Communication pubs.acs.org/IC
Th3[Th6(OH)4O4(H2O)6](SO4)12(H2O)13: A Self-Assembled Microporous Open-Framework Thorium Sulfate Jian Lin, Geng Bang Jin,* and L. Soderholm* Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States S Supporting Information *
Using thermodynamic solution stabilities as a guide, in combination with materials precedents, we were able to preselect aqueous solution conditions favoring the synthesis of another large thorium sulfate cluster that includes oxo, hydroxo, and sulfato bridging. Herein, we report the preparation and structure elucidation of Th3[Th6(OH)4O4(H2O)6](SO4)12(H2O)13· xTh4+·ySO42−·nH2O (1; Table S1). Its structure features a microporous open framework, composed of [Th6(OH)4O4(H2O)6]12+ hexamers linked via bridging sulfates through thorium(IV) monomers. Simple evaporation of an aqueous solution (2.40 < pH ≤ 2.50) made by dissolving thorium hydroxide in sulfuric acid resulted in compound 1 and a second phase, 2, in almost identical crystal habits (section S1 and Figure S1a). Unfortunately, all examined crystals of 2 are severely twinned, resulting in an overall less than satisfactory final structural refinement, and, consequently, only the unit cell parameters are reported in the Supporting Information. Nonetheless, the distinctive Th−Th connectivities strongly suggest 2 as another thorium sulfate hydrate cluster containing both hexanuclear thorium(IV) cores and thorium(IV) monomeric units (section S2). At pH ∼2.40, a coformation of 1, 2, and a known compound, Th(SO4)2(H2O)7·(H2O)2 (3), was observed.7 In contrast to the titled compound, the structure of 3 exclusively contains Th(SO4)2(H2O)7 monomeric units without any hydroxo, oxo, and sulfato bridging (Figure S3).7b Evaporation of lower-pH solutions (1.50 ≤ pH < 2.40) yielded only 3. It is noted that the syntheses of compound 3 from evaporation reactions under even more acidic conditions have been reported in the literature.7 Structural details were established through analysis of singlecrystal X-ray diffraction data (Supporting Information). Compound 1 crystallizes in the monoclinic space group C2/c and adopts a three-dimensional (3D) structure with a microporous open framework, Th 3 [Th 6 (OH) 4 O 4 (H 2 O) 6 ](SO4)12(H2O)13 (Figure 1). Most open-framework structures employ in their syntheses an alkali-metal ion or organic ligand, usually an amine or dicarboxylate group, as a templating agent.11 Compound 1 represents a less-common open framework prepared without the use of such agents. Included among these is Th3(SO4)6(H2O)6·H2O,12 which also combines the binding complexities associated with both the ThIV and sulfate ions. The channels in the structure of 1 extend along both the c and b axes with approximate dimensions of 13 Å × 11 Å (Figure 1a) and 11 Å × 8 Å (Figure 1b), respectively. The solvent-accessible volume calculated by PLATON13 is 12034.4 Å3, corresponding to
ABSTRACT: A neutral-framework thorium oxohydroxosulfate hydrate has been isolated from aqueous solution. This microporous structure, which self-assembles without a templating agent, is built from [Th6(OH)4O4(H2O)6]12+ hexamers and thorium(IV) monomers linked through bridging sulfates. Solution conditions were chosen to enable an active competition between sulfate and hydroxide for thorium coordination. Synthetic requirements are discussed for this rare example of a thorium(IV) polynuclear complex containing mixed oxo-, hydroxo-, and sulfato-bridging moieties.
