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Synthesis and characterization of the one-dimensional zincophosphate Mu-22: [Zn(HPO4)2]8[C5H13N2]8• 8 H2O
Solid State Sciences 4 (2002) 135–141 www.elsevier.com/locate/ssscie
Synthesis and characterization of the one-dimensional zincophosphate Mu-22: [Zn(HPO4 )2 ]8[C5 H13 N2]8 •8 H2O Sandrine Fleith a , Ludovic Josien a , Angélique Simon-Masseron a,∗ , Volker Gramlich b , Joël Patarin a a Laboratoire de Matériaux Minéraux, ENSCMu, Université de Haute-Alsace, UMR-CNRS 7016,
3 rue Alfred Werner, F-68093 Mulhouse cedex, France b Laboratorium für Kristallographie, ETH-Zentrum, CH-8092 Zürich, Switzerland
Received 26 June 2001; received in revised form 19 September 2001; accepted 1 October 2001
Abstract A new zincophosphate, Mu-22, has been synthesized under mild conditions in water medium in the presence of 1-methylpiperazine as organic template. The structure was determined by single crystal X-ray diffraction. The inorganic framework consists of infinite chains built from (Zn2 P2 O4 ) four-membered rings sharing their Zn atoms. Two symmetry equivalent chain directions along [1 1 0] and [1 1 0] directions are observed. The anionic chains make strong hydrogen bond interactions with the protonated 1-methylpiperazine. [Zn(HPO4 )2 ][C5 H13 N2 ]•H2 O crystallizes in the monoclinic system, space group C2/c (No 15) with cell parameters: a = 13.917(13), b = 9.091(14), c = 20.49(2) Å and β = 102.36(8)◦ , Z = 8. 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Zincophosphate; 1-methylpiperazine; Single crystal structure
1. Introduction Over the past few years, the organic species used in the zincophosphate system has been extensively studied in order to discover new compounds with open frameworks. This extremely reactive system offers large possibilities to work under mild (room temperature (RT)) or drastic (high temperature, high pressure) conditions. A large variety of new microporous zincophosphates with one-, two- or three-dimensional structure has already been reported in the literature [1]. In particular the zincophosphate ND-1, synthesized by Yang and Sevov in 1999, is one of the five microporous solids with the largest rings (24 T, T = Zn, P) [2]. Amines derived from piperazine are very reactive templates for microporous phosphates. They allow to synthesize zincophosphates [3–5], aluminophosphates [6], cobalt phosphates [7] and gallophosphates [8,9]. But their role as structure-directing agents is not understood. One-dimensional framework zincophosphates are stabilized by van der Waals interactions [10] or by strong hy* Correspondence and reprints.
E-mail address: [email protected] (A. Simon-Masseron).
drogen bondings with the organic template [11]. These 1-D structures generally contain tetrahedral 4-rings connected to each other and leading to infinite corner-shared chains or edge-shared ladders [3,10,12–14]. Only one 1-D zincophosphate synthesized by Harrison et al. [15] is built from tetrahedral 3-rings. These 1-D zincophosphates are synthesized in aqueous medium at various temperatures (RT–180 ◦ C) using different amines as template. At the present time their mechanism of formation is not established. This paper reports the synthesis and the crystal structure determination of a new 1-D zincophosphate [Zn(HPO4)2 ][C5 H13 N2 ]•H2 O named Mu-22 obtained in aqueous medium using 1-methylpiperazine as template. The characterization by 31 P and 13 C solid state NMR spectroscopy is also reported. 2. Experimental section 2.1. Synthesis Mu-22 was prepared at room temperature from a gel containing 1-methylpiperazine (MPIP) as structure-directing agent. Typically, the synthesis was made as follows: 1.04 g
1293-2558/02/$ – see front matter 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 1 2 9 3 - 2 5 5 8 ( 0 1 ) 0 1 2 2 2 - 5
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Fig. 1. Scanning electron micrographs of some crystals of the zincophosphate Mu-22.
of zinc oxide (Carlo Erba, 99%) was stirred until complete dissolution in a mixture of 10.40 g of deionized water and 5.80 g of orthophosphoric acid (Labosi, 85%). 2.55 g of 1-methylpiperazine (Aldrich, 99%) were then added and the mixture was stirred again for one hour. The initial pH was 4. The final molar composition of the gel is 0.5 ZnO : 1 P2 O5 : 25 H2 O : 1 MPIP. The mixture placed in a polypropylene bottle was kept at 28 ◦ C for 13 days. The washing procedure appears to be critical because this new zincophosphate partially transforms into a non-identified compound on washing with water and ethanol. Therefore the large translucent crystals obtained (average dimensions: 850 × 650 × 200 µm3 , Fig. 1) were filtered and dried in air at RT. 2.2. Characterization The powder XRD patterns were obtained with Cu Kα1 radiation on a STOE STADI-P diffractometer equipped with a curved germanium (1 1 1) primary monochromator and a linear position sensitive detector. High-temperature Xray diffraction was performed using a variable temperature photographic chamber (Huber, model 631), attached to the same X-ray generator (Cu Kα1 radiation) in which the sample was kept in flowing dry air. XRD patterns were collected over a temperature range 30–750 ◦ C. The morphology and average size of the crystals were determined by scanning electron microscopy using a Philips XL30 microscope. Elemental analysis has been realized by Induced Coupled Plasma technique using Atomic Energy Spectroscopy (ICP AES) for Zn and P, and by coulometric and catharometric methods for C and N quantifications, respectively. Thermogravimetric (TGA) and differential thermal (DTA) analyses were performed under air on a Setaram Lab-
sys thermoanalyser with a heating rate of 5 deg min−1 from 10 to 750 ◦ C. The 13 C CP MAS NMR spectrum was recorded on a Brüker MSL 300 spectrometer and the 31 P MAS and DEC MAS NMR spectra on a Brüker DSX 400 spectrometer. 31 P T relaxation time was measured using the inversion1 recovery pulse sequence with a recycle delay of 1443 s (π/2 = 4.65 µs). The other acquisition parameters are gathered in Table 1. XRD studies on single crystal have been performed by the Weissenberg method on a PHILIPS PW1140 diffractometer with a nickel filtered Cu Kα radiation (λ = 1.54178 Å). For the structure determination, a crystal was selected from the batch and mounted on a SYNTEX P21 4-circle diffractometer. 2428 reflections were recorded from 2.7 up to 25.2◦ in θ using Mo Kα radiation in omega scan mode. 1904 ones fulfilled the condition I > 2σ (I ). A summary of the experimental and crystallographic data is reported in Table 2. The structure was solved by direct methods using S HELXS -86 [16] and refined using S HELXL -93 [17]. All non-hydrogen atoms were refined with anisotropic displacement parameters (not reported). The refinement con (R1 = Fo | − |Fc / |Fo |) and verged to R1 = 0.0268 wR2 = 0.0740 (R2 = { w(Fo2 − Fc2 )2 / w(Fo2 )2 }1/2 ) for 1904 reflections (I > 2σ (I )). The atomic coordinates and isotropic displacement parameters are given in Table 3. Selected bond lengths and angles are reported in Table 4.
