Synthesis and Crystal Structures of Various Phases of the Microporous

Article pubs.acs.org/crystal

Synthesis and Crystal Structures of Various Phases of the Microporous Three-Dimensional Coordination Polymer [Zr(OH)2(C2O4)]n

Monia Hamdouni,† Siwar Walha,† Ahlem Kabadou,† Carine Duhayon,‡,§ and Jean-Pascal Sutter*,‡,§ †

Laboratoire des Sciences des Matériaux et de l’Environnement, Faculté des Sciences de Sfax, Université de Sfax, Sfax, BP 1171, 3000, Tunisia ‡ CNRS, LCC (Laboratoire de Chimie de Coordination), 205, route de Narbonne, F-31077 Toulouse, France § Université de Toulouse, UPS, INPT, LCC, F-31077 Toulouse, France S Supporting Information *

ABSTRACT: A homometallic Zr(IV)-oxalate three-dimensional (3-D) coordination polymer of formula [Zr(OH)2(C2O4)·0.5H2O] is reported. This compound was found to be a microporous solid with reversible sorption abilities. Upon guest release and sorption, the crystalline material undergoes single crystal to single crystal transitions. The crystal structures for three phases have been solved from single crystal diffraction studies. They consist of the guest containing frameworks [Zr(OH)2(C2O4)·0.5H2O], 1, 3, and the guest-free porous phase [Zr(OH)2(C2O4)], 2; all are found with tetragonal space group I4/m. Phase 1 has been obtained by controlled diffusion of the reagents (ZrO(NO3)2 and H2C2O4) in a silica gel medium; the other phases have been formed from 1 by thermal activation (2) and re-adsorption of H2O (3).

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association with oxalate, Zr4+ was involved in the preparation of heterometallic coordination polymers of formula [MZr(C2O4)4]2− (M stands for divalent cation).9 These frameworks are described on the basis of mixed MO8 and ZrO8 polyhedra interconnected through bis-chelating oxalate ligands. They exhibit interconnected channels with elliptic or square cross sections hosting the counter-cations and solvent (H2O) molecules. The molecular complexes [Zr(C2O4)4]4− and [Zr2(C2O4)7]6− have also been successfully involved as metallo-tectons for the construction of supramolecular openframework materials.10 Herein we report on a homometallic [Zr-oxalate] 3-D framework material of formula [Zr(OH)2(C2O4)]. For this system, the Zr surrounding is only partially occupied by oxalate ligands; two hydroxo moieties complete the 8-fold coordination sphere. The guest-free structure obtained after lattice H2O release reveals a microporous framework that is able to reversibly sorb H2O. The structural features for the three phases are described.

INTRODUCTION In recent years, one of the most promising and innovating approaches in porous materials search arises from coordination chemistry with the development of the so-called metal−organic framework (MOFs). In such compounds, organic moieties act as a spacer or linker between metal centers; the resulting structures are conceptualized in terms of the building unit and net connectivity.1 Carboxylic acid derivatives have been intensively used as anionic ligands and lead to spectacular examples illustrating how the organic ligand symmetry, as well as the metal geometry, can be exploited for conceiving novel architectures with increased porosity and various topologies. Indeed, metal carboxylates networks are robust enough to show permanent porosity with sometimes giant surface areas,2 yielding materials virtually interesting for selective sorption and separation processes, exchange properties, catalytic applications or gas and nanomaterials storage.3 Among carboxylate ligands, oxalate [C2O4]2− is a main linker because of its coordination capability to a vast variety of metal ions, its great solubility in many solvents and especially in H2O compared to more sophisticated carboxylates, and its good thermal robustness. This ligand has been and still is widely involved in the development of material-directed coordination compounds targeting magnetic,4 multiferroic,5 and conducting6 or optical properties,7 for instance. The tetravalent metal ion Zr4+ has attracted a great deal of interest because with oxy-ligands, it is very frequently 8-fold coordinated. Moreover, the chemical and hydrothermal stabilities of the metal−organic frameworks formed with higher oxidation states metal ions are drastically increased.8 In © XXXX American Chemical Society

