Article pubs.acs.org/IC
Amino-Functionalized Layered Crystalline Zirconium Phosphonates: Synthesis, Crystal Structure, and Spectroscopic Characterization Marco Taddei,*,† Paola Sassi,‡ Ferdinando Costantino,‡ and Riccardo Vivani§ †
Laboratory for Catalysis and Sustainable Chemistry, Paul Scherrer Institute, 5232 Villigen-PSI, Villigen, Switzerland Department of Chemistry Biology and Biotechnology, University of Perugia, Via Elce di Sotto 8, 06123 Perugia, Italy § Department of Pharmaceutical Sciences, University of Perugia, Via del Liceo 1, 06123 Perugia, Italy ‡
S Supporting Information *
ABSTRACT: Two new layered zirconium phosphonates functionalized with amino groups were synthesized starting from aminomethylphosphonic acid in the presence of different mineralizers, and their structures were solved from powder Xray diffraction data. Their topologies are unprecedented in zirconium phosphonate chemistry: the first, of formula ZrH[F3(O3PCH2NH2)], prepared in the presence of hydrofluoric acid, features uncommon ZrO2F4 units and a remarkable thermal stability; the second, of formula Zr2H2[(C2O4)3(O3PCH2NH2)2]·2H2O, prepared in the presence of oxalic acid, is based on ZrO7 units with oxalate anions coordinated to the metal atom, which were never observed before in any zirconium phosphonate. In addition, the structure of another compound based on (2-aminoethyl)phosphonic acid is reported, which was the object of a previously published study. This compound has layered α-type structure with −NH3+ groups located in the interlayer space. All of the reported compounds were further characterized by means of vibrational spectroscopy, which provided important information on fine structural details that cannot be deduced from the powder X-ray diffraction data.
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INTRODUCTION Functionalization of solid supports with amine groups is a topic of investigation that has recently been boosted by the rapidly growing interest that solid supported amines (SSAs) are arousing in the field of carbon dioxide capture by means of solid sorbents, to replace the old, but still largely spread, technology based on the scrubbing by aqueous amine solutions.1 Another important field of application of SSAs is related to the wide range of possible uses in organic chemistry as heterogeneous catalysts or reagents for solid-phase synthesis.2 In addition, the presence of amino groups grafted on a solid matrix allows to perform anion exchange, a process that can be exploited for a wide range of purposes, notably the trapping of chromates.3 The two dominant approaches to prepare SSAs are based on the covalent grafting of amino groups to the surface of mesoporous silica supports, so as to have large surface areas,4 or to polymeric matrices.5 These platforms are rather stable, but also poorly crystalline; therefore, fine characterization at the atomic level is precluded. Aminofunctionalized metal−organic frameworks (MOFs) have recently received considerable attention for use in catalysis and CO2 capture, because they combine porosity and crystallinity, although their stability is not always exceptional.6 The use of zirconium phosphonates could be a convenient strategy to expand the range of materials for the aforementioned applications, owing to their outstanding chemical (they are highly insoluble in almost every solvent and stable in a wide range of pH) and thermal (they display high decomposition temperatures, up to 400−500 °C) properties.7 These character© 2016 American Chemical Society
istics have promoted the application of zirconium phosphonates in various fields, such as fillers for polymeric membranes, solid-state proton conductors, ion exchangers, and heterogeneous catalysts.8 To date, only one example of zirconium phosphonate functionalized with a primary amino group was reported, which was based on the commercial (2-aminoethyl)phosphonic acid (AEPA) ligand (Chart 1). The material (hereafter ZAEPACl) Chart 1. Molecular Structure of the Ligands Used in This Work
was initially obtained in hydrochloride form and was subsequently titrated with NaOH to yield the amine form (ZAEPA), which showed to be able to intercalate alkyl carboxylate anions.9 The structure of ZAEPACl was recently solved from powder X-ray diffraction (PXRD) data, and it is reported herein. Other compounds based on AEPA in Received: April 15, 2016 Published: June 2, 2016 6278
DOI: 10.1021/acs.inorgchem.6b00943 Inorg. Chem. 2016, 55, 6278−6285
Article
Inorganic Chemistry
