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Dynamic Uptake and Release of Water in the Mixed-Metal EDTA Complex M3[Yb(EDTA)(CO3)] (M = K, Rb, Cs) Khai-Nghi Truong, Paul Müller, Richard Dronskowski, and Ulli Englert* Institute of Inorganic Chemistry, RWTH Aachen University, Aachen, Germany S Supporting Information *

ABSTRACT: Ethylenediaminetetraacetic acid (H4EDTA) acts as a multidentate ligand toward ytterbium nitrate in the presence of M2CO3 (M = K, Rb, Cs). All structurally characterized compounds are three-dimensional coordination polymers with eight-coordinated ytterbium and three alkali metal cations in the asymmetric unit. In the presence of potassium cations, two different phase pure reaction products can be obtained. From a water-containing solution, first a waterdeficient compound with composition K 3 [Yb(EDTA) (CO3)](H2O)·H2O precipitates. When kept in the reaction mixture, this kinetic product transforms into the more waterrich mixed-metal coordination network K3[Yb(EDTA)(CO3)](H2O)4·2H2O; alternatively, the conversion can be achieved by isolating the water-deficient product and immersing it into a water-containing solvent. The reverse reaction, partial dehydration, may be induced by prolonged drying in a desiccator, vacuum treatment, or heating. For the heavier alkali cations Rb+ and Cs+, only one crystalline structure type is found; it is isomorphous to the water-rich potassium derivative. Dehydration leads to amorphous products.

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INTRODUCTION Ditopic ligands can concomitantly coordinate to different metal cations. Substituted acetylacetones such as 3-(4-pyridyl)pentane-2,4-dione, HacacPy,1−9 1,3-di(pyridyl)pentane-2,4dione,10,11 or (3-cyano)pentane-2,4-dione, HacacCN,12−15 have been used to assemble extended structures. Bimetallic coordination polymers contain two different cations at the Ångström scale and may be applied as precursor materials: A derivative of the latter ligand, the coordination polymer {[Yb(acacCN)4]Ag}14 can be thermally decomposed to a mixture of Ag nanoparticles and Yb oxide. The solid thus obtained showed promising catalytic activity for the conversion of N2O to the elements in the intermediate temperature range.16 Nitrous oxide, N2O, is an important greenhouse gas17 and responsible for a significant part of anthropogenic ozone depletion.18 For its decomposition into nitrogen and oxygen, a variety of solid catalysts have been employed.17 Despite the catalytic activity of our candidate {[Yb(acacCN)4]Ag}, the laborious successive syntheses of the organic ditopic ligand, its Yb complex, and the mixed-metal polymer only allow proof-ofprinciple studies and preclude any industrial application. The obvious alternative, coprecipitation of Ag and Yb oxides followed by thermal decomposition, also resulted in metallic Ag and Yb2O3, but this system proved catalytically inactive, likely due to a larger Ag particle size.16 In our attempt to continue the successful precursor strategy but alleviate its synthetic restrictions, we tested commercially available and economically affordable ditopic ligands. First attempts to © XXXX American Chemical Society

directly obtain mixed-metal ytterbium−silver coordination polymers from, e.g., nicotinic acid19 or isonicotic acid20 were not successful: single crystal and X-ray powder diffraction experiments showed that only Ag coordination in structurally already characterized solids occurred.21−24 Brouca-Cabarrecq et al. successfully employed pentetic acid as multidentate ligand in an ytterbium−silver coordination polymer.25 The successful ligand of these authors resembles the popular and significantly cheaper ethylenediaminetetraacetic acid, H4EDTA. We are not aware of any prior structurally characterized EDTA complex combining rare-earth and Ag cations, and we also have not been able to obtain such a compound directly. We, therefore, decided for a two-step approach. In a first reaction, we synthesize ytterbium-alkali coordination compounds which will in a second step be (partially) converted to ytterbium−silver derivatives. In this contribution, we report the syntheses and crystal chemistry of the intermediate mixed-metal ytterbium-alkali coordination polymers summarized in Scheme 1 and discuss their structural systematics and hydration/dehydration properties.

