Fast Microwave Synthesis of a Microporous Lanthanide−Organic

DOI: 10.1021/cg900884d

Fast Microwave Synthesis of a Microporous Lanthanide-Organic Framework

2010, Vol. 10 2025–2028

Patrı´ cia Silva, Anabela A. Valente, Jo~ ao Rocha, and Filipe A. Almeida Paz* University of Aveiro, CICECO, Department of Chemistry, Campus Universit ario de Santiago, 3810-193 Aveiro, Portugal Received July 28, 2009; Revised Manuscript Received March 10, 2010

ABSTRACT: A microporous cationic lanthanide-organic framework, [Ce2(pydc)2(Hpydc)(H2O)2]Cl 3 (9þy)H2O (where pydc2- is

the diprotonated residue of 2,5-pyridinedicarboxylic acid), has been prepared under just 30 min (total reaction time) by applying microwave heating. The microporous framework (ca. 43% of accessible volume) contains prominent channels (cross section ca. 12  7 A˚2) running parallel to the [001] direction housing disordered charge-balancing chloride anions and water molecules of crystallization. The BET surface area of the degassed material was calculated as approximately 106 m2/g. The solvent could be partially exchanged by chloroform or benzyl alcohol by crystal immersion at room temperature over a period of several days. Structural details and robustness, and solvent exchange tests, were investigated by using in tandem X-ray diffraction (single-crystal and powder), electron microscopy (SEM and EDS), and FT-IR spectroscopy. With almost two full decades of worldwide research on metalorganic frameworks (MOFs) which led to thousands of new structures,1 a new paradigm has been presented to crystal engineers: is it possible to develop new synthetic concepts to transpose the laboratory-scale strategies to the materials science field, where the compounds may find a direct (and potential industrially interesting) application?2 The creation of this bridge is difficult because industry usually requires fast, inexpensive, and environmentally friendly fabrication methods. Current synthetic procedures of MOFs (solvothermal approaches) are poorly attractive to industry, requiring a considerable amount of time (typically days) and energy, and usually producing small amounts of useful material. It is, thus, not surprising why BASF developed a commercially viable large-scale approach (electrochemical method)2 to replace the traditional method reported by Williams and collaborators3 for the preparation of HKUST-1. Some groups have been directing their research efforts to answer the aforementioned question by employing microwaveassisted synthesis (MWAS). Even though it has been widely used for several decades with great success in various branches of synthetic organic chemistry,4 only recently it captivated the attention of crystal engineers: on the one hand, the investigation of the influence of reaction parameters of MWAS on crystal quality, morphology, and size has been performed using known MOF structures such as MOF-5,5 IRMOFs 1, 2, and 3,6 and Cu-BTC;7 on the other, and while thinking on applications, several groups focused instead on the preparation of nanosized crystals of MIL101,8 on the growth of MOF-5 thin films on porous substrates,9 or on the preparation of new materials which can be used in the separation of CO2 from CH410 or as target-specific magnetic resonance imaging compounds.11 Following our interest in MOFs,12 we have recently directed our attention to their practical use as functional materials (e.g., as catalysts, ethanol or pH sensors, or photoluminescent compounds).13 While investigating the lanthanide/2,5-pyridinedicarboxylic acid system (H2pydc; Scheme 1)14 using MWAS, for which only a handful of structures is available in the literature,14b,15 we unexpectedly discovered a completely novel MOF structure with large one-dimensional channels. The material could be isolated under very mild conditions and in just 20 min of reaction: [Ce2(pydc)2(Hpydc)(H2O)2]Cl 3 (9þy)H2O (1). It is noteworthy that this heating approach is known

Scheme 1. 2,5-Pyridinedicarboxylic Acid (H2pydc)

*To whom correspondence should be addressed. E-mail: filipe.paz@ ua.pt. Fax: þ351 234 370084. Telephone: þ351 234 370200.