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hether in the laboratory, in atmospheric aerosols, or in the geosphere, the presence of dissolved sulfate can have a significant impact on the chemistry of metal ions in aqueous solution.1 Because sulfate can exhibit different binding modes, monodentate or multidentate, in both solutions and solids, and because the energetics of these modes can be very similar, sulfates have a rich but unpredictable effect on the speciation and structure. For the harder tetravalent metal ions (MIV), the chemistry is further complicated by their strong tendency to hydrolyze in all but the most acidic solutions.2 Although sulfate binding is generally stronger than hydroxide for a specific MIV, variables including temperatures, relative concentrations, and pH values can play a critical role in influencing competition for ligation. This has been specifically demonstrated for the hard ZrIV and HfIV ions, where high-energy X-ray scattering (HEXS) data reveal solution conditions in which SO42− and OH− compete for metal ligation.3 Precipitates obtained under these select conditions contain a variety of mixed oxo/hydroxo/sulfato metal clusters.4 Unlike the dihydroxo-bridged tetrameric “zirconyl” species found under acidic aqueous conditions,5 ThIV, the softest of the MIV ions, presents as the homoleptic decahydrate Th(OH2)10 complex.6 Oligomeric hydroxide species have also been reported as hydrated thorium sulfates7 and selenates.8 Thorium sulfate ligation is relatively more stable, compared with hydroxide, than zirconium(IV) sulfate, as judged by published thermodynamic stability constants. As a result, solution conditions favoring mixed hydroxide−sulfate coordination are expected to be more restrictive in the case of ThIV.9 This observation is borne out by the current literature, which includes only limited reports of mixed species, specifically Th(OH)2SO4,10 Th4(SO4)7(H2O)7(OH)2·H2O,7b and Th4(SO4)7(OH)2(H2O)6·2H2O.7a © XXXX American Chemical Society
Received: July 21, 2016
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DOI: 10.1021/acs.inorgchem.6b01762 Inorg. Chem. XXXX, XXX, XXX−XXX
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Figure 2. Representations of the (a) Th6−4Th tetrahedral motif, (b) hexanuclear core [Th6(OH)4O4(H2O)6]12+, and (c) SO42− bridging the ThIV ions in the core. ThIV atoms are shown in light blue, S in gray, and O in red. Th(1)−Th(6) polyhedra are shown light blue, Th(7)−Th(9) in dark blue, and S in gray.
in a tetrahedral arrangement on the faces of the hexagon, a positioning that maximizes their distances, provides the most energetically favorable positions for protons.15 This thorium hexamer is one of an isostructural series [M6(μ3−OH)4(μ3O4)(H2O)6]12+ prevalent in both MIV solution and solid state. Detailed single-crystal structural characterizations have been previously reported for Th3a,16 and other MIV (M = Zr,17 Ce,10,18 U,16a,19 Np,4e Pu20) cations. The capping H2O molecules are located on each vertex of the thorium(IV) octahedra. Th atoms are chelated by one SO42− anion along each of the 12 octahedral edges, forming a [Th6(OH)4O4(H2O)6](SO4)1212− unit (Figure 2c). As a result, each Th ion within this cluster is coordinated by two O2−, two OH−, one H2O, and four bridging monodentate SO42− groups (Figure 3a). In contrast, the coordination
Figure 1. Th3[Th6(OH)4O4(H2O)6](SO4)12(H2O)13 framework projected along the c (a) and b (b) axes. Hexanuclear core [Th6(OH)4O4(H2O)6]12+ polyhedra shown in light blue, thorium(IV) monomeric polyhedra in dark blue, and SO42− anions in gray.
51.5% of the unit-cell volume of 1. Despite this relatively significant void space, the calculated density of 1 from X-ray diffraction data is around 2.4 g/cm3, comparable to 2.801 g/cm3 found for hydrated Th(SO4)2, 3. This is largely due to the much denser framework of 1 than the isolated monomeric units found in 3. X-ray diffraction reveals electron density within the pores indicating disordered entities, which could include H2O molecules, SO42−, and ThIV ions. The character and quantity of these species are crystal specific, whereas the framework structure remains essentially unchanged (section S2). The high degree of disorder within the voids, combined with the variability between crystals is consistent with a charge-neutral framework, wherein electrostatics do not play a strong role in binding occluded ions. For the specific structure reported here, some disordered H2O, ThIV, and SO42− were identified in the channels. In comparison, the structure of Th3(SO4)6(H2O)6·H2O contains 11.5 Å square channels, and no specific species were identified in the voids.12 The framework in 1 can be viewed in terms of building blocks common to other known structures.14 They include 1 crystallographically independent hexanuclear [Th6(OH)4O4(H2O)6]12+ core, 3 thorium(IV) monomers, and 12 bridging SO42− anions (10 μ3-SO42− and 2 μ4-SO42−). Each [Th6(OH)4O4(H2O)6]12+ unit is connected with two Th(7), one Th(8), and one Th(9) monomers via SO42− bridges, forming an aggregated Th(hexamer)−4Th(monomer) tetrahedral motif (Figure 2a). The hexanuclear [Th6(OH)4O4(H2O)6]12+ unit forms the core about which the structure is built. The octahedral hexamer itself is constructed from six ThIV cations bridged by four μ3-O and four μ3-OH groups (Figure 2b). Although the H atoms are not explicitly located in the structural refinement, the longer Th− O bonds suggest four bridging O atoms located on alternating faces of the thorium octahedron (Table S2). Calculations have demonstrated that the highest symmetry structure, with protons
Figure 3. Local coordination environments of (a) Th(1)−Th(6), (b) Th(7), (c) Th(8), and (d) Th(9).