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RESULTS AND DISCUSSION The potassium−ytterbium coordination polymer 1 is readily available in good yields and can be considered a promising Received: August 18, 2016 Revised: November 3, 2016 Published: November 16, 2016 A

DOI: 10.1021/acs.cgd.6b01227 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Scheme 1. Schematic Representation of the Products Obtained from the Reaction of Ytterbium Nitrate Pentahydrate with the Deprotonated H4EDTA Using Different Alkali Metal Carbonates M2CO3 (M = K, Rb, Cs)

At the very heart of the coordination polymer is the polydentate ethylenediaminetetraacetate linker: it coordinates the Yb(III) with both nitrogen atoms and an oxygen of each acetate arm; the overall 8-fold coordination of the rare-earth cation is completed by a chelating carbonate anion. The resulting coordination polyhedron corresponds to a slightly distorted trigonal dodecahedron (see Figure 2, left) in which the Yb−N distances are significantly longer than Yb−O (see Table 1). Each EDTA ligand connects the Yb1 center to eight potassium cations; in agreement with chemical intuition, they are exclusively coordinated by oxygen. K1 and K3 are sixcoordinated and adopt strongly distorted octahedral coordination, whereas the seven O donors around K2 are disposed in a pentagonal−bipyramidal fashion. Each carbonate anion coordinates an Yb and five K cations as shown in Figure 3; Yb−O distances are significantly shorter than K−O (see Table 1). When 1 is not isolated but kept in the reaction medium, its rod-shaped crystals slowly transform into significantly larger blocks (Figure 4, right); this new solid 1a is characterized by a different X-ray powder pattern (Figure 4, left). A single-crystal diffraction experiment revealed that 1a corresponds to a coordination polymer with higher water content in which the asymmetric unit can be assigned the formula K3[Yb(EDTA)(CO3)](H2O)4·2H2O. In 1a, the overall 8-fold coordination of the ytterbium cation by EDTA and the carbonate anion in slightly distorted trigonal dodecahedral geometry and the coordination around the carbonate anion by one ytterbium and five potassium cations correspond to that in 1. However, the four additional water molecules incorporated into 1a have two significant consequences: (a) 1a is associated with a larger volume per formula unit of 597 Å3; for the water-deficient polymer 1, the formula unit requires 495 Å3. The volume increase amounts to around 25 Å3 per extra water molecule and is slightly larger than the Cambridge Structural Database-based value suggested by

intermediate for future Yb−Ag networks and catalyst precursors. Its asymmetric unit corresponds to the formula K3[Yb(EDTA)(CO3)](H2O)·H2O. We will provide detailed experimental proof for the composition of the compound in the experimental part; in particular, we will show that the XO3 anion corresponds to a carbonate rather than to a nitrate anion. Compound 1 represents a layer structure in the ab plane. In the c direction, polar and apolar layers alternate as shown in Figure 1. The former contain the N and O donors and the coordinated cations; the latter essentially comprise the organic periphery of the EDTA ligand.

Figure 1. Alternating polar and apolar layers in 1. B



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Figure 2. Coordination polyhedra around the metal cations in 1. Polyhedron around Yb1, left, K1 and K2, middle, K3, right (symmetry operations: A: −1/2 + x, 1/2 + y, z; B: 3/2 − x, 3/2 − y, 1 − z; C: 1 − x, 1 − y, 1 − z; D: 3/2 − x, 1/2 − y, 1 − z; E: 2 − x, 1 − y, 1 − z).