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RESULTS AND DISCUSSION Synthesis. [Zr(OH)2(C2O4)]·0.5H2O 1 was obtained by interdiffusion of oxalic acid and ZrO(NO3)2 in silicate gel. The crystals formed in the Liesegang rings over a period of 3 weeks as shown in Figure 1. With time, they do not grow beyond the Received: August 26, 2013 Revised: October 4, 2013

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dx.doi.org/10.1021/cg401286a | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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phase, 2, was obtained by warming crystals of 1 at 100 °C. The capability for the activated framework to adsorb back H2O was tested by immersing 2 in H2O, which yielded phase 3. During these guest-exchange processes, the crystals remained of sufficient quality to allow the investigation of the crystal structures for 3 by single X-ray diffraction. For structure investigation of the activated phase 2, a single crystal of 1 was heated directly on the diffractometer setup with a N2 gas flow at 100 °C. This flow was maintained during data collection. Structure Description. The diffraction data were collected at 293 K for [Zr(OH)2(C2O4)]·0.5H2O, 1, 3, and at 373 K for [Zr(OH)2(C2O4)] 2. All structures were solved with tetragonal symmetry in the centrosymmetric I4/m (No. 87) space group (Table 1). Selected bond distances and angles are reported in Table 2. Refined atomic positions and equivalent thermal parameters are given in Table SI1, Supporting Information, and atomic displacement parameters are reported in Table SI2, Supporting Information. ORTEP plots can be also found as Supporting Information (Figures SI1, SI2, and SI3). The three phases exhibit a 3-D neutral coordination framework build from [ZrO8] polyhedra bridged through

Figure 1. Single tube technique for the growth of Zr(OH)2(C2O4)· 0.5H2O, 1 crystals.

size of a few hundred micrometers but become more abundant. Only low amounts of 1 are isolated, typically 10 mg. Attempts to obtain 1 by slow interdiffusions without the gel failed, while powder synthesis by mixing the reagents’ solutions leads to a complex mixture of nonidentified compounds. The dehydrated

Table 1. Crystallographic Data and Structural Refinement Parameters for Compounds 1−3 Zr(OH)2(C2O4)·0.5H2O, 1

Zr(OH)2(C2O4), 2

Zr(OH)2(C2O4)·0.5H2O, 3

Crystal Data empirical formula formula weight (g·mol−1) crystal system space group unit cell dimensions a (Å) c (Å) volume (Å3) Z-space group density (g·cm−3) absorption coefficient (mm−1) F(000) crystal size (mm) crystal habit diffractometer monochromator radiation type, λ (Å) temperature (K) index ranges

theta range for data collection (°) absorption correction type reflections collected independent reflections observed refl (I > 3σ(1)) R(int) refinement on data/restraints/parameters final R indices goodness-of-fit (GOF) on F2 largest difference in peak and hole (e Å−3) CSD deposit number

ZrC2H3O6.5 222.264 tetragonal I4/m

ZrC2H2O6 213.256 tetragonal I4/m

ZrC2H3O6.5 222.264 tetragonal I4/m

12.799(5) 7.527(5) 1233.0(1) 8 2.35 1.750 816 0.15; 0.15; 0.25 colorless blocks Data Collection Bruker Kappa Apex2 graphite Mo Kα; 0.71073 293 −10 ≤ h ≤ 28 −26 ≤ k ≤ < 28 l ± 16 2−52 multiscan 13022 3597 1977 0.0680 Refinement F2 1977/0/49 R1 = 0.036 wR2 = 0.039 1.10 1.67; −1.24 956917

12.7611(8) 7.5400(6) 1227.86(1) 8 2.31 1.752 800 0.15; 0.15; 0.25 colorless blocks

12.7982(8) 7.5231(1) 1232.2(2) 8 2.347 1.751 816 0.16; 0.16; 0.26 colorless blocks

Oxford Gemini graphite Mo Kα; 0.71073 373 −13 ≤ h ≤ 14 k ± 14 l±8 3−23 multiscan 6414 486 383 0.0473

Bruker Kappa Apex2 graphite Mo Kα; 0.71073 293 h ± 15 −11 ≤ k ≤ 15 l±8 2−52 multiscan 2623 597 402 0.0560

F2 383/0/46 R1 = 0.032 wR2 = 0.0296 1.0544 0.57; −0.48 956918

F2 402/0/49 R1 = 0.0527 wR2 = 0.0616 1.04 1.82; −1.11 956919.

