DOI: 10.1021/cg100909x
Evolution of Guanazolium Fluoroaluminates within the Composition-Space Diagram and with the Temperature
2010, Vol. 10 5159–5168
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Amandine Cadiau,† Armel Le Bail,† Annie Hemon-Ribaud,† Marc Leblanc,† Monique Body,‡ Franck Fayon,§ Etienne Durand, Jean-Claude Boulou,^ and Vincent Maisonneuve*,† Laboratoire des Oxydes et Fluorures, UMR 6010 CNRS, and ‡Laboratoire de Physique de l’Etat Condens e, UMR 6087 CNRS, Facult e des Sciences et Techniques, Universit e du Maine, emes et Mat eriaux: Haute Avenue O. Messiaen, 72085 Le Mans Cedex 9, France, §Conditions Extr^ Temp erature et Irradiation, CNRS UPR 3079, 1D Avenue de la Recherche Scientifique, ere Condens ee de Bordeaux, 45071 Orl eans Cedex 2, France, Institut de Chimie de la Mati UPR 9048-CNRS, 87 Avenue du Docteur Schweitzer, 33608 Pessac, France, and ^Bruker Optics Sarl, 4 all ee Hendrik Lorentz, Parc de la Haute Maison;B^ at A5, Champs sur Marne, 77447 Marne la Vall ee Cedex 2, France )
†
Received July 8, 2010; Revised Manuscript Received September 17, 2010
ABSTRACT: The 2D composition-space diagram of the Al(OH)3-Am2TAZ-HFaq-ethanol system is established under microwave heating at 190 C for [Al3þ] = 1 mol 3 L-1. Four new fluoroaluminates are evidenced when the [HF]/[Am2TAZ] ratio is increased in the starting solution, and the dimensionality of the inorganic frameworks is increased from 0D in [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (Pc, Z = 2), to 1D in [HAm2TAZ]2 3 (AlF5) and [HAm2TAZ]2 3 (Al2F8) (Fdd2, Z = 8), and to 2D in [HAm2TAZ]2 3 (Al5F17) (Imm2, Z = 2). This evolution is partially paralleled by the thermal decomposition of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O; on heating, this hydrate gives [HAm2TAZ]2 3 (AlF5) at 100-150 C and [HAm2TAZ]2 3 (Al2F8) at 180 C; the loss and simultaneous decomposition of [HAm2TAZ]F leave a solid residue of polymeric paracyanogen (CN)2n that is further decomposed and hydrolyzed into HCN and HNCO by atmospheric water traces. NMR 19F spectroscopy of [HAm2TAZ]2 3 (AlF5) is in agreement with the crystallographic determination, and the 27Al spectrum demonstrates that a significant F-/OH- substitution is excluded.
Introduction The search for new hybrid organic-inorganic porous solids is still intensively investigated because of the very wide spectrum of promising applications in the fields of catalysis,1 gas selective adsorption,2 ion-exchange,3 and drug delivery.4 The quasi-infinite combinations of organic linkers and inorganic cations enable tuning of the pore size and enhancement of the targeted properties. Hybrid materials can be classified into two classes as a function of the nature of the interactions between the organic moiety and the inorganic part.5 In Class I hybrids, the organic and inorganic components are linked by weak interactions such as van der Waals or hydrogen bonds whereas in Class II hybrids this connection is ensured by strong covalent or iono-covalent bonds. The dominant synthetic route to prepare these materials remains the hydro(solvo)thermal reaction under mild conditions (autogenous pressure, T < 250 C). During the last 10 years, we have focused our work on the search for new porous Class I compounds with a purely fluorinated framework. The study of the M(OH)x-aliphatic amine-HFaq-solvent systems led to numerous fluorides with 0D (isolated polyanions),6 1D (infinite chains),7 and 2D (layers)8 inorganic networks. As a reason for the very fast reaction durations, combined with a good reproducibility of the experiments, microwave heating was applied to explore the chemical systems over large concentration domains.9 To date, however, no 3D network is evidenced; nonetheless, we have discovered several extended
aluminum polyanions such as Al4F186- (0D),10 Al7F309(0D),7 Al8F3511- (0D),11 Al7F298- (1D),7 and Al5F176- (2D).8 The access to 3D hybrid fluoroaluminates seems to be a real challenge; it must be noted that only four 3D fluorides containing beryllium, yttrium, or zirconium cations are known.12-14 Until now, very few cyclic conjugated amines were considered, though it is suspected that the presence of aromatic linkers and the number of their conjugated rings could improve the hydrogen gas uptake in Class II hybrids.15 Consequently, we are currently testing several conjugated cyclic amines with one or two five- and/or six-membered rings and with multiple protonation sites, such as melamine,16 triazole, aminotriazole, guanazole (3,5-diamino-1,2,4-triazole = Am2TAZ), aminotetrazole, purine, and adenine.17 In this paper, we report on the synthesis of four new hybrid Class I guanazolium fluoroaluminates in the Al(OH)3-Am2TAZ-HFaq-ethanol system: [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I), [HAm2TAZ]2 3 (AlF5) (II), [HAm2TAZ]2 3 (Al2F8) (III), and [HAm2TAZ]2 3 (Al5F17) (IV). The study of the thermal decomposition of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I) by mass and infrared spectroscopy coupled TGA is also presented together with the NMR study of [HAm2TAZ]2 3 (AlF5) (II) and [HAm2TAZ]2 3 (Al5F17) (IV). Experimental Section
*Correspondence and reprints. E-mail address: vincent.maisonneuve@ univ-lemans.fr. Telephone: 33 2 43 83 35 61. Fax: 33 2 43 83 35 06.
