitution on Zn(1) or Zn(2) sites. The reliability factor R1 remained constant (0.0399) with a substitution on Zn(1) site and increased to R1 = 0.0429 for a substitution on Zn(2). Then, it can be admitted that divalent iron cations adopt preferentially a 6-fold coordination in this compound. In structure 5, a similar strategy was applied with the twin operator TWIN (1̅ 0 0, 0 1̅ 0, 0 0 1). The reliability factor R1 decreased in the monoclinic P2/m space group from 0.1307 to 0.0557. Crystallographic data (excluding structure factors) for structures 1− 5 have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. 989614 ([Hdma]· (ZnFeIII(H2O)4F6) (1)), 989613 ([Hdma]·[Hgua]2·(FeIIIF6)·H2O (2)), 989615 ([Hdma]2·[Hgua]·[NH4]·[ZnFeIIIF5(amtetraz)2]2 (3)), 989616 ([Hdma]2·[Zn1.6FeII0.4FeIIIF6(amtetraz)3] (4)), and 989617 ([Hdma]·[Zn4F5(amtetraz)4] (5)). Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK, (fax: + 44 1223 336033 or e-mail: [email protected]. ac.uk). 57 Fe Mossbauer Spectrometry. Mössbauer experiments of 4 were performed in transmission geometry with a 925 MBq γ-source of 57 Co/Rh mounted on a conventional constant acceleration drive. The sample of 4 was prepared from a softly milled powder with 5 mg Fe/ cm2. The Mössbauer spectra were recorded at 300 and 77 K using a bath cryostat. The data were fitted using the MOSFIT program involving quadrupolar components with Lorentzian lines; the isomer shift values are referred to that of α-Fe at RT. It should be noted that Mössbauer experiments were not performed for 1−3 due to the presence of several impurities. Thermal Analysis. Thermal analyses of 4 and 5 were performed with a TGA-TA Instruments SDT Q600 under O2 flow with a heating rate of 2 °C·min−1 between 25 and 900 °C. X-ray thermodiffractometry of 4 and 5 was carried out under air atmosphere from 40 to 600 °C in an Anton Paar XRK 900 high temperature furnace using a Panalytical X’Pert Pro diffractometer (CuKα radiation). The sample was heated with a heating rate of 10 °C·min−1 with powder data collection at 10 °C intervals from room temperature up to 400 °C and at 50 °C intervals up to 600 °C. Powder patterns were collected in the 5−100° 2θ range.

Haen), Hamtetraz (99%, Alfa Aesar), and DMF (99.8%, SigmaAldrich). The composition space diagram of FeF3/ZnF2−HFaqHamtetraz in 1 mL of DMF solvent was explored for a constant molar concentration [ZnII] + [FeIII] = 0.15 mol·L−1 and a ratio [ZnII]/ [FeIII] = 1, under solvothermal conditions at 160 °C for 3 days under autogenous pressure in a multiautoclave system. The solid products were washed with solvent and dried at room temperature. Despite attempts to achieve phase purity for 1, 2, and 3 by modifications of the reactant contents and the synthesis temperature, only 4 and 5 were obtained pure (Figure S1); microwave plasma analyses of Zn and Fe confirm the given formula (Experimental Section S1 and Figure S3). The compositions of the best starting mixtures leading to phases 1−5 are given in Table 1. Figure 1 illustrates the diagram of FeF3/ZnF2− HFaq-Hamtetraz at 160 °C for 72 h: the limits of the domains are roughly established from the results of the X-ray powder diffraction. Each point of the ternary diagram corresponds to the starting mixture composition and the labels refer to the formula of the solids. These labels are attributed to the major phase determined from the X-ray pattern. In the gray domain, the impurity [NH4]3·(FeF6) appears. Characterization. Single Crystal X-ray Structure Determination. Single crystals 1−5 were selected and isolated using an optical microscope; they were mounted on MicroMount needles (MiTeGen). X-ray single crystal data were collected on an APEX II Quazar diffractometer (4-circle Kappa goniometer, IμS microfocus source (Mo Kα), CCD detector). Intensities were collected at 296 K for 1−3 and at 150 K for 4 and 5. The structures were determined by direct methods with SHELXS-97 and SHELXL-97 programs included in WINGX package.29,30 Thermal motion of all non-hydrogen atoms was refined anisotropically. Hydrogen atoms of the amine molecules were geometrically constrained (HFIX options), whereas hydrogen atoms of the water molecules were constrained with DFIX and DANG options. The assignment of the atoms in metal environments was based on M−(O/F/N) distances and thermal motion considerations (Table S21).31−33 The conditions of data collection are summarized in Table 2. The crystalline quality of 3 was poor and final reliability converged to R = 0.1369/Rw = 0.3881. Twinning treatment and attempts to improve crystalline quality did not allow decreasing of the reliability factors. The porosity of 5 was estimated using PLATON software.34 It must be noted that the determinations of structures 4 and 5 were challenging due to crystal twinning. In the case of 4, the best reliability was obtained with the P21 space group; however, the high R value, 0.1830, and the flack parameter x = 0.46(3) led us to consider crystal twinning. The crystal shape with the well-defined (100) and (010) faces helped to define the twin law. The input of the twin operator TWIN (1̅ 0 0, 01̅ 0, 1 0 1) decreased the reliability factor to R = 0.0399 with a twin fraction of 0.50(0.02). Finally, a small substitution Zn2+/ Fe2+, established by Mössbauer spectrometry, was introduced. Two