to, in some rare cases, lead to unprecedented frameworks, as described here.8,16 We believe that 1 constitutes the first example of a new microporous system, with large accessible channels, prepared under these reaction conditions. While reacting H2pydc with CeCl3 3 7H2O in distilled water for just 20 min (120 °C, 50 W microwave power),17 large single crystals of 1 (formulated on the basis of single-crystal X-ray diffraction studies18 in combination with EDS analyses) were directly isolated from the reaction vial via filtration. A second phase was systematically present and was identified as identical to the structure reported by Huang et al.: [Ce2(pydc)3(H2O)2].15a A systematic change of the MWAS conditions to promote the sole preparation of 1 proved to be unsuccessful: we found that we could only improve the ratio between the desired microporous phase (1) and [Ce2(pydc)3(H2O)2] to 4:1 (i.e., ca. 20% of the dense material; see phase quantification from powder X-ray diffraction data in Figure S1 in the Supporting Information). Nevertheless, the considerable difference in particle size allowed an easy segregation of 1 for further detailed X-ray diffraction studies (see below). The framework is based on a single crystallographically independent Ce3þ (Figure 1). The nine-coordination sphere is composed of one water molecule, six oxygen atoms from syn, skew- or syn,syn-bridging carboxylate groups, plus a N,O-chelate. Considering the C1i syn,syn-bridge as a single coordination site [bite angle of 48.86(12)°], the coordination polyhedron resembles a highly distorted dodecahedron with the two bisphenoids having lateral triangular faces with distances ranging from ca. 3.07 to 4.65 A˚ (all belonging to the elongated bisphenoid, which is composed by O1W, O1, O6i, and C1i; Figure 1). The two single H2-xpydcx- residues have markedly distinct structural functions. The fully deprotonated N,O-chelated moiety (Figure 1) promotes close proximity between Ce3þ centers via a combination of five coordinative bonds and strong π-π offset stacking contacts (Figure S2 in the Supporting Information), ultimately directing the formation of undulated layers placed in the bc plane of the unit cell (Figure 2a) which contain zigzag-distributed

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lanthanide centers. The shortest intermetallic distance is 4.6832(5) A˚. The Hpydc- moiety promotes porosity by acting as rigid pillars

Figure 1. Distorted dodecahedral {LnNO8} coordination environment of the Ce3þ center present in [Ce2(pydc)2(Hpydc)(H2O)2]Cl 3 (9þy)H2O. Bond lengths (in A˚): Ce1-O1, 2.489(4); Ce1-O1i, 2.599(4); Ce1-O2i, 2.719(5); Ce1-O3iii, 2.480(5); Ce1-O4ii, 2.469(5); Ce1-O5, 2.470(5); Ce1-O6i, 2.446(5); Ce1-O1W, 2.566(6); Ce1-N1, 2.713(5). A detailed list of all polyhedral bond angles is provided in Table S2 (see the Supporting Information). Symmetry transformations used to generate equivalent atoms: (i) x, 1 - y, 1/2 þ z; (ii) 1.5 - x, -1/2 þ y, 1.5 - z; (iii) 1.5 - x, 1.5 - y, 2 - z.

Silva et al. along the [100] direction. The pillaring process seems to be completely random, with the heteroatom being protonated [ν(Nþ-H) at 2925 and 2853 cm-1; Figure S8 in the Supporting Information] and engaged in strong and highly directional N-H 3 3 3 Cl hydrogen bonds (Table S3 and Figure S3 in the Supporting Information), with the charge-balancing (and partially occupied) chloride anions located inside the channels. This structural arrangement leads to channels with large apertures running parallel to the c axis. A simulation of the crystal habit using the BFDH method19 is in good agreement with that observed for crystals of 1 (Figure 2b), further evidencing that crystal growth occurs predominantly in the direction of the channels. This result is another indication of the existence of strong connections composing the aforementioned undulated layer, and it further indicates that the formation of extra channels to enlarge the crystal size is more erratic and, thus, less favorable. Channels confine water molecules of crystallization for which it was possible to model 7 crystallographic locations, totally adding up to 4.5 chemical entities per Ce3þ. Not all confined water could be modeled into the final structure: the inner section of the channels contains extra unaccounted electron density (hence, the y in the empirical formula of 1) which encompasses a total volume of 363 A˚3 (181 electrons; Figure S4 in the Supporting Information). In total, the channels contain the impressive volume of 1671 A˚3 as solvent accessible area, i.e., ca. 43% of the volume of the unit cell, with apertures of about 12  7 A˚2 (Figure 2c). Based on the structural features highlighted above, it is feasible to consider as network nodes the centers of gravity of the H2-xpydcx- residues and Ce3þ. Because the former are topologically equivalent, 1 is thus a binodal network having 4- (the centers of gravity) and 6- (Ce3þ) connected nodes (Figure S5 in the Supporting Information). The network is stp22 with point symbol {44.62}3{49.66}2, which, to the best of our knowledge, has only been observed a handful of times only among MOFs.