All phases were synthesized from a mixture of Al(OH)3 (Sochal), guanazole (Am2TAZ), hydrofluoric acid solution (40% HF, Prolabo), and ethanol. The compositions of the best starting mixtures, leading to phases I-IV, are given in Table 1. The reactions were performed under solvothermal conditions at 190 C in a CEM microwave oven during 1 h, and the solid products were washed with ethanol and dried at room temperature. II was contaminated by a
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Figure 1. Final profile refinement of [HAm2TAZ]2 3 (Al5F17) (IV): observed (line), calculated (point), and difference (bottom) profiles of X-ray diffraction data. Vertical bars are related to the calculated Bragg reflection positions. Table 1. Molar Proportions of the Starting Materials (Al(OH)3-Am2TAZ-HFaq-Ethanol) for the Synthesis of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I), [HAm2TAZ]2 3 (AlF5) (II), [HAm2TAZ]2 3 (Al2F8) (III), and [HAm2TAZ]2 3 (Al5F17) (IV) and Elemental Analyses formulation molar ratio elemental analysis (exp/meas) Al/F/N/C [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I) [HAm2TAZ]2 3 (AlF5) (II) [HAm2TAZ]2 3 (Al2F8) (III) [HAm2TAZ]2 3 (Al5F17) (IV)
1/5/4/17 1/3/6/17 1/0.7/3.7/17 1/1/38/17
small amount of an unknown impurity while larger amounts of impurities were found in III and IV. Single crystals were selected by using an optical microscope. X-ray intensity data were collected on a Bruker APEX II Quazar diffractometer (4-circle Kappa goniometer, IμS microfocus source, CCD detector) at 173 K for I and 293 K for II or a Bruker KappaCCD diffractometer, graphite-monochromated at 293 K for III. The structure solutions were obtained by direct methods (SHELXS-97),18 extended by successive difference Fourier syntheses, and refined by full-matrix least-squares on all F2 data using SHELXL-97;18 these programs are included in the WinGX package.19 The nature of the atoms was differentiated from bond distance considerations. The final refinements included the anisotropic thermal motion parameters for all non-hydrogen atoms. The hydrogen atoms of [HAm2TAZ]þ were geometrically constrained (HFIX option) whereas the O-H distances of water molecules were fixed using the DFIX option. The structure of I was first determined in the centrosymmetric space group P21/c at room temperature, and a disorder F-/H2O was found to affect two opposite vertices of the aluminum octahedra. An order between F- and H2O was tested in the non-centrosymmetric Pc space group, and new diffraction data were collected at 173 K. Then, several very weak (0k0) reflections with k = 2n þ 1 were observed, and the structure was correctly determined in the Pc space group. In II, the non-centrosymmetric space group Fdd2 was unambiguously deduced from systematic extinction conditions and was further confirmed by a positive test of optical frequency doubling; a similar space group was found for III. The absolute configurations of the structures were not determined as a reason for small anomalous dispersion factors. Polycrystalline powders of IV were always obtained, and consequently, diffraction patterns were recorded with a Panalytical X’Pert Pro diffractometer (Cu KR). A body-centered orthorhombic cell was established from the McMaille20 indexing software (figures of merit: M(20) = 28, F(20) = 44 (0.006, 75)). This cell was confirmed by a satisfying cell-constrained whole powder pattern fit (WPPF) by the Le Bail method21 using the Fullprof software.22 No additional extinction occurred than those associated with the I Bravais lattice. A few nonindexed weak-intensity peaks whose line widths were considerably narrower than those of the main compound could not be attributed to any known phase. The three most intense of these impurity peaks are at the diffracting angles 15.14, 15.54, and 16.41 (2θ), with their intensities being respectively 3.9, 7.4, and 2.4% of the most intense first peak at low diffracting angle. Such few and