B



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Table 2. Bond Lengths (Å) and Angles (°) for 1−3 Zr(OH)2(C2O4)·0.5H2O, 1 Zr1−O1 Zr1−O1i Zr1−O1ii Zr1−O1iii Zr1−O2 Zr1−O2ii Zr1−O3 Zr1−O4 C1−C1ii C1−O1 C1−O2iv O1ii−Zr1−O1i O1ii−Zr1−O1iii O1i−Zr1−O1iii O1ii−Zr1−O1 O1i−Zr1−O1

2.5843(1) 2.587(2) 2.5843(1) 2.587(2) 2.5648(2) 2.5648(2) 2.570(3) 2.610(3) 1.554(3) 1.248(2) 1.250(2) 130.15(4) 70.75(6) 137.83(7) 62.96(7) 70.75(4)

O1iii−Zr1−O1 O2ii−Zr1−O1ii O2ii−Zr1−O1i O2ii−Zr1−O1iii O2ii−Zr1−O1 O2ii−Zr1−O2 O1ii−Zr1−O2 O1i−Zr1−O2 O1iii−Zr1−O2 O1−Zr1−O2 O2ii−Zr1−O3 O1ii−Zr1−O3 O1i−Zr1−O3 O1iii−Zr1−O3 O1−Zr1−O3 O2ii−Zr1−O4 Zr(OH)2(C2O4), 2

130.15(3) 110.23(7) 76.05(7) 137.17(5) 78.49(7) 62.95(8) 78.49(7) 137.17(5) 76.05(5) 110.23(8) 148.52(4) 84.45(1) 73.39(6) 73.39(6) 84.45(1) 80.10(1)

O1ii−Zr1−O4 O1i−Zr1−O4 O1iii−Zr1−O4 O1−Zr1−O4 O2−Zr1−O3 O2−Zr1−O4 O3−Zr1−O4 C1ii−C1−O2iv C1ii−C1−O1 O2iv−C1−O1 Zr1−O1−Zr1i Zr1−O1−C1 Zr1i−O1−C1 Zr1−O2−C1v

148.03(4) 81.25(6) 81.25(6) 148.03(4) 148.52(4) 80.10(1) 102.38(1) 116.73(1) 117.31(9) 125.94(1) 109.25(6) 119.76(1) 130.75(1) 121.44(1)

Zr1−O1 Zr1vi−O1 Zr1−O2 Zr1−O3 Zr1−O4 C1−C1vii C1−O2viii C1−O1 C1vii−C1−O2viii C1vii−C1−O1 O2viii−C1−O1 Zr1vi−O1−C1 Zr1vi−O1−Zr1 C1−O1−Zr1 C1ix−O2−Zr1

2.591(3) 2.585(3) 2.576(4) 2.584(6) 2.610(6) 1.546(9) 1.249(6) 1.235(6) 116.7(3) 117.7(3) 125.6(4) 119.2(3) 109.08(1) 131.7(3) 121.3(3)

62.43(2) O2−Zr1−O2x O2−Zr1−O1vi 108.78(1) O2x−Zr1−O1vi 77.41(1) O3−Zr1−O1vi 86.49(2) O2−Zr1−O1xi 77.41(1) O2x−Zr1−O1xi 108.78(1) O3−Zr1−O1xi 86.49(2) O1vi−Zr1−O1xi 62.79(1) O2−Zr1−O1 136.86(1) O2x−Zr1−O1 76.14(1) O3−Zr1−O1 73.36(9) O1vi−Zr1−O1 70.92(1) O1xi−Zr1−O1 130.34(8) O2−Zr1−O3 148.79(9) O2x−Zr1-O3 148.79(9) Zr(OH)2(C2O4)·0.5H2O, 3

O2−Zr1−O1x O2x−Zr1−O1x O3−Zr1−O1x O1vi−Zr1−O1x O1xi−Zr1−O1x O2−Zr1−O4 O2x−Zr1−O4 O3−Zr1−O4 O1vi−Zr1−O4 O1xi−Zr1−O4 O1−Zr1−O1x O1−Zr1−O4