Figure 2. (a) Mixed ball-and-stick and polyhedral representation of the crystal structure of [Ce2(pydc)2(Hpydc)(H2O)2]Cl 3 (9þy)H2O, emphasizing the large one-dimensional channels running parallel to the [001] direction and filled with water molcules of crystallization and charge-balancing chloride anions. (b) SEM picture of the crystals directly isolated from the MWAS showing a similar crystal habit to that predicted theoretically using the Bravais-Friedel-Donnay-Harker (BFDH) method19 (simulation performed using mercury).20 (c) Connolly surface21 (probe molecule with average radius of 1.2 A˚, such as water) encompassing the channels and having an approximate cross section of 12  7 A˚2.

Communication Topologically similar structures known to date also contain lanthanide centers and exhibit remarkable porosity evidenced by their large channels.23 The material exhibits a type I adsorption isotherm behavior, typical of microporous materials (Figure S11).24 A maximum N2 uptake of ca. 1.1 mmol 3 g-1 was reached at a relative pressure (p/p0) of ca. 0.16, remaining constant as p/p0 tends to unity. The specific pore volume calculated for p/p0 = 0.9 is 0.037 cm3 3 g-1. It is noteworthy that the experimental points for p/p0 < 0.16 do not correspond to equilibrium conditions, which could not be reached after 6 h. Nevertheless, the approximate BET specific surface area calculated for the p/p0 range of 0.03-0.16 is 106 m2 3 g-1. This microporosity further explains, for example, why single crystals of 1 release water when pressed (an occurrence observed during the preparation of the KBr pellets for the FT-IR measurements). Solvent exchange studies were performed using benzyl alcohol (1_Bz_Alc) and chloroform (1_CHCl3).25 Single-crystal X-ray studies in conjunction with SEM showed that exchanged crystals preserved their structural integrity (Figures S6-S8 in the Supporting Information). Additionally, when treated for 3 days at ca. 50 °C (1_50C), X-ray studies failed to show a significant loss of water molecules of crystallization (data not shown), which agrees well with the TGA data (Figure S10 in the Supporting Information), thus suggesting some structural robustness and the existence of strong hydrogen bonding interactions mediating the interwater connections inside the channels. Indeed, FT-IR studies (Figure S9 in the Supporting Information) show that the ν(O-H) vibrational modes of water fall in the 3300-3125 cm-1 region, which supports (i) a general weakening of the O-H bond via hydrogen bonding interactions and (ii) a distribution of the strength of these interactions, with, most probably, the water moieties closer to the framework interacting more strongly than those in the inner section of the channels. This assumption is supported by the TGA measurements, which indicate two distinct weight losses up to ca. 320 °C: despite the fact that none of them could be solely attributed to one particular type of water molecule, it is feasible to assume that those released below ca. 120 °C should be those more weakly bound to the structure (i.e., in the inner positions of the channels). Variable-temperature powder X-ray diffraction studies performed in the 40-200 °C range further confirm the assumed structural robustness and clearly point to a gradual contraction of the channels with increasing temperature (Figure S12 in the Supporting Information) rather than their collapse. X-ray analysis of the solvent-exchanged crystals revealed a significant increase in overall electron density registered for the channels. The structural modeling of benzyl alcohol or chloroform molecules did not lead to sensible refinements. We have instead investigated the electron density as a whole by using the SQUEEZE subroutines implemented in the software package PLATON: a general increase in electron count per unit cell is observed for 1_Bz_Alc and 1_CHCl3 when compared with the evacuated structure of 1 (i.e., 1 except for the water molecules of crystallization, which were manually taken; Table S1 in the Supporting Information). EDS analyses for 1 and 1_CHCl3 clearly denote a reduction in the Ce/Cl ratio (Figures S7 and S8 in the Supporting Information). It is also important to stress that even though the crystal structure remains intact, the unit cell volume of 1_Bz_Alc is about 10% smaller than that of 1 (Table S1 in the Supporting Information). These data constitute clear evidence that benzyl alcohol and chloroform molecules are truly incorporated into the microporous structure by simple diffusion at ambient temperature. In conclusion, we have shown that by using microwave heating it is possible to prepare, in a very short period of time, a microporous lanthanide-organic framework having H2-xpydcxresidues. Our results indicate that the materials undergo singlecrystal-to-single-crystal solvent exchange at ambient temperature