Zirconium and phosphorus contents of samples were obtained by inductively coupled plasma optical emission spectroscopy using a Varian Liberty Series II instrument working in axial geometry, after mineralization of the samples with hydrofluoric acid. Fluorine content was determined as fluoride by ion chromatography: ∼0.1 g of sample was refluxed for 3 h with 10 mL of 1 M NaOH up to complete hydrolysis. The resulting solution was filtered, properly diluted, and analyzed with a Dionex series 2000 i/sp instrument, using an IonPack AS4A column and a buffer solution, of the following composition: 1.7 × 10−3 M in NaHCO3 and 3.5 × 10−3 M in Na2CO3 as eluent. PXRD patterns for structure determinations and Rietveld refinements were collected with a PANalytical X’PERT PRO diffractometer equipped with an X’Celerator solid-state fast detector in the 3−100 2θ range and with a 60 s/step counting time. Thermogravimetric analyses (TGA) were performed using a Netzsch STA490C thermoanalyzer under a 20 mL min−1 air flux with a heating rate of 5 °C min−1. Raman spectra were excited using the 632.8 nm radiation from an He−Ne laser; the laser power on the sample was always less than 5 mW. Backscattering illumination and collection of the scattered light were made through an Olympus confocal microscope MOD BX40 (50× and 100× objectives). When an 1800 lines per millimeter grating was used, a spectral resolution of ∼2 cm−1 was achieved. Spectral measurements were made with continuous scans in the range of 200− 1800 cm−1, exposure times in the range of 30−60 s, and 10 accumulations. Detection of scattered light was accomplished by a 1024 × 128 CCD array, model Spectrum-One by Horiba−Jobin− Yvon. Calibration of the spectrometer was accomplished using the Raman lines of a polystyrene standard. Mid-Fourier transform infrared (FT-IR) measurements were performed with a Bruker TENSOR27 spectrophotometer equipped with a globar source, a high-throughput patented RockSolid cube corner interferometer, a deuterated L-alanine tryglycine sulfate detector, and a KBr beamsplitter. Transmission spectra were collected at room temperature in the 400−4000 cm−1 range. Each spectrum was the average of 50 scans, measured with a resolution of 2 cm−1. The samples were dispersed into anhydrous KBr pellets. Structure Determination and Refinement for ZAMPAF, ZAMPAOX, and ZAEPACl. A preliminary profile fit was conducted on the diffraction patterns of ZAMPAF, ZAMPAOX, and ZAEPACl using a split Pearson VII profile function. The position of the first 20 lines (Kα1 maxima) were determined and used for indexing with the TREOR9012 program. Space groups were assigned on the basis of a systematic comparison of the number of peaks found and the number of possible peaks, within all space groups of the respective crystal symmetry, using the Chekcell13 program. For ZAEPACl, the best group was C2/c, but P21/c was preferred, because it allowed to better model the interlayer disorder. The structures were solved using global optimization methods (FOX14 program). The FOX program is able to optimize in direct space the molecules described in terms of bond lengths and angles. Optimization is performed over a cost function, in our case the integrated Rwp. The reverse Montecarlo parallel tempering algorithm15 was used, and antibump distances between metals and other atoms were also added. A ZrO6 octahedron with distances Zr−O of 2.05 Å with standard deviations of 0.05 Å was used. The molecules of AMPA and AEPA ligands were described in terms of bond lengths and angles set at their literature values with standard deviations of 0.15 Å and 10°, respectively. Structural refinement was performed using the Rietveld method implemented in the GSAS16 program. Cell parameters, sample displacements, background, and profile were first refined, then atomic coordinates and atomic displacement parameters were also refined. Soft restraints were used for bond distances and angles. The statistical weight of these restraints was decreased as the refinement proceeded. Atomic displacement parameters (ADPs) for ZAMPAF were not refined and set at a value of 0.025 Å2. ADPs for ZAMPAOX were refined constraining the program to apply the same shift except for Zr and P atoms, which were refined independently. ADPs for ZAEPACl
combination with divalent metals have been described in the literature.10 In addition, the present work reports on the synthesis and characterization of two new layered zirconium phosphonates based on the aminomethylphosphonic acid (AMPA) ligand (Chart 1). This ligand was also previously combined with some divalent metals.11 The two compounds were obtained by using different mineralizers, and their crystal structures were also solved from PXRD data, revealing that they are based on novel topologies never observed to date in zirconium phosphonates. The compound of formula ZrH[F3(O3PCH2NH2)] (hereafter ZAMPAF) was synthesized in the presence of hydrofluoric acid, while the compound of formula Zr2H2[(C2O4)3(O3PCH2NH2)2]·2H2O (hereafter ZAMPAOX) was prepared in the presence of oxalic acid. Thorough characterization by means of vibrational spectroscopy gave an insight on some fine structural details, primarily the protonation state of the amino groups, helping to improve the understanding of the overall crystal structures.