Table 1. Coordination Distances around the Metal Cations in 1a Yb1−O2 Yb1−O4 Yb1−O6 Yb1−O8 Yb1−O9 Yb1−O10 Yb1−N1 Yb1−N2 a

2.323(2) 2.236(2) 2.246(2) 2.326(2) 2.307(2) 2.304(2) 2.569(3) 2.536(3)

K1−O1 K1−O8A K1−O10A K1−O10B K1−O11B K1−O12

2.717(2) 2.980(2) 2.718(2) 2.739(2) 2.807(3) 2.671(3)

K2−O2 K2−O6 K2−O7A K2−O9 K2−O9C K2−O11C K2−O12

2.986(3) 2.948(2) 2.690(2) 2.632(3) 2.750(2) 2.803(3) 2.818(4)

K3−O1B K3−O3E K3−O4E K3−O5C K3−O7D K3−O11

2.754(2) 2.709(2) 2.896(2) 2.697(2) 2.840(2) 2.629(3)

In Å; symmetry operations: ref. Fig 2.

The existence of hydrates with different water content is in principle rather common, both in the realm of inorganic and organic compounds; we can only refer to a small number of recent examples for the study of reversible hydration/ dehydration processes.29−31 It is surprising, however, that our water-deficient compound 1 and its water-rich derivative 1a form single crystals under the same conditions, in particular, temperature and humidity. In the following section, we will investigate the hydration and potential dehydration reactions more closely. Compound 1a can not only be obtained from the mother liquor of the reaction: alternatively, 1 may be isolated and then converted into 1a. This hydration can be quantitatively achieved in a slurry of 1 in THF with 3% of water (see Supporting Information, Figure S5). Although we could not detect a straightforward relationship between the unit cells of 1 and 1a, we tested whether hydration might be conducted as a single-crystal-to-single-crystal process. For this purpose, the orientation matrix for a crystal of 1 was determined; the crystal was kept on the goniometer head and immersed into moist THF in order to determine the new orientation matrix of a potential product crystal. This experiment, however, did not result in a single crystal but rather in a powder of 1a. The opposite reaction, partial dehydration of 1a to 1, may be achieved under a vacuum, by removing water in a desiccator or at higher temperatures. The former approach is depicted in Figure 6: the diffractogram shown in red corresponds to phase pure 1a. Immediately after this solid is exposed to a vacuum, a broad reflection around 6.2° in 2θ indicates the onset of dehydration to 1 (Figure 6, blue curve); at this stage, Rietveld refinement gives a composition 1a/1 = 80:20. Prolonged exposure to a vacuum results in full conversion to 1 (green diffractogram, G645 Guinier instrument, and pink diffracto-

Figure 3. Coordination around a carbonate anion in 1 (symmetry operations: A: 1 − x, 1 − y, 1 − z; B: 3/2 − x, 3/2 − y, 1 − z; C: 1/2 + x, −1/2 + y, z).

Hofmann.26 It ranges between the experimentally observed volume increments for the irreversible dehydration of a (4carboxylatopyridine)silver(I) hydrate (22.5 Å3)27 and that for the reversible hydration/dehydration in a europium complex (30 Å3).28 (b) Not only potassium coordination number and geometry (see Table 2) but also the disposition of the K cations change: the extra water molecules result in significant “dilution” of the alkali cations with longer K···K separations in 1a. The coordination polyhedra around the alkali cations are depicted in Figure 5: K1 is six-coordinated with slightly distorted trigonal prismatic geometry, the seven O donors around K2 are disposed in a pentagonal−bipyramidal fashion, and K3 is five-coordinated and adopts an almost perfect square pyramidal coordination. C



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Figure 4. Changes in powder diffraction pattern (1 experimental, red; 1 simulated, black; 1a experimental, blue) and crystal shape during conversion of 1 to 1a.

