Phosphorus, Sulfur, and Silicon and the Related

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Phosphorus, Sulfur, and Silicon and the Related Elements

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Synthesis, Structure, and Characterization of a New Cyclohexaphosphate [4-CH3CH2OC6H4NH3]6P6O18.8H2O H. Marouania; M. Rzaiguia; S. S. Al-Deyabb a Laboratoire de Chimie des Matériaux, Faculté des Sciences de Bizerte, Zarzouna, Tunisia b Petrochemical Research Chair, College of Science, King Saud University, Riyadh, Saudi Arabia Online publication date: 19 February 2011

To cite this Article Marouani, H. , Rzaigui, M. and Al-Deyab, S. S.(2011) 'Synthesis, Structure, and Characterization of a

New Cyclohexaphosphate [4-CH3CH2OC6H4NH3]6P6O18.8H2O', Phosphorus, Sulfur, and Silicon and the Related Elements, 186: 2, 255 — 262 To link to this Article: DOI: 10.1080/10426507.2010.494645 URL: http://dx.doi.org/10.1080/10426507.2010.494645

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Phosphorus, Sulfur, and Silicon, 186:255–262, 2011 C Taylor & Francis Group, LLC Copyright ISSN: 1042-6507 print / 1563-5325 online DOI: 10.1080/10426507.2010.494645

SYNTHESIS, STRUCTURE, AND CHARACTERIZATION OF A NEW CYCLOHEXAPHOSPHATE [4-CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O H. Marouani,1 M. Rzaigui,1 and S. S. Al-Deyab2 1

Downloaded By: [Marouani, H.] At: 08:39 19 February 2011

Laboratoire de Chimie des Matériaux, Faculté des Sciences de Bizerte, Zarzouna, Tunisia 2 Petrochemical Research Chair, College of Science, King Saud University, Riyadh, Saudi Arabia GRAPHICAL ABSTRACT

Abstract Chemical preparation, X-ray characterization, IR spectroscopy, and thermal analysis of a new cyclohexaphosphate, [4-CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O, are reported. The atomic arrangement can be described by layers formed by cyclohexaphosphate anions P6 O6− 18 and water molecules connected by hydrogen bonds (O H. . .O). These inorganic layers are developed around bc planes at x = 0 and are interconnected by the H-bonds created by ammonium groups of organic cations. All the hydrogen bonds, the van der Waals contacts, and electrostatic interactions between the different entities give rise to a three-dimensional network in the structure and add stability to this compound. The thermal behavior and the IR spectroscopic studies of this new cyclohexaphosphate are discussed. Supplemental materials are available for this article. Go to the publisher’s online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Keywords Crystal structure; hybrid compound; infrared spectroscopy; thermal analysis; X-ray diffraction

Received 8 April 2010; accepted 16 May 2010. Address correspondence to Houda Marouani, Laboratoire de Chimie des Matériaux, Faculté des Sciences, 7021 Zarzouna, Bizerte, Tunisie. E-mail: [email protected] 255

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INTRODUCTION The design and synthesis of inorganic–organic hybrid materials have been of great interest due to their unique opportunity to combine the remarkable features of organic materials with those of inorganic compounds. In particular the family of materials that combines phosphate anions with organic molecules has received much attention in recent years due to their technological interest in several areas such as biomolecular sciences, catalysts, and optics.1–3 In order to enrich these materials and to investigate the influence of hydrogen bonds on the chemical and structural features, we report in this article the synthesis, crystal structure, thermal analysis, and IR spectroscopy of a new organic cyclohexaphosphate, [4-CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O.


RESULTS AND DISCUSSION Crystal Structure The title compound (Figure 1) is a hybrid of organic and inorganic entities (4-ethoxyaniline, P6 O18 , and H2 O). The asymmetric unit of [4-CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O contains one-half of the anion, three organic cations, and four water molecules crystallographically independent. The atomic arrangement of the title compound can be described by layers of inorganic entities developed in the bc planes (Figure 2). Adjacent P6 O18 groups are linked pairwise with O14 (respectively, O15) water molecules so as to form an infinite chain spreading

Figure 1 ORTEP11 drawing of the P6 O6− 18 anion and the crystallographical independent components of the molecular structure (30% thermal ellipsoids). Symmetry code: i: −x, −y, –z.