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EXPERIMENTAL SECTION
Chemicals. ZrOCl2·8H2O was a Merck Pro Analysi product. AMPA was purchased from Epsilon Chimie. All of the other chemicals were purchased from Sigma-Aldrich. Synthesis of ZrH[F3(O3PCH2NH2)] (ZAMPAF). ZAMPAF was prepared as follows: a clear solution of AMPA (333 mg, 3 mmol) in 45 mL of 1.3 M HCl was added to a solution of ZrOCl2·8H2O (644 mg, 2 mmol) in HF 2.9 M (4.8 mL, 14 mmol). This mixture was maintained in a closed plastic vessel at 80 °C for 2 d. The white precipitate was filtered under vacuum, washed with water, and dried at 80 °C, and 320 mg of product was recovered. Yield = 62% (calculated on the basis of Zr). Analysis: Calcd for CH5NO3F3PZr (1) C = 4.7%, H = 1.9%, N = 5.4%, F = 22.1%, P = 12.0%, Zr = 35.3%. Exp: C = 5.6%, H = 2.2%, N = 5.4%, F = 22.2%, P = 12.1%, Zr = 35.9%. Synthesis of Zr2H2[(C2O4)3(O3PCH2NH2)2]·2H2O (ZAMPAOX). ZAMPAOX was prepared as follows: a clear solution of AMPA (222 mg, 2 mmol) in 10 mL of water was added to a solution of ZrOCl2· 8H2O (322 mg, 1 mmol) and oxalic acid (1 g, 8 mmol) in 10 mL of water. This mixture was maintained in a closed plastic vessel at 80 °C for 2 d. The white precipitate was filtered under vacuum, washed with water, and dried at 60 °C, and 190 mg of product was recovered. Yield = 60% (calculated on the basis of Zr). Analysis: Calcd for C4H7NO10PZr (2) C = 13.7%, H = 2.0%, N = 4.0%, P = 8.8%, Zr = 25.9%. Exp: C = 13.4%, H = 2.2%, N = 4.4%, P = 8.7%, Zr = 25.8%. Synthesis of Zr(O3PCH2CH2NH3)2Cl2 (ZAEPACl). ZAEPACl was prepared by slightly modifying the procedure reported in ref 9: a clear solution of AEPA (500 mg, 4 mmol) in 40 mL of 3 M HCl was added to a solution of ZrOCl2·8H2O (644 mg, 2 mmol) in HF 2.9 M (6.2 mL, 18 mmol). The ratio Zr/P/F/Cl was 1:2:9:60. This mixture was maintained in a closed plastic vessel at 80 °C for 2 d. The white precipitate was centrifuged, washed two times with water, and dried at 80 °C, and 400 mg of product was recovered. Yield = 49% (calculated on the basis of Zr). H/D exchange on ZAEPACl was performed by soaking the powder in D2O overnight. The material was then vacuum-filtered and dried. All of these steps were performed under protected atmosphere in a glovebox. Analysis: Calcd for C4H14N2O6Cl2P2Zr (3) C = 11.7%, H = 3.4%, N = 6.8%, P = 15.1%, Zr = 22.2%. Exp: C = 11.9%, H = 3.2%, N = 6.7%, P = 15.7%, Zr = 21.8%. Analytical and Instrumental Procedures. Carbon, nitrogen, and hydrogen contents were determined by elemental analysis using an EA 1108 CHN Fisons instrument. 6279
DOI: 10.1021/acs.inorgchem.6b00943 Inorg. Chem. 2016, 55, 6278−6285
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Inorganic Chemistry were refined constraining the program to apply the same shift. At the end of the refinement, the shifts in all parameters were less than their standard deviations. Crystal data and details of the refinement for ZAMPAF, ZAMPAOX, and ZAEPACl are reported in Table 1. Figure 1 shows the final Rietveld and difference plots.
