Synthesis of Diamondoid and Lonsdaleite Networks from the Same Ag

Article pubs.acs.org/crystal

Synthesis of Diamondoid and Lonsdaleite Networks from the Same Ag(I)−Ligand Combination, with Lonsdaleite the Softer Network Komal M. Patil,† Michelle E. Dickinson,‡ Thomas Tremlett,‡ Stephen C. Moratti,† and Lyall R. Hanton*,† †

Department of Chemistry, University of Otago, Te Tari Hua-Ruanuku, P.O. Box 56, Dunedin 9054, New Zealand Department of Chemical and Materials Engineering, The University of Auckland, Auckland 1010, New Zealand

‡

S Supporting Information *

ABSTRACT: The design and synthesis of a Lonsdaleite (lon) network is an attractive and challenging supramolecular target. Our reticular synthesis strategy of slow diffusion of solutions of a simple rigid tetrahedral ligand and a Ag(I) metal ion, at room temperature and atmospheric pressure, resulted in both lonMOFs and diamondoid (dia-MOFs) and associated 2D honeycomb networks. Solvent appeared to play a key role in templating the formation of these related networks. Nanoindentation studies show that a dia-MOF was 42% harder than a lon-MOF counterpart. The lon-MOFs were thermally stable and retained integrity until 370 °C while dia-MOFs exhibited stepwise collapse after initial loss of solvents. As lon networks are often only qualitatively identified, Cremer−Pople ring puckering analysis was used to quantify the degree of distortion in the lon and related 4-connected 66 networks.

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based9−16 and two contain azolate-based ligands.17,18 Interestingly, three of these lon networks were also synthesized along with dia network analogues or in one case a hexagonal adamantanoid analogue by varying the solvents under solvothermal conditions.9,16,18 In addition, a family of e-lon porous networks has been described.19 In many of these systems the solvents used for crystallization have a strong affinity toward the metal ion or metal cluster nodes resulting in unpredictable node geometries. Many of these networks which are claimed to have a lon topology rely on the way in which the nodes and topological networks are chosen. Using Cremer− Pople (CP) parametrization of ring pucker to analyze the conformation of six-membered rings (Figure 1 and Supporting Information section S5), it can be shown that the boat conformations required by the lon topology in these reported examples are often very distorted.20 In addition, the ligands used to generate these dia and lon networks are not always designed from a reticular synthetic approach often giving a poor correlation between the reactants and the products. Reticulations based on the lon network using simple tetrahedral building blocks are rare because the network obtained is usually the simpler, higher symmetry dia network.21 Herein, we describe the use of a rigid tetrahedral ligand, tetrakis(4-cyanophenyl)adamantane (L), and Ag(I) salts to prepare a 1:1 M:L series of interpenetrated lon {[AgL]X· nCH3NO2}∞ [X = CF3SO3−, n = 4 (1a); BF4−, n = 3 (1b);

INTRODUCTION Carbon exhibits a variety of allotropes renowned for their uniqueness in formation, structure, and mechanical and thermal properties. The 3D reticular allotropes of carbon are diamond (C-dia) and Lonsdaleite (C-lon). C-lon is believed to be formed by astral impact on the surface of the earth.1,2 The hexagonal space group of graphite is retained by C-lon (P63/ mmc), and hence, Lonsdaleites are often called “hexagonal diamonds”. In 2009, it was reported that C-lon is 58% harder than C-dia.3 Interestingly, the archetypal zinc sulfide structures of wurtzite and sphalerite are reported to have similar hardnesses.4 The mechanical properties of C-lon have been the subject of continuing controversy. For example, the boat-tochair ratio has been suggested as a factor in the unexpected hardness of C-lon.5 Further, it has been reported that C-lon is the result of twinning and stacking faults in C-dia and the claimed superior hardness is due to grain size reduction in twinned C-dia rather than the lon topology.6 Recently, a quantitative analysis of the cubic and hexagonal stacking in diamond samples found that C-lon comprised at best 60:40 hexagonal:cubic stacking sequences and was considered stacking disordered diamond.7 These studies have challenged the existence of C-lon as a pure discrete material. In metal−organic framework (MOF) chemistry most 4connected 66 networks have a dia topology. However, lon and neb topologies are other possible outcomes8 but comprise only about 0.6% and 0.2% of all reported 66 network structures, respectively. The lon network is an attractive, if challenging, target for network synthesis. In total there are only ten reported examples of lon networks, of which eight contain carboxylate© XXXX American Chemical Society

Received: November 11, 2015 Revised: December 14, 2015

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DOI: 10.1021/acs.cgd.5b01601 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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and dia-MOF (2a) and showed that 2a was 42% harder than 1a.