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Figure 2 The atomic arrangement of [4-CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O in projection along the b-axis. The phosphoric groups are given in tetrahedral representation. The other atoms are indicated by their symbols. Intermolecular H-bonds are denoted by dotted lines.

along the c (respectively, b) direction. The remaining O13 and O16 link these infinite chains to give rise to infinite layers. Each cyclohexaphosphate group is connected to its adjacent neighbors by eight water molecules through O H. . .O hydrogen bonds. Between these layers, separated by a distance of 15.248(7) Å, organic cations establish hydrogen bonds to interconnect the different anions and to compensate their negatives charges. Inside such a structure, the phosphoric ring has −1 internal symmetry. It develops around the inversion center located at (1/2, 0, 0), so it is built up by only three independent tetrahedra, P(1)O4 , P(2)O4 , and P(3)O4 . The geometry of this ring does not differ from the other known cyclohexaphosphates. The P O distances range in [1.463(1)–1.599(1) Å] and the O P O bond angles in [99.4 (2)–121.2 (2)◦ ]. It is the same for the P P distances ranging from 2.897 (1) to 2.940 (1) Å, which are comparable to values generally measured.4–6 The calculated average values of the distortion indices7 corresponding to the different angles and distances in the PO4 tetrahedra [DI (OPO) = 0.041; DI (PO) = 0.039; and DI (OO) = 0.012] show a pronounced distortion of the PO distances and OPO angles if compared to OO distances. So, the PO4 group can be considered as a rigid regular arrangement of oxygen atoms, with the phosphorus atom slightly displaced from the tetrahedron gravity center. Three independent 4-ethoxyanilinium cations are identified in the title compound. Interatomic bond lengths and angles of these groups spread respectively within the ranges [1.355(2)–1.498(2) Å] and [106.33(19)–125.21(16)◦ ]. The aromatic rings are planar with an average deviation of 0.000054 Å and form dihedral angles of 15.38◦ , 9.19◦ , and 14.53◦


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between them. These values are similar to those obtained for the same organic group in other compounds.8,9 The 4-ethoxyanilinium cations occupy the interlayer spaces and establish with the anionic framework N H. . .O hydrogen bonds. The N(3)H3 groups produce the internal P6 O18 ring cohesion through hydrogen bonds involving external oxygen atoms of each PO4 tetrahedron. The N(1)H3 groups link two different rings and so contribute to the layer cohesion of this compound, while the N(2)H3 groups are bound to three different water molecules. The organic groups are also interconnected through weak C H. . .O hydrogen bonds with the C. . .O separation of 3.170(2)–3.521(2) Å. The C H. . .O bonds have already been evidenced by several authors in molecular crystals.10 There are four crystallographically independent water molecules, O(13), O(14), O(15), and O(16), in this atomic arrangement. They interconnect the cyclohexaphosphate rings and the organic groups by establishing the hydrogen bonds, thus the water molecules act as proton donors and acceptors while the protonated amine groups are exclusively acceptors (Figure S1, see the Supplemental Materials, available online). The cohesion forces in this compound are assured by electrostatic interactions, van der Waals contacts, and hydrogen bonds (O H. . .O, N—H. . .O, and C H. . .O). Thermal Analysis The two curves corresponding to DTA and TGA analysis carried out in an argon atmosphere in the temperature range 298 K–923 K are given in Figure 3. The DTA curve shows an important endothermic peak at about 382 K. The TGA curve shows a weight loss for this peak. A calculation of the percentage of weight loss shows that this peak corresponds to a release of the eight water molecules of the formula (% experimental: 9.82%,

Figure 3 DTA and TGA thermograms of the title compound.


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calculated: 9.95%). At about 556 K, another endothermic peak appears, corresponding to the degradation of the organic entities of the molecules, accompanied with a significant weight loss clearly observed on the TGA curve. This degradation gives a viscous substance of polyphosphoric acids contaminated with a carbon black deposit.