3. Results and discussion According to the elemental analyses the as-synthesized Mu-22 sample has the following composition (wt%): Zn, 17.49; P, 16.11; C, 15.79; N, 7.25. It is in good agreement with the crystal structure determination: Zn, 17.24; P, 16.45; C, 15.93; N, 7.43. The Zn/P molar ratio is close to 0.5, as previously observed for other zincophosphates [1,3,11]. The thermal behavior of Mu-22 was investigated by hightemperature XRD and TG/DTA thermal analyses. The TG and DTA curves of as-synthesized Mu-22 are given in Fig. 2. Until 200 ◦ C, the desorption of water induced a weight loss close to 4.5% which is associated to a broad endothermic peak on the DTA curve. Between 200 and 650 ◦ C exothermic peaks attributed to the partial removal of the organic species are observed (weight loss: ∼ 29%). The thin endothermic
Table 1 Recording conditions of the MAS NMR spectra
Chemical shift standard Frequency (MHz) Pulse width (µs) Flip angle Contact time (ms) Recycle time (s) Spinning rate (Hz) Scans number Decoupling power (kHz)
13 C CP MAS
31 P MAS with high-power decoupling
31 P MAS
TMS 75.47 3.85 π/2 1 5 4000 242 –
85% H3 PO4 161.98 1.2 π/6 – 60 8000 32 58
85% H3 PO4 161.98 1.55 π/6 – 240 10000 4 –
S. Fleith et al. / Solid State Sciences 4 (2002) 135–141
Table 2 Crystal data and structure refinement for Mu-22 Empirical formula
[Zn(HPO4 )2 ][C5 H13 N2 ]•H2 O
Formula weight Wavelength (Å) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) β (deg) Volume (Å3 ) Z Density (calculated) Absorption coefficient (mm−1 ) F (000) Crystal size (mm3 ) Diffractometer θ range (deg) Index ranges
377.52 0.71073 Monoclinic C2/c
Reflections collected Independent reflections Independent reflections with I > 2σ (I ) Absorption correction Refinement method Data/restraints/parameters Goodness-of-fit on F 2 Final R indices [I > 2σ (I )] R indices (all data) Extinction coefficient Largest diff. peak and hole (e A−3 )
13.917(13) 9.091(14) 20.49(2) 102.36(8) 2532(5) 8 1.981 2.237 1552 0.1 × 0.1 × 0.1 SYNTEX P21 4-circles 2.70 to 25.18 0 h 16, 0 k 10, −24 l 23 2428 2251 [Rint = 0.0269] 1904 None Full-matrix least-squares on F 2 2251/4/189 0.853 R1 = 0.0268, wR2 = 0.0740 R1 = 0.0304, wR2 = 0.0751 0.0057(4) 0.736 and −0.344
peak centered at 280 ◦ C probably corresponds to the removal of water arising from dehydroxylation reactions due to the presence of terminal P–OH groups (weight loss: 4.5%). After heating the sample at 750 ◦ C, a grey residue is obtained revealing the presence of residual organic species. The latter can be eliminated by calcination of the sample at 1000 ◦ C in air. The weight loss is close to 3%. From high-temperature XRD analysis, the structure of Mu-22 collapses at 170 ◦ C, Zn(PO3 )2 (ICDD 30-1488) crystallizing at 480 ◦ C. After heating at 670 ◦ C, the sample is amorphous. The total weight loss observed is close to 41 wt%, which is in good agreement with the total weight loss calculated by the crystal structure determination (40.8 wt%). Taking into account the whole of these analyses, the following unit cell formula can be proposed for the zincophosphate Mu-22: [Zn(HPO4)2 ]8 [C5 H13 N2 ]8 •8 H2 O. The experimental powder XRD pattern of Mu-22 (Fig. 3(a)) can be indexed in the monoclinic system with the following cell parameters: a = 14.0310(3), b = 9.1406(14), c = 20.642(3) Å and β = 102.242(16)◦. These results were confirmed by the Weissenberg method (a ∼ 13.8–14.0, b ∼ 9.0–9.1, c ∼ 19.3–20.0 Å and β ∼ 102◦ ). The extinction rules observed suggest the two possible space groups C2/c and Cc. For comparison the simulated XRD pattern calcu-
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Table 3 Atomic coordinates and equivalent isotropic displacement parameters (Å2 ) for Mu-22a Atom Zn P1 P2 O1 O2 O3 O4 O5 O6 O7 O8 Ow N1 N4 C2 C3 C5 C6 C7
x
y
z
Ueq
0.3683(1) 0.3604(1) 0.4452(1) 0.4328(1) 0.3860(1) 0.2582(1) 0.3708(2) 0.4424(1) 0.5474(1) 0.3951(1) 0.3819(1) 0.3743(2) 0.3795(2) 0.3200(2) 0.3302(2) 0.3516(2) 0.3656(2) 0.3465(2) 0.3621(2)
0.1270(1) 0.3632(1) −0.1180(1) 0.4854(2) 0.2909(2) 0.4251(2) 0.2480(2) −0.0069(2) −0.1714(2) −0.0618(2) −0.2533(2) 0.9402(3) 0.5448(2) 0.7448(2) 0.4923(3) 0.5934(3) 0.7987(3) 0.6960(3) 0.4437(3)
0.4734(1) 0.5918(1) 0.5870(1) 0.6169(1) 0.5318(1) 0.5791(1) 0.6489(1) 0.6402(1) 0.5878(1) 0.5181(1) 0.6001(1) 0.7568(1) 0.3293(1) 0.4212(1) 0.3820(1) 0.4414(1) 0.3671(1) 0.3085(1) 0.2714(2)
0.016(1) 0.015(1) 0.015(1) 0.025(1) 0.028(1) 0.030(1) 0.038(1) 0.027(1) 0.024(1) 0.026(1) 0.031(1) 0.044(1) 0.021(1) 0.021(1) 0.027(1) 0.026(1) 0.024(1) 0.024(1) 0.039(1)
Ueq is defined as one third of the trace of the orthogonalized Uij tensor. a Calculated standard deviations in parentheses.