7.2/7.5 8.4/7.8
25.2/25.1 37.2/32.4 29.5/27.9 43.5/43.5 no elemental analysis (impurity) no elemental analysis (impurity)
4.8/4.9 3.8/4.0
extremely narrow peaks could be the signature of a few small crystals of a second phase in diffracting position by haphazard in the powder; their intensities were found to vary on different patterns of the same or different preparations. The extracted intensities were used for structure solution by direct space methods (ESPOIR software).23 With two of the cell parameters (9.56 and 3.58 A˚) being characteristic of layers of corner sharing [AlF6] octahedra with the [Al5F17] formulation, such units were fixed in the cell and one Am2TAZ molecule (without H atoms) was allowed to be translated and rotated by a Monte Carlo process while fitting the |Fcalc| to the extracted |Fobs|. All possible space groups were tested (Immm, I222, etc.), finding finally an optimum result in acentric Imm2, with an equal distribution of the HAm2TAZ cations on two sites related by a mirror symmetry. Then, Rietveld refinements,24 using distance constraints on Al-F, F-F, C-N, and N-N, led to a satisfying fit, as shown in Figure 1. Attempts to describe the structure with one fully ordered Am2TAZ molecule always led to poorer fits (R factors higher by more than 5%). Such a disorder of the intercalated molecules or ions is frequent in layer compounds. Crystallographic structure data are given in Table 2; the main bond lengths and the hydrogen bond distances are listed in Tables 3 and 4, respectively. Thermogravimetric analyses (argon or helium atmosphere, heating rate 10 C/min) were performed with a Setsys Evolution Setaram coupled to a Thermo Nicolet 380 FTIR spectrometer and to a Pfeiffer Omnistar Mass Spectrometer (1-200 amu mass range) or with a TG 201 F1 Iris Netzsch coupled to a Bruker Optics Vertex70 FTIR or with a SDT-Q600 TA Instruments. The transfer lines were heated at 170 C (Nicolet) or 200 C (Bruker). Aluminum, fluorine, nitrogen, and hydrogen were analyzed in [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I) and [HAm2TAZ]2 3 (AlF5) (II) (Table 1). III and IV were not analyzed because of the presence of a larger amount of impurities. A small amount of one unknown impurity was detected by 1H, 19F, and 27Al NMR spectroscopy in II, and this spectroscopy confirmed the presence of a different impurity in IV, previously evidenced by X-ray diffraction. Thermodiffraction patterns were collected using a Panalytical X’Pert Pro diffractometer, employing Cu KR radiation, and a RTMS X’Celerator detector, equipped with an Anton Paar XRK 900 high temperature furnace. The samples were heated under nitrogen from room temperature to 400 C at a heating rate of 10 C min-1. XRD patterns were collected at 10-30 C intervals in the 5-40 2θ range with a scan time of 10 min.
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Table 2. Crystallographic Data of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I), [HAm2TAZ]2 3 (AlF5) (II), [HAm2TAZ]2 3 (Al2F8) (III), and [HAm2TAZ]2 3 (Al5F17) (IV) I formula weight (g 3 mol-1) crystal system space group a (A˚) b (A˚) c (A˚) β (deg) V (A˚3), Z wavelength (A˚) μ (mm-1) Fcalc (g 3 cm-3) temperature (K) 2θ range (deg) refl meas/uni (I>2σ(I)) refined parameters R/Rw goodness of fit ΔFmin/ΔFmax (e 3 A˚-3) no. independent reflections no. independent parameters distance restraints RP/Rwp RB/RF