IR-Absorption Spectroscopy


The infrared absorption spectrum is reported in Fig. S2 (Supplemental Materials). It exhibits the following: • Broad bands between 3600–2800 cm−1 and 1600–1370 cm−1 corresponding, respectively, to the stretching and bending modes of NH3 and CH. They are indicative of the presence of the 4-ethoxylaniline molecules in their protonated form.12 The broadness of the IR bands is probably due to the existence of hydrogen bonds of varying strengths in the crystal. • Various valency vibration bands whose positions, between 1350 and 660 cm−1, are characteristic of cyclohexaphosphate anion.13 In this type of anion, the stretching vibrations ν as (OPO)− and ν s (OPO)− are observed respectively between 1350–1180 cm−1 and 1180–1060 cm−1, while the stretching vibration bands originating from both asymmetric νas(POP and symmetric ν s POP modes are, respectively, observed in the 1060–960 and 850–660 cm−1 region, and those below 660 cm−1 correspond to bending, translation, and rotation of the P6 O18 ring.

CONCLUSION In this article, the new organic cyclohexaphosphate [4-CH3 CH2 O-C6 H4 NH3 ]6 P6 O18 . 8H2 O is reported and characterized by X-ray diffraction, thermal behavior, and IR spectroscopic. The crystal structure of this compound was found to be built by infinite layers of P6 O6− 18 and water molecules parallel to the bc planes around x = 0. Between these layers, the 4-ethoxyanilinium cations are located. Both inorganic and organic components perform different interactions (electrostatic, H-bonds, and van der Waals) to stabilize the three-dimensional network. When heated, the compound loses the crystallization water molecules at 382 K. By heating further, the compound exhibits a degradation of the organic entities confirmed by the obtained carbon black residue at the end of the experiment.

EXPERIMENTAL Chemical Preparation The title compound was prepared by an acid/base reaction in two steps. In the first step, we prepared Li6 P6 O18 .6H2 O according to the process described by Schülke and Kayser.14 From this lithium salt, we prepared an aqueous solution of cyclohexaphosphate acid H6 P6 O18 by passing a solution of Li6 P6 O18 .6H2 O (1 g, 2.3 mmol) through an ion-exchange resin in its H-state (Amberlite IR 120). In the second step, at 20 mL of the aqueous solution of H6 P6 O18 freshly prepared, we add dropwise a solution of 4-ethoxyaniline (1.77 mL, 13.8 mmol, d = 1.065) in 20 mL of ethanol under continuous stirring. Schematically, the

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reaction can be written as follows: H6 P6 O18 + 6(4 − CH3 CH2 OC6 H4 NH2 ) + 8H2 O [4 − CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O In order to avoid the hydrolysis of the ring anion, the above reaction was performed at room temperature. The obtained solution was then slowly evaporated until the formation of colorless prisms of [4-CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O (m = 1.8 g, yield = 62%). The title compound was stable for months under normal conditions of temperature and relative humidity.


Investigation Techniques The title compound has been studied by various physicochemical methods: X-ray diffraction. The intensity data were collected at room temperature using an Enraf-Nonius CAD4 diffractometer with MoKα¯ radiation. The cell parameters were determined from a least squares refinement of 25 reflections. Two standard reflections were periodically measured for every 120 min during data collection. Unique reflections (8709) were measured, of which only 6829 had I ≥ 2σ (I) and were used for structure determination and refinement. The structure was solved by direct methods using the program SHELXS-9715 in the WinGX package16 and was refined by full-matrix least-squares method with the program SHELXL-97.15 All nonhydrogen atoms were refined isotropically and then anisotropically by full matrix least-squares method. All hydrogen atoms were placed geometrically and treated as riding. The main bond distances and bond angles for the title Table 1 Main interatomic distances (Å) and angles (◦) in the P6 O18 ring of [4-CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O Tetrahedron P(1)O4 P1 O1 O1 1.4633(12) O2 119.84(7) O3 108.61(7) O4 110.92(8) Tetrahedron P(2)O4 P2 O4 O4 1.5989(13) O5 110.70(7) O6 107.17(8) O7 100.58(6) Tetrahedron P(3)O4 P3 O3 O3 1.5764(14) O7 103.34(7) O8 104.94(7) O9 110.54(8) P1–P2 2.8969(5) P3–P2–P1 104.92(1) P2–P1–P3 112.30(1) P2–P3–P1 98.61(1)