lated from the atomic coordinates reported in Table 3 is also given in Fig. 3(b). The structure was solved by single crystal X-ray diffraction methods. From direct methods the position of zinc and phosphorus and some oxygen atoms were revealed and all the remaining atoms, except hydrogen atoms, were located from successive Fourier maps. All hydrogen atoms could be identified in a final difference Fourier map after anisotropic refinement but were finally refined with geometrical constraints. The asymmetric unit represented in Fig. 4 shows that oxygen atoms O1, O2, O3, O4 and O5, O6, O7, O8 are bonded to P1 and P2 atoms, respectively. A bond valence calculation using the relations proposed by Brown [18], has shown that the oxygens O4 and O8 correspond to OH groups (Table 5) as it was suggested by the P–O distances (d(P1–O4) = 1.553(2) and d(P2–O8) = 1.570(2) Å). The short P–O distances between P1 and O1 (d = 1.514(2) Å) and P2 and O5 (d = 1.493(2) Å) can be attributed to doubly bonded oxygen atoms as observed for other zincophosphates [19,20]. Oxygen O1 is also hydrogen bonded to the amine (d(O1. . .H1A–N1) = 1.736 Å) whereas O5 is hydrogen bonded to the water molecule (d(O5. . .Hw1–Ow) = 1.945 Å). Zinc and phosphorus atoms are tetrahedrally coordinated with average Zn–O and P–O bond lengths of 1.925 and 1.519 Å, respectively. The existence of one doubly bonded oxygen atom and one OH group on each phosphorus site explains why no P–O–P linkage is observed despite a Zn/P ratio equal to 0.5. The structure of Mu-22 consists of one-dimensional chains built from (Zn2P2 O4 ) four rings sharing their zinc atoms. Two symmetry equivalent chains propagating along
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Table 4 Selected bond distances (Å) and angles (deg) for Mu-22a Zn–O2 Zn–O31 Zn–O62 Zn–O7
1.895(3) 1.915(3) 1.933(2) 1.944(3)
O2–Zn1–O31 O2–Zn1–O62 O31 –Zn1–O62 O2–Zn1–O7 O31 –Zn1–O7 O62 –Zn1–O7
121.88(9) 103.35(10) 107.51(11) 114.19(12) 96.11(10) 114.15(9)
P1–O1 P1–O4 P1–O3 P1–O2
1.514(2) 1.553(2) 1.499(2) 1.503(2)
O3–P1–O4 O2–P1–O4 O1–P1–O4 O3–P1–O2 O3–P1–O1 O2–P1–O1
108.48(14) 108.69(14) 106.9(2) 113.81(14) 108.80(14) 109.90(13)
P2–O5 P2–O6 P2–O7 P2–O8
1.493(2) 1.499(2) 1.522(2) 1.570(2)
O5–P2–O6 O5–P2–O7 O6–P2–O7 O5–P2–O8 O6–P2–O8 O7–P2–O8
112.60(13) 111.82(13) 111.40(13) 107.58(14) 108.03(13) 104.99(12)
N1–C7 N1–C2 N1–C6 N4–C5 N4–C3 C2–C3 C5–C6
1.478(4) 1.478(4) 1.483(4) 1.473(3) 1.477(4) 1.504(4) 1.498(4)
C7–N1–C2 C7–N1–C6 C2–N1–C6 C5–N4–C3 N1–C2–C3 N4–C3–C2 N4–C5–C6 N1–C6–C5 P1–O2–Zn1 P1–O3–Zn11 P2–O6–Zn12 P2–O7–Zn1
111.3(2) 111.1(2) 110.2(2) 111.8(2) 110.6(2) 110.3(2) 111.3(2) 110.9(2) 147.13(13) 136.82(14) 129.10(12) 137.50(11)
Symmetry transformations used to generate equivalent atoms: 1 −x + 1/2, −y + 1/2, −z + 1;
2 −x + 1, −y, −z + 1.
a Calculated standard deviations in parentheses.
Table 5 Bond valence calculation for oxygen atoms O(4) and O(8), according to Brown [18]. The results refer to the equations: s = exp[(R0 −d)/B] or s = (d −R0 )−N with d = experimental distance, R0 = 1.62, B = 0.36 for P–O and R0 = 0.87, N = 2.2 for H–O b Atoms H(4) H(8) P(1) P(2) Expected valence s O(4) O(8) Expected valence s
0.80a – 1 0.80
a Calculated from distances of 0.96 Å.