II
376.23 monoclinic Pc 9.4027(6) 6.2754(3) 12.4023(7) 98.539(3) 723.7(3), 2 Mo KR 0.23 1.73 173 4-60 8208/3369/3248 116 0.030/0.083 1.077 -0.28/0.31
I
II 1.782(1) 1.782(1) 1.811(1) 1.815(1) 1.816(1) 1.989(2) 1.83 1.327(2) 1.409(2) 1.320(2) 1.357(3) 1.379(2) 1.342(3) 1.335(2) 1.329(2) 1.412(2) 1.315(2) 1.355(3) 1.382(2) 1.344(3) 1.335(2)
IV
406.15 orthorhombic Fdd2 35.93(1) 20.746(8) 3.590(3)
658.09 orthorhombic Imm2 26.614(1) 9.5626(3) 3.5796(1)
2238.8(4), 8 Mo KR 0.26 1.91 293 4-60 3814/1407/1148 91 0.045/0.098 1.029 -0.42/0.35
2676(3), 8 Mo KR 0.33 2.01 293 6-55 6021/1479/954 110 0.051/0.083 0.967 -0.33/0.40
911.0(1), 2 Cu KR 2.35 293 5-70
164 77 32 0.100/0.096 0.038/0.032
Table 3. Selected Interatomic Distances (A˚) in [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I), [HAm2TAZ]2 3 (AlF5) (II), [HAm2TAZ]2 3 (Al2F8) (III), and [HAm2TAZ]2 3 (Al5F17) (IV) Al(1)-F(5) Al(1)-F(3) Al(1)-F(4) Al(1)-F(1) Al(1)-F(2) Al(1)-O(1) ÆAl-(F,O)æ N(1A)-C(2A) N(1A)-N(2A) N(2A)-C(1A) N(3A)-C(2A) N(3A)-C(1A) N(4A)-C(1A) N(5A)-C(2A) N(1B)-C(2B) N(1B)-N(2B) N(2B)-C(1B) N(3B)-C(2B) N(3B)-C(1B) N(4B)-C(1B) N(5B)-C(2B)
III
322.18 orthorhombic Fdd2 29.749(3) 20.727(2) 3.6309(3)
III
Al(1)-F(2) Al(1)-F(3) Al(1)-F(1) Al(1)-F(1)0
2 1.768(2) 2 1.793(2) 1.810(3) 1.821(3)
ÆAl-Fæ N(1)-C(2) N(1)-N(2) N(2)-C(1) N(3)-C(2) N(3)-C(1) N(4)-C(1) N(5)-C(2)
1.79 1.325(3) 1.399(3) 1.302(3) 1.347(3) 1.377(3) 1.356(4) 1.319(4)
Al(1)-F(3) Al(1)-F(2) Al(1)-F(1) Al(1)-F(1) Al(1)-F(4) Al(1)-F(4) ÆAl-Fæ N(1)-C(2) N(1)-N(2) N(2)-C(1) N(3)-C(2) N(3)-C(1) N(4)-C(1) N(5)-C(2)
1.707(2) 1.747(2) 1.790(4) 1.803(4) 1.838(2) 1.883(2) 1.79 1.309(4) 1.405(4) 1.303(4) 1.352(4) 1.368(4) 1.331(5) 1.311(4)
Table 4. Selected N-F, N-O, N-N, O-O and O-F distances (A˚) in [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I), [HAm2TAZ]2 3 (AlF5) (II), [HAm2TAZ]2 3 (Al2F8) (III), and [HAm2TAZ]2 3 (Al5F17) (IV) A-H 3 3 3 B d(A 3 3 3 B) A-H 3 3 3 B d(A 3 3 3 B) I N(1A)-H(1A) 3 3 3 Ow(2) N(3A)-H(3A) 3 3 3 F(2) N(4A)-H(4A1) 3 3 3 F(2) N(4A)-H(4A2) 3 3 3 F(3) N(5A)-H(5A1) 3 3 3 O(1) N(5A)-H(5A2) 3 3 3 N(2A) N(1B)-H(1B) 3 3 3 Ow(1) N(3B)-H(3B) 3 3 3 F(4) N(4B)-H(4B1) 3 3 3 F(4) N(4B)-H(4B2) 3 3 3 F(5) N(5B)-H(5B1) 3 3 3 F(1) N(5B)-H(5B2) 3 3 3 N(2B) O(1)-H(11A) 3 3 3 Ow(2) O(1)-H(11B) 3 3 3 Ow(1) Ow(1)-Hw(1A) 3 3 3 F(5) Ow(1)-Hw(1B) 3 3 3 F(1) Ow(2)-Hw(2A) 3 3 3 F(1) Ow(2)-Hw(2B) 3 3 3 F(3)
2.764(1) 2.638(1) 2.764(1) 2.842(1) 3.044(1) 3.066(1) 2.785(1) 2.664(1) 2.822(1) 2.835(1) 2.979(1) 3.077(1) 2.720(1) 2.724(1) 2.633(1) 2.714(1) 2.716(1) 2.649(1)
II N(1)-H(1) 3 3 3 F(3) N(3)-H(3) 3 3 3 F(3) N(4)-H(4B) 3 3 3 F(2) N(5)-H(5A) 3 3 3 F(2) N(5)-H(5B) 3 3 3 N(2) III N(1)-H(1) 3 3 3 F(2) N(3)-H(3) 3 3 3 F(2) N(4)-H(4A) 3 3 3 F(3) N(5)-H(5B) 3 3 3 N(2) IV N(2) 3 3 3 F(2) N(4) 3 3 3 F(2) N(5) 3 3 3 F(2)
2.646(2) 2.620(2) 2.877(2) 2.756(2) 2.964(2) 2.716(4) 2.626(4) 2.820(4) 3.081(5) 2.65(1) 2.714(8) 2.774(9)
IV Al(1)-F(4) Al(1)-F(1) Al(1)-F(2) Al(1)-F(1) Al(1)-F(3) Al(1)-F(5) ÆAl(1)-Fæ N(1)-C(2) N(1)-N(2) N(2)-C(1) N(3)-C(2) N(3)-C(1) N(4)-C(1) N(5)-C(2)
1.778(2) 1.787(3) 1.789(3) 1.795(3) 1.816(3) 1.818(2) 1.80 1.316(8) 1.41(1) 1.313(8) 1.37(1) 1.381(7) 1.35(1) 1.33(1)
Al(2)-F(6) Al(2)-F(3) Al(2)-F(6)
1.763(6) 4 1.811(2) 1.817(6)
ÆAl(2)-Fæ
1.80
NMR experiments were performed on an Avance 300 Bruker spectrometer (phase II) and on an Avance 750 Bruker spectrometer (phase IV) using high speed CP-MAS probes with 2.5 mm rotors
Figure 2. View of the structure of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I) along [010]. The heights of aluminum atoms along b are given in hundreds.