76.14(1) 136.86(1) 73.36(9) 130.34(8) 70.92(1) 81.17(2) 81.17(2) 100.4(3) 148.05(8) 148.05(8) 138.49(1) 81.16(9)

Zr1−O1vii Zr1−O1vi Zr1−O1xii Zr1−O1 Zr1−O2vii Zr1−O2 Zr1−O3 Zr1−O4 O1−C1 O2−C1xiii C1−C1vii O2vii−Zr1−O1vii O2vii−Zr1−O1vi O1vii−Zr1−O1vi O2vii−Zr1−O1xii O1vii−Zr1−O1xii

2.583(5) 2.593(5) 2.593(5) 2.583(5) 2.564(6) 2.564(6) 2.616(1) 2.567(1) 1.239(1) 1.244(1) 1.559(2) 78.6(2) 137.0(2) 130.11(1) 72.2(1) 70.99(2)

O1vi−Zr1−O1xii O2vii−Zr1−O1 O1vi−Zr1−O1 O1vi−Zr1−O1 O1xii−Zr1−O1 O2vi−Zr1−O2 O1vii−Zr1−O2 O1vi−Zr1−O2 O1xii−Zr1−O2 O1−Zr1−O2 O2vii−Zr1−O3 O1vii−Zr1−O3 O1vi−Zr1−O3 O1xii−Zr1−O3 O1−Zr1−O3 O2vii−Zr1−O4

O1vii−Zr1−O4 O1vi−Zr1−O4 O1xii−Zr1−O4 O1−Zr1−O4 O2−Zr1−O3 O2−Zr1−O4 O3−Zr1−O4 Zr1−O1−Zr1vi Zr1−O1−C1 Zr1vi−O1−C1 Zr1−O2−C1xiii C1vii−C1−O2xiv C1vi−C1−O1 O2xiv−C1−O1

84.3(3) 73.46(2) 73.46(2) 84.3(3) 79.7(3) 148.69(1) 103.0(4) 109.01(2) 120.2(5) 130.5(5) 121.9(6) 116.4(5) 117.1(4) 126.6(8)

137.7(3) 110.1(2) 62.7(2) 70.99(2) 130.11(1) 62.6(3) 110.1(2) 76.2(2) 137.0(2) 78.6(2) 79.7(3) 148.10(1) 81.30(2) 81.30(2) 148.10(1) 148.69(1)

oxalate ligands (ox2−). The forthcoming description corresponds to the structure of 1, but the same applies to 2 and 3. Each zirconium ion is surrounded by four oxalate groups, two of which being chelating and two bound by a single O atom, and by two hydroxo ligands in cis-positions (Figure 2a). Analyses of Zr−O bond distances and the charge balances are in agreement with the OH groups. The Zr−O bond distances do not allow discriminating oxo, hydroxo, or aqua ligands; however, since the crystallographic data have shown no trace of any peak that would correspond to a counterion, the electric

neutrality is verified for two hydroxyl groups or one oxo and one aqua ligand. Taking into account that the starting material, ZrO(NO3)2, has been shown to be actually a dihydroxo species,11 it is very likely that [Zr(OH)2(C2O4)] properly describes the framework formula of 1, in agreement with earlier tentative formulations.12 It might be stressed that hydroxo groups are common for Zr(IV) compounds.8a,13 The distances and angles for oxalate groups are listed in Table 2. They are in good agreement with the mean values reported by Hahn14 for oxalate compounds, i.e., 1.24 and 1.55 Å, 117 and 126° for the C



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Å). While countless oxalate-bridged coordination polymers have been reported, including numerous 3-D networks where the bis-chelating and μ2-O bridging modes of the oxalate ligand are found,9f,17 a search on the CCDC structure data bank (02/ 2013 release) suggests that the association scheme observed for 1 is unique. The projection along the (001) direction displays the channels which are occupied by solvent molecules (Figure 4).

Figure 2. View of (a) the coordination sphere of Zr(IV) and (b) its coordination polyhedron (color codes: Zr, blue; O, red; and C, gray). Symmetry transformations used to generate equivalent atoms: i, 0.5 − x, 0.5 − y, −0.5 + z; ii, x, y, z; iii, 0.5 − x, 0.5 − y, 0.5 − z; iv, x, y, −z.