– 0.80a 1 0.80
1.20 –
– 1.15
2 2
2.00 1.95
b s = sum of bond valences.
the [1 1 0] and [1 1 0] directions are present (Fig. 5(a),(b)). The angle between the two directions is close to 73.5◦ . As shown in Fig. 5(c), the organic species and water molecules are localized along the chains and, as mentioned above, are hydrogen bonded with the inorganic framework. The framework topology of Mu-22 is very similar to that of [Zn8 (HPO4 )8 (H2 PO4 )8 ](C2 H8 N)8 •4 H2 O, a zincophosphate previously synthesized in our laboratory in the presence of dimethylamine as structure-directing agent [13]. Nevertheless, as confirmed by 31 P MAS NMR spectroscopy (see below), the symmetry of Mu-22 is higher. This can be explained by the presence in Mu-22 of a diprotonated
organic species and consequently the absence of H2 PO4 groups. The 13 C CP MAS spectrum of the as-synthesized zincophosphate Mu-22 displays four different signals at 41.8, 42.5, 49.2 and 50.3 ppm (Fig. 6). The first two signals are assigned to the methyl group (CH3 ) and to the two CH2 groups in α position of N1 bonded to the methyl group. The two other signals are attributed to the two other CH2 (C3 and C5) groups linked to N4. These chemical shift values (reference TMS) are closer to those observed by 13 C liquid NMR spectroscopy for the 1-methylpiperazine molecule at pH = 5 (δ 41.6, 44.2 and 50.7 ppm) than those obtained at pH = 11
S. Fleith et al. / Solid State Sciences 4 (2002) 135–141
Fig. 2. Thermal analyses (TG and DTA) under air of the zincophosphate Mu-22.
Fig. 3. (a) Experimental and (b) calculated XRD patterns of Mu-22 (Cu Kα1 radiation).
139
(a)
(b)
Fig. 4. Asymmetric unit of the structure of the zincophosphate Mu-22. Dotted lines: hydrogen bondings.
(δ 44.9, 45.9 and 55.1 ppm). This confirms that the amine is occluded in its protonated form. The 31 P MAS NMR spectrum reported in Fig. 7(a) displays only one peak at −1.22 ppm characterized by a 31 P T1 value of ca. 286 s. Such a chemical shift value has already been observed for PO2 O(OH) group in the zincophosphate
(c) Fig. 5. Projections of the structure of Mu-22 (a) along the [0 0 1] direction, (b) and (c) along the [1 1 0] direction. Oxygen atoms of the framework are omitted for clarity. (c): location of the organic template and of the water molecules.
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S. Fleith et al. / Solid State Sciences 4 (2002) 135–141
chain topology. They can be divided into three subgroups as proposed Sugiyama et al. for aluminophosphates [21]. The zincophosphate Mu-22 belongs to subgroup 1 which gathers structures with chains of simple corner-shared fourmembered rings (aluminophosphates: [22–25], gallophosphate: [26], cobalt phosphates: [7]). The phosphate structure of subgroup 2 consists of chains of edge-shared fourmembered rings with additional PO4 tetrahedra with one or two hydroxyl ligands (aluminophosphates: [27,28]). Subgroup 3 includes phosphates with rather complicated structural units (aluminophosphates: [21,29]).
4. Conclusion Fig. 6. 13 C CP MAS NMR spectrum of Mu-22.
The use of 1-methylpiperazine as organic-structure directing agent leads to the new 1-D zincophosphate, Mu-22, of chemical formula: [Zn(HPO4 )2 ][C5 H13 N2 ]•H2 O (Z = 8). Its framework topology is similar to that of [Zn8(HPO4 )8 (H2 PO4 )8 ](C2 H8 N)8 •4 H2 O synthesized in the presence of dimethylamine as structure-directing agent. The structure consists of chains which propagates in two directions. These chains are built from Zn2 P2 O4 four-membered ring sharing their Zn atoms. Four ring network is obtained by connection of ZnO4 and HPO4 groups. The structure is stabilized by strong hydrogen bondings with the organic template and water molecules. However, this new zincophosphate displays a very low thermal stability. After heating the as-synthesized sample at 170 ◦ C, the structure collapses and Zn(PO3 )2 crystallizes at 430 ◦ C.
Supplementary material Fig. 7. (a) 31 P MAS and (b) MAS with high-power decoupling NMR spectra of Mu-22. Insert: 31 P MAS NMR spectrum of the zincophosphate synthesized by Reinert et al. [13]. “∗”: spinning side bands.
Mu-19 [20]. The experiment with the high-power decoupling (Fig. 7(b)) induces a decrease of the width of the signal (%ν1/2 = 130 Hz versus %ν1/2 = 505 Hz). This proves that phosphorus atoms are close to protons. The two crystallographic phosphorus sites cannot be distinguished by 31 P NMR. Their close environment is then very similar. The small differences between P1 and P2 come from their hydrogen bondings through their doubly bonded oxygen. It is worthy to note that the zincophosphate synthesized by Reinert et al. [13] which displays a similar framework topology crystallizes in the non-centrosymmetric space group Cc. The lower symmetry (four distinct crystallographic phosphorus sites) is confirmed by 31 P NMR spectroscopy. In that case 3 main signals with relative intensities close to 2 : 1 : 1 are observed on the corresponding spectrum (insert Fig. 7). Other one-dimensional microporous phosphates display the same kind of MP2 (M for metal, P for phosphorus)
Hydrogen coordinates (×104 ) and isotropic displacement parameters (Å2 × 103 ) for Mu-22.