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and that the mild heating of the crystals does not lead to the release of the confined water molecules. Framework integrity is also not compromised with increasing temperature. We believe that this work can open new perspectives in this field of research envisaging new approaches to obtain large quantities of functional materials (for example with applications based on porosity) in an economically viable period of time. Future work by our research group on this novel system includes further optimization of the synthetic procedure using MWAS to allow the inclusion of other lanthanide centers and to produce larger quantities in even shorter periods of time. In addition, we are now investigating this intriguing and potential new microporous structure as a functional material, to act, for example, as an adsorbent of molecules (or gases) or as an anion-exchanging capable compound. Acknowledgment. We are grateful to Fundac-a~o para a Ci^ encia e a Tecnologia (FCT, Portugal) for their financial support (PTDC/QUI-QUI/098098/2008), for specific funding toward the purchase of the single-crystal diffractometer, and also for Doctoral Research Grant No. SFRH/BD/46601/2008 (to P.S.). We also wish to thank Marta Ferro and Ros ario Soares for assistance with the electron microscopy and powder X-ray diffraction studies, respectively. Supporting Information Available: Crystallographic information file (CIF) for 1. Experimental details on the single-crystal X-ray studies of 1, 1_Bz_Alc, and 1_CHCl3. Phase quantification from powder X-ray diffraction studies, framework stability with variable temperature, and nitrogen adsorption studies. Additional structural drawings and topological studies. SEM, EDS, FT-IR, and TGA data. This material is available free of charge via the Internet at http://pubs.acs.org.

References (1) (a) Champness, N. R. In Making Crystals by Design;Methods Techniques and Applications, 1st ed.; Braga, D., Grepioni, F., Eds.; Wiley-VCH Verlag GmbH & Co. KGaA: Weinheim, 2007; pp 193-208. (b) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed. 2004, 43, 2334–2375. (c) Kitagawa, S.; Uemura, K. Chem. Soc. Rev. 2005, 34, 109–119. (d) Tranchemontagne, D. J.; Mendoza-Cortes, J. L.; O'Keeffe, M.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1257–1283. (e) Shimizu, G. K. H.; Vaidhyanathan, R.; Taylor, J. M. Chem. Soc. Rev. 2009, 38, 1430–1449. (f) Natarajan, S.; Mahata, P. Chem. Soc. Rev. 2009, 38, 2304–2318. (g) Ma, L. Q.; Abney, C.; Lin, W. B. Chem. Soc. Rev. 2009, 38, 1248–1256. (h) Long, J. R.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1213–1214. (i) Lee, J.; Farha, O. K.; Roberts, J.; Scheidt, K. A.; Nguyen, S. T.; Hupp, J. T. Chem. Soc. Rev. 2009, 38, 1450–1459. (j) Czaja, A. U.; Trukhan, N.; Muller, U. Chem. Soc. Rev. 2009, 38, 1284–1293. (k) Allendorf, M. D.; Bauer, C. A.; Bhakta, R. K.; Houk, R. J. T. Chem. Soc. Rev. 2009, 38, 1330–1352. (l) Eddaoudi, M.; Moler, D. B.; Li, H. L.; Chen, B. L.; Reineke, T. M.; O'Keeffe, M.; Yaghi, O. M. Acc. Chem. Res. 2001, 34, 319–330. (2) Mueller, U.; Schubert, M.; Teich, F.; Puetter, H.; Schierle-Arndt, K.; Pastre, J. J. Mater. Chem. 2005, 16, 626–636. (3) Chui, S. S. Y.; Lo, S. M. F.; Charmant, J. P. H.; Orpen, A. G.; Williams, I. D. Science 1999, 283, 1148–1150. (4) (a) de la Hoz, A.; Diaz-Ortiz, A.; Moreno, A. Chem. Soc. Rev. 2005, 34, 164–178. (b) Kuhnert, N. Angew. Chem., Int. Ed. 2002, 41, 1863– 1866. (5) Choi, J. Y.; Kim, J.; Jhung, S. H.; Kim, H. K.; Chang, J. S.; Chae, H. K. Bull. Korean Chem. Soc. 2006, 27, 1523–1524. (6) Ni, Z.; Masel, R. I. J. Am. Chem. Soc. 2006, 128, 12394–12395. (7) Seo, Y. K.; Hundal, G.; Jang, I. T.; Hwang, Y. K.; Jun, C. H.; Chang, J. S. Microporous Mesoporous Mater. 2009, 119, 331– 337. (8) Jhung, S. H.; Lee, J. H.; Yoon, J. W.; Serre, C.; Ferey, G.; Chang, J. S. Adv. Mater. 2007, 19, 121–124. (9) Yoo, Y.; Jeong, H. K. Chem. Commun. 2008, 2441–2443. (10) Bae, Y. S.; Mulfort, K. L.; Frost, H.; Ryan, P.; Punnathanam, S.; Broadbelt, L. J.; Hupp, J. T.; Snurr, R. Q. Langmuir 2008, 24, 8592– 8598. (11) Taylor, K. M. L.; Rieter, W. J.; Lin, W. B. J. Am. Chem. Soc. 2008, 130, 14358–14359.

