Not Too Big and Not Too Small: âGoldilocksâ Anion ... - ACS Publications

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Not Too Big and Not Too Small: “Goldilocks” Anion Size for ThreeDimensional Metal−Organic Frameworks Containing Oligothiophene Dinitrile Ligands (C4H2S)n(CN)2 (n = 1, 2, 3) Bridging Silver(I) Cations Nicholas R. Andreychuk,† Sheena R. Allard,† Shawna L. M. Parent,† Abdeljalil Assoud,‡ and Craig D. MacKinnon*,† †

Department of Chemistry, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada Department of Chemistry, University of Waterloo 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on August 25, 2015 | http://pubs.acs.org Publication Date (Web): August 24, 2015 | doi: 10.1021/acs.cgd.5b00698

‡

S Supporting Information *

ABSTRACT: A series of oligothiophene dinitriles, containing one, two, or three oligothiophene rings between nitrile donors NC-(C4H2S)n-CN are reacted with silver(I) salts to form coordination compounds. In most cases, the resulting metal−organic frameworks are one-dimensional coordination polymers containing roughly linear divalent Ag(I) centers. However, in the case of bithiophene (n = 2) and terthiophene (n = 3) bridges, a three-dimensional structure is also possible if the silver(I) counterion is just the right size to fit into the diamondoid pores that form with four-coordinate tetrahedrally oriented Ag(I) centers. Thus, only ClO4− and BF4− form three-dimensional structures with the bithiophenebridged ligands, while the larger CF3SO3− and SbF6− anions will support a threedimensional structure for the terthiophene-bridged ligand. Any counterion larger or smaller than the “just right” size will result in the one-dimensional structure instead.

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INTRODUCTION The simplest node-and-spacer designs for engineering metal− organic frameworks (MOFs) use the geometry of the metal node to determine the shape of the crystal structure, while the length of the divalent (usually linear) ligand determines the dimensions.1 In the case of d10 metal cations, however, the metal node has no geometric preference, meaning that subtle differences in such factors as counterion2−8 or solvent8−11 might give rise to very different structures. Coordination and organometallic compounds of d10 cations are also of current practical and theoretical interest because, for example, gold(I),12−14 silver(I),4,15 and copper(I)16 compounds are emissive (potentially useful in light-emitting diodes). The presence of a d10 metal cation and a particular solid-state structure (aurophilic bonding17) are both necessary ingredients for the desired electronic property,18 so crystal engineers are actively looking at d10 cations to investigate these secondary interactions and their effect on solid-state structures. Silver(I)-nitrile complexes are especially popular in crystal engineering studies due to the low cost of silver, the ready availability of nitriles, and the simplicity of the Ag(I)−NC interaction19,20 (as opposed to the cluster-forming Ag(I)− acetylide interaction21−24). Hydrocarbon bridges are commonly used because they are inert spacers.25−30 For example, the rodlike ligand 4,4′-dicyanobiphenyl can form a one-dimensional polymer with divalent Ag(I) centers when using a 1:1 ligand:metal stoichiometry or a diamondoid structure with tetrahedral Ag(I) centers when using a 2:1 ratio.7 The inclusion © XXXX American Chemical Society

of heteroatoms in the bridge adds an additional level of complexity: while biphenyl forms mutually parallel 1-D polymers, 4,4′-dicyano-2,2′-bipyridyl coordination polymers are cross-hatched with the bipy unit forming a chelating cross-link at the Ag(I) centers.31 As part of our ongoing research into oligothiophenes,32−35 we have synthesized the dinitriles with varying numbers of thiophene rings in the bridge.36 We now present the coordination chemistry of three of these dinitriles, ligands 1, 2, and 3 (Scheme 1). We have already communicated the results for ligand 2, which forms coordination polymers with several silver(I) salts.37,38 Herein we extend the chemistry to shorter (1) and longer (3) ligands in order to study the effect of Scheme 1. Ligands Used in This Study