x H1A H4A H4B H8 H4 H2A H2B H5A H5B H6A H6B H3A H3B H7A H7B H7C H1W H2W
4447(2) 2541(2) 3368(2) 4070(28) 3962(34) 3526(2) 2606(2) 4353(2) 3399(2) 2773(2) 3806(2) 3168(2) 4207(2) 3841(2) 2931(2) 3977(2) 4019(29) 4188(36)
y 5478(2) 7472(2) 8049(2) −3390(30) 1642(34) 3948(3) 4880(3) 8079(3) 8943(3) 6948(3) 7301(3) 5595(3) 5920(3) 3465(3) 4415(3) 4779(3) 9463(49) 9199(74)
z
Ueq
3464(1) 4074(1) 4567(1) 6037(20) 6449(25) 3954(1) 3645(1) 3835(1) 3531(1) 2890(1) 2753(1) 4743(1) 4611(1) 2858(2) 2517(2) 2390(2) 7230(16) 7857(26)
30 29 29 60(12) 88(16) 38 38 33 33 34 34 37 37 55 55 55 70(14) 148(28)
S. Fleith et al. / Solid State Sciences 4 (2002) 135–141
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Synthesis and characterization of the one-dimensional zincophosphate Mu-22: [Zn(HPO4 )2 ]8[C5 H13 N2]8 •8 H2O Sandrine Fleith a , Ludovic Josien a , Angélique Simon-Masseron a,∗ , Volker Gramlich b , Joël Patarin a a Laboratoire de Matériaux Minéraux, ENSCMu, Université de Haute-Alsace, UMR-CNRS 7016,
3 rue Alfred Werner, F-68093 Mulhouse cedex, France b Laboratorium für Kristallographie, ETH-Zentrum, CH-8092 Zürich, Switzerland
Received 26 June 2001; received in revised form 19 September 2001; accepted 1 October 2001
Abstract A new zincophosphate, Mu-22, has been synthesized under mild conditions in water medium in the presence of 1-methylpiperazine as organic template. The structure was determined by single crystal X-ray diffraction. The inorganic framework consists of infinite chains built from (Zn2 P2 O4 ) four-membered rings sharing their Zn atoms. Two symmetry equivalent chain directions along [1 1 0] and [1 1 0] directions are observed. The anionic chains make strong hydrogen bond interactions with the protonated 1-methylpiperazine. [Zn(HPO4 )2 ][C5 H13 N2 ]•H2 O crystallizes in the monoclinic system, space group C2/c (No 15) with cell parameters: a = 13.917(13), b = 9.091(14), c = 20.49(2) Å and β = 102.36(8)◦ , Z = 8. 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. Keywords: Zincophosphate; 1-methylpiperazine; Single crystal structure
1. Introduction Over the past few years, the organic species used in the zincophosphate system has been extensively studied in order to discover new compounds with open frameworks. This extremely reactive system offers large possibilities to work under mild (room temperature (RT)) or drastic (high temperature, high pressure) conditions. A large variety of new microporous zincophosphates with one-, two- or three-dimensional structure has already been reported in the literature [1]. In particular the zincophosphate ND-1, synthesized by Yang and Sevov in 1999, is one of the five microporous solids with the largest rings (24 T, T = Zn, P) [2]. Amines derived from piperazine are very reactive templates for microporous phosphates. They allow to synthesize zincophosphates [3–5], aluminophosphates [6], cobalt phosphates [7] and gallophosphates [8,9]. But their role as structure-directing agents is not understood. One-dimensional framework zincophosphates are stabilized by van der Waals interactions [10] or by strong hy* Correspondence and reprints.
E-mail address: [email protected] (A. Simon-Masseron).
drogen bondings with the organic template [11]. These 1-D structures generally contain tetrahedral 4-rings connected to each other and leading to infinite corner-shared chains or edge-shared ladders [3,10,12–14]. Only one 1-D zincophosphate synthesized by Harrison et al. [15] is built from tetrahedral 3-rings. These 1-D zincophosphates are synthesized in aqueous medium at various temperatures (RT–180 ◦ C) using different amines as template. At the present time their mechanism of formation is not established. This paper reports the synthesis and the crystal structure determination of a new 1-D zincophosphate [Zn(HPO4)2 ][C5 H13 N2 ]•H2 O named Mu-22 obtained in aqueous medium using 1-methylpiperazine as template. The characterization by 31 P and 13 C solid state NMR spectroscopy is also reported. 2. Experimental section 2.1. Synthesis Mu-22 was prepared at room temperature from a gel containing 1-methylpiperazine (MPIP) as structure-directing agent. Typically, the synthesis was made as follows: 1.04 g
1293-2558/02/$ – see front matter 2002 Éditions scientifiques et médicales Elsevier SAS. All rights reserved. PII: S 1 2 9 3 - 2 5 5 8 ( 0 1 ) 0 1 2 2 2 - 5
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Fig. 1. Scanning electron micrographs of some crystals of the zincophosphate Mu-22.
of zinc oxide (Carlo Erba, 99%) was stirred until complete dissolution in a mixture of 10.40 g of deionized water and 5.80 g of orthophosphoric acid (Labosi, 85%). 2.55 g of 1-methylpiperazine (Aldrich, 99%) were then added and the mixture was stirred again for one hour. The initial pH was 4. The final molar composition of the gel is 0.5 ZnO : 1 P2 O5 : 25 H2 O : 1 MPIP. The mixture placed in a polypropylene bottle was kept at 28 ◦ C for 13 days. The washing procedure appears to be critical because this new zincophosphate partially transforms into a non-identified compound on washing with water and ethanol. Therefore the large translucent crystals obtained (average dimensions: 850 × 650 × 200 µm3 , Fig. 1) were filtered and dried in air at RT. 2.2. Characterization The powder XRD patterns were obtained with Cu Kα1 radiation on a STOE STADI-P diffractometer equipped with a curved germanium (1 1 1) primary monochromator and a linear position sensitive detector. High-temperature Xray diffraction was performed using a variable temperature photographic chamber (Huber, model 631), attached to the same X-ray generator (Cu Kα1 radiation) in which the sample was kept in flowing dry air. XRD patterns were collected over a temperature range 30–750 ◦ C. The morphology and average size of the crystals were determined by scanning electron microscopy using a Philips XL30 microscope. Elemental analysis has been realized by Induced Coupled Plasma technique using Atomic Energy Spectroscopy (ICP AES) for Zn and P, and by coulometric and catharometric methods for C and N quantifications, respectively. Thermogravimetric (TGA) and differential thermal (DTA) analyses were performed under air on a Setaram Lab-
sys thermoanalyser with a heating rate of 5 deg min−1 from 10 to 750 ◦ C. The 13 C CP MAS NMR spectrum was recorded on a Brüker MSL 300 spectrometer and the 31 P MAS and DEC MAS NMR spectra on a Brüker DSX 400 spectrometer. 31 P T relaxation time was measured using the inversion1 recovery pulse sequence with a recycle delay of 1443 s (π/2 = 4.65 µs). The other acquisition parameters are gathered in Table 1. XRD studies on single crystal have been performed by the Weissenberg method on a PHILIPS PW1140 diffractometer with a nickel filtered Cu Kα radiation (λ = 1.54178 Å). For the structure determination, a crystal was selected from the batch and mounted on a SYNTEX P21 4-circle diffractometer. 2428 reflections were recorded from 2.7 up to 25.2◦ in θ using Mo Kα radiation in omega scan mode. 1904 ones fulfilled the condition I > 2σ (I ). A summary of the experimental and crystallographic data is reported in Table 2. The structure was solved by direct methods using S HELXS -86 [16] and refined using S HELXL -93 [17]. All non-hydrogen atoms were refined with anisotropic displacement parameters (not reported). The refinement con (R1 = Fo | − |Fc / |Fo |) and verged to R1 = 0.0268 wR2 = 0.0740 (R2 = { w(Fo2 − Fc2 )2 / w(Fo2 )2 }1/2 ) for 1904 reflections (I > 2σ (I )). The atomic coordinates and isotropic displacement parameters are given in Table 3. Selected bond lengths and angles are reported in Table 4.