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EXPERIMENTAL SECTION

Materials and Methods. Phenyliodinebis(trifluoroacetate) (PIFA) was synthesized by the reported procedure23 and also purchased from Sigma-Aldrich. All chemicals from commercial sources were used as received without further purification. Infrared (IR) spectra were recorded on a Bruker Optics Alpha FT-IR spectrometer (with a diamond Attenuated Total Reflectance top-plate). 1H and 13C NMR spectra were collected on a 400 MHz Varian UNITY INOVA spectrometers at 298 K. CDCl3 was used as the solvent for NMR studies and all comparisons were made using this solvent. The spectra were referenced to the internal solvent signal of 7.26 and 77.16 ppm for 1H and 13C NMR spectra, respectively, with chemical shifts reported in δ units (ppm). Electrospray Mass Spectroscopy (ESMS) was carried out on a Bruker micro-TOFQ instrument (Bruker Daltronics, Bremen, Germany). The sample was introduced using direct infusion into an ESI source in a negative mode. Melting points were recorded on Digimelt SRS (MPA161) melting point apparatus using open capillary tubes. Thermal gravimetric analyses (TGA) were performed on a TGA Q50 V20.10 Build 36 device with a platinum pan and dinitrogen as balance and sample gas at a temperature increase rate of 20 °C/min. The nanoindentation measurements were carried at The University of Auckland, New Zealand using a Hysitron Triboindenter (TI-950) with an in situ atomic force microscope (AFM). Powder X-ray diffraction (PXRD) data were collected on a Agilent Technologies Supernova system using Cu Kα (λ = 1.54184 Å) radiation. The powder materials were finely ground, homogenized and packed in Lindemann glass capillary (1.0 mm outer diameter and 0.01 mm wall thickness). The data were collected at 2θ from 5° to 60° with the step size of 0.044°. Simulated powder X-ray diffraction patterns were generated from the single crystal data using Mercury 3.5.1. Caution! Although no problems were encountered in this work, transition metal perchlorates are potentially explosive. They should be prepared in small amounts and handled with care. Reaction of L with AgCF3SO3: Synthesis of powder IIa. Under a blanket of N2 gas, a mixture of solid AgCF3SO3 (9.5 mg, 0.036 mmol) and L (10 mg, 0.018 mmol) was dissolved in 6 mL CHCl3. A mixture of solvents (0.5 mL CH3CN and 2 mL CH3NO2) was added dropwise to this solution. The resultant solution was stirred overnight to yield a tan precipitate. The precipitate was filtered washed with diethyl ether and dried in vacuo. Yield (based on L): 13.4 mg, 69%. Selected IR/ cm−1: 2927 (w, br), 2238 (m, br), 1602 (m, sh), 1503 (w, sh), 1446 (w, sh), 1362 (w, sh), 1275−1228 (vs, br), 1159 (s, br), 1022 (s, sh), 835 (m, sh), 633 (vs, sh), 564 (s, sh), 516 (m, sh). Synthesis of crystalline 1a. Solid AgCF3SO3 (29.0 mg, 0.113 mmol) dissolved in CH3OH (1 mL) was added dropwise to a 1 mL CH3NO2 solution of L (5 mg, 0.009 mmol). The resultant solution was sonicated and allowed to concentrate by slow evaporation for a few weeks to yield X-ray quality colorless hexagonal crystals of {[AgL](CF3SO3)·4CH3NO2}∞ [1a]. Selected IR/cm: 2956−2853 (m, br), 2248 (m, sh), 1709 (m, br), 1603 (m, sh), 1554 (m, sh), 1504 (w, sh), 1402 (w, sh), 1362 (w, sh), 1285−1156 (vs, br), 1028 (vs, sh), 844 (m, sh), 634 (vs, sh), 569 (s, sh), 515 (m, sh). Synthesis of crystalline 2d. Solid AgCF3SO3 (14.6 mg, 0.046 mmol) dissolved in CH3OH (1 mL) was added dropwise to a 1 mL CH3NO2 solution of L (2.5 mg, 0.005 mmol). The resultant solution was sonicated and allowed to concentrate by slow evaporation for a few months to yield poor quality colorless blocks of {[AgL](CF3SO3) ·xSolvent}∞ [2d]. Selected IR/cm−1: 3453 (m, br), 2936−2857 (w, br), 2246 (m, sh), 1640 (m, br), 1603 (m, sh), 1504 (w, sh), 1405 (w, sh), 1363 (w, sh), 1219−1165 (vs, br), 1021 (vs, sh), 837 (m, sh), 629 (vs, sh), 566 (s, sh), 512 (m, sh). Synthesis of crystalline 3a. A mixture of solid AgCF3SO3 (9.5 mg, 0.036 mmol) and L (10 mg, 0.018 mmol) was dissolved in 6 mL CHCl3. A mixture of solvents (0.5 mL CH3CN and 2 mL CH3NO2) was added dropwise to the solution. The resultant solution was sonicated and allowed to concentrate by slow evaporation followed by

Figure 1. 2D polar projection of the 4-connected networks with 66 topology from this work and from the literature. CSD refcodes are given in bold capitals together with the reported topology (lon, dia, neb, and X-nets, where the topology is unidentified). The θ2 and ϕ2 polar coordinates were calculated using CP puckering analysis. A perfect dia network would occupy the center of this projection (θ2,ϕ2 = 0,0). A perfect lon network would occupy the outer circle of θ2 = 90° with ϕ2 values of 0, 60, 120, ..., 300.