Received: May 20, 2015 Revised: August 17, 2015

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DOI: 10.1021/acs.cgd.5b00698 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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to a flame-dried Pyrex reaction tube (homemade, approximately 20 mm diameter by 10 cm long). Dried solvent (benzene, toluene, or nitrobenzene) was added (20 mL) and the tube subjected to one freeze−pump−thaw cycle before being sealed under vacuum. The tube was heated to 100 °C until ligand and silver(I) salt had dissolved. The tube was then cooled to room temperature in a tube furnace, at a rate of 1°/h. Crystals were harvested in the air, but were left in the mother liquor until transferred to oil (for crystallography) or dried under N2 (for IR or CHN analysis). Characterization of 1•AgSbF6•PhCH3. IR: 2253 (m), 1234 (w), 1219 (m), 1164 (s), 836 (s) cm−1. Due to the high solubility of the complex, we have been unable to isolate sufficient quantities for combustion analysis (reactions give a few very small crystals; using a higher concentration causes AgSbF6 to precipitate concurrent with the complex). We have, however, been able to isolate analytically pure microcrystalline powder from benzene solvent with the same formula as the crystal structure (replacing PhCH3 with PhH).43 Characterization of 3•AgBF4•PhNO2. IR: 2239 (s), 1534 (w), 1513 (m), 1347 (s), 1067 (s, br), 800 (m), 721 (m) cm−1. Anal. Calcd for C20H11AgBF4N3O2S3: C, 39.0; H, 1.8; N, 6.8. Found: C, 39.0; H, 2.0; N, 6.6%. Characterization of 3•AgCF3SO3•PhH. IR: 2235 (s), 1287 (m), 1235 (m), 1153 (s), 1023 (s), 796 (m), 721 (s), 699 (m) cm−1. Anal. Calcd for C21H12AgF3N2O3S4: C, 39.6; H, 2.1; N, 4.3. Found: C, 39.8; H, 2.2; N, 4.6%. Characterization of 4•AgBF4•PhH. IR: 1098 (s, br), 1003 (s, br), 818 (w), 687 (s) cm−1. Anal. Calcd for C42H34AgBF4P2S2: C, 56.5; H, 3.8; S, 7.9. Found: C, 56.5; H, 3.7; S, 7.8%. Characterization of 32•AgCF3SO3. IR: 2227 (s), 1433 (s), 1332 (w), 1284 (m), 1261 (m), 1221 (w), 1154 (m), 1055 (w), 1026 (m), 800 (m) cm−1. Anal. Calcd for C29H12AgF3N4O3S7: C, 40.8; H, 1.4; N, 6.6. Found: C, 40.5; H, 1.7; N, 6.4%.

ligand length on the solid-state structure. It will be shown that the one-dimensional coordination polymer (with divalent Ag+) is the most common packing motif, but a three-dimensional structure is also possible with the right choice of counterion size.