C−O and C−C bond lengths and O−C−C and O−C−O angles, respectively. These oxalate groups are close to planarity. The zirconium site does not exhibit an ideal geometry (Figure 2b). The eight-vertex polyhedral was analyzed by continuous shape measures15 performed with the program SHAPE16 revealing a distorted square antiprism shape. This was found also for the phases 2 and 3 (see Table SI3, Supporting Information). The Zr(OH)2(C2O4) units are interconnected through the oxalate ligand to develop a 3-D network. As can be seen from Figure 2a, each oxalate ligand is involved in two types of bridges. The first one is ensured by oxygen atoms O1i and O1iv each bound to a neighboring Zr. Concomitantly, each of those Zr units makes a related bridge with the central Zr by the means of O1ii and O1iii, yielding two μ-O bridging two Zr. This association scheme develops parallel to the crystallographic c axis to give rise to one-dimensional (1-D) chains of edge-shared ZrO8 polyhedra (Figure 3a). Right- and left-handed metaloxalate helical wires are formed. These 1-D arrays are interconnected by the second bridge established by oxalate. Here the ligand is connected in a chelating manner by two of its oxygen atoms to a metal ion, while the two remaining oxygens chelate a second Zr (Figure 3b,c). Each of these Zr centers belong to a different wire; a 3-D network is achieved with the helices arranged side by side in the c direction with respect to 4fold symmetry axis (Figure 3d). The resulting framework displays channels along the c axis with a square cross section with side dimensions of 6.492(2) Å (Zr−Zr separation) decorated by the hydroxo units (O···O separation, 3.382(4)

Figure 4. Ball-stick (left) and polyhedral (right) presentations of the view along the c axis of the framework highlighting the channels running through the structure; the red square shows the space between the OH units (O···O separation, 3.382 Å); (bottom) a channel, where zeolitic H2O is located, is shown by a yellow rod.

In 1, there is one “zeolitic” water per asymmetric unit. This O atom is localized on 4e (half-occupied) crystallographic site (Figure SI4, Supporting Information), in the space which separate eight ZrO8 polyhedra. The solvent-accessible void has been calculated by means of the program SOLV included in the software PLATON18 yielding 116 Å3, which represents 9.4% of the unit-cell volume (1233 Å3). This is in the range usually found for metal oxalate structures with zeolithic features.17a

Figure 3. Details of the [Zr(OH)2(C2O4)] ladder organization and ladder interconnections showing the intercluster oxalate connectivity: (a) Helical chains formed by interconnection of framework’s elementary fragments via μ2-oxygen atoms of two oxalate groups; (b) Interconnection of the chains by bidentate oxalate bridges; (c) polyhedral view of two interconnected [ZrO8] helices; (d) 3-D [Zr(OH)2(C2O4)] framework with a polyhedral view for the [ZrO8] units. D



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The X-ray diffraction data for the evacuated phase, [Zr(OH)2(C2O4)] 2, were collected after heating a single crystal of 1 at 100 °C. Nondestructive water release takes place when warming the crystal. The general crystal structure features of 2 are the same as those of 1 except that the water has gone revealing a permanent porosity (Figure 5). Cell parameters

Figure 6. Thermogravimetric analysis (TGA) for 1 performed under N2 flow with a ramp rate of 10 °C/min.

dehydration process involving the hydroxo groups leading to the release of one H2O. This is followed by a weight decrease by ca. 10% leading to a species stable between 250 and 400 °C. We tentatively attribute this to a partial decomposition of the oxalate ligands to carbonate with CO2 release (formally 0.5 CO2 per Zr, i.e., 10 % weight loss) yielding [Zr2O(CO3)(C2O4)]. Complete decomposition of the oxalate framework takes place above 400 °C.