CF3CO2−, n = 5.5 (1c); BF4−, n = 4 (1d)] and interpenetrated dia {[AgL]X·nH2O}∞ [X = PF6−, n = 2 (2a), BF4−, n = 3 (2b), ClO4−, n = 2 (2c), CF3SO3−, (2d)] networks along with their associated 2D honeycomb (hcb) networks {[AgL](CF3SO3)· 2CH3NO2·H2O}∞ (3a) and {[AgL(NO3)]·4CH3NO2·H2O}∞ (3b) (Figure 2). The use of soft nitrile L and a Ag(I) node allowed construction of [AgL]∞ cationic frameworks by selfassembly. Unlike other lon networks, which have been synthesized under solvothermal conditions, these were synthesized under mild conditions at ambient temperature and pressure. The solvents, CH3NO2, CH3OH, and H2O were selected, as they did not compete strongly with the ligand for coordination to the Ag(I) ions. The rate of evaporation and the inclusion of solvent appeared to play a critical role in determining the topology of the framework. The lon-MOFs were 3-fold interpenetrated and more solvent rich than their 4fold interpenetrated dia-MOF analogues. This is a very rare example of an interpenetrated lon network and is only the second reported example. Lon networks are considered more resistant to interpenetration than dia. This is due to the lon building unit having three smaller and two larger windows while dia has four equally sized windows.22 In addition, the arrangement of the windows in dia is consistent with the cubic symmetry of the tetrahedron in contrast to the hexagonal symmetry of lon. These frameworks were characterized using IR, elemental, and thermogravimetric analysis (TGA) and SCXRD. In the SCXRD studies, the anions and solvent molecules often could not be adequately modeled and were SQUEEZEd from structures (Supporting Information section S2.2). Assignments of residual electron density to specific solvent molecules were consistent with the number of SQUEEZEd electrons and with TGA analyses. Nanoindentation studies were performed on single crystals of lon-MOF (1a) B



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Figure 2. Top left: A view of a 3D network of the lon-MOF (1a) (representative for lon-MOFs) with the 12 node building unit highlighted in red. Top right: A view of a 3D network of the dia-MOF 2a (representative for dia-MOFs) with the 10 node building unit highlighted in red. Bottom left: A view of a 2D hcb-network (3a) displaying a conformation between boat and an envelope. Bottom right: A view of a 2D hcb-network (3b) displaying a chair conformation. The centroid of the adamantane core (Cg1) for 3D networks is in yellow while those for 2D networks are in green. diffusion of CH2Cl2 slowly for weeks to yield X-ray quality colorless crystals of {[AgL](CF3SO3)·2CH3NO2·H2O}∞ [3a]. Selected IR/ cm−1: 2922 (s, br), 2250 (m, br), 1604 (w, sh), 1551 (m, sh), 1458 (w, sh), 1370 (w, sh), 1272−1239 (vs, br), 1161 (s, br), 1023 (s, sh), 836 (m, sh), 635 (vs, sh), 566 (s, sh), 518 (m, sh). Reaction of L with AgBF4: Synthesis of powder IIb. Under a blanket of N2 gas, a mixture of solid AgBF4 (5.4 mg, 0.028 mmol) and L (15 mg, 0.028 mmol) was dissolved in 6 mL CH3NO2. The resultant solution was stirred overnight to yield a precipitate. The precipitate was filtered, washed with excess diethyl ether and dried in vacuo. Yield (based on L): 22.1 mg, 50%. Selected IR/cm−1: 2932 (w, br), 2248 (m, br), 1603 (m, br), 1504 (w, sh), 1407 (w, br), 1364 (w, br), 1364 (w, br), 1047 (vs, br), 832 (s, sh), 567 (s, sh). Synthesis of powder IIc. Under a blanket of N2 gas, a mixture of solid AgBF4 (54.0 mg, 0.277 mmol) and L (15 mg, 0.028 mmol) was dissolved in 8 mL CH3NO2. The resultant solution was stirred for 2 days and concentrated in vacuo. The residue was washed with excess diethyl ether and dried in vacuo. Yield (based on L): 15.4 mg, 61%. Selected IR/cm−1: 2931 (w, br), 2228 (m, br), 1603 (m, br), 1503 (m, sh), 1404 (w, br), 1361 (m, br), 1021 (vs, br), 835 (s, sh), 565 (s, sh). Synthesis of crystalline 1b. Solid AgBF4 (18.0 mg, 0.092 mmol) dissolved in CH3NO2 (1 mL) was added dropwise to a 1 mL CH3NO2 solution of L (5 mg, 0.009 mmol). The resultant solution was sonicated and allowed to concentrate by slow evaporation for a few

weeks to yield colorless hexagonal crystals of {[AgL](BF4)· 3CH3NO2}∞ ([1b]). Synthesis of crystalline 1d. Solid AgBF4 (18.0 mg, 0.092 mmol) dissolved in CH3NO2 (2 mL) was added dropwise to a 2 mL CH3NO2 solution of L (5 mg, 0.009 mmol). The resultant solution was sonicated and allowed to concentrate by slow evaporation for a few months to yield X-ray quality colorless hexagonal crystals of {[AgL](BF4)·4CH3NO2}∞ ([1d]). Synthesis of crystalline 2b. Solid AgBF4 (14.5 mg, 0.046 mmol) dissolved in CH3OH (1 mL) was added dropwise to a 1 mL CH3NO2 solution of L (2.5 mg, 0.005 mmol). The resultant solution was sonicated and allowed to concentrate by slow evaporation for a few months to yield X-ray quality colorless blocks of {[AgL](BF4)· 3H2O}∞ ([2b]). Reaction of L with AgCF3CO2: Synthesis of powder IId. Under a blanket of N2 gas, a mixture of solid AgCF3CO2 (6.2 mg, 0.028 mmol) and L (15 mg, 0.028 mmol) was dissolved in 6 mL CH3NO2. The resultant solution was stirred overnight to yield a white precipitate. The precipitate was filtered and washed with excess diethyl ether. The precipitate was filtered and dried in vacuo. Yield (based on L): 20.4 mg, 82%. Selected IR/cm−1: 3065 (w, br), 2930 (w, br), 2229 (m, br), 1660 (s, br), 1604 (m, br), 1504 (w, sh), 1407 (w, br), 1362 (w, br), 1188−1133 (vs, br), 1024 (s, sh), 834 (s, br), 721 (s, br), 565 (s, br). C