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RESULTS AND DISCUSSION

Phase Evolution in the Ternary Diagram (Figure 1). The DMF solvent is hydrolyzed when exposed to high temperatures and acidic conditions. The hydrolysis results in the in situ formation of [Hdma]+ cations and formic acid.35 It 4250



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Figure 4. [100] projection of [Hdma]·[Hgua]2·(FeIIIF6)·H2O (2).

Figure 2. 57Fe Mössbauer spectrum of 4 recorded at 77 K in the conventional geometry.

has already been described that [Hdma]+ cations can be incorporated in the structures, establishing weak interactions with the anionic frameworks.36,37 The (HCOO)− anion, the conjugated base of formic acid, can play the role of a bridging ligand of two metal polyhedra.38 When Hamtetraz is exposed to similar conditions, the tetrazole cycles split and guanidinium cations [Hgua]+ together with nitrogen gas are generated.39,40 NH4+ cations also stem from the decomposition of 5aminotetrazole; they can be inserted in hybrid networks or in inorganic compounds such as [NH4]3·(FeF6), which is found in a large region of the space diagram. As a consequence of the evolution of HF and aminotetrazole concentrations together with the previously mentioned decomposition reactions, high aminotetrazole concentration increases the presence of [NH4]+ and [Hgua]+ fragments. Thus, in this region of the space diagram, the formation of Class I hybrids is favored. Simultaneously, the phase [NH4]3·(FeF6) appears, and its amount increases with the Hamtetraz/HFaq ratio. Class II phases with high dimensionality are preferentially found in acidic conditions and low concentration of aminotetrazole. Apart from [NH4]3·(FeF6), all phases exhibit a constant equimolar Hamtetraz:metal ratio and the 1,2,4 nitrogen binding mode of aminotetrazole only. The presence of ZnF2 in the metal-rich part of the diagram is due to the incomplete reaction of the starting fluoride.

Figure 5. Hydrogen bonding of water molecules (left), [Hgua]+ (left and right) and [Hdma]+ (right) cations in [Hdma]·[Hgua]2·(FeIIIF6)· H2O (2).

Mössbauer Spectrometry. At 300 and 77 K, the hyperfine structure of the Mö s sbauer spectrum of [Hdma] 2 · [Zn1.6FeII0.4FeIIIF6(amtetraz)3] (4) exhibits four well-defined lines that can be unambiguously decomposed into two asymmetrical quadrupolar doublets (Figure 2). It is important to emphasize that no iron containing magnetic impurity can be found, as confirmed from an additional spectrum obtained with a larger velocity scale. In addition, the asymmetry of the quadrupolar components observed when the spectrum was obtained in the conventional geometry (normal to the γ-beam) is expected to be due to some preferential orientation: indeed, this hypothesis has been ruled out after rotating the sample with respect to the γ-beam. The isomer shift values, 0.50(1) and 1.19(2) mm s−1, are unambiguously consistent with the presence of high spin Fe3+ and Fe2+ cations, respectively. The

Figure 3. [100] Projection (left) and hydrogen bonding (right) of [Hdma]·(ZnFeIII(H2O)4F6) (1). 4251



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Figure 6. [010] projection (left), hydrogen bonding (bottom right), and pseudosquare cavities (top right) of [Hdma]2·[Hgua]·[NH4]· [ZnFeIIIF5(amtetraz)2]2 (3).

Figure 7. View of the structure (left), ∞[(Zn(1)/Fe(1))FN4] and ∞[Zn(2)FN3] chains in the ab plane (center) and hydrogen bonding (right) of [Hdma]2·[Zn1.6FeII0.4FeIIIF6(amtetraz)3] (4).