environments of Th(7), Th(8), and Th(9) monomers can best be described as a distorted tricapped trigonal prism (Figure 3b− d). More specifically, each Th(7) atom bonds to six bridging monodentate SO42− anions and three H2O molecules (Figure 3b), whereas each Th(8) or Th(9) atom is surrounded by four bridging monodentate SO42− anions and five H2O molecules B
DOI: 10.1021/acs.inorgchem.6b01762 Inorg. Chem. XXXX, XXX, XXX−XXX
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studies suggesting the predominance of monomeric thorium species in strongly acidic solutions6,22 and the growing importance of oligomers in solutions as a function of increasing pH.3a Compared to ThIV, the crystallization regions of ZrIV/HfIV oligomeric hydroxide species extend into much more acidic solutions, 0.25 M < [H2SO4] < 1.50 M.3a,4b,d,e Such differences in the crystallization conditions point to the increased propensity for thorium sulfate ligation over that for ZrIV/HfIV. This is consistent with the trend observed for their thermodynamic stability constants.9 Furthermore, a variety of mixed oxo/ hydroxo/sulfato ZrIV/HfIV clusters have been reported from a systematic investigation of their sulfate chemistry, but no examples of isolated octahedral hexamers similar to those in 1 have been reported.4e,17 This result is consistent with MIV hydrolysis behaviors predicted based on hardness arguments. In conclusion, we have used the pH to fine-tune the competition between available anions for ligation to ThIV. The result is a new thorium sulfate compound, 1, with a microporous open-framework structure. The framework of 1, formed without the use of a templating agent, is built from [Th6(OH)4O4(H2O)6]12+ hexanuclear cores and thorium(IV) monomers bridged by μ3/μ4-sulfates. 1 represents a rare example of a thorium(IV) product containing oxo, hydroxo, and sulfato bridging. Variation of the complexing ligands in evaporation products as a function of the pH reveals some underlying fundamental chemistry of competing reactions in this system: hydrolysis, condensation, and complexation. Further understanding can be achieved from additional systematic studies that examine the concentration and pH dependence of crystallization products and thorium oligomerization and sulfate complexation in solutions.
(Figure 3c,d). Selected interatomic distances for Th−Th and Th−O are listed in Table S2), which agree well with the literature.7b,16b The ligation modes between ThIV and bridging ligands, particularly sulfates, are expected to play a central role in directing the structure and building of the framework in 1. All of the Th−OSO3 linkages are monodentate, consistent with most other structures.7b,10,12,21 The pKa2 values for the studies of thorium(IV) sulfato complexation in aqueous solution have suggested that monodentate coordination prevails at low [SO42−]/[Th] ratios, in line with that employed in the syntheses of 1.22 Compared to the bidentate mode, monodentate ligation is important in 1 for framework building because it allows additional bridging between the clusters and monomer metal centers. Bridging sulfate ligands are known to promote oligomerization and direct the structure of metal−oxo/hydroxo clusters in solution including zirconium(IV) and hafnium(IV).3a,4d,23 Recently, the the formation of thorium(IV) hexanuclear clusters was observed after the addition of glycine to an aqueous solution containing dimeric ThIV units, suggesting that the bridging ligand glycine plays a role in directing oligomer formation.3a Similar studies have not been conducted in the thorium sulfate system, where sulfate would replace carboxylic acid as the bridging ligand. Furthermore, μ3/μ4-sulfates connect each hexamer to four