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Figure 3. Environment of water molecules, guanazole molecule (top), [HAm2TAZ]þ cation (bottom), pseudocentrosymmetric arrangement of guanazolium cations, and hydrogen bond network in the (b,c) plane of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I). Table 5. Acquisition Parameters of NMR Experiments
(spinning frequency up to 35 kHz). The acquisition parameters are given in Table 5. The 19F MAS Hahn echo spectra were recorded with an interpulse delay synchronized with the rotor period. For 27Al NMR SATRAS experiments, the linear regime was ensured by using short pulse durations and low RF field strengths. 3Q-MAS experiments25 were
carried out using the three pulse z-filter sequence. A two-dimensional Fourier transformation followed by a shearing26 transformation gave pure absorption 2D spectra. The Hahn echo and MQ-MAS spectra were reconstructed using the Dmfit software.27 When needed, the discrimination of isotropic peaks from side bands was achieved by recording spectra at various
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Figure 4. Comparison of the structures of [HAm2TAZ]2 3 (AlF5) (II) (top left) with the AlF5 trans-chain (top right) and of [HAm2TAZ]2 3 (Al2F8) (III) (bottom left) with the Al2F8 double chain (bottom right). spinning rates. Reconstruction of the SATRAS spectra was achieved using a homemade FORTRAN 95 code based on the theoretical treatment developed by Skibtsted et al.28,29 and lately corrected.30,31 The external references used for 1H and 19F and 27Al isotropic chemical shift determination were respectively TMS, CFCl3, and a 1 M aqueous solution of Al(NO3)3. Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication nos. CCDC 729134 ([HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O), CCDC 729135 ([HAm2TAZ]2 3 (AlF5)), CCDC 729136 ([HAm2TAZ]2 3 (Al2F8)), and CCDC 729137 [HAm2TAZ]2 3 (Al5F17). Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax, þ44 1223 336033; e-mail, deposit@ ccdc.cam.ac.uk).
Results and Discussion 1. Crystal Structures. The crystal structure of I contains isolated AlF5(H2O) octahedra between which [HAm2TAZ]þ cations and water molecules are inserted (Figure 2). F-/H2O order is observed in two trans positions of elongated [AlF5(H2O)]2- polyhedra: the Al-OH2 distance, 1.989(2)A˚, is longer than the other Al-F distances (1.801 A˚). Such polyhedra are found in [Zn(H2O)6][AlF5(H2O)]32 and CoAlF5(H2O)733 with similar distances. Every free water molecule, hydrogen bonded with two fluoride anions and one water molecule of three aluminum octahedra and with one N(1)
Figure 5. [001] projection of the structure of [HAm2TAZ]2 3 (Al5F17) (IV). The [HAm2TAZ]þ cation occupies statistically two sites related by a mirror in the ac plane. Only one site is represented; the mirror effect is shown for one molecule at the lower left.
atom, adopts a tetrahedral coordination, as encountered in solids with low hydration degree.34 Water molecules and Al octahedra build ¥[AlF5(H2O)] 3 (H2O)2 layers in the (100) planes (Figure 3). Moreover, eight hydrogen bonds establish between the N-H groups of six [HAm2TAZ]þ cations and the anions of one AlF5(H2O) octahedron to ensure the stability of the 3D network. Both crystal structures of II and III exhibit 1D linear chains along the c axis and a similar disposition of the [HAm2TAZ]þ cations (Figure 4). Both compounds are described in the Fdd2 space group, and their b and c parameters
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are very similar. II is composed of ¥[AlF5]2- trans-chains of slightly distorted AlF6 octahedra (Figure 4 top). The Al-F distances lie in the range 1.810-1.821 A˚ for bridging F(1) and 1.768-1.793 A˚ for nonbridging fluorine atoms. In III,
Figure 6. Experimental and calculated 19F NMR spectra (34 kHz) of [HAm2TAZ]2 3 (AlF5) (II). The calculated spectrum corresponds to the summation of lines 1, 2, 3, and I (impurity line). Lines indicated by stars correspond to the spinning side bands.
Figure 7. 27Al NMR spectra of [HAm2TAZ]2 3 (AlF5) (II) recorded at 25 kHz. The calculated spectrum corresponds to the summation of lines 1 and 2 (impurity line).