between terminal fluorine F(2) and hydrogen atoms from water molecules and dimethylammonium cations via moderate Ow(1)−H···F(2) (≈ 2.63 Å), N(1)−H···F(1) (≈ 3.16 Å) and C(1)−H···F (≈ 3.37 Å) interactions (Figure 3 right). The structure of [Hdma]·[Hgua]2·(FeIIIF6)·H2O (2) is built up from FeIIIF6 octahedra, free water molecules, [Hdma]+ and [Hgua]+ cations (Figure 4). The FeIII−F distances are in good agreement with the distances already found in numerous fluorides that contain isolated FeIIIF62− anions.41−49 The FeF6 polyhedra are weakly hydrogen bonded to organic cations and water molecules by N−H···A (A = F, O) (2.65−3.24 Å) and Ow−H···F (2.76−2.87 Å) bonds (Figure 5). Isolated water molecules are hydrogen bonded with two fluorine atoms and one NH2+ group of guanidinium cations. [Hgua]+ cations display a planar triangular configuration and [Hdma]+ cations are arranged in a tetrahedral geometry.

relative absorption area of the quadrupolar doublets Fe2+/Fe3+ is 0.29(1)/0.71(1) at 77 K 0.31(1)/0.69(1) at 300 K. Assuming that the recoilless Lamb−Mössbauer factors are equal for both Fe sites, this value suggests clearly that the formulation [Hdma]2·[Zn2FeIIIF6(amtetraz)3], initially determined from single crystal X-ray diffraction data, was approximate: consequently, another refinement of the X-ray data was performed by using the composition 0.4Fe2+ for 1Fe3+, i.e., a ratio of 0.29/0.71. A substitution Zn2+/Fe2+ had to be considered, leading to the new formulation [Hdma]2· [Zn1.6FeII0.4FeIIIF6(amtetraz)3] (4). Structural Descriptions. The structure of [Hdma]· (ZnFe I I I (H 2 O) 4 F 6 ) (1), isostructural of [Hdma]· (FeIIFeIII(H2O)4F6),23 exhibits anionic [ZnFe(H2O)4F6]− trans-chains of alternating FeIIIF6 and ZnF2(H2O)4 octahedra linked by opposite fluorine corners F(1) (Figure 3 left). The stability of the structure network is ensured by hydrogen bonds 4252



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Figure 8. View of the structure (left), [100] chains (center), and connection mode of zinc polyhedra (right) of [Hdma]·[Zn4F5(amtetraz)4] (5).

ammonium cations; they are constituted of FeF4N2 polyhedra and ∞[ZnFN4] chains connected by tetrazolate anions along the [101] and [101̅] directions (Figure 6, bottom right). The N1, N2, N4 bridging mode of Scheme 1 is adopted by azolate anions. The octahedral FeF4N2 units are strongly distorted with two long distances (≈ 2.20 Å) between FeIII and nitrogen atoms (N(4) and N(6)) and four short distances (≈ 1.91 Å) between FeIII and terminal fluorine atoms (F(2), F(3), F(4), and F(5)). In the ∞[ZnFN4] chains, the Zn(1) atoms are connected by μ2-F(1) corners, and the Zn(1)−F(1)−Zn(1) angle is equal to 109.6°. The N−H···Fterminal bonds lie in the range 2.67−3.26 Å. [Hdma]2·[Zn1.6FeII0.4FeIIIF6(amtetraz)3] (4) exhibits a 3D network (Figure 7 left) with rectangular cavities. In the ab plane, the structure results from the connection of [010] chains associated with two crystallographic Zn2+ sites (Figure 7, center). The first chain ∞[Zn(2)FN3] involves square pyramidal Zn(2)F2N3 entities, and the connection of Zn(2) centers is ensured by opposite μ2-F(5) corners and by amtetraz ligands. In the second chain ∞[Zn(1)/Fe(1)FN4], every (Zn(1)/Fe(1))F2N4 octahedral unit is connected to two adjacent polyhedra through two opposite μ2-F(6) atoms and amtetraz ligands. All bridging modes of the amtetraz anions are identical: it is the N1, N2, N4 mode of Scheme 1. A strong tilt of the octahedra from the b axis is then induced. Along [102], the previous chains in the ab plane are connected by the FeIIIF4N2 octahedra. [Hdma]+cations are located in the cavities, and they exchange N−H···F bonds with the FeIIIF4N2 entities (Figure 7 right). The 3D framework of [Hdma]·[Zn4F5(amtetraz)4] (5) displays pseudo square [100] tunnels in which [Hdma]+ cations are statistically disordered (Figure 8 left). In this structure, two types of [100] chains are distinguished; they are connected by [amtetraz]− anions along the [011] and [01̅1] directions (Figure 8 center). The tetrazolate ligands adopt the N1, N2, N4-bridging mode of Scheme 1. The first chain ∞[ZnFN4] results from the condensation of ZnF2N4 octahedra by two opposite F− vertices; it is also observed in 4. In the second chain, metal cations adopt a trigonal bipyramidal geometry; two polyhedra are linked by one edge (2 μ2-F(2) connection) and form Zn2F4N4 dimers. The dimers are then connected to the adjacent dimers through μ2-F(1) corners, giving trans-∞[Zn2F3N4] chains (Figure 8 right). Both 1 and 2 belong to Class I hybrids that exhibit hydrogen bonds between organic cations and metal fluoride entities only.