thorium(IV) monomers, leading to the construction of an extended framework. This contrasts sharply with the μ2monocarboxylate ligands, which terminate the clusters and result in discrete, neutral molecular clusters.3a,16a−c The incorporation of both MIV hexanuclear cores and monomeric moieties to form an extended framework is unprecedented despite their prevalence in solutions and solids. The only reported examples of open frameworks constructed are either by MIV hexanuclear cores [e.g., Zr6O6(OH)2(DTTDC)4(BC)2],19a,24 the Hf-UiO-66 MOF,25 or monomeric units [e.g., Th3(SO4)6(H2O)6·H2O].12 Sulfates are relatively uncommon as tetrahedral anions in open-framework materials, particularly compared with the silicates and phosphates that comprise most zeolitic phases.11a In part, this may be due to the higher charge on S relative to Si or P, with the latter two more likely to form polyanions. As a result, sulfate is normally expected to be associated with low-valent metal ions.11a Under the solution conditions used to synthesize 1, there is a competition between H 2 O, OH − , O 2−, and SO 4 2− for coordination with Th4+.9b The pKa2 value for HSO4− to SO42− is about 2, so that both species may be present in equilibrium under the conditions of our synthesis. In addition, the solution is acidic enough to somewhat limit hydrolysis and favor the presence of the aqua-coordinated Th ion. The influence of solution conditions (temperatures, relative concentrations, and pH) on the competition between SO42− and OH− for metal ligation has been demonstrated for the harder ZrIV and HfIV ions.3,4d,26 For the titled evaporation reactions, the temperature and relative concentration of Th/SO42− remained almost constant. Variability was introduced through the pH of the initial solution, which was systematically adjusted in the range of 1.5−2.5. A monomeric sulfate solid product (3) without oxo or OH− ligands was the only product obtained up to pH 2.4. Only amorphous precipitates were observed in scoping studies with pH values higher than 2.5. Crystalline precipitates containing complex sulfato, oxo, and hydroxo bridges were obtained over a very limited pH range. These results confirm previous solution
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01762. Synthesis, X-ray structure determination, Raman spectroscopy, crystallographic data, selected bond distances, crystal images, structural illustration of 3, and ORTEP diagram of the coordination of Th(9) (PDF) X-ray crystallographic data in CIF format (CIF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail:
[email protected]. *E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The work is supported by the U.S. DOE BES Heavy Elements Program under Contract DE-AC0206CH11357. REFERENCES
(1) Stumm, W.; Morgan, J. J. Aquatic Chemistry: An Introduction Emphasizing Chemical Equilibria in Natural Waters; John Wiley & Sons: New York, 1981; p 780. (2) (a) Baes, C. E.; Mesmer, R. F. The Hydrolysis of Cations; Wiley: New York, 1976. (b) Knope, K. E.; Soderholm, L. Solution and solidstate structural chemistry of actinide hydrates and their hydrolysis and condensation products. Chem. Rev. 2013, 113, 944−994. C
DOI: 10.1021/acs.inorgchem.6b01762 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry (3) (a) Hu, Y.