two simple trans-chains are associated by edges to form 2double chains (Figure 4 bottom), already described in one other hybrid fluoroaluminate [Hpy]2 3 [C6H3(CO2H)3] 3 (Al2F8).35 These double chains are built up from strongly distorted octahedra because of three different bonding configurations for fluoride anions; the Al-F distances decrease from Al-F(4), 1.838-1.883 A˚ (edge-bridging), to Al-F(1), 1.790-1.803 A˚ (corner-bridging) and to Al-F(3) and Al-F(2), 1.707-1.747 A˚ (terminal). Such distances were previously observed in [Hpy]2 3 [C6H3(CO2H)3] 3 (Al2F8). In II and III, the inorganic chains are linked to protonated cyclic amines; the hydrogen bonds with terminal fluoride ions lie in the range 1.76-2.01 A˚ for N-H 3 3 3 F and 2.63-2.90 A˚ for N 3 3 3 F. In the structures of I, II, and III, determined by X-ray single crystal diffraction, the [HAm2TAZ]þ guanazolium cations present the same geometry (bond distances and angles), corresponding to the 1(H) tautomer. The smallest angle (102-103) is always C(1)-N(2)-N(1), in which N(2) is the only nonprotonated nitrogen atom; the largest angle is always N(2)-N(1)-C(2) (Figure 3). IV presents a layered structure with the alternation of inorganic layers ¥[Al5F17]2- and monoprotonated amines (Figure 5) along the a axis. Similar inorganic layers were recently found in one other hybrid fluoroaluminate [Hgua]2 3 (Al5F17).36 This inorganic sheet is built up from the corner sharing connection of ReO3 type Al(1)4F16 columns with trans-Al(2)F5 chains. It is also described as the intergrowth of HTB type Al5F19 columns and ReO3 type Al4F16 columns.37 The stability of the 3D structure is ensured by strong hydrogen bonds between nonbridging F(2) anions of Al(1) octahedra and organic cations (dN 3 3 3 F = 2.65-2.77 A˚). 2. NMR Spectroscopy of [HAm2TAZ]2 3 (AlF5) (II). [HAm2TAZ]2 3 (AlF5) (II) presents three fluorine sites, F(1), F(2), and F(3) with respective multiplicities 8a, 16b, and 16b. Three lines with respective intensities 20, 40, and 40% are expected on ¥[Al2F8]
Table 6. Line Label, Isotropic Chemical Shift, and Relative Intensity from the Reconstruction of the 19F NMR Spectra of [HAm2TAZ]2 3 (AlF5) (II) and of [HAm2TAZ]2 3 (Al5F17) (IV) phase
NMR lines
δiso (ppm) ( 0.2 ppm
relative intensity (%) ( 1%
II
1 2 3 4 1 2 3 4 5 6 7 8 9 10
-160.2 -149.5 -134.6 -140.0 -181.7 -172.3 -169.6 -165.4 -160.1 -156.7 -153.1 -150.3 -148.9 -144.9
18.3 38.3 40.4 3.0 0.3 4.6 36.3 41.5 0.8 1.8 11.8 1.1 1.3 0.6
IV
attribution bridging F nonbridging F impurity impurity bridging F
nonbridging F
Figure 8. 27Al 3Q-MAS spectrum of [HAm2TAZ]2 3 (Al5F17) (IV) recorded at 33 kHz (17.6 T); the top and right curves are the projections on the MAS (F2) and isotropic (F1) axes, respectively. The dashed lines correspond to the reconstructed spectrum.
Table 7. Line Label, Isotropic Chemical Shift, and Relative Intensity from the Reconstruction of the 27Al NMR Spectra of [HAm2TAZ]2 3 (AlF5) (II) and [HAm2TAZ]2 3 (Al5F17) (IV) νQ (kHz) ( 50 kHz ηQ ( 0.05 relative intensity (%) ( 1% attribution compd NMR lines δiso (ppm) ( 0.5 ppm II IV
1 2 2 1
-2 -5.5 -10.5 -13.9
1175 300 980 240
0.75 nd 0.35 0.5
98.5 1.5 76 24
Al(1) impurity Al(1) Al(2)
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Figure 9. Experimental (black) and reconstructed (red) 19F (left) and 1H (right) MAS spectra of [HAm2TAZ]2 3 (Al5F17) (IV) recorded at 33 kHz (17,6 T); lines indicated by stars correspond to the spinning side bands. Table 8. Line Label, Isotropic Chemical Shift, and Relative Intensity from the Reconstruction of the 1H NMR Spectra of [HAm2TAZ]2 3 (Al5F17) (IV) δiso (ppm) relative intensity (%) ( 1% attribution NMR lines ( 0.2 ppm 1 2 3 4 5 6 7 8 19
0.8 1.0 1.4 6.2 6.5 7.6 10.2 11.6
3.8 0.2 0.8 13.8 47.1 1.4 7.7 25.2
impurities 1
H in NH2 or in OH groups
1
H in NH groups
F NMR spectra. The spectrum shown in Figure 6 is reconstructed using four isotropic lines; the δiso and relative intensity values are gathered in Table 6. The line at -140 ppm presents a low relative intensity, 3%, and is assigned to an unknown impurity. Lines 1, 2, and 3 are at -160, -149.5, and -134.5 ppm, with respective intensities 18, 38, and 40%. From the site multiplicities, line 1 can be surely assigned to bridging F(1) in 8a sites. [HAm2TAZ]2 3 (AlF5) (II) presents one aluminum site. The 27 Al SATRAS spectrum, shown in Figure 7, evidences a main component and a small one related to an unknown impurity. The reconstruction is performed with two lines. The main component (line 1), assigned to phase II, appears to be well-defined in the isotropic dimension of the 3Q-MAS spectrum (Supporting Information); consequently, no structural disorder is evidenced in the Al environment. This conclusion rules out any noticeable substitution of fluoride ions by hydroxyl groups, in agreement with chemical analyses. Line 2 presents a relative intensity around 1.5%. Due to this low relative intensity, determination of reliable NMR parameters was not possible for the impurity. The NMR parameters leading to the best reconstruction are gathered in Table 7. 3. NMR Spectroscopy of [HAm2TAZ]2 3 (Al5F17) (IV). The [HAm2TAZ]2 3 (Al5F17) (IV) structure presents two aluminum sites; their contributions are clearly evidenced on the 3Q-MAS spectrum presented in Figure 8. The reconstructions of both 3Q-MAS and SATRAS spectra (Supporting Information) are carried out using the same set of parameters, asserting their reliability. Moreover, the relative intensity values issued from the SATRAS spectrum reconstruction are in agreement with the site multiplicities (Table 7). This allows attribution of line 1 to Al(2) and line 2 to Al(1). Isotropic chemical shift values are typical of AlF6, AlF5(OH), and AlF4(OH)2 species,38,39 indicating a low to moderate substitution rate of F- by OH- groups. Moreover,
Figure 10. Composition space of the Al(OH)3-Am2TAZ-HFaqethanol system at 190 C and [Al3þ] = 1.0 mol 3 L-1.