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Table 1. Crystal Data for MOF 1a−d Structure

lon-MOF 1a

lon-MOF 1b

lon-MOF 1c

lon-MOF 1d

Formula Formula weight Crystal System Space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z T/K μ/mm−1 Total reflections Unique reflections (Rint) R1 indices [I > 2σ(I)] ωR2 (all data) Goodness-of-fit Flack parameter Radiation type

C43H40AgF3N8O11S 1041.76 Hexagonal P65 17.304(2) 17.304(2) 27.965(6) 90 90 120 7252(2) 6 100.01(10) 4.408 46538 6550 (0.0463) 0.0585 0.1724 1.011 0.048(16) Cu Kα

C41H37AgBF4N7O6 918.46 Hexagonal P65 17.311(2) 17.311(2) 27.636(6) 90 90 120 7172(2) 6 99.98(10) 3.930 35260 6497 (0.1308) 0.0724 0.2610 1.076 0.002(2) Cu Kα

C45.5H44.5AgF3N9.5O13 1097.25 Hexagonal P61 17.4299(5) 17.4299(5) 28.4893(12) 90 90 120 7495.6(4) 6 100.01(10) 0.486 40362 9209 (0.0497) 0.0909 0.2508 1.075 0.11(8) Mo Kα

C42H40AgBF4N8O8 979.50 Monoclinic P21 16.7489(2) 28.5492(3) 17.0230(2) 90 116.7870(18) 90 7266.37(17) 6 100.01(10) 3.951 105125 26402 (0.0552) 0.0539 0.1592 1.034 0.01(4) Cu Kα

Table 2. Crystal Data for MOF 2a−c; 3a−b Structure

dia-MOF 2a

dia-MOF 2b

dia-MOF 2c

hcb-net 3a

hcb-net 3b

Formula Formula weight Crystal System Space group a/Å b/Å c/Å α/deg β/deg γ/deg V/Å3 Z T/K μ/mm−1 Total reflections Unique reflections (Rint) R1 indices [I > 2σ(I)] ωR2 (all data) Goodness-of-fit Flack parameter Radiation type

C38H32AgF6N4O2P 829.48 Tetragonal I4̅2d 16.69948(19) 16.69948(19) 26.7579(4) 90 90 90 7462.06(17) 8 100.0(11) 0.652 23108 3645 (0.0251) 0.0510 0.1441 1.132 −0.001(11) Mo Kα

C38H34AgBF4N4O3 789.38 Tetragonal I4̅2d 16.1998(2) 16.1998(2) 27.6196(5) 90 90 90 7248.30(19) 8 100.00(10) 4.997 35143 3308 (0.0585) 0.0519 0.1385 1.074 −0.005(9) Cu Kα

C38H32AgClN4O6 784.02 Tetragonal I4̅2d 16.1538(5) 16.1538(5) 27.7196(10) 90 90 90 7233.3(4) 8 99.99(10) 0.682 34499 3360 (0.0530) 0.0808 0.2357 1.088 −0.08(3) Mo Kα

C41H36AgF3N6O8S 937.70 Monoclinic C2/c 30.6473(12) 16.4901(6) 17.1241(6) 90 94.0213(18) 90 8632.8(6) 8 90(2) 0.585 25770 7915 (0.0356) 0.0827 0.2431 1.052

C42H42AgN9O12 972.703 Monoclinic P21/c 17.01280(10) 16.45190(10) 17.2028(2) 90 116.1650(10) 90 4321.54(7) 4 100.01(14) 4.370 84223 7847 (0.0735) 0.0545 0.1540 1.064

Mo Kα

Cu Kα

Synthesis of crystalline 1c. Solid AgCF3CO2 (10.2 mg, 0.046 mmol) dissolved in CH3OH (1 mL) was added dropwise to a 1 mL CH3NO2 solution of L (2.5 mg, 0.005 mmol). The resultant solution was sonicated and allowed to concentrate by slow evaporation for a few months to yield X-ray quality colorless hexagonal crystals of {[AgL](CF3CO2)·5.5CH3NO2}∞ ([1c]). Reaction of L with AgPF6: Synthesis of powder IIe. Under a blanket of N2 gas, a mixture of solid AgPF6 (70.1 mg, 0.277 mmol) and L (15 mg, 0.028 mmol) was dissolved in 8 mL CH3NO2. The resultant solution was stirred overnight to yield a small amount of white precipitate. The precipitate was filtered and discarded and the complex was precipitated from the filtrate by addition of excess diethyl ether. The precipitate was filtered, washed with diethyl ether and dried in vacuo. Yield (based on L): 7.9 mg, 31%. Selected IR/cm−1: 2926 (w,

br), 2238 (m, br), 1603 (w, br), 1503 (w, sh), 1404 (w, sh), 1361 (w, sh), 1020 (w, br), 832 (vs, br), 558 (s, br). Synthesis of crystalline 2a. Solid AgPF6 (28.8 mg, 0.113 mmol) dissolved in CH3OH (1 mL) was added dropwise to a 1 mL CH3NO2 solution of L (5 mg, 0.009 mmol). The resultant solution was sonicated and allowed to concentrate by slow evaporation for a few months to yield X-ray quality colorless blocks of {[AgL](PF6)2H2O}∞ ([2a]). Reaction of L with AgClO4: Synthesis of powder IIf. Under a blanket of N2 gas, a mixture of solid AgClO4·H2O (57.5 mg, 0.277 mmol) and L (15 mg, 0.028 mmol) was dissolved in 8 mL CH3NO2. The resultant solution was stirred overnight to yield a white precipitate. The precipitate was filtered, washed with diethyl ether and dried in vacuo. Yield (based on L): 20.4 mg, 84%. Selected IR/ cm−1: 2931 (w, br), 2234 (m, br), 1719 (m, br), 1603 (m, sh), 1503 D