3. Results and discussion According to the elemental analyses the as-synthesized Mu-22 sample has the following composition (wt%): Zn, 17.49; P, 16.11; C, 15.79; N, 7.25. It is in good agreement with the crystal structure determination: Zn, 17.24; P, 16.45; C, 15.93; N, 7.43. The Zn/P molar ratio is close to 0.5, as previously observed for other zincophosphates [1,3,11]. The thermal behavior of Mu-22 was investigated by hightemperature XRD and TG/DTA thermal analyses. The TG and DTA curves of as-synthesized Mu-22 are given in Fig. 2. Until 200 ◦ C, the desorption of water induced a weight loss close to 4.5% which is associated to a broad endothermic peak on the DTA curve. Between 200 and 650 ◦ C exothermic peaks attributed to the partial removal of the organic species are observed (weight loss: ∼ 29%). The thin endothermic
Table 1 Recording conditions of the MAS NMR spectra
Chemical shift standard Frequency (MHz) Pulse width (µs) Flip angle Contact time (ms) Recycle time (s) Spinning rate (Hz) Scans number Decoupling power (kHz)
13 C CP MAS
31 P MAS with high-power decoupling
31 P MAS
TMS 75.47 3.85 π/2 1 5 4000 242 –
85% H3 PO4 161.98 1.2 π/6 – 60 8000 32 58
85% H3 PO4 161.98 1.55 π/6 – 240 10000 4 –
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Table 2 Crystal data and structure refinement for Mu-22 Empirical formula
[Zn(HPO4 )2 ][C5 H13 N2 ]•H2 O
Formula weight Wavelength (Å) Crystal system Space group Unit cell dimensions a (Å) b (Å) c (Å) β (deg) Volume (Å3 ) Z Density (calculated) Absorption coefficient (mm−1 ) F (000) Crystal size (mm3 ) Diffractometer θ range (deg) Index ranges
377.52 0.71073 Monoclinic C2/c
Reflections collected Independent reflections Independent reflections with I > 2σ (I ) Absorption correction Refinement method Data/restraints/parameters Goodness-of-fit on F 2 Final R indices [I > 2σ (I )] R indices (all data) Extinction coefficient Largest diff. peak and hole (e A−3 )
13.917(13) 9.091(14) 20.49(2) 102.36(8) 2532(5) 8 1.981 2.237 1552 0.1 × 0.1 × 0.1 SYNTEX P21 4-circles 2.70 to 25.18 0 h 16, 0 k 10, −24 l 23 2428 2251 [Rint = 0.0269] 1904 None Full-matrix least-squares on F 2 2251/4/189 0.853 R1 = 0.0268, wR2 = 0.0740 R1 = 0.0304, wR2 = 0.0751 0.0057(4) 0.736 and −0.344
peak centered at 280 ◦ C probably corresponds to the removal of water arising from dehydroxylation reactions due to the presence of terminal P–OH groups (weight loss: 4.5%). After heating the sample at 750 ◦ C, a grey residue is obtained revealing the presence of residual organic species. The latter can be eliminated by calcination of the sample at 1000 ◦ C in air. The weight loss is close to 3%. From high-temperature XRD analysis, the structure of Mu-22 collapses at 170 ◦ C, Zn(PO3 )2 (ICDD 30-1488) crystallizing at 480 ◦ C. After heating at 670 ◦ C, the sample is amorphous. The total weight loss observed is close to 41 wt%, which is in good agreement with the total weight loss calculated by the crystal structure determination (40.8 wt%). Taking into account the whole of these analyses, the following unit cell formula can be proposed for the zincophosphate Mu-22: [Zn(HPO4)2 ]8 [C5 H13 N2 ]8 •8 H2 O. The experimental powder XRD pattern of Mu-22 (Fig. 3(a)) can be indexed in the monoclinic system with the following cell parameters: a = 14.0310(3), b = 9.1406(14), c = 20.642(3) Å and β = 102.242(16)◦. These results were confirmed by the Weissenberg method (a ∼ 13.8–14.0, b ∼ 9.0–9.1, c ∼ 19.3–20.0 Å and β ∼ 102◦ ). The extinction rules observed suggest the two possible space groups C2/c and Cc. For comparison the simulated XRD pattern calcu-
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Table 3 Atomic coordinates and equivalent isotropic displacement parameters (Å2 ) for Mu-22a Atom Zn P1 P2 O1 O2 O3 O4 O5 O6 O7 O8 Ow N1 N4 C2 C3 C5 C6 C7
x
y
z
Ueq
0.3683(1) 0.3604(1) 0.4452(1) 0.4328(1) 0.3860(1) 0.2582(1) 0.3708(2) 0.4424(1) 0.5474(1) 0.3951(1) 0.3819(1) 0.3743(2) 0.3795(2) 0.3200(2) 0.3302(2) 0.3516(2) 0.3656(2) 0.3465(2) 0.3621(2)
0.1270(1) 0.3632(1) −0.1180(1) 0.4854(2) 0.2909(2) 0.4251(2) 0.2480(2) −0.0069(2) −0.1714(2) −0.0618(2) −0.2533(2) 0.9402(3) 0.5448(2) 0.7448(2) 0.4923(3) 0.5934(3) 0.7987(3) 0.6960(3) 0.4437(3)
0.4734(1) 0.5918(1) 0.5870(1) 0.6169(1) 0.5318(1) 0.5791(1) 0.6489(1) 0.6402(1) 0.5878(1) 0.5181(1) 0.6001(1) 0.7568(1) 0.3293(1) 0.4212(1) 0.3820(1) 0.4414(1) 0.3671(1) 0.3085(1) 0.2714(2)
0.016(1) 0.015(1) 0.015(1) 0.025(1) 0.028(1) 0.030(1) 0.038(1) 0.027(1) 0.024(1) 0.026(1) 0.031(1) 0.044(1) 0.021(1) 0.021(1) 0.027(1) 0.026(1) 0.024(1) 0.024(1) 0.039(1)
Ueq is defined as one third of the trace of the orthogonalized Uij tensor. a Calculated standard deviations in parentheses.