the shape of line 2 is characteristic of a well crystallized aluminum environnement. This indicates that, at least for this aluminum site, the F-/OH- substitution rate is low. The [HAm2TAZ]2 3 (Al5F17) (IV) structure presents six fluorine sites, with 8:8:8:4:4:2 multiplicities. The unique nonbridging fluorine site, F(2), has a multiplicity of 8, which implies that one line is expected with a relative intensity of 23.5% and a δiso value above -160 ppm.38 From the 19F (IV) spectrum, shown in Figure 9, left, two clusters of lines are discriminated, one with δiso values below -160 ppm and the other with δiso values above -160 ppm. The parameters extracted from the spectrum reconstruction are gathered in Table 6. Line 1 is attributed to an unknown impurity. From their δiso values, lines 2-5 are attributed to bridging fluorine atoms and correspond to a total relative intensity of 83%. Lines 6-10, attributed to nonbridging fluorine atoms, are needed to reconstruct the second cluster; the corresponding relative intensity, equal to 17% instead of the expected value, 23.5%, is indicative of a substitution of F- by OH- groups. This substitution accounts for the larger than expected number of lines used for the reconstruction;37-40 the substitution rate is probably small, but its accurate determination is impossible. It must be noted that the separation between bridging and nonbridging fluorine atoms is found at very similar values in II and IV: -156 ppm in II, -158 ppm in IV. Three sets of lines are distinguished in the 1H spectrum of [HAm2TAZ]2 3 (Al5F17) (IV), shown in Figure 9, right. Lines with δiso smaller than 5 ppm present relative intensities below 2% and are attributed to unknown impurities (Table 8). Lines 4-6 have δiso values between 6 and 8 ppm and are attributed to protons in NH2 or in OH groups, whereas lines 7-8, having δiso values above 10 ppm, are attributed to protons in NH groups. The protonated amine presents two
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Figure 11. X-ray thermodiffraction of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I).
Figure 12. Thermal analysis of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I).
NH2 and two NH groups. The relative intensity ratio between the sets of lines attributed to NH2 and NH groups close to 1.9 is found to be in good agreement with the expected value of 2 and confirms the protonation of the amine. 4. Evolution within the Composition Diagram and with the Temperature. Five formation domains, illustrated in Figure 10, are evidenced in the 2D composition space diagram of the Al(OH)3-Am2TAZ-HFaq-ethanol system at 190 C and [Al3þ] = 1 mol 3 L-1. The limits are approximately located, and phase mixtures exist at the boundaries. The variations of the fluoroaluminate formulations are compatible with the evolution of the compositions of the starting mixtures (Table 1). The factor governing the composition of the crystalline products in the composition space diagram is the [Am2TAZ]/[HF] ratio. When this ratio decreases, the inorganic sublattice dimensionality increases from 0D (I) to 1D (II and III) and to 2D (IV). This evolution agrees with the condensation of AlX6 units (X = F-, OH-, H2O). Condensation was also found to occur with the
temperature. A thermal analysis and an X-ray thermodiffraction study (Figure 11) of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I) were performed in the range 25-400 C. Thermodiffraction indicates that [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O (I) dehydrates on heating at 100-150 C; the loss of hydration and Al coordinated water molecules implies the condensation of the isolated AlF5(H2O) units to give trans-AlF5 chains in [HAm2TAZ]2 3 (AlF5) (II). A further condensation of these AlF5 chains leads to double chains in [HAm2TAZ]2 3 (Al2F8) (III) at 180 C and, finally, to R-AlF3 at 290 C. The resulting decomposition scheme is as follows: ½HAm2 TAZ2 3 ðAlF5 ðH2 OÞÞ 3 2H2 O f ½HAm2 TAZ2 3 ðAlF5 Þ
f 1 =2 ½HAm2 TAZ2 3 ðAl2 F8 Þ f R-AlF3 These preliminary results on the thermal behavior of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O were then compared with
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Figure 13. Thermogravimetric analysis of [HAm2TAZ]2 3 (AlF5) (II). Intensity of the infrared signals of HF (3790 cm-1), NH3 (965 cm-1), HCN (715 cm-1), and HNCO (2285 cm-1) and of the mass spectrometry signal of HCN (M/Z = 27) as a function of the temperature.