Table 1. Structural Parameters and Refinement Details for ZAMPAF, ZAMPAOX, and ZAEPACl compound
ZAMPAF
ZAMPAOX
ZAEPACl
empirical formula formula weight crystal system space group a, Å b, Å c, Å α, deg β, deg γ, deg volume, Å3 Z calc. density/g cm−3 pattern range, 2θ, deg no. of data no. of reflections no. of variables no. of restraints Rp Rwp RF2 χ
CH5NO3F3PZr
C4H7NO10PZr
C4H14N2O6Cl2P2Zr
258.20 triclinic P1̅ 5.4103(2) 5.79443(9) 10.3622(3) 87.474(2) 78.441(3) 89.239(2) 317.95(1) 2 2.70
351.23 monoclinic C2/c 24.4652(7) 7.8268(2) 12.3063(3)
410.13 monoclinic P21/c 9.3484(8) 5.3938(4) 29.593(1)
118.591(2)
102.988(7)
2069.12(9) 8 2.26
1454.0(1) 8 1.87
10−100
6−120
3−140
5294 655
6706 1533
8058 2619
51 37
78 40
84 66
0.046 0.064 0.086 4.34
0.034 0.046 0.056 3.08
0.061 0.086 0.123 5.3
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RESULTS AND DISCUSSION Description of the Structures. Figure 2 shows the structure of ZAMPAF viewed along the a- and the c-axes and the structure of a single layer. It has a lamellar structure with the layers lying in the ac plane and separated by a 5.79 Å distance. These layers can be considered as built from single chains running along the a-axis direction and constituted of PO3C tetrahedra and ZrO4F2 octahedra, connected via ZrO2F4 octahedra linking adjacent chains in the c-axis direction. The chain structure formed represents a common way of assembling Zr octahedra and P tetrahedra and was already observed in other compounds reported in the literature.8 However, the octahedra built around the central Zr1 atom, consisting of four fluorine atoms and just two oxygen atoms, were never observed before in any compound of the same class. The resulting structure displays an unprecedented topology. The phosphonate group is tridentate, connecting three different zirconium atoms: two oxygen atoms (O2 and O4) are bonded to Zr2, thus allowing the development of the chains in the c-axis direction, whereas O3 is bonded to Zr1. The NH2 groups occupy the interlayer space and are involved in a network of hydrogen bonds with five negatively charged fluorine atoms (distances ranging from 2.81 to 3.03 Å): the high number of noncovalent interactions suggests that a tautomeric equilibrium could take place, with
Figure 1. Final Rietveld and difference plots for ZAMPAF (a), ZAMPAOX (b), and ZAEPACl (c).