lated from the atomic coordinates reported in Table 3 is also given in Fig. 3(b). The structure was solved by single crystal X-ray diffraction methods. From direct methods the position of zinc and phosphorus and some oxygen atoms were revealed and all the remaining atoms, except hydrogen atoms, were located from successive Fourier maps. All hydrogen atoms could be identified in a final difference Fourier map after anisotropic refinement but were finally refined with geometrical constraints. The asymmetric unit represented in Fig. 4 shows that oxygen atoms O1, O2, O3, O4 and O5, O6, O7, O8 are bonded to P1 and P2 atoms, respectively. A bond valence calculation using the relations proposed by Brown [18], has shown that the oxygens O4 and O8 correspond to OH groups (Table 5) as it was suggested by the P–O distances (d(P1–O4) = 1.553(2) and d(P2–O8) = 1.570(2) Å). The short P–O distances between P1 and O1 (d = 1.514(2) Å) and P2 and O5 (d = 1.493(2) Å) can be attributed to doubly bonded oxygen atoms as observed for other zincophosphates [19,20]. Oxygen O1 is also hydrogen bonded to the amine (d(O1. . .H1A–N1) = 1.736 Å) whereas O5 is hydrogen bonded to the water molecule (d(O5. . .Hw1–Ow) = 1.945 Å). Zinc and phosphorus atoms are tetrahedrally coordinated with average Zn–O and P–O bond lengths of 1.925 and 1.519 Å, respectively. The existence of one doubly bonded oxygen atom and one OH group on each phosphorus site explains why no P–O–P linkage is observed despite a Zn/P ratio equal to 0.5. The structure of Mu-22 consists of one-dimensional chains built from (Zn2P2 O4 ) four rings sharing their zinc atoms. Two symmetry equivalent chains propagating along
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Table 4 Selected bond distances (Å) and angles (deg) for Mu-22a Zn–O2 Zn–O31 Zn–O62 Zn–O7
1.895(3) 1.915(3) 1.933(2) 1.944(3)
O2–Zn1–O31 O2–Zn1–O62 O31 –Zn1–O62 O2–Zn1–O7 O31 –Zn1–O7 O62 –Zn1–O7
121.88(9) 103.35(10) 107.51(11) 114.19(12) 96.11(10) 114.15(9)
P1–O1 P1–O4 P1–O3 P1–O2
1.514(2) 1.553(2) 1.499(2) 1.503(2)
O3–P1–O4 O2–P1–O4 O1–P1–O4 O3–P1–O2 O3–P1–O1 O2–P1–O1
108.48(14) 108.69(14) 106.9(2) 113.81(14) 108.80(14) 109.90(13)
P2–O5 P2–O6 P2–O7 P2–O8
1.493(2) 1.499(2) 1.522(2) 1.570(2)
O5–P2–O6 O5–P2–O7 O6–P2–O7 O5–P2–O8 O6–P2–O8 O7–P2–O8
112.60(13) 111.82(13) 111.40(13) 107.58(14) 108.03(13) 104.99(12)
N1–C7 N1–C2 N1–C6 N4–C5 N4–C3 C2–C3 C5–C6
1.478(4) 1.478(4) 1.483(4) 1.473(3) 1.477(4) 1.504(4) 1.498(4)
C7–N1–C2 C7–N1–C6 C2–N1–C6 C5–N4–C3 N1–C2–C3 N4–C3–C2 N4–C5–C6 N1–C6–C5 P1–O2–Zn1 P1–O3–Zn11 P2–O6–Zn12 P2–O7–Zn1
111.3(2) 111.1(2) 110.2(2) 111.8(2) 110.6(2) 110.3(2) 111.3(2) 110.9(2) 147.13(13) 136.82(14) 129.10(12) 137.50(11)
Symmetry transformations used to generate equivalent atoms: 1 −x + 1/2, −y + 1/2, −z + 1;
2 −x + 1, −y, −z + 1.
a Calculated standard deviations in parentheses.
Table 5 Bond valence calculation for oxygen atoms O(4) and O(8), according to Brown [18]. The results refer to the equations: s = exp[(R0 −d)/B] or s = (d −R0 )−N with d = experimental distance, R0 = 1.62, B = 0.36 for P–O and R0 = 0.87, N = 2.2 for H–O b Atoms H(4) H(8) P(1) P(2) Expected valence s O(4) O(8) Expected valence s
0.80a – 1 0.80
a Calculated from distances of 0.96 Å.