O2 2.5426(16) 1.4751(12) 111.02(7) 105.14(7)

O3 2.4833(19) 2.5294(17) 1.5928(12) 99.34(7)

O4 2.5194(17) 2.4382(15) 2.4293(18) 1.5939(12)

O5 2.5207(15) 1.4639(12) 120.18(8) 107.29(7)

O6 2.4708(18) 2.5432(18) 1.4700(13) 109.17(8)

O7 2.4526(15) 2.4600(16) 2.4942(18) 1.5893(11)

O7 2.4757(17) 1.5796(12) 111.07(6) 106.66(7) P1–P3 P1–O3–P3 P1–O4–P2 P3–O7–P2

O8 2.4235(18) 2.5221(15) 1.4785(11) 119.21(8) 2.9330(6) 135.47(9) 130.28(7) 136.21(7)

O9 2.5060(18) 2.4485(16) 2.5451(16) 1.4720(12) P2–P3

Estimated standard deviations are given in parentheses.

2.9404(4)


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Table 2 Crystal data and experimental parameters used for the intensity measurements Empirical formula [4-CH3 CH2 OC6 H4 NH3 ]6 P6 O18 .8H2 O Formula weight 1447.06 Crystal system Triclinic Space group P¯i a 15.248 (4) b 11.036 (2) c 10.620 (3) Å α 108.35 (2) β 95.56 (2) γ 99.16 (2)◦ Z 1 V 1653.7(7) Å3 ρ cal. 1.453 g cm−3 F(000) 764 µ (MoKα) ¯ 0.255 mm−1 Crystal size [mm] 0.40 × 0.30 × 0.25 Index ranges: ±h, ±k, l hmax. = 21, kmax. = 14, lmax. = 14 Collected unique reflections 8709 (Rint = 0.01) Unique reflections included [I >[2σ (I)]: 6829 with 454 refined parameters R[F2>2σ (F2)] 0.039 wR(F2) 0.099 ρ min , ρ max −0.47, 0.07 e Å 3 Goodness-of-fit 1.09

compound are provided in Table 1, and the main geometrical features of the hydrogenbond scheme are compiled in Table S1 (Supplemental Materials). The parameters used for the X-ray diffraction data collection as well as the strategy used for the crystal structure determination and its final results are reported in Table 2. Crystallographic data (CIF) for the structure reported in this article have been deposited in the Cambridge Crystallographic Data Centre as supplementary materials No CCDC 770618. Copies of the data can be obtained, free of charge, on application to the CCDC, 12 Union Road, Cambridge CB12EZ, UK (Fax: ++44(1223) 336-033; email: [email protected]). Thermal analysis. Thermal analysis was performed using the “multimodule 92 Setaram analyser” operating from room temperature up to 723 K at an average heating rate of 5 K min−1. Infrared spectroscopy. IR spectrum is recorded in the range 4000–400 cm−1 with a PerkinElmer FTIR spectrometer using a sample dispersed in a spectroscopically pure KBr pellet. REFERENCES 1. Gani, D.; Wilkie, J. Chem. Soc. Rev. 1995, 24, 55. 2. Tananaev, I. V.; Grünze, H.; Chudinova, N. N. Izv. Akad. Nauk SSSR Neorg. Mater. 1984, 20, 887. 3. Masse, R.; Bagieu-Beucher, M.; Pecaut, J.; Lévy, J. P.; Zyss, J. Nonlinear Opt. 1993, 5, 413. 4. Marouani, H.; Rzaigui, M.; Bagieu-Beucher, M. E. J. Solid State Inorg. Chem. 1998, 35, 459. 5. Marouani, H.; Rzaigui, M. Solid State Sci. 1999, 1, 395.

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