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(12) (a) Cunha-Silva, L.; Ananias, D.; Carlos, L. D.; Paz, F. A. A.; Rocha, J. Z. Kristallogr. 2009, 224, 261–272. (b) Shi, F. N.; Trindade, T.; Rocha, J.; Paz, F. A. A. Cryst. Growth Des. 2008, 8, 3917–3920. (c) Chelebaeva, E.; Larionova, J.; Guari, Y.; Ferreira, R. A. S.; Carlos, L. D.; Paz, F. A. A.; Trifonov, A.; Guerin, C. Inorg. Chem. 2008, 47, 775–777. (d) Shi, F. N.; Cunha-Silva, L.; Ferreira, R. A. S.; Mafra, L.; Trindade, T.; Carlos, L. D.; Paz, F. A. A.; Rocha, J. J. Am. Chem. Soc. 2008, 130, 150–167. (e) Paz, F. A. A.; Rocha, J.; Klinowski, J.; Trindade, T.; Shi, F. N.; Mafra, L. Prog. Solid State Chem. 2005, 33, 113–125. (13) (a) Harbuzaru, B. V.; Corma, A.; Rey, F.; Jorda, J. L.; Ananias, D.; Carlos, L. D.; Rocha, J. Angew. Chem., Int. Ed. 2009, 48, 6476-6479. (b) Cunha-Silva, L.; Lima, S.; Ananias, D.; Silva, P.; Mafra, L.; Carlos, L. D.; Pillinger, M.; Valente, A. A.; Paz, F. A. A.; Rocha, J. J. Mater. Chem. 2009, 19, 2618–2632. (c) Harbuzaru, B. V.; Corma, A.; Rey, F.; Atienzar, P.; Jorda, J. L.; Garcia, H.; Ananias, D.; Carlos, L. D.; Rocha, J. Angew. Chem., Int. Ed. 2008, 47, 1080–1083. (d) Cunha-Silva, L.; Mafra, L.; Ananias, D.; Carlos, L. D.; Rocha, J.; Paz, F. A. A. Chem. Mater. 2007, 19, 3527–3538. (14) (a) Shi, F. N.; Cunha-Silva, L.; Trindade, T.; Paz, F. A. A.; Rocha, J. Cryst. Growth Des. 2009, 9, 2098–2109. (b) Soares-Santos, P. C. R.; Cunha-Silva, L.; Paz, F. A. A.; Ferreira, R. A. S.; Rocha, J.; Trindade, T.; Carlos, L. D.; Nogueira, H. I. S. Cryst. Growth Des. 2008, 8, 2505– 2516. (15) (a) Huang, Y.; Song, Y. S.; Yan, B.; Shao, M. J. Solid State Chem. 2008, 181, 1731–1737. (b) Huang, Y. G.; Jiang, F. L.; Yuan, D. Q.; Wu, M. Y.; Gao, Q.; Wei, W.; Hong, M. C. Cryst. Growth Des. 2008, 8, 166–168. (c) Huang, Y. G.; Wu, B. L.; Yuan, D. Q.; Xu, Y. Q.; Jiang, F. L.; Hong, M. C. Inorg. Chem. 2007, 46, 1171–1176. (d) Liu, C. M.; Zhang, D. Q.; Zhu, D. B. Inorg. Chem. Commun. 