the proton shared between the nitrogen atom and the surrounding fluorine atoms (Figure 3). This supposition is well-supported by the FT-IR and Raman data discussed herein. Figure 4 shows the structure of ZAMPAOX viewed along the b- and the c-axes. This compound has a layered structure, and it also features a previously unobserved topology. The layers are constituted from the connection of ZrO7 polyhedra, PO3C tetrahedra, and oxalate groups. The presence of ZrO7 polyhedra is a peculiar feature of this compound, since zirconium is normally octahedral in similar systems. These polyhedra are constituted as follows (Figure 5): the apical oxygen atoms (O7 and O9) belong to two different PO3C groups; of the five equatorial oxygen atoms, one belongs to another PO3C group (O8), two belong to two different carboxylate groups of a bidentate oxalate ligand (O2 and O4), and the last two belong to the same carboxylate group of a tetradentate oxalate ligand (O5 and O6). The O−Zr−O bond angles in the equatorial plane are all comprised between 70 and 75 degrees. The phosphonic group is tridentate and is bonded to three different zirconium 6280
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Figure 3. Network of hydrogen bonds (red dashed lines) involving the amino group (blue) and the fluorine atoms (yellow) in ZAMPAF.
Figure 2. Polyhedral representation of the structure of ZAMPAF viewed along the a- (a) and the c-axes (b) and the structure of a single layer (c; the organic part of the framework is omitted). ZrO4F2 octahedra are represented in purple, ZrO2F4 octahedra are represented in gray, and PO3C tetrahedra are represented in green. Nitrogen atoms are represented in blue. Hydrogen bonds are not shown.
atoms. The oxalate ligands show two different types of connectivity: one (marked as A in Figure 5) is bidentate, connecting to the same zirconium atom through both of its carboxylate groups, with the two free oxygen atoms pointing toward the interlayer region and involved in a network of hydrogen bonds with the water molecules and the NH2 groups (Figure 6); the other one (marked as B in Figure 5) is
Figure 4. Polyhedral representation of the structure of ZAMPAOX viewed along the b- (a) and the c-axes (b). ZrO7 octahedra are represented in purple, and PO3C tetrahedra are represented in green. Nitrogen atoms are represented in blue. Hydrogen bonds are not shown. 6281
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Inorganic Chemistry
Figure 5. Portion of the connectivity of ZAMPAOX evidencing the different bonding modes of the oxalate ligands, marked as A and B. Zirconium atoms are represented in purple, phosphorus atoms in green, oxygen atoms in red, carbon atoms in gray.
Figure 7. Polyhedral representation of the structure of ZAEPACl viewed down the b-axis. ZrO6 octahedra are represented in purple, and PO3C tetrahedra are represented in green. Nitrogen atoms are represented in blue, chlorine atoms are represented in teal.
Figure 6. Network of hydrogen bonds (represented as red dashed lines) existing among the amino groups (represented in blue), the oxalate groups of type A and the intercalated water molecules in ZAMPAOX.
tetradentate, lying over an inversion center (located on the middle of the C−C bond) and connecting two crystallographically equivalent zirconium atoms. The aminomethyl groups point toward the interlayer region and alternate with the oxalate groups marked as A. Similarly to ZAMPAF, also in ZAMPAOX the acidic hydrogen atoms are shared between the amino groups and other groups. In this case these are the free C−O groups belonging to the oxalate ligand of type A, as shown by FT-IR data. Figure 7 shows the structure of ZAEPACl, viewed along the b axis. This compound shows the typical α-layered structure derived from zirconium phosphate,17 with the protonated aminoethyl groups located in the interlayer space. The chloride ions also reside in the interlayer space, thus forming pseudolayers where they alternate with the amino groups: in this arrangement, each anion is surrounded by five amino groups that, in turn, are surrounded by five anions. This minimizes the electrostatic repulsions between ions of the same charge and consequently allows the disposition of the charged groups in a bilayer arrangement. Thermal Behavior. The TG curves of ZAMPAF, ZAMPAOX, and ZAEPACl are reported in Figure 8. ZAMPAF shows an excellent thermal stability and starts losing weight at ∼500 °C, when decomposition of the framework occurs in two steps: the first accounts for the 19.5% of the total weight and is likely due to the oxidation of the organic part of the compound; the second weight loss (15.4%) is larger than the calculated loss (5.4% for the single step, 24.9% total), if we suppose that the final product is an equimolar mixture of ZrO2 and ZrP2O7 (as observed in similar
Figure 8. TG curves of ZAMPAF (black), ZAMPAOX (red), and ZAEPACl (blue).