– 0.80a 1 0.80
1.20 –
– 1.15
2 2
2.00 1.95
b s = sum of bond valences.
the [1 1 0] and [1 1 0] directions are present (Fig. 5(a),(b)). The angle between the two directions is close to 73.5◦ . As shown in Fig. 5(c), the organic species and water molecules are localized along the chains and, as mentioned above, are hydrogen bonded with the inorganic framework. The framework topology of Mu-22 is very similar to that of [Zn8 (HPO4 )8 (H2 PO4 )8 ](C2 H8 N)8 •4 H2 O, a zincophosphate previously synthesized in our laboratory in the presence of dimethylamine as structure-directing agent [13]. Nevertheless, as confirmed by 31 P MAS NMR spectroscopy (see below), the symmetry of Mu-22 is higher. This can be explained by the presence in Mu-22 of a diprotonated
organic species and consequently the absence of H2 PO4 groups. The 13 C CP MAS spectrum of the as-synthesized zincophosphate Mu-22 displays four different signals at 41.8, 42.5, 49.2 and 50.3 ppm (Fig. 6). The first two signals are assigned to the methyl group (CH3 ) and to the two CH2 groups in α position of N1 bonded to the methyl group. The two other signals are attributed to the two other CH2 (C3 and C5) groups linked to N4. These chemical shift values (reference TMS) are closer to those observed by 13 C liquid NMR spectroscopy for the 1-methylpiperazine molecule at pH = 5 (δ 41.6, 44.2 and 50.7 ppm) than those obtained at pH = 11
S. Fleith et al. / Solid State Sciences 4 (2002) 135–141
Fig. 2. Thermal analyses (TG and DTA) under air of the zincophosphate Mu-22.
Fig. 3. (a) Experimental and (b) calculated XRD patterns of Mu-22 (Cu Kα1 radiation).
139
(a)
(b)
Fig. 4. Asymmetric unit of the structure of the zincophosphate Mu-22. Dotted lines: hydrogen bondings.
(δ 44.9, 45.9 and 55.1 ppm). This confirms that the amine is occluded in its protonated form. The 31 P MAS NMR spectrum reported in Fig. 7(a) displays only one peak at −1.22 ppm characterized by a 31 P T1 value of ca. 286 s. Such a chemical shift value has already been observed for PO2 O(OH) group in the zincophosphate
(c) Fig. 5. Projections of the structure of Mu-22 (a) along the [0 0 1] direction, (b) and (c) along the [1 1 0] direction. Oxygen atoms of the framework are omitted for clarity. (c): location of the organic template and of the water molecules.
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S. Fleith et al. / Solid State Sciences 4 (2002) 135–141
chain topology. They can be divided into three subgroups as proposed Sugiyama et al. for aluminophosphates [21]. The zincophosphate Mu-22 belongs to subgroup 1 which gathers structures with chains of simple corner-shared fourmembered rings (aluminophosphates: [22–25], gallophosphate: [26], cobalt phosphates: [7]). The phosphate structure of subgroup 2 consists of chains of edge-shared fourmembered rings with additional PO4 tetrahedra with one or two hydroxyl ligands (aluminophosphates: [27,28]). Subgroup 3 includes phosphates with rather complicated structural units (aluminophosphates: [21,29]).
4. Conclusion Fig. 6. 13 C CP MAS NMR spectrum of Mu-22.
The use of 1-methylpiperazine as organic-structure directing agent leads to the new 1-D zincophosphate, Mu-22, of chemical formula: [Zn(HPO4 )2 ][C5 H13 N2 ]•H2 O (Z = 8). Its framework topology is similar to that of [Zn8(HPO4 )8 (H2 PO4 )8 ](C2 H8 N)8 •4 H2 O synthesized in the presence of dimethylamine as structure-directing agent. The structure consists of chains which propagates in two directions. These chains are built from Zn2 P2 O4 four-membered ring sharing their Zn atoms. Four ring network is obtained by connection of ZnO4 and HPO4 groups. The structure is stabilized by strong hydrogen bondings with the organic template and water molecules. However, this new zincophosphate displays a very low thermal stability. After heating the as-synthesized sample at 170 ◦ C, the structure collapses and Zn(PO3 )2 crystallizes at 430 ◦ C.
Supplementary material Fig. 7. (a) 31 P MAS and (b) MAS with high-power decoupling NMR spectra of Mu-22. Insert: 31 P MAS NMR spectrum of the zincophosphate synthesized by Reinert et al. [13]. “∗”: spinning side bands.
Mu-19 [20]. The experiment with the high-power decoupling (Fig. 7(b)) induces a decrease of the width of the signal (%ν1/2 = 130 Hz versus %ν1/2 = 505 Hz). This proves that phosphorus atoms are close to protons. The two crystallographic phosphorus sites cannot be distinguished by 31 P NMR. Their close environment is then very similar. The small differences between P1 and P2 come from their hydrogen bondings through their doubly bonded oxygen. It is worthy to note that the zincophosphate synthesized by Reinert et al. [13] which displays a similar framework topology crystallizes in the non-centrosymmetric space group Cc. The lower symmetry (four distinct crystallographic phosphorus sites) is confirmed by 31 P NMR spectroscopy. In that case 3 main signals with relative intensities close to 2 : 1 : 1 are observed on the corresponding spectrum (insert Fig. 7). Other one-dimensional microporous phosphates display the same kind of MP2 (M for metal, P for phosphorus)
Hydrogen coordinates (×104 ) and isotropic displacement parameters (Å2 × 103 ) for Mu-22.
x H1A H4A H4B H8 H4 H2A H2B H5A H5B H6A H6B H3A H3B H7A H7B H7C H1W H2W
4447(2) 2541(2) 3368(2) 4070(28) 3962(34) 3526(2) 2606(2) 4353(2) 3399(2) 2773(2) 3806(2) 3168(2) 4207(2) 3841(2) 2931(2) 3977(2) 4019(29) 4188(36)
y 5478(2) 7472(2) 8049(2) −3390(30) 1642(34) 3948(3) 4880(3) 8079(3) 8943(3) 6948(3) 7301(3) 5595(3) 5920(3) 3465(3) 4415(3) 4779(3) 9463(49) 9199(74)
z
Ueq
3464(1) 4074(1) 4567(1) 6037(20) 6449(25) 3954(1) 3645(1) 3835(1) 3531(1) 2890(1) 2753(1) 4743(1) 4611(1) 2858(2) 2517(2) 2390(2) 7230(16) 7857(26)
30 29 29 60(12) 88(16) 38 38 33 33 34 34 37 37 55 55 55 70(14) 148(28)
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