2008, 11, 903–906. (e) Luo, F.; Che, Y. X.; Zheng, J. M. Cryst. Growth Des. 2008, 8, 2006– 2010. (f) Qin, C.; Wang, X. L.; Wang, E. B.; Su, Z. M. Inorg. Chem. 2005, 44, 7122–7129. (g) Song, Y. S.; Yan, B.; Chen, Z. X. J. Mol. Struct. 2005, 750, 101–108. (h) Zhang, X. F.; Huang, D. G.; Chen, C. N.; Liu, Q. T.; Liao, D. Z.; Li, L. C. Inorg. Chem. Commun. 2005, 8, 22–26. (16) (a) Amo-Ochoa, P.; Givaja, G.; Miguel, P. J. S.; Castillo, O.; Zamora, F. Inorg. Chem. Commun. 2007, 10, 921–924. (b) Jhung, S. H.; Lee, J. H.; Forster, P. M.; Ferey, G.; Cheetham, A. K.; Chang, J. S. Chem.;Eur. J. 2006, 12, 7899–7905. (c) Lin, Z. J.; Wragg, D. S.; Morris, R. E. Chem. Commun. 2006, 2021–2023. (d) Liu, B.; Zou, R. Q.; Zhong, R. Q.; Han, S.; Shioyama, H.; Yamada, T.; Maruta, G.; Takeda, S.; Xu, Q. Microporous Mesoporous Mater. 2008, 111, 470– 477. (e) Liu, W. L.; Ye, L. H.; Liu, X. F.; Yuan, L. M.; Lu, X. L.; Jiang, J. X. Inorg. Chem. Commun. 2008, 11, 1250–1252. (f) Wang, X. F.; Zhang, Y. B.; Huang, H.; Zhang, J. P.; Chen, X. M. Cryst. Growth Des. 2008, 8, 4559–4563. (17) Starting chemicals were readily available from commercial sources and were used as received without further purification: 2,5-pyridinedicarboxylic acid (2,5-H2pydc, C7H5NO4, purum g 98%, Fluka), cerium(III) chloride heptahydrate (CeCl3 3 7H2O, Aldrich), and sodium hydroxide (NaOH pellets, Panreac). Microwave-assisted synthesis: a mixture containing 2,5-H2pydc, CeCl3 3 7H2O, and NaOH was manually ground in a mortar for 1 min and then transferred to a 10 mL IntelliVent microwave reactor. Approximately 6 mL of distilled water was added to the mixture without stirring. The overall suspension, with an approximate molar ratio of about 1:1:2.5:800, was reacted inside CEM Focused Microwave Synthesis System Discover S-Class equipment. Reaction took place without magnetic stirring and by monitoring the temperature and pressure inside the vessel. A constant flow of air (ca. 10 psi of pressure) ensured a close control of the temperature. The final product was recovered by vacuum filtration, followed by washing