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Figure 3. Top Left: The cationic framework of the 3D lon-MOFs 1a−d (in yellow) showing building units of 3-fold interpenetration in pink and blue. Top Right: The cationic framework of the 3D dia-MOFs 2a−c (in yellow) showing building units of 4-fold interpenetration in pink, red and blue. Bottom left: A view along the c axis of lon-MOF 1a showing the 3-fold interpenetrating networks generate 65 screw axes. These axes occur where the three networks appear to intersect. Bottom right: A view along the c axis of dia-MOF 2a showing the regularity of the interpenetration. The centroid of the adamantane core (Cg1) for 3D networks is in green, and the Ag(I) cations are shown in magenta. yield X-ray quality colorless plates of {[AgL(NO3)]·4CH3NO2·H2O}∞ ([3b]). Structural Crystallography. Single crystals were mounted in paratone-N oil on a nylon loop. SCXRD data (except for 3a) were collected on an Agilent Technologies Supernova system at 100 K at the University of Otago using mirror monochromated Mo Kα (λ = 0.71073 Å) or Cu Kα (λ = 1.54184 Å) radiation. The data were treated using CrysAlisPro24 software and Gaussian absorption corrections were applied. SCXRD data for 3a were collected on a Bruker APEX II CCD diffractometer at 90 K at the University of Otago with graphite monochromated Mo Kα (λ = 0.71073 Å) radiation. Intensities were corrected for Lorentz and polarization effects and a multiscan absorption correction was applied. The structures were solved by direct methods SHELXL-201425 or SIR-9726 and refined on F2 using all data by full-matrix least-squares procedures SHELXL-2014,25 interfaced through the program WINGX.27 Non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms were placed in ideal positions unless specified in special refinements. Detailed analyses of the extended structure were carried out using PLATON28 and MERCURY (Version 3.5.1).29,30 Owing to the high

(w, sh), 1405 (m, sh), 1362 (m, sh), 1081 (vs, br), 836 (s, br), 621 (s, sh), 564 (s, br). Synthesis of crystalline 2c. Solid AgClO4 (10.2 mg, 0.046 mmol) dissolved in CH3OH (1 mL) was added dropwise to a 1 mL CH3NO2 solution of L (2.5 mg, 0.005 mmol). The resultant solution was sonicated and allowed to concentrate by slow evaporation for a number of months to yield block shaped colorless X-ray quality crystals of {[AgL](ClO4)·2H2O}∞ ([2c]). Reaction of L with AgNO3: Synthesis of powder III. Under a blanket of N2 gas, 3 mL methanolic solution of AgNO3 (4.71 mg, 0.028 mmol) was added to a solution of L (15 mg, 0.028 mmol) dissolved in 3 mL CH3NO2. The resultant solution was stirred for 2 days to yield a white precipitate. The precipitate was filtered, washed with diethyl ether and dried in vacuo. Yield (based on L): 9.9 mg, 40%. Selected IR/cm−1: 2926 (w, br), 2226 (m, sh), 1603 (m, sh), 1503 (w, sh), 1400−1291 (s, br), 1173−1018 (w, br), 833 (m, sh), 563 (vs, sh). Synthesis of crystalline 3b. Solid AgNO3 (16 mg, 0.094 mmol) dissolved in CH3OH (2 mL) was added dropwise to a 1 mL CH3NO2 solution of L (5 mg, 0.009 mmol). The resultant solution was sonicated and allowed to evaporate slowly for a number of months to E



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symmetry space group and low residual electron density, it was impossible to locate anion and solvent molecules in some structures. These structures were treated with PLATON SQUEEZE31 and the electron contribution from disordered anions and solvent molecules was calculated using this program. Crystallographic data are listed in Tables 1 and 2. Crystallographic data has been deposited at the Cambridge Crystallographic Data Center; the numbers are from 1430432 to 1430440.