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EXPERIMENTAL SECTION

General. The ligands 139 and 336 were synthesized by the literature methods from the corresponding dibromo species40 and were purified by fractional sublimation prior to use. Solvents benzene, toluene, and tetrahydrofuran (THF) (Caledon) were purified by passage through an alumina column under an atmosphere of nitrogen;41 nitrobenzene was dried by distillation over phosphorus pentoxide.42 Other reagents, including silver(I) salts, were purchased from Aldrich and used as received. Nuclear magnetic resonance (NMR) spectra were recorded in CDCl3 solutions on a Varian Unity Inova 500 (1H at 500 MHz) at room temperature; chemical shifts are reported in ppm referenced to TMS added to the solvent. Infrared absorption spectra were recorded as Nujol mulls on a Nicolet 380 FT-IR spectrometer; vibrational frequencies are reported as wavenumbers (cm−1) with an experimental resolution of 1 cm−1. Combustion analyses were performed on a CEC (SCP) 240-XA Analyzer with an experimental error of ±0.3% (C) and 0.15% (other elements). Gradient vacuum sublimation and crystal growth for X-ray crystallography were performed in an Applied Test Systems model 3210 split tube furnace attached to a series 2404 3zone temperature control system. Melting points were recorded on an Electrothermal 9100 apparatus and are uncorrected. Crystallography. Single-crystal data were collected using the Smart Apex CCD (Bruker) and Kappa APEX II (Bruker) equipped with an area detector utilizing graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). The data were collected using omega and phi scan and corrected for Lorentz and polarization effects. Absorption corrections were based on fitting a function to the empirical transmission surface as sampled by multiple equivalent measurements of numerous reflections using SADABS included in the APEX II software. The space groups for all compounds were determined on the basis of the systematic absences using the x-prep part of the APEX II package. Structure solution and refinement using the SHELXTL package of APEX II were successful in the chosen space groups. The structure solution via direct method led to the identification of the position of atoms in the crystal structure and the refinement on F2 using least-squares method resulted in good R values. Full details of the structures have been deposited with the Cambridge Crystallographic Data Centre as CDCC 1401847− 1401853. This information may be obtained free of charge via http://www.ccdc.cam.ac.uk/data_request/cif. Synthesis of 5,5′-Bis(diphenylphosphino)-2,2′-bithiophene (4). Under an atmosphere of nitrogen in dry THF at −78 °C, bithiophene (1.72 g, 10.4 mmol) was lithiated with butyllithium (15.1 mL of a 1.6 M solution, 24.2 mmol). The solution was allowed to warm to 0 °C before recooling to −78 °C for the addition of chlorodiphenylphosphine (4.7 mL, 5.6 g, 25 mmol). The solution was again allowed to warm to room temperature and stirred for a further 1 h. The reaction mixture was quenched with 150 mL of degassed distilled water and extracted into 2 × 75 mL of toluene. The crude was run through a column of neutral alumina and rotary evaporated to give a light orange−brown solid. The crude is a mixture of monosubstituted H(C4H2S)2PPh2 and 4. The two materials can be separated by vacuum sublimation over a gradient of 170−110 °C; the desired product collects at ∼140 °C as a liquid, which subsequently solidifies as a solid below 100 °C. Isolated, purified yield of 4: 0.16 g (2.9%). Melting point: 180−181 °C. 1H NMR: δ 7.33−7.40 (m, 20 H), 7.18 (dd, J = 3.5, 6.3 Hz, 2 H), 7.118−7.128 (m, 2 H) ppm. 13C {1H} NMR: 124.87 (d, J = 8.2 Hz), 128.55 (d, J = 6.9 Hz), 129.00, 133.08 (d, J = 19.9 Hz), 137.28 (d, J = 28.0 Hz), 137.51 (d, J = 8.3 Hz), 137.86 (d, J = 30.4 Hz), 143.43 ppm. 31P {1H} NMR: −18.87 ppm. Anal. Calcd for C56H44P2S2: C, 71.9; H, 4.5; S, 12.0. Found: C, 71.5; H, 4.4; S, 12.0%. General Procedure for Reaction of Ligands with AgX Salts. Ligand (0.1 mmol) and an equimolar amount of AgX salt were added

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RESULTS AND DISCUSSION Synthesis and Crystal Growth of the Coordination Compounds. Solubility of oligothiophenes in common organic solvents44 decreases as the number of thiophene rings increases, and odd-numbered oligomers are more soluble than their even-numbered neighbors. Thus, solubility of the three oligomers is on the order of 1 ≫ 2 ≈ 3. Silver(I) salts have a range of solubilities in aromatic solvents44 approximating CF3SO3− > ClO4− > BF4− ≈ PF6− > SbF6−; for all intents and purposes, the CH3CO2−, CF3CO2−, and p-CH3C6H4SO3− salts are insoluble. Finally, the solvents tend to dissolve the combination of ligand plus salt on the order PhNO2 > PhCH3 > PhH. We have previously reported that other solvents such as ethers and dichloromethane tend to give decomposition (e.g., THF reacts with the silver salt to give Ag2O), while the nitrile in acetonitrile competes with the ligand nitrile leading to no reaction.37 Therefore, obtaining crystals of these compounds necessarily involves a balancing act between the competing solubilities of ligand and salt in a given solvent. Because of the solubility of ligand 1, only one coordination compound could be crystallized, with the hexafluoroantimonate anion, while several examples of compounds using 2 and 3 have been crystallographically characterized. In all cases, the crystals were prepared by sealing the ligand, salt, and solvent in a glass tube (freezing the contents in liquid nitrogen and then flamesealing under vacuum). The tubes were then heated until everything dissolved, between 100 and 140 °C, with temperatures >115 °C only being used for nitrobenzene reactions. The tubes are then slow-cooled in a programmable tube furnace at a rate of 1°/h. The initial test for coordination was infrared spectroscopy: typically the ligand nitrile stretch will increase between 8 and 30 wavenumbers upon coordination. For crystallographic experiments, the crystals are transferred from B