Table 2. Coordination Distances around the Metal Cations in 1aa Yb1−O2 Yb1−O4 Yb1−O6 Yb1−O8 Yb1−O9 Yb1−O10 Yb1−N1 Yb1−N2 a

2.299(2) 2.234(2) 2.323(2) 2.238(2) 2.313(2) 2.293(2) 2.548(2) 2.530(2)

K1−O6D K1−O9 K1−O9D K1−O12 K1−O13 K1−O14A

2.866(2) 2.723(2) 2.785(2) 2.684(3) 2.951(3) 2.743(3)

K2−O3B K2−O5F K2−O8 K2−O10 K2−O13C K2−O14 K2−O15

2.893(3) 2.807(2) 2.970(2) 2.750(2) 2.937(3) 2.883(3) 2.890(2)

K3−O1 K3−O3F K3−O6E K3−O10E K3−O11C

2.692(2) 2.695(2) 2.866(2) 2.756(2) 2.633(2)

In Å; symmetry operations: A: x, 1 + y, z; B: x, −1 + y, z; C: 1 − x, 1 − y, 1 − z; D: 2 − x, 2 − y, 1 − z; E: −1 + x, y, z; F: −1 + x, −1 + y, z.

complete at around 48 °C. The 2D contour diagrams for the full diffraction range can be found in the Supporting Information, Figure S6. The three-dimensional surface profile diagram provided in Figure 7 (right) shows diffraction intensity over the full measurement range (4−20° in 2θ) as a function of temperature in a combined heating and cooling experiment. The experiment starts with phase pure 1a at room temperature; the corresponding pattern is shown in the rear of the diagram. Upon heating, conversion to 1 occurs. Its diffraction pattern remains essentially unaltered during heating to 100 °C and also upon successive cooling back to the starting temperature, i.e., throughout the central and front part of the diagram. Similar results were obtained on a flat sample (see Supporting Information, Figure S7). We conclude that the transformation of 1a to 1 is irreversible under ambient atmosphere; not surprisingly, it requires the presence of moisture. The reaction products with the heavier alkali cations Rb, 2a, and Cs, 3a, are isomorphous with the water-rich potassium derivative 1a (see Scheme 1). As expected, the coordination distances between the alkali metal cations and the ligand oxygens atoms increase significantly with the size of the alkali cation (K···O: 2.7−3.0 Å, Rb···O: 2.8−3.1 Å, Cs···O: 2.9−3.3 Å;32 see Tables 2, S1, S2). As an example for packing in the isomorphous compounds 1a, 2a, and 3a, a projection of the crystal structure of 2a is shown in Figure 8, left. Different from the packing in 1, the interlayer interface for 2a is not strictly apolar; rather, H bonds connect subsequent layers. Figure 8, right, depicts a displacement ellipsoid plot of the asymmetric unit in 2a. In contrast to the situation observed for the K+ derivatives 1 and 1a, the water-rich polymers 2a and 3a are the direct

Figure 5. Coordination around the potassium cations in 1a; view directions are arbitrary and have been chosen to easily identify the underlying polyhedra (symmetry operations: A: x, 1 + y, z; B: x, −1 + y, z; C: 1 − x, 1 − y, 1 − z; D: 2 − x, 2 − y, 1 − z; E: −1 + x, y, z; F: −1 + x, −1 + y, z).

gram, Stoe & Cie STADI P instrument). The final product was a mixture of crystalline powder and single crystals of 1. Alternatively, dehydration may be achieved by storing crystalline 1a over silica gel beads in a desiccator for 5 days. Powder diffraction and weight loss of the sample prove the formation of 1. Finally, powder patterns of 1a were registered in intervals of 5 °C between 30 and 100 °C. The outcome of this temperature-dependent diffraction experiment is summarized in Figure 7. On the left, a color-coded 2D contour diagram in the 2θ range 4−14° shows that 1a (on the bottom of the diagram) is converted to 1 upon heating; starting material and product coexist over a wider temperature range. When we focus on the reflections at 5.5 and 11°, the change in the diffraction pattern upon heating becomes obvious: the intensity of these reflections starts to decrease at around 35 °C and new reflections, for instance, around 6.5°, indicate the formation of the water-deficient compound 1. The conversion to 1 is D



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Figure 6. Partial dehydration of 1a to 1 under a vacuum.