-J.; Knope, K. E.; Skanthakumar, S.; Kanatzidis, M. G.; Mitchell, J. F.; Soderholm, L. Understanding the role of aqueous solution speciation and its application to the directed syntheses of complex oxidic Zr chlorides and sulfates. J. Am. Chem. Soc. 2013, 135 (38), 14240−14248. (b) Kalaji, A.; Skanthakumar, S.; Kanatzidis, M. G.; Mitchell, J. F.; Soderholm, L. Changing hafnium speciation in aqueous sulfate solutios: A high-energy X-ray scattering study. Inorg. Chem. 2014, 53, 6321−6328. (4) (a) McWhan, D. B.; Lundgren, G. The crystal structure of Zr2(OH) (SO4)3(H2O)4. Inorg. Chem. 1966, 5, 284−289. (b) Squattrito, P. J.; Rudolf, P. R.; Clearfield, A. Crystal structure of a complex basic zirconium sulfate. Inorg. Chem. 1987, 26 (25), 4240−4244. (c) Clearfield, A. Hydrolytic polymerization of zirconyl solutions. J. Mater. Res. 1990, 5, 161−162. (d) Kalaji, A.; Soderholm, L. Aqueous hafnium sulfate chemistry: structures of crystalline precipitates. Inorg. Chem. 2014, 53 (20), 11252−11260. (e) Kalaji, A.; Soderholm, L. A novel nonanuclear hafnium oxide-hydroxide-sulphate cluster crystallised from aqueous solution. Chem. Commun. 2014, 50 (8), 997−999. (5) Clearfield, A.; Vaughan, P. A. The crystal structure of zirconyl chloride octahydrate and zirconyl bromide ocathydrate. Acta Crystallogr. 1956, 9, 555−8. (6) Wilson, R. E.; Skanthakumar, S.; Burns, P. C.; Soderholm, L. Structure of the homoleptic thorium(IV) aqua ion [Th(H2O)10]Br4. Angew. Chem., Int. Ed. 2007, 46, 8043−8045. (7) (a) Albrecht, A. J.; Sigmon, G. E.; Moore-Shay, L.; Wei, R.; Dawes, C.; Szymanowski, J.; Burns, P. C. The crystal chemistry of four thorium sulfates. J. Solid State Chem. 2011, 184 (7), 1591−1597. (b) Knope, K. E.; Wilson, R. E.; Skanthakumar, S.; Soderholm, L. Synthesis and characterization of thorium(IV) sulfates. Inorg. Chem. 2011, 50 (17), 8621−8629. (8) Knope, K. E.; Vasiliu, M.; Dixon, D. A.; Soderholm, L. Thorium(IV)−selenate clusters containing an octanuclear Th(IV) hydroxide/oxide core. Inorg. Chem. 2012, 51 (7), 4239−4249. (9) (a) Mompean, F. J.; Perrone, J.; Illemassène, M. Chemical Thermodynamics of Zirconium; Elsevier Science: New York, 2005. (b) Rand, M. H.; Mompean, F. J.; Perrone, J.; Illemassène, M. Chemical Thermodynamics of Thorium; OECD Publishing: Paris, 2008. (10) Lundgren, G. The structures of oxide and hydroxide salts of some tetrapositive ions. Recl. Trav. Chim. Pay-B 1956, 75 (5), 585−588. (11) (a) Rao, C. N. R.; Behera, J. N.; Dan, M. Organically-templated metal sulfates, selenites, and selenates. Chem. Soc. Rev. 2006, 35, 375− 387. (b) Yu, J.; Xu, R. Rational approaches toward the design and synthesis of zeolitic inorganic open-framework materials. Acc. Chem. Res. 2010, 43, 1195−1204. (c) Rimer, J. D.; Tsapatsis, M. Nucleation of open framework materials: Navigating the voids. MRS Bull. 2016, 41, 393− 398. (12) Wilson, R. E.; Skanthakumar, S.; Knope, K. E.; Cahill, C. L.; Soderholm, L. An open-framework thorium sulfate hydrate with 11.5 Å voids. Inorg. Chem. 2008, 47 (20), 9321−9326. (13) Spek, A. L. Single-crystal structure validation with the program PLATON. J. Appl. Crystallogr. 2003, 36 (1), 7−13. (14) Soderholm, L.; Mitchell, J. F. Perspective: Toward ″synthesis by design″: Exploring atomic correlations during inorganic materials synthesis. APL Mater. 2016, 4 (5), 053212. (15) Vasiliu, M.; Knope, K. E.; Soderholm, L.; Dixon, D. A. Spectroscopic and energetic properties of thorium(IV) molecular clusters with a hexanuclear core. J. Phys. Chem. A 2012, 116 (25), 6917− 6926. (16) (a) Takao, S.; Takao, K.; Kraus, W.; Emmerling, F.; Scheinost, A. C.; Bernhard, G.; Hennig, C. First hexanuclear UIV and ThIV formate complexes − Structure and stability range in aqueous solution. Eur. J. Inorg. Chem. 2009, 32, 4771−4775. (b) Knope, K. E.; Wilson, R. E.; Vasiliu, M.; Dixon, D. A.; Soderholm, L. Thorium(IV) molecular clusters with a hexanuclear Th core. Inorg. Chem. 2011, 50 (19), 9696− 9704. (c) Hennig, C.; Takao, S.; Takao, K.; Weiss, S.; Kraus, W.; Emmerling, F.; Scheinost, A. C. Structure and stability range of a hexanuclear Th(IV)-glycine complex. Dalton Trans. 2012, 41 (41), 12818−12823. (d) Falaise, C.; Charles, J.-S.; Volkringer, C.; Loiseau, T.