the results of TGA analysis (Figure 12): the total weight loss value (80.0%) is close to the theoretical value (77.6%) expected for the formation of AlF3. The first and second weight losses (10.2% and ≈6.3%) at ≈120 C and ≈200 C are also in rough agreement with the loss of two hydration water molecules (9.6%) and one Al coordinated water molecule (4.8%). However, the following weight loss values cannot absolutely fit with two further losses of HAm2TAZF entities (exp 34.9%, theor 63.4%) expected from the results of thermodiffraction and associated with the formation of AlF3 at T = 400 C. In order to explain this complex thermal behavior and to exclude the influence of an eventual hydrolysis due to water molecules or F-/OH- substitution, a complementary study, starting from synthetic [HAm2TAZ]2 3 (AlF5) (II), free of F-/OH- substitution (see NMR results), was undertaken, and the evolution of the gaseous species was followed by coupled infrared and mass spectroscopies. The thermogravimetric curve is given in Figure 13 together with the intensity of the infrared signals of HF (3790 cm-1), NH3 (965 cm-1), HCN (715 cm-1), and HNCO (2285 cm-1) and the intensity of the mass spectrometry signal of HCN (M/Z = 27). [HAm2TAZ]2 3 (AlF5) (II) is stable until ≈200 C (a small weight loss of 0.5% at ≈110 C can be attributed to surface adsorbed HF and/or water molecules). A continuous weight loss occurs above 200 C until a pseudoplateau is reached at ≈395 C and a final plateau at ≈800 C. Thermodiffractometry indicates that only one poorly crystalline compound is formed at the first plateau (R-AlF3); nonetheless, the experimental weight loss value, 41.7%, is very far from the theoretical value, 74.0%, associated with the loss of two expected HAm2TAZF entities. Then, it must be assumed that one extra amorphous solid is left at 395 C. Only the formation of NH3 and HF, indicative of the decomposition of the HAm2TAZF moieties, is detected by infrared and mass spectrometry below this temperature. Then, it was suspected that paracyanogen (CN)2n could be the cited amorphous solid; it is known that cyanogen (CN)2 polymerizes at
300-500 C to give a brown mass named paracyanogen (CN)2n. This assertion is confirmed by the FTIR analysis of the residual solid obtained at 400 C.41 Above 400 C, in the presence of water traces coming from the surrounding atmosphere, the paracyanogen polymer undergoes decomposition to give hydrogen cyanide HCN and isocyanic acid HNCO, which are also detected by infrared and mass spectroscopies. This evolution is in good agreement with the experimental weight loss of 31.0% (theor 32.3%). Then, the thermal decomposition of [HAm2TAZ]2 3 (AlF5) can be given by the following equations: - 10=3NH3 - 4=3N2 - 2HF
½HAm2 TAZ2 3 ðAlF5 Þ s f R-AlF3 þ H2 O - HCN - HNCO
þ 2ðCNÞ2 s f R-AlF3 Conclusion New phases, built up from AlF63- or AlF5(H2O)2- anions, amine cations, and, eventually, water molecules, are obtained from the reaction of Al(OH)3 with guanazole and aqueous HF in ethanol at 190 C. The inorganic network dimensionalities range from 0D to 2D. The condensation of the building AlF6 units to give successively AlF5 and Al2F8 chains in [HAm2TAZ]2 3 (AlF5) and [HAm2TAZ]2 3 (Al2F8) is found to occur with the increase of the HF concentration in the starting solutions and also with the increase of the temperature during the decomposition of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O. 19F NMR spectroscopy of [HAm2TAZ]2 3 (AlF5) excludes a significant F-/OH- substitution; moreover, the bridging and nonbridging fluoride anions are well differentiated. The thermal decomposition of [HAm2TAZ]2 3 (AlF5(H2O)) 3 2H2O gives successively [HAm2TAZ]2 3 (AlF5), [HAm2TAZ]2 3 (Al2F8), and, finally, R-AlF3. [HAm2TAZ]2 3 (AlF5) follows the same last decomposition steps. Above 250 C, the loss of HAm2TAZF leaves a solid residue of paracyanogen (CN)2n that is further decomposed and hydrolyzed by water traces above 400 C.
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Acknowledgment. The authors are very indebted to Pr. N. Mercier (Laboratoire IMM, UMR-CNRS 6200, Universite d’Angers) for the X-ray data collection of [HAm2TAZ]2 3 (Al2F8) and to Dr. S. Pascual (Laboratoire UCO2M, UMR-6011, Universite du Maine) for bibliography documents. The authors wish to thank Dr. N. Chigarev and D. Mounier (ENSIM, Le Mans) for SHG tests. Financial support from the TGE RMN THC Fr3050 for conducting the research is gratefully acknowledged. Supporting Information Available: Thermal decomposition of [HAm2TAZ]2 3 (AlF5): TGA-DTA analysis; comparison of FTIR spectra of the reference and emitted gaseous species at 156 C (HF), 295 C (NH3), 380 C (HCN), and 525 C (HNCO); FTIR spectrum of residual solid obtained from the decomposition of [HAm2TAZ]2 3 (AlF5) at 400 C. 27Al NMR spectrum of [HAm2TAZ]2 3 (Al5F17). 27Al 3Q-MAS spectrum of [HAm2TAZ]2 3 (AlF5). This material is available free of charge via the Internet at http:// pubs.acs.org.
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