number of SQUEEZEd electrons and with TGA analyses (vide supra). In each structure the Ag(I) cation was coordinated by the CN moieties of four symmetry-related L ligands and adopted a slightly distorted tetrahedral geometry. The Ag(I) cation and L each resided on 2-fold symmetric special positions. The bridging of the completely coordinated tetrahedral ligands L by the Ag(I) ions generated 3D quadruply interpenetrated diaMOFs. The dia networks were constructed from 10 equiv nodes comprising four Cg1 and six Ag(I) nodes (or vice versa) arranged in alternation (Figure 2).32 The resultant building block possessed four six-membered fused rings in chair conformations. CP puckering analysis for the chairs in 2a−c indicated genuine dia networks (Figure 1; Supporting Information section S5). Honeycomb Network. In a similar fashion to the 3D lon and dia networks, 2D hcb networks could be isolated and characterized which contained boat 3a and chair 3b conformations. The complexes 3a and 3b crystallized in the space groups C2/c and P21/c, respectively. Both formed 2D (6,3) hcb networks in the ac planes. The asymmetric units of both complexes comprised one Ag(I) cation, one complete ligand L, one anion, H2O and CH3NO2 solvent molecules. In both complexes the Ag(I) cation coordinated to three CN moieties of L. In 3a the CF3SO3− anion, one H2O and one CH3NO2 solvent molecules could not be adequately modeled and were SQUEEZEd from the structure. While in 3b one H2O and one CH3NO2 solvent molecule were SQUEEZEd from the structure. In both complexes the Ag(I) cation coordinated to three CN moieties of L. In 3a the Ag(I) cation adopted a slightly distorted trigonal planar geometry while in 3b two O atoms of a NO3− anion further symmetrically coordinated to the Ag(I) cation which adopted a slightly distorted square pyramidal geometry (τ5 = 0.08).36 The Ag(I) cations bridged the L ligands and generated 2D hcb networks. In both complexes one CN moiety of L remained uncoordinated. The Cg1 and the Ag(I) centers occupied alternate corners of each hexagon of the hcb network. In 3a the CP puckering analysis indicated that each hexagon adopted a conformation between an envelope and a boat. As a consequence of this particular conformation, in each hexagon, two uncoordinated CN arms pointed to one side; while one CN arm pointed to the opposite side of the hcb network. In an unusual interaction, the protruding CN arm weakly interacted with a CH3NO2 solvent molecule and prevented the 2D sheet from propagating in the third dimension. Similar nitrile···CH3NO2 interactions have been a contributing factor in preventing complete metalation of the hexadentate ligand hexakis(4-cyanophenyl)[3]radialene.37 The hcb networks were doubly interpenetrated and resulted in a 2D → 2D network in the ac plane. Within the 2-fold interpenetrated framework weak π−π interactions existed. The protruding CN arms of the 2-fold interpenetrated framework interdigitated the adjacent frameworks on either side of this framework. In contrast, for 3b the CP puckering analysis indicated that each hexagon adopted a chair conformation. As a consequence of the chair conformation, the uncoordinated CN arms were all arranged on the same side of the hcb network with the NO3− anions on the opposite side. Again the protruding CN arm interacted with a CH3NO2 solvent molecule preventing the 2D sheet from propagating in the third dimension. On one side of each hcb layer all of the NO3− groups interdigitated an adjacent hcb monolayer while on the other side the uncoordinated CN

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RESULTS Lonsdaleite Network. Four lon-MOFs were isolated and structurally characterized (Figure 2). Three of these 1a−c were isomorphous and crystallized in the hexagonal chiral space groups P61 or P65 while a pseudopolymorph 1d crystallized in the chiral space group P21. The lon networks were all 3-fold interpenetrated (Figure 3). This interpenetration appeared to be responsible for the chirality of the packing with the arrangement of the three individual networks generating 61 or 65 screw axes (Figure 3; bottom left). The solvent was unlikely to be responsible for the chiral packing as it was disordered randomly and the amount of solvent varied slightly in each lon-MOF system. Also, in each of the various lon-MOFs there were different disordered counteranions present and these would interact differently with the solvent in each of the lon-MOFs, yet all the lon-MOFs grew in chiral space groups. As interpenetration in Lonsdaleite networks is rare this 3-fold interpenetration and its consequences have not been previously observed. Owing to the high symmetry and low residual electron density, the anions and solvent molecules could not be adequately refined and were SQUEEZEd from the structures (see Supporting Information section S2.2). In the case of the lower symmetry structure 1d, attempts at modeling the residual electron density clearly indicated the presence of CH3NO2 in the structure. Assignment of the residual electron density (in 1a−d) to between 3 to 6 molecules of CH3NO2 was consistent with the number of squeezed electrons and with TGA analyses (vide supra). Further evidence was provided by crystals of 1b and 1d being isolated solely from CH3NO2 solvent. In each structure the Ag(I) cation was coordinated by the CN moieties of four symmetry-related L ligands and adopted a slightly distorted tetrahedral geometry. The bridging of the completely coordinated tetrahedral ligands L by the Ag(I) ions generated 3D triply interpenetrated lon MOFs. The lon networks were constructed from 12 equiv nodes comprising six centroids of the adamantane cores (Cg1) and six Ag(I) nodes arranged in alternation (Figure 2).32 The resultant building blocks possessed three six-membered fused rings in boat conformations and two six-membered rings in chair conformations. CP puckering analyses showed ideal chair and boat conformations for 1a−d, indicating genuine lon networks (Supporting Information section S5).33,34 Diamondoid Network. Four isomorphous dia-MOFs 2a− d (Figure 2) were crystallized in the tetragonal I4̅2d space group35 and were found to be 4-fold interpenetrated (Figure 3). In 2a, a solvent H2O molecule and the PF6− anion were disordered over two sites in the asymmetric unit. In 2b and 2c, the anions and solvent molecules could not be adequately modeled and were SQUEEZEd from the two structures (see S2.2). Attempts at modeling the residual solvent electron density in 2b and 2c suggested the presence of 2 to 3 H2O molecules in the structures. Assignment of the residual electron density to specific solvent molecules was consistent with the F