Figure 7. Transformation of 1a to 1 by annealing at different temperatures. 2D contour diagram of a heating experiment (left); series of powder diffraction patterns as 3D surface monitoring heating and subsequent cooling (right).

the alkali cations. Table 3 lists differences in the unit cell volumes for our isomorphous compounds and, for easier comparison with the earlier literature, volume increments in units of cm3 per mole. The compilation in Table 3 shows that ΔV(2a−1a), the difference between the unit cells of the isomorphous K+ and Rb+ compounds, is smaller than ΔV(3a− 2a). This is in agreement with the situation encountered in simple inorganic salts.33 The series of isomorphous alkali (K, Rb, Cs) graphite intercalation compounds34 suggests a more pronounced difference in volumes for the two lighter alkali cations, and, hence, ΔV(Rb−K) is larger than ΔV(Cs−Rb), in contrast with our results. The discrepancy might well indicate a comparatively large volume and reduced stability for the waterrich potassium compound 1a; as a consequence, the waterdeficient structure can become competitive. We plan to exchange the alkali cations in the compounds described here by Ag(I). We expect to achieve partial exchange in a reproducible manner and, thus, obtain catalyst precursors

reaction products. Can they be partially dehydrated, and will their dehydration products be isomorphous to 1? When defined quantities of crystalline 2a and 3a were placed in a desiccator for 5 days, loss of weight, corresponding to more than two water molecules per formula unit, was observed but in contrast to the situation with the lighter congener K+, amorphous products formed. Their diffraction patterns are provided in the Supporting Information (see Figures S8 and S9).

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CONCLUSION AND FUTURE WORK In a series of mixed-metal alkali-ytterbium derivatives M3[Yb(EDTA)(CO3)] (M = K, Rb, Cs), only for potassium two compounds with different degrees of hydration have been obtained and structurally characterized. Why could no such water-deficient compounds be obtained for the heavier, although the water-rich polymers are isomorphous for all three alkali cations? We can offer a hypothesis based on volume increments. Not surprisingly, the unit cell volume for 1a−3a follows the trend of E



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Figure 8. Layer structure of 2a in the ab plane (left). Displacement ellipsoid plot (drawn with 70% probability, H atoms of EDTA omitted) of the asymmetric unit in 2a (right). alternatively, ytterbium triflate. Diffraction experiments showed that 1 had formed in the absence of any nitrate. Synthesis of K3[Yb(EDTA)(CO3)](H2O)4·2H2O, 1a. Colorless, blockshaped single crystals of 1a formed over a period of several days when 1 was kept in the mother liquor. After 3 days, X-ray powder diffraction revealed the coexistence of 1 and 1a. After 1 week, phase purity of 1a was confirmed by X-ray powder diffraction (see Figures 4 and S13). Yield: 74%. Analysis: CHN: Anal. Calcd for C11H24N2O17K3Yb: C 17.70%, H 3.24%, N 3.75%; found: C 17.62%, H 3.35%, N 3.83%. Synthesis of Rb3[Yb(EDTA)(CO3)](H2O)4·2H2O, 2a. H4EDTA (0.0292 g, 0.1 mmol, 1 equiv) was dissolved in a mixture of MeOH/H2O (7 mL/2 mL). Rb2CO3 (0.0693 g, 0.3 mmol, 3 equiv) was slowly added to the reaction mixture over a period of 15 min. After addition of the base was completed, ytterbium nitrate pentahydrate (0.0359 g, 0.1 mmol, 1 equiv) was added into the solution of the deprotonated ligand. The reaction mixture was stirred for another 15 min at ambient temperature. Colorless block-shaped crystals of 2a were obtained by layering the resulting solution with acetone (10 mL) and allowing for slow diffusion. Crystals suitable for single-crystal X-ray diffraction formed after 3 h. Phase purity of the bulk product was confirmed by X-ray powder diffraction (see Figure S14). Yield: 84%. Analysis: CHN: Anal. Calcd for C11H24N2O17Rb3Yb: C 14.92%, H 2.73%, N 3.16%; found: C 14.12%, H 2.56%, N 2.96%. Decomposition point: 310.5 °C. Synthesis of Cs3[Yb(EDTA)(CO3)](H2O)4·2H2O, 3a. Similar to the synthesis of 2a, the reaction of Cs2CO3 (0.0978 g, 0.3 mmol, 3 equiv) and ytterbium nitrate pentahydrate (0.0359 g, 0.1 mmol, 1 equiv) with the deprotonated H4EDTA (0.0292 g, 0.1 mmol, 1 equiv) afforded a clear, colorless solution. Crystals of 3a for single-crystal X-ray diffraction experiments were grown by reaction diffusion. Phase purity of the bulk product was confirmed by X-ray powder diffraction (see Figure S15). Yield: 67%. Analysis: CHN: Anal. Calcd for C11H24N2O17Cs3Yb: C 12.85%, H 2.35%, N 2.72%; found: C 12.53%, H 2.22%, N 2.75%. Decomposition point: 345.6 °C. Solid-State Reactivity and Reactivity in Solution. Transformation of 1 to 1a. Crystals of the water-deficient polymer 1 were isolated and placed in a vial containing tetrahydrofuran (THF) with 3% water; the solid did not dissolve. The resulting slurry was slowly stirred for 4 days at ambient temperature. The reaction product was recovered; X-ray powder diffraction confirmed complete conversion to phase pure 1a. A second experiment was performed to test for a potential 3D relationship between starting material and product: A single crystal of 1 was glued to a sample holder and immersed into a