Figure 5. Space-filling model view for the crystal structure of 2 (color codes: Zr, blue; O, red and green for the OH groups; C, gray).

only very slightly change upon guest release. The effective porosity for 2 was evaluated by PLATON to correspond to 109 Å3 per unit cell (1228 Å3), which corresponds to 8.9%. In the presence of moisture, 2 takes up again H2O guest molecules leading to 3 (Figures SI3 and S4, Supporting Information). At the single crystal scale, the cell parameters obtained for 3 suggest the recovery of the as-synthesized phase, and the structure revealed the presence of H2O again at the 4e crystallographic site. The sorption of MeOH by 2 was also examined, but the presence of the alcohol in the framework could not be confirmed by X-ray diffraction experiments. The ZrO8 polyhedra in 1, 2, and 3 show no significant deviations in Zr−O distances, which range from 2.5645 to 2.605 Å in 1, from 2.576 to 2.600 Å in 2, and from 2.565 to 2.629 Å in 3. Vibrational Spectroscopy and Thermal Behavior. The frequencies of infrared peaks for 1 are plotted in Figure SI5, Supporting Information. The coordinated hydroxo ligand as well as water molecules give rise at high wavenumbers to an absorption assignable to the typical symmetric and asymmetric stretching ν(O−H) vibration; this appears as broad peaks centered at 3350 cm−1. The bending mode of water expected around 1600 cm−1 is overlapped with the intense oxalate band characteristic of acid carbonyl groups and asymmetric stretching vibration of CO2− groups. The band at 1300 cm−1 is due to the symmetric stretching vibrations of CO2− groups. The value of the Δν[νas(CO2) − νs(CO2) ] parameter is larger than 200 cm−1, which is characteristic for bidentate oxalate groups participating in bridges.19 Single bands indicate the equivalent symmetry of oxalate ligand interactions in bridges. The medium intensity band at 920 cm−1 is ascribed to O−C O in plane bending vibrations; moreover, the 798 cm−1 band can also be attributed to the O−CO out of plane bending vibrations and to stretching vibration of Zr−O−Zr bridges.20 The thermogravimetric behavior obtained for [Zr(OH)2(C2O4)·0.5H2O] 1 shows features revealing a multistep decomposition process (Figure 6). The weight loss between 30 and 100 °C is attributed to the release of the zeolitic water molecules. The next loss is likely to correspond to a

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CONCLUDING REMARKS The 3-D coordination polymer [Zr(OH)2(C2O4)] reported here is a very rare example of a homometallic neutral Zr(IV)oxalate framework. It exhibits the peculiarity to comprise two hydroxo-moieties as a complementary ligand for Zr. Despite the limited metal−metal separation achieved by the oxalate ligands, this compound accommodates guest molecules and reversibly sorbs small molecules. More interestingly, it is a microporous solid as demonstrated by the crystal structure obtained for the guest-free framework. It also shows exceptional crystal stability, that is single crystal to single crystal transitions take place upon guest sorption. It is very likely that the hydroxo-groups contribute to this by stabilizing the guest molecules through Hbond interaction. Further investigation of this microporous solid will necessitate developing a more efficient synthesis methodology; work along this line is in progress.

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EXPERIMENTAL SECTION

General. All reagents were purchased from commercial sources and used as received. The chemicals used are ZrO(NO3)2·xH2O 99.99% pure (i.e., [Zr(OH)2(NO3)2(H2O)x]),11 oxalic acid H2C2O4·2H2O, sodium metasilicate Na2SiO3·5H2O (1.04 g·cm−3), and nitric acid. The FT-IR spectrum was obtained in the range 4000−400 cm−1 with a Perkin-Elmer Spectrum 100 FT-IR spectrometer. The thermal behavior was studied under nitrogen flow in a Perkin-Elmer Diamond TG/DTA instrument, at a heating rate of 10 °C/min between 30 and 600 °C. Syntheses. [Zr(OH)2(C2O4)·0.5H2O], 1. Na2SiO3·5H2O (212 g, 1 mol) was added to 1000 mL of distilled water in order to obtain a 1 M solution. This solution was kept undisturbed for three days to separate the insoluble impurities present, which collect at the bottom. 50 mL of a 1 M oxalic acid solution was added drop-by-drop with constant stirring. A 3 M nitric acid solution (ca. 50 mL) was added to this mixture with continuous stirring, and the pH was adjusted to 3.5−4. The resulting solution was then allowed to sit in a glass test tube of E