compounds where the P/Zr ratio is 1).8d A comparison of analyses performed at different heating rate on the same batch (see Figure S1) shows that the first step of weight loss is always the same, whereas the second step is variable from ∼10% up to ∼15%. We were not able to give a reliable explanation for this behavior, because to the best of our knowledge there are no compounds that could be taken as adequate terms of comparison. ZAMPAOX shows a first weight loss starting at ∼100 °C, due to the loss of the intercalated water molecules. The observed value (5.3%) is in good agreement with the calculated one (5.1%). The decomposition of the organic part of the framework starts a few degrees before 400 °C, when a rapid weight loss takes place, followed by another step beginning at 800 °C. At the end of the analysis, when the temperature is 1200 °C, an equimolar mixture of ZrO2 and ZrP2O7 is left, and the observed weight loss is 46.8% (calculated: 44.7%). The TG curve of ZAEPACl was already reported and discussed in ref 9, but we reported it again for the sake of completeness. 6282
DOI: 10.1021/acs.inorgchem.6b00943 Inorg. Chem. 2016, 55, 6278−6285
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Inorganic Chemistry Vibrational Spectroscopy. An important contribution to the characterization of the reported compounds comes from the analysis of vibrational spectral features. FT-IR and Raman spectra of different samples are shown in Figures 9−12. The
Figure 10. IR spectra of ZAEPACl: spectral profile of light (red) and deuterated (black) compound. Because of the isotopic substitution the intensities of bands of the light −NH3+ group (★) are reduced, and those of deuterated species appear (■). This is visible both in the region of NH stretching modes (a) and in the region of deformation bands (b).
Figure 9. IR spectra of ZAMPAF (1), ZAMPAOX (2), and ZAEPACl (3) in the 700−1800 cm−1 region. NH3+ deformation bands (★) are detected in all the samples. IR spectra of ZAMPAF and ZAMPAOX also evidence the −NH2 deformation band, respectively, at 1613 and 1618 cm−1 (●). The intense and broad bands at 1408, 1670, and 1740 cm−1 in the spectrum of ZAMPAOX are assigned to the complex system of oxalate ligands.
has not the doublet shape of corresponding bands of the light compound, and the low-frequency side of the spectrum is enriched by the appearance of multiple bands (see Figure 10b). The same NH3+ deformation bands of ZAEPACl are also revealed in the IR spectra of ZAMPAF and ZAMPAOX. Figure 9 shows that for ZAMPAF and ZAMPAOX the NH 3 + deformations are broader and slightly blue-shifted. A reduction of NH3+ content is probably observed for these compounds: this is suggested by the presence of the 1620 cm−1 absorption, characteristic of NH2 group.10f In ZAMPAOX this NH2 inplane deformation is partially overlapped to the bands assigned to CO groups. This compound has a complex system of oxalate ligands giving rise to the strong absorptions at 1670 and 1408 cm−1 (asymmetric and symmetric stretchings of bidentate units), and to the 1740 cm−1 signal assigned to the stretching of noncoordinated CO bonds. The evidence of a reduced NH3+ content in ZAMPAF and ZAMPAOX also emerges from analysis of the high-frequency region of IR spectra: as shown in Figure 11, a sensitive blue shift of N−H stretching vibrations with respect to ZAEPACl is observed for these compounds and particularly for ZAMPAF. This shift is consistent with an increase of average strength of N−H bond on increasing the fraction of NH2 groups. In ZAMPAF the NH3+ stretching modes are probably hidden by the strong and broad absorption at 3094 cm−1 that is associated with the presence of HF units, as recently observed in similar zirconium phosphonates containing fluorine.8e,f The coordination of fluorine to Zr atoms in ZAMPAF is clearly suggested by the presence of characteristic signals in the 500−