Table 3. Volume Relationships for the Alkali Cations ΔV ions [cm3 mol−1] ΔV unit cells [Å ]

this work

30

31

50.3 73.7

5.0 7.4

4 6

4.6 3.3

3

Rb−K Cs−Rb

with adjustable Ag content for the decomposition of N2O to the elements.

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EXPERIMENTAL SECTION

Chemicals and Reagents. All chemicals were used as purchased without further purification: Ethylenediaminetetraacetic acid (98.5%, Sigma-Aldrich), cesium carbonate (99.5%, Merck Millipore), potassium carbonate (99.9%, Merck Millipore), rubidium carbonate (99%, Merck Millipore), ytterbium nitrate pentahydrate (99.9%, ABCR GmbH), and LLG desiccant beads (ϕ1−3.15 mm, orange selfindication gel, LLG Labware). Syntheses and Crystallization. Synthesis of K3[Yb(EDTA)(CO3)](H2O)·H2O, 1. Ethylenediaminetetraacetic acid, H4EDTA (0.0292 g, 0.1 mmol, 1 equiv), was dissolved in a mixture of MeOH/H2O (7 mL/ 2 mL). K2CO3 (0.0415 g, 0.3 mmol, 3 equiv) was slowly added to the reaction mixture over a period of 15 min. After addition of the base was completed, ytterbium nitrate pentahydrate (0.0359 g, 0.1 mmol, 1 equiv) was added into the solution of the deprotonated ligand. The reaction mixture was stirred for another 15 min at ambient temperature. Single crystals of 1 were grown by layering the above solution with acetone (10 mL) and allowing for slow diffusion. Colorless rod-shaped crystals formed overnight. Phase purity of the crystalline bulk product was confirmed by X-ray powder diffraction (see Figure S12). Yield: 79%. Analysis: CHN: Anal. Calcd for C11H16N2O13K3Yb: C 19.59%, H 2.39%, N 4.15%; found: C 18.60%, H 2.67%, N 3.91%. This analysis indicates a higher water content than expected for pure 1, presumably due to contamination with a noncrystalline higher hydrate. Decomposition point: 323.5 °C. The following experiments were conducted with respect to the identity of the XO3 anion: (a) 1 evolves CO2 when treated with an excess of HCl; the gas generates precipitates of BaCO3 when injected into a solution of Ba(OH)2, thus proving the presence of carbonate. (b) 1 was prepared as above but starting from ytterbium chloride or, F