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length 20 cm and internal diameter 2 cm for a gelling time of 144 h at room temperature. The open end of the tube was closed with a cotton plug.21 After which, an aqueous solution (50 mL) of ZrO(NO3)2 (0.231g, 1 mmol) was added above the gel carefully to prevent the gelled surface from cracking. At some stage, the development of a rhythmic pattern of precipitate known as “Liesegang rings” was observed and crystals formed in this zone within 3 weeks. Once the precipitate stopped advancing, crystals of 1 were removed from the gel, washed with warm water to remove adhering gel particles, and dried at room temperature (yielding to 10 mg of product). These crystals are suitable for single crystals X-ray diffraction investigations. [Zr(OH)2(C2O4)], 2. Phase 2 corresponds to the guest-free compound obtained by heating a single crystal of 1 under N2 gas flow at 100 °C. [Zr(OH)2(C2O4)·0.5H2O], 3. Crystals of 2 were put several hours in water at room temperature yielding phase 3. These crystals were suitable for single crystals X-ray diffraction investigations. Crystallographic Studies. Transparent single crystals suitable for single crystal X-ray structure determination were carefully chosen under an optical microscope. They were mounted on glass fibers for Xray measurement. Reflection data were collected on a Bruker APEX II CCD diffractometer using a graphite monochromatozed Mo Kα radiation (λ = 0.7107 Å) at 293 K for 1 and 3. For 2, they have been collected at 100 °C on an Oxford Gemini diffractometer with graphite monochromatized Mo Kα radiation. Crystal structures were solved by the method of heavy atom using the program SHELXS-97.22 This method allows obtaining the position of zirconium atoms. The positions of oxygen and carbon atoms have been identified on the subsequent Fourier difference map. The refinement based on F2 was performed using the program CRYSTALS.23 Fourier difference maps, made by including the atoms of the framework, revealed a completely delocalized electronic density inside the channels corresponding to guest molecules. Indeed, Fourier map analyses showed a quasi-continuous electron density. This feature could correspond to either a statistical occupancy or to the presence of less bonded molecules displaying dynamic properties. Water molecules were localized for compound 1 and 3, which were thus constrained to lie along the c axis in the tunnels of the two frameworks. The oxygen atoms O5 was thus located on the maximum density peaks at the 4e site, which was fully occupied by water molecules. We have not localized hydrogen atoms for guest molecules in tunnels and for hydroxyl groups. A summary of crystal and data collection parameters is given in Table 1. The structural graphics were created with the Diamond24 program.

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ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic files in CIF format, ORTEP plots (Figures S1−3), and additional crystallographic data (Tables S1−S2) of 1−3; results of continuous shape measures analysis (Table S3), and IR spectrum for 1 (Figure S5). This material is available free of charge via the Internet at http://pubs.acs.org. The cif for 1−3 have been deposited at CCDC with references 956917, 956918, and 956919. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request.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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REFERENCES

(1) (a) Eddaoudi, M.; Kim, J.; Rosi, N.; Vodak, D.; Wachter, J.; O’Keeffe, M.; Yaghi, M. O. Science 2002, 295, 469−472. (b) Ferey, G. Z. Anorg. Allg. Chem. 2012, 638, 1897. (c) Schröder, M. Functional F



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Z.-B.; Cai, Y.-C.; Lu, X.-W.; Zeller, M. Z. Anorg. Allg. Chem. 2011, 637, 578−582. (18) Spek, A. L. J. Appl. Cryst. 2003, 36, 7−13. (19) Deacon, G. B.; Phillips, R. J. Coord. Chem. Rev. 1980, 33, 227− 250. (20) Nakamoto, K. Infrared and Raman Spectra of Inorganic and Coordination Compounds; Wiley: New York, 1997. (21) Hensisch, H. K. Crystals in Gels and Liesegang Rings; Cambridge University Press: Cambridge, England, 1988. (22) Sheldrick, G. M. Acta Crystallogr. 2008, A 64, 112−122. (23) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.; Watkin, D. J. J. Appl. Crystallogr. 2003, 36, 1487−1487. (24) Brandenburg, K. DIAMOND v3.2; Crystal Impact: Bonn (Germany), 1997−2012.

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Synthesis and Crystal Structures of Various Phases of the Microporous

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