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arms interdigitated another adjacent hcb monolayer. The resultant interdigitated hcb monolayers interacted with each other by virtue of the weak π−π interactions. The two hcb networks appeared to be reminiscent of sections through the larger 3D networks, in particular, 3a mirrored the planes of boats present in the lon networks while 3b mirrored the planes of chairs in both the lon and dia networks. PXRD and microanalyses of the powder samples (IIa-f, III) indicated that the materials were not pure under the reaction conditions. PXRD of powder reactions suggested that lon, dia and unknown phases were formed in combination (Figures S16,17). In principle, the ligand L can react with the Ag cation resulting in an array of compounds with 1:1 M:L ratios. The lon and dia networks are not the only possibilities as 2D nets and 1D chains can also be formed (Figure S18). The PXRD analyses suggested that for the powder material the dia network was preferred as opposed to the lon network. However, under crystallization conditions lon or dia or 2D hcb network crystals, all showing different crystal habits (Figure S1), were formed exclusively and never together. For these reasons TGA was performed on single crystals rather than powder material. Nanoindentation Studies. While comparative nanoindentation studies have been carried out on C-lon and Cdia,3 individual synthetic lon and dia networks have not been studied. The lon- and dia-MOFs 1 and 2 possessed similar [AgL]∞ cationic frameworks and were found to be suitable candidates for nanoindentation studies. Nanoindentation studies revealed that the dia- MOF 2a was 42% harder than the lon-MOF 1a counterpart. The softness of lon-MOF could be attributed to the lesser 3-fold interpenetration compared to 4-fold for the dia-MOF and larger amount of solvent molecules entrapped in the cavities. The hardness and elastic modulus values reported in Table 3 showed that the lon and dia MOFs

Figure 4. Representative P−h curves from the nanoindentation studies on lon-MOF 1a and dia-MOF 2a crystals.

Figure 5. Representative thermograms of lon (1a) and dia (2a) crystals obtained by heating at a temperature increase rate of 20 °C/ min under a N2 atmosphere.

Table 3. Hardness and Reduced Elastic Modulus for dia and lon MOFs MOF

Hardness H (MPa)a

Reduced Elasticity Modulus Er (MPa)a

lon-MOF 1a dia-MOF 2a

234(35) 331(53)

4046(363) 6905(396)

a

crystallization, the frameworks of the dia-MOFs appeared to degrade in a stepwise fashion perhaps involving a concerted collapse of the interpenetrated networks. By comparison, the lon-MOFs and the hcb framework 3b retained their integrity and were stable until decomposition of L began.

Standard deviation based on 7−10 indents.

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CONCLUSIONS In conclusion, four lon and four dia-MOFs are reported from a reticular synthesis using Ag(I) cations and a rigid tetrahedral nitrile ligand. Studies indicated the dia-MOFs were harder than the lon-MOFs while the latter were thermally more stable. In contrast to the dia-MOFs, which crystallized in a lower symmetry tetragonal space group and were 4-fold interpenetrated; the lon-MOFs were 3-fold interpenetrated, reflecting the hexagonal symmetry of the space groups in which they crystallized. Significantly, both lon- and dia-MOFs were formed with CF3SO3− and BF4− anions. This suggested that since the same anions gave different networks the anions were not involved in any templating process and it was the solvent that was key to forming the different networks. For 1a− d and 3a it was observed that the crystallization occurred early on from the solvent mix while compounds 2a−d and 3b were formed toward the end after evaporation of solvents nearly to dryness. As a result the lon-MOFs contained CH3NO2 while the dia-MOFs contained H2O. Interestingly, related 2D sheets were isolated with CF3SO3− (3a) and NO3− (3b) anions. These

were harder than MOF-5 (H = 40 MPa; E = 3000 MPa) and had values in the range for ZIFs (H = 300−1100 MPa; E = 3000−10 000 MPa).38 For both dia- and lon-MOF samples, the P-h curves were smooth with no pop-ins or pop-outs (Figure 4). The smooth curves indicated homogeneous plastic deformation of the 3D networks.39 Despite a number of attempts to capture the indentation impressions immediately after unloading only one residual indent image of the dia-MOF sample 2a could be captured. This image showed significant pile up and no signs of cracking (Figure S19). The residual indent image of the lon-MOF 1a samples could not be obtained. The fast elastic recovery could be attributed to the soft nature of the MOFs and the dynamic coordination geometry of the Ag(I) cations. Thermogravimetric Analyses. TG analyses for all networks showed that the major decomposition was associated with the degradation of L and commenced between 370 and 430 °C (Figure 5). The high thermal stability of these networks was attributed to the presence of the thermally stable adamantane core in L.40 After the initial loss of solvent of G