presence of strong absorptions at 950−1100 cm−1, characteristic of P−C and P−O stretching motions, is observed for all the compounds. A number of intense and distinct spectral components help define the state of alkylamino groups in the layer. IR absorptions of C−NH2 and C−NH3+ derivatives can be easily recognized in the 1300−1800 cm−1 range of our spectra (see Figure 9). The presence of −NH3+ groups is clearly evidenced by the sharp bands at 1500 and 1280 cm−1 in the spectrum of ZAEPACl. This assignment, in perfect agreement with literature data,10f,11−16,17a,18 is also confirmed by results of H/D isotopic substitution (Figure 10). The isotopic exchange is likely to be effective on amine groups located on the surface of zirconium phosphonate layers, thus leading at least to the partial substitution of NH3+ protons. Such substitution is testified by the decrease of intensity for the 1500 (NH3+ asymmetric deformation) and 1280 (NH3+ symmetric deformation) cm−1 bands in Figure 10b. A similar spectral change is also observed in the high-frequency side of IR profile (Figure 10a): a decrease of relative intensities at 3000 and 3100 cm−1 (NH3+ stretching modes) is balanced by the increase of a new signal at 2260 cm−1 ca. (N-D stretching). Because of the mild conditions adopted for the isotopic exchange and because of the compact and highly crystalline structure of ZAEPACl, mixed structures (NH2D+; NHD2+) are probably formed. For this reason the new band at 2260 cm−1 6283
DOI: 10.1021/acs.inorgchem.6b00943 Inorg. Chem. 2016, 55, 6278−6285
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Inorganic Chemistry
Table 2. Zr−F Stretching Modes: IR and Raman Frequencies vibrationa
compound ZAMPAF
ν ν ν ν δ
s (F−Zr−F: axial ligand) as (F−Zr−F: axial ligand) s (ZrF4) as (ZrF4) (ZrF4)
IRb (cm−1)
Ramanb (cm−1)
n.a. 530.0 n.a. 570.0 n.a.
541.0 n.a. 581.0 n.a. 562.0
ν s: symmetric stretching; ν as asymmetric stretching; δ: bending mode. bn.a.: nonactive.
a
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CONCLUSIONS Two new layered zirconium phosphonates displaying unprecedented topologies were synthesized starting from AMPA using different mineralizing agents. Their structures, along with that of another derivative based on AEPA that shows the typical α-layered structure, were solved from laboratory PXRD data. Information obtained from vibrational spectroscopy gave further insight on some fine structural details that cannot be described by using solely PXRD data. The combination of different characterization techniques provided a comprehensive picture of the interactions existing in the materials, especially those involving the amino groups placed in the interlayer region. The deep characterization of the reported materials can represent a key point for understanding their behavior in the applications for which they will be employed. Investigation is currently in progress on their utilization as reactive stationary phases in continuous flow catalytic synthesis of pharmaceutically interesting intermediates.
Figure 11. IR spectra of ZAMPAF (1), ZAMPAOX (2), and ZAEPACl (3) in the 2200−4000 cm−1 region.
600 cm−1 region of IR and Raman spectra (Figure 12): the presence of both ZrO4F2 and ZrO2F4 octahedra is confirmed by the assignments shown in Table 2.
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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.inorgchem.6b00943. Tables with atomic coordinates, bond lengths and angles, additional figure (PDF) X-ray crystallographic information (CIF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS M.T. gratefully acknowledges Regione Umbria-POR UMBRIA FSE 2007-2013 for funding. REFERENCES
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Figure 12. Raman (a) and IR (b) spectra of ZAMPAF in the 400−650 cm−1 region. The assignment of Zr−F vibrations (●) is shown in Table 2. 6284
DOI: 10.1021/acs.inorgchem.6b00943 Inorg. Chem. 2016, 55, 6278−6285
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DOI: 10.1021/acs.inorgchem.6b00943 Inorg. Chem. 2016, 55, 6278−6285