Figure 9. Thermogravimetric curve and thermal evolution of the X-ray diffractograms under air at 2 °C/min of [Hdma]2·[Zn1.6FeII0.4FeIIIF6(amtetraz)3] (4).

Figure 10. Thermogravimetric curve and thermal evolution of the Xray diffractograms under air at 2 °C/min of [Hdma]· [Zn4F5(amtetraz)4] (5).

The two-dimensional (2D) structure of [Hdma]2·[Hgua]· [NH4]·[ZnFeIIIF5(amtetraz)2]2 (3) is built up from (100) III ∞{[NH4]·[ZnFe F5(amtetraz)2]2} sheets separated by dimethylammonium and guanidinium cations (Figure 6, left and top right). These sheets include pseudocubic cavities that contain 4253



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3, 4, and 5 are considered as Class II hybrids in which the organic anions are strongly linked to divalent metal cations via N−M2+ bonds; however, amine cations are also inserted in the cavities or intersheet space and exchange hydrogen bonds. Thermal Analysis. The thermogravimetric (TG) curve of [Hdma]2·[Zn1.6FeII0.4FeIIIF6(amtetraz)3] (4) indicates only one weight loss starting at 220 °C; it is attributed to hydrolysis and the loss of amine fluoride and hydrofluoric acid (Figure 9). The final residue at 900 °C is a mixture of ZnFe2O4 and ZnO (65% and 35%). The experimental and theoretical weight loss values are in good agreement (theo./exp.: 62.5/62.2%). X-ray thermodiffraction confirms that 4 is stable up to 220 °C (Figure 9, top right). Above this temperature, an amorphous phase appears and transforms slowly into the previously cited oxides. The TG curve of 5 exhibits two weight losses (Figure 10). The first step, observed between 170 and 280 °C, is assigned to the loss of one dimethylammonium fluoride (theo./exp.: 8.8/ 8.4%), as also followed by infrared spectroscopy (Figure S2). After the narrow pseudo plateau, the second event is attributed to the elimination of organic linkers and fluoride entities and to hydrolysis that leads to the formation of ZnO at 900 °C (theo./ exp.: 47.1/45.2%). X-ray thermodiffraction shows that [Hdma]· [Zn4F5(amtetraz)4] (5) is stable up to 190 °C and decomposes to give a crystalline intermediate between 200 and 300 °C (Figure 10, top right). Above this temperature, hydrolysis occurs, and the final product at 500 °C is identified as zinc oxide. This experiment reveals the existence of a crystalline intermediate, after the loss of dimethylammonium fluoride. The X-ray pattern of this new phase, very similar to that of 5, suggests that the architecture of 5 is roughly maintained. It is supposed that dimethylammonium fluoride elimination leads to unsaturated zinc coordination, well-known to be propitious to sorption properties. A significant increase of the free space in the channels of the structure can be assumed (estimated porosity before/after loss of dimethylammonium fluoride: 9%/ 32%).34 Our current work is devoted to the analysis of this intermediate phase. After the structure determination, solid state 19F NMR and the adsorption measurements will be performed. Also, the influence of the solvent is under study, and networks with similar properties were found. This work will be fully described in a forthcoming paper.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b00530. Selected X-ray crystallographic information, and valence bond calculations for compounds 1−5. Powder X-ray patterns (experimental and simulated) for 4 and 5. Infrared spectra for 5 (PDF) Crystallographic information file for 1 (CIF) Crystallographic information file for 2 (CIF) Crystallographic information file for 3 (CIF) Crystallographic information file for 4 (CIF) Crystallographic information file for 5 (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address †

ICCF-UMR 6296, Université Blaise Pascal, Chimie 5, Campus des Cézeaux, 24 avenue des Landais, BP 80026, 63171 AUBIERE Cedex, France.

Notes

The authors declare no competing financial interest.

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REFERENCES

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CONCLUSION

Five new hybrid structures are identified in the exploration of the composition space diagram FeF3/ZnF2−Hamtetraz-HFDMF. 4 displays an original 3D framework with mixed valence and mixed metal architecture; a small FeII/ZnII substitution is evidenced by 57Fe Mössbauer spectrometry. 5 exhibits a porous 3D network with pseudosquare cavities, occupied by [Hdma]+ cations. Although 5 initially displays an anionic framework, the thermal analysis reveals the existence of a narrow stability plateau consistent with the loss of dimethylammonium fluoride. The ab initio structure determination of this hypothetical neutral 3D framework is under scrutiny. A supposed topoctatic transformation after elimination of dimethylammonium fluoride could open the access to insaturated metal sites that favor gas absorption. 4254



Article

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Evidence of New Fluorinated Coordination Compounds in the

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