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(7) Salzmann, C. G.; Murray, B. J.; Shephard, J. J. arXiv.org, e- Print Arch., Condens. Matter 2015, 1−14. (8) Guo, S.-Q.; Tian, D.; Zheng, X.; Zhang, H. CrystEngComm 2012, 14, 3177−3182. (9) Kishan, M. R.; Tian, J.; Thallapally, P. K.; Fernandez, C. A.; Dalgarno, S. J.; Warren, J. E.; McGrail, B. P.; Atwood, J. L. Chem. Commun. 2010, 46, 538−540. (10) Cui, P.; Wu, J.; Zhao, X.; Sun, D.; Zhang, L.; Guo, J.; Sun, D. Cryst. Growth Des. 2011, 11, 5182−5187. (11) Chen, Z.-L.; Jiang, C.-F.; Yan, W.-H.; Liang, F.-P.; Batten, S. R. Inorg. Chem. 2009, 48, 4674−4684. (12) Sreenivasulu, B.; Vittal, J. J. Cryst. Growth Des. 2003, 3, 635− 637. (13) Zou, Y.; Yu, C.; Li, Y.; Lah, M. S. CrystEngComm 2012, 14, 7174−7177. (14) Chun, H.; Bak, W.; Hong, K.; Moon, D. Cryst. Growth Des. 2014, 14, 1998−2002. (15) Kim, H.; Sun, Y.; Kim, Y.; Kajiwara, T.; Yamashita, M.; Kim, K. CrystEngComm 2011, 13, 2197−2200. (16) Yang, J.; Zhang, L.; Wang, X.; Wang, R.; Dai, F.; Sun, D. RSC Adv. 2015, 5, 62982−62988. (17) Chen, R.-Y.; Tian, D.; Li, Y.-W.; Lv, Y.-B.; Sun, H.-W.; Chang, Z.; Bu, X.-H. RSC Adv. 2015, 5, 24655−24660. (18) Wang, F.; Hou, D.-C.; Yang, H.; Kang, Y.; Zhang, J. Dalton Trans. 2014, 43, 3210−3214. (19) Schoedel, A.; Boyette, W.; Wojtas, L.; Eddaoudi, M.; Zaworotko, M. J. J. Am. Chem. Soc. 2013, 135, 14016−14019. (20) The Cartesian coordinates were identified using CrystalMaker (V 9.2.2) software and converted to polar coordinates using the Cremer−Pople parameter calculator designed by S. Fushinobu. (21) Yaghi, O. M.; O’Keeffe, M.; Ockwig, N. W.; Chae, H. K.; Eddaoudi, M.; Kim, J. Nature 2003, 423, 705−714. (22) Batten, S. R.; Neville, S. M.; Turner, D. R. In Coordination polymers: Design, analysis and application; Royal Society of Chemistry: Cambridge, 2008; p 39. (23) Zagulyaeva, A. A.; Yusubov, M. S.; Zhdankin, V. V. J. Org. Chem. 2010, 75, 2119−2122. (24) CrysAlisPRO; Oxford Diffraction/Agilent Technologies UK Ltd: Yarnton, England. (25) Sheldrick, G. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 3−8. (26) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115−119. (27) Farrugia, L. J. Appl. Crystallogr. 1999, 32, 837−838. (28) Spek, A. L. PLATON. A Multipurpose Crystallographic Tool.; Utrecht University: Utrecht, The Netherlands. 1999. (29) Bruno, I. J.; Cole, J. C.; Edgington, P. R.; Kessler, M.; Macrae, C. F.; McCabe, P.; Pearson, J.; Taylor, R. Acta Crystallogr., Sect. B: Struct. Sci. 2002, 58, 389−397. (30) Macrae, C. F.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Shields, G. P.; Taylor, R.; Towler, M.; van de Streek, J. J. Appl. Crystallogr. 2006, 39, 453−457. (31) Spek, A. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71, 9−18. (32) Banfalvi, G. RSC Adv. 2014, 4, 3003−3008. (33) Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97, 1354−1358. (34) Evans, D. G.; Boeyens, J. C. A. Acta Crystallogr., Sect. B: Struct. Sci. 1989, 45, 581−590. (35) For dia-MOF (2d) only poor quality X-ray data could be obtained (Cu Kα). 2d was isomorphous with other dia-MOFs; a = b = 16.5286(4) Å, c = 27.5783(9) Å. (36) Addison, A. W.; Rao, T. N.; Reedijk, J.; Van Rijn, J.; Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349−1356. (37) Hollis, C. A.; Batten, S. R.; Sumby, C. J. Cryst. Growth Des. 2013, 13, 2350−2361. (38) Tan, J. C.; Bennett, T. D.; Cheetham, A. K. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 9938−9943. (39) Ghosh, S.; Mondal, A.; Kiran, M. S. R. N.; Ramamurty, U.; Reddy, C. M. Cryst. Growth Des. 2013, 13, 4435−4441.

contained either an all boat (3a) or all chair (3b) arrangement, suggesting the energy differences between the chair and boat arrangements in these systems were small. Both 2D networks were unable to expand their dimensionality due to the termination of growth by solvent blocking through nitrile··· CH3NO2 interactions. This points to the complication of solvent in reticular synthesis. On the one hand it was responsible for a templating effect generating both lon- and dia-MOFs, whereas on the other it caused the termination of the growth of the network, thwarting the reticular outcome.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b01601. Detailed experimental procedures (PDF) Accession Codes

CCDC 1430432−1430440 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]. Author Contributions

All authors contributed extensively to the work presented in this paper, with M.E.D. and T.T. being responsible for the nanoindentation studies. All authors have given approval to the final version of the manuscript. L.R.H. and S.C.M. designed and conceived the experiments with input from K.M.P. The synthetic work and TGA and Cremer−Pople ring puckering analyses were undertaken by K.M.P. The X-ray diffraction data were collected, solved, and refined by K.M.P. with input from L.R.H. The manuscript was written by K.M.P. and L.R.H. with input from the other authors. Funding

This work was supported by Ministry of Business Innovation and Employment (UOOX1206) and University of Otago doctoral scholarship to K.M.P. Notes

The authors declare no competing financial interest.

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ABBREVIATIONS MOF, metal−organic framework; lon, Lonsdaleite; dia, diamondoid; hcb, honeycomb; CP, Cremer−Pople; Cg1, centroids of the adamantane cores; ZIF, Zeolitic imidazolate frameworks

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REFERENCES

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Synthesis of Diamondoid and Lonsdaleite Networks from the Same Ag

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