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Table 4. Crystal Data: Data Collection Parameters and Convergence Results for All EDTA Compounds 1, 1a, 2a, and 3aa compound empirical formula moiety formula

a

1

1a

2a

3a

C11H16K3N2O13Yb C11H14K3N2O12Yb, H2O 674.60 colorless rod 0.16 × 0.15 × 0.07 monoclinic C2/c 10.5999(8) 13.4901(10) 27.729(2)

C11H24N2O17Rb3Yb C11H20N2O15Rb3Yb, 2(H2O) 885.77 colorless block 0.19 × 0.16 × 0.12 triclinic P1̅ 8.8945(8) 9.4275(8) 16.8353(15) 97.2095(14) 98.8956(15) 114.2806(13) 1243.00(19) 2 9.676 11524/5020 0.0534 0.6303 0.0393 0.0855 1.026 343 50 2.796/−2.989

C11H24Cs3N2O17Yb C11H20Cs3N2O15Yb, 2(H2O) 1028.09 colorless block 0.27 × 0.23 × 0.23 triclinic P1̅ 8.9609(6) 9.7916(6) 17.0908(11) 98.7384(12) 98.2842(13) 114.1410(11) 1316.71(15) 2 7.712 17381/4761 0.0594 0.6020 0.0340 0.0858 1.064 343 23 2.532/−2.539

1498784

1498785

formula weight (g/mol) crystal description crystal size (mm) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z μ (mm−1) total/unique reflections Rint (sin θ/λ)max (Å−1) R [F2 > 2σ(F2)] wR2 (F2) GOF no. of parameters no. of restraints Δρmax/Δρmin (e Å−3)

3963.1(5) 8 5.420 27616/5031 0.0356 0.6722 0.0234 0.0570 1.077 275 11 1.776/−1.460

C11H24K3N2O17Yb C11H20K3N2O15Yb, 2(H2O) 746.66 colorless block 0.12 × 0.12 × 0.11 triclinic P1̅ 8.8642(3) 9.1929(4) 16.6273(6) 95.9935(6) 100.1982(6) 114.1191(5) 1193.30(8) 2 4.522 18365/6426 0.0322 0.7218 0.0276 0.0646 1.024 343 14 2.779/−2.851

CCDC

1498782

1498783

91.7580(10)

Experiments were carried out at 100(2) K with Mo Kα radiation using a CCD area detector diffractometer. G645 equipped with a scintillation counter. Experiments involved temperature-dependent diffraction between 30 and 60 °C and high vacuum experiments at ambient temperature. (b) Measurements in a 0.3 mm closed glas capillary were performed with a Guinier powder diffractometer G644 (Fa. Huber, Rimsting) in asymmetric transmission geometry. A Cu anode (40 kV, 20 mA) and a focused germanium monochromator after Johansson generated Cu− Kα1 radiation (λ = 1.54059 Å). Intensities were measured with a scintillation counter at a step width of 0.02° in 2θ with a measurement time per step of 50 s in the range between 4° and 20° in 2θ. Temperature was controlled using a U-shaped oven shielded by Kapton foil. The experiment included heating from 30 to 100 °C and cooling back to 30 °C. Crystallographic Studies. Crystal data, data collection parameters, and refinement results for 1, 1a, 2a, and 3a have been compiled in Table 4. Intensity data were collected on a Bruker D8 goniometer with APEX CCD area detector in ω-scan mode using Mo−Kα radiation (λ = 0.71073 Å) from an Incoatec microsource with multilayer optics. A temperature of 100(2) K was maintained with the help of an Oxford Cryostream 700 instrument. Data were integrated with SAINT+40 and corrected for absorption by multiscan methods with SADABS.41 The structures for 1 and 1a were solved by Direct methods using SHELXS97;42 the atomic coordinates for 1a were used as initial structure model for 2a and 3a. Full-matrix least-squares refinements based on F2 were performed with SHELXL-13.43 Non-hydrogen atoms were assigned anisotropic displacement parameters unless stated otherwise. H atoms bonded to oxygen were located from Fourier difference maps and refined an O−H distance restraint of 0.83 Å. Other hydrogen atoms were placed in idealized positions and included as riding. Isotropic displacement parameters for all H atoms were constrained to multiples of the equivalent displacement parameters of their parent atoms with Uiso(H) = 1.2Ueq(C). We note that tentative refinement of the central atom X in the XO3 anion resulted in slightly less favorable agreement factors and more serious rigid-bond