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(18)

(19) (20) (21) (22) (23)

(24) (25)

with copious amounts of distilled water, and then air-dried overnight. Experimental microwave conditions: temperature, 120 °C; power, 50 W; reaction time, 20 min of microwave irradiation. Large-scale microwave-assisted synthesis using a 35 mL IntelliVent microwave reactor: reactive suspension with the same molar ratios as mentioned above for a total volume of ca. 21 mL of distilled water. Experimental microwave conditions: temperature, 120 °C; power, 100 W; reaction time, 15 min of microwave irradiation. Single-Crystal X-ray Structure Analysis: single-crystals of 1 (and its solvent-exchanged compounds; see Supporting Information for additional data) were mounted on Hampton Research CryoLoops using FOMBLIN Y perfluoropolyether vacuum oil (LVAC 25/6) purchased from Aldrich with the help of a Stemi 2000 stereomicroscope equipped with Carl Zeiss lenses. Data were collected at 150(2) K on a Bruker X8 Kappa APEX II charge-coupled device (CCD) area-detector diffractometer (Mo KR graphite-monochromated radiation, λ = 0.71073 A˚) controlled by the APEX-2 software package (Version 2-1-RC13; 2006) and equipped with an Oxford Cryosystems Series 700 cryostream. Images were processed using the software package SAINTþ (version 7.23a; 1997-2005), and data were corrected for absorption by the multiscan semiempirical method implemented in SADABS (version 2.01; 1998). The structure of 1 was solved using the Patterson synthesis algorithm implemented in SHELXS-97, which allowed the immediate location of the Ln3þ metallic center. All remaining non-hydrogen atoms were located from difference Fourier maps calculated from successive full-matrix least-squares refinement cycles on F2 using SHELXL-97. All non-hydrogen atoms were successfully refined using anisotropic displacement parameters. Additional details on the refinement of the structures and data treatment of the solvent accessible area using the SQUEEZE program are provided in the Supporting Information. Crystal Data for 1: C21H32Ce2ClN3O23, M = 1010.19, monoclinic, space group C2/c, Z = 4, a = 31.283(4) A˚, b = 14.5442(18) A˚, c = 8.6817(10) A˚, β = 96.033(7)°, V = 3928.1(8) A˚3, μ(Mo KR) = 2.438 mm-1, Dc = 1.708 g cm-3, colorless needles with crystal size of 0.12  0.08  0.03 mm3. Independent reflections 5239 (Rint = 0.0467). Final R1 = 0.0511 [I > 2σ(I)] and wR2 = 0.1465 (all data). Data completeness to θ = 29.13°, 99.1%. CCDC 741253. (a) Bravais, A. Etudes Crystallographiques; Academie des Sciences: Paris, 1913. (b) Donnay, J. D. H.; Harker, D. Am. Mineral. 1937, 22, 446–467. (c) Friedel, G. Bull. Soc. Fr. Mineral. 1907, 30, 326. Bruno, I. J.; Cole, J. C.; Edgington, P. R.; Kessler, M.; Macrae, C. F.; McCabe, P.; Pearson, J.; Taylor, R. Acta Crystallogr., B 2002, 58, 389–397. Connolly, M. L. J. Am. Chem. Soc. 1985, 107, 1118–1124. (a) Blatov, V. A. IUCr Comput. Comm. Newsl. 2006, 7, 4–38. (b) O'Keeffe, M.; Peskov, M. A.; Ramsden, S. J.; Yaghi, O. M. Acc. Chem. Res. 2008, 41, 1782–1789. (a) Jia, J. H.; Lin, X.; Blake, A. J.; Champness, N. R.; Hubberstey, P.; Shao, L. M.; Walker, G.; Wilson, C.; Schroder, M. Inorg. Chem. 2006, 45, 8838–8840. (b) Abrahams, B. F.; Moylan, M.; Orchard, S. D.; Robson, R. CrystEngComm 2003, 5, 313–317. (c) Millange, F.; Serre, C.; Marrot, J.; Gardant, N.; Pelle, F.; Ferey, G. J. Mater. Chem. 2004, 14, 642–645. Gregg, S. J.; Sing, K. S. W. Adsorption, Surface Area and Porosity, 2nd ed.; Academic Press: London, 1982. Crystals of 1 were manually selected and placed, at ambient temperature and static conditions, inside vials containing benzyl alcohol (1_Bz_Alc) or chloroform (1_CHCl3). One portion was placed inside an MMM oven at 50 °C with internal air convection (1_50C). After 72 h, crystals were preserved in FOMBLIN oil for immediate single-crystal X-ray diffraction studies.