Thorium terephthalates coordination polymers synthesized in solvothermal DMF/H2O system. Inorg. Chem. 2015, 54 (5), 2235−2242. (17) Pan, L.; Heddy, R.; Li, J.; Zheng, C.; Huang, X.-Y.; Tang, X.; Kilpatrick, L. Synthesis and structural determination of a hexanuclear zirconium glycine compound formed in aqueous solution. Inorg. Chem. 2008, 47 (13), 5537−5539. (18) Estes, S. L.; Antonio, M. R.; Soderholm, L. Tetravalent Ce in the nitrate-decorated hexanuclear cluster [Ce6(m3-O)4(m3-OH)4]12+. J. Phys. Chem. C 2016, 120, 5810−5818. (19) (a) Falaise, C.; Volkringer, C.; Loiseau, T. Mixed formatedicarboxylate coordination polymers with tetravalent uranium: Occurrence of tetranuclear {U4O4} and hexanuclear {U6O4(OH)4} motifs. Cryst. Growth Des. 2013, 13 (7), 3225−3231. (b) Falaise, C.; Assen, A.; Mihalcea, I.; Volkringer, C.; Mesbah, A.; Dacheux, N.; Loiseau, T. Coordination polymers of uranium(IV) terephthalates. Dalton Trans. 2015, 44 (6), 2639−2649. (20) Knope, K. E.; Soderholm, L. Plutonium(IV) cluster with a hexanuclear Pu6(OH)4(O4)12+ core. Inorg. Chem. 2013, 52 (12), 6770− 6772. (21) (a) Lundgren, G. The crystal structure of Th(OH)2SO4; Arkiv Kemi: Stockholm, Sweden, 1950; Vol. 2, pp 535−549. (b) Habash, J.; Beddoes, R. L.; Smith, A. J. Structure of aquabis(sulfato)tetrakis(urea)thorium(IV) dihydrate. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1991, 47 (8), 1595−1597. (c) Habash, J.; Smith, A. J. Structure of disodium triaquatri-μ-sulfatothorate(IV) trihydrate. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 1990, 46 (6), 957−960. (d) Habash, J.; Smith, A. J. Crystal structure of dicesium thorium trisulfate dihydrate, Cs2Th(SO4)3.2H2O. J. Crystallogr. Spectrosc. Res. 1992, 22 (1), 21−4. (e) Behera, J. N.; Rao, C. N. R. Organically-templated zinc and thorium sulfates with chain and layered structures. Z. Anorg. Allg. Chem. 2005, 631 (15), 3030−3036. (22) Hennig, C.; Schmeide, K.; Brendler, V.; Moll, H.; Tsushima, S.; Scheinost, A. C. EXAFS investigation of U(VI), U(IV), and Th(IV) sulfato complexes in aqueous solution. Inorg. Chem. 2007, 46 (15), 5882−5892. (23) Matijevic, E. Monodispersed metal (hydrous) oxides - a fascinating field of colloid science. Acc. Chem. Res. 1981, 14 (1), 22−29. (24) (a) Cavka, J. H.; Jakobsen, S.; Olsbye, U.; Guillou, N.; Lamberti, C.; Bordiga, S.; Lillerud, K. P. A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability. J. Am. Chem. Soc. 2008, 130 (42), 13850−13851. (b) Bon, V.; Senkovskyy, V.; Senkovska, I.; Kaskel, S. Zr(IV) and Hf(iIV) based metal-organic frameworks with reo-topology. Chem. Commun. 2012, 48 (67), 8407− 8409. (c) Vermoortele, F.; Ameloot, R.; Vimont, A.; Serre, C.; De Vos, D. An amino-modified Zr-terephthalate metal-organic framework as an acid-base catalyst for cross-aldol condensation. Chem. Commun. 2011, 47 (5), 1521−1523. (25) Jakobsen, S.; Gianolio, D.; Wragg, D. S.; Nilsen, M. H.; Emerich, H.; Bordiga, S.; Lamberti, C.; Olsbye, U.; Tilset, M.; Lillerud, K. P. Structural determination of a highly stable metal-organic framework with possible application to interim radioactive waste scavenging: HfUiO-66. Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 86, 125429. (26) Clearfield, A. Structural aspects of zirconium chemistry. Rev. Pure Appl. Chem. 1964, 14, 91−108.
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DOI: 10.1021/acs.inorgchem.6b01762 Inorg. Chem. XXXX, XXX, XXX−XXX