THF/water solution as above. After 3 days, an increase in crystal size in each dimension could be observed. A single crystal diffraction experiment on this product was attempted but revealed its polycrystalline nature; powder diffraction confirmed complete transformation to the water-rich coordination polymer 1a as observed in the slurry experiment. Transformation of 1a to 1. Exposure of 1a to a vacuum resulted in the release of water molecules and in the formation of the waterdeficient polymer 1. The gradual conversion was monitored by in situ powder diffraction before, during and after vacuum treatment (see Figure 6). In addition, annealing experiments were performed at different temperatures with the Guinier powder diffractometers G644 and G645. These experiments show slow transformation of 1a to 1; the conversion started at a temperature of around 35 °C and gave phase pure 1 at around 47 °C. The series of powder patterns obtained in the context of this experiment is depicted in Figure 7 and in the Supporting Information (see Figures S6 and S7). The diagrams have been plotted using the programs FullProf Suite, WinPLOTR-2006.35,36 Rietveld refinement has been accomplished using the program MAUD.37−39 Bulk Analysis. IR spectra were recorded on a Nicolet Avatar 360 E.S.P. spectrometer in KBr windows. Elemental (CHN) analyses for 1, 1a, 2a, and 3a were carried out at the Institute of Organic Chemistry, RWTH Aachen University, using a HERAEUS CHNO-Rapid VarioEL. X-ray powder diffraction experiments were performed at ambient temperature on flat samples with a Stoe & Cie STADI P diffractometer equipped with an imageplate detector with constant ω angle of 55° using germanium-monochromated Cu−Kα1 radiation (λ = 1.54059 Å) at the Institute of Inorganic Chemistry, RWTH Aachen University. Temperature-dependent diffraction data were obtained on two diffractometers: (a) Flat samples were measured with germanium-monochromated Cu−Kα1 radiation (λ = 1.54059 Å) on a Guinier powder diffractometer G



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violations44 for X = N than for X = C; the anion must be associated with carbonate rather than nitrate. Additional details concerning structure models and refinement strategies have been compiled in the Supporting Information.

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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.cgd.6b01227. Infrared spectra for 1, 1a, 2a, and 3a. Full powder diffraction patterns illustrated as 2D contour diagram measured at the Guinier powder diffractometer G644 and G645. Powder patterns for 2a and 3a after 5 days in desiccator. Coordination around the potassium cations in 2a and 3a. Metal···O distances in compounds 2a and 3a. Powder patterns for 1, 1a, 2a, and 3a. Refinement details for 1, 1a, 2a, and 3a (PDF) Accession Codes

CCDC 1498782−1498785 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: +49 241 8094666. Fax: +49 241 8092288. ORCID

Richard Dronskowski: 0000-0002-1925-9624 Ulli Englert: 0000-0002-2623-0061 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by RWTH Education Fund - Germany Scholarship/LANXESS AG (K.-N.T.) is gratefully acknowledged. Comments from two anonymous reviewers are thankfully acknowledged.

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REFERENCES

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Article

(43) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3−8. (44) Hirshfeld, F. L. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1976, 32, 239−244.

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