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Figure 1. Single-crystal structures, showing the one-dimensional silver(I)-dinitrile coordination polymers of (a) 1•AgSbF6•PhCH3, (b) the previously published 2•AgCF3SO3•PhH,37 and (c) 3•AgBF4•PhNO2; H atoms have been removed for clarity, only one of each noncoordinating unit (anion or solvent) is shown. Silver(I) cations are pink, nitrogen atoms are blue, carbons are gray, oxygens are red, sulfurs are yellow, fluorines are lime, antimonies are purple, and borons are pink.

and the silver(I) cation. A difference in coordination environment for the silver(I) in these structures is the fact that the anion forms a silver−oxygen contact with the CF3SO3− anion (2.46 Å for 2•AgCF3SO3•PhH and 2.54 Å (average) for 3•AgCF3SO3•PhH) and a silver−fluorine contact with BF4− (2.57 Å), while the SbF6− does not have any contacts with the silver cation. The disubstituted ligands are linked through divalent cations, in a roughly linear fashion, with the thiophenes lined up on the same side of the silver (∪•∪•∪•∪), rather than alternating like a sine wave (∪•∩•∪•∩). As a result, the N−Ag+−N bond angles are not 180° (156°, 157°, and 163° for the complexes 1•AgSbF6•PhCH3, 2•AgCF3SO3•PhH, and 3•AgBF4•PhNO2, respectively). While the bent nature of the ligands 1 and 3 might naturally impart a nonlinear geometry at the silver(I) center, ligand 2 might be expected to adopt an offaxis linear orientation with anti thiophene rings, rather than the bent orientation with syn rings found here. 20,45 The uncoordinated ligand itself does adopt the anti orientation,38 as do the structures of unsubstituted oligothiophenes.46−50 In our previously published analysis, we concluded that the syn orientation in 2•AgCF3SO3 must be due to secondary

the reaction solution into the mounting oil. For combustion analysis, they are pumped dry on a vacuum line for several minutes or dry nitrogen is blown over the material; exposure to ambient air is minimized as much as possible. The coordination compounds are very stable to light if kept in sealed tubes containing the reaction solution (in one case for over a year with no evidence of degradation), but crystals will discolor and turn from transparent to opaque if left in the ambient air for more than a few minutes. One-Dimensional Coordination Polymers of 1, 2, and 3. The majority of the compounds isolated were onedimensional coordination compounds and although different in some details, the gross structures are the same. Figure 1 shows the structures of the three compounds 1•AgSbF6•PhCH3, 2•AgCF3SO3•PhH,37 and 3•AgBF4•PhNO2; the last is also isolable as a toluene solvate (the structure is given in the Supporting Information). Ligand 3 can also form a one-dimensional polymer with silver triflate, 3•AgCF3SO3•PhH, when the ligand:metal ratio is 1:1 in the reaction mixture. Table 1 gives details on the crystallographic experiments. In no cases are there any contacts within the sum of the van der Waals radii between the sulfur on the thiophene C



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Table 1. Details of Crystallographic and Refinement Data chemical formula Mr/g mol−1 crystal system space group μ (Mo Kα)/mm−1 a/Å b/Å c/Å α/° β/° γ/° V/Å3 Z Dc/g cm−1 T/K F(000) θ range/° R, wR [I > 2σ(I)] R, wR (all data) reflections: collected unique observed

1•AgSbF6•PhCH3

3•AgBF4•PhNO2

3•AgCF3SO3•PhH

4•AgBF4•1-2/3PhH

32•AgCF3SO3•0.45H2O

C13H10AgF6N2SSb 569.92 monoclinic P21/c 2.841 11.5741(10) 14.1549(12) 10.9185(9) 90 102.2340(10) 90 1748.2(3) 4 2.165 296(2) 1080 3.23 to 28.00 0.0470, 0.0847 0.0680, 0.0950

C20H11AgBF4N3O2S3 616.27 monoclinic P21/n 1.229 10.282(3) 16.864(5) 13.621(4) 90 107.265(4) 90 2255.4(11) 4 1.815 296(2) 1216 2.88 to 30.00 0.0377, 0.0709 0.0505, 0.0776

C21H12AgF3N2O3S4 633.47 triclinic P1 1.251 11.685(3) 12.440(4) 13.933(4) 80.464(4) 77.996(4) 64.417(4) 1780.1(9) 3 1.773 200(2) 942 3.17 to 24.99 0.0390, 0.1028 0.0433, 0.1083

C42H34AgBF4P2S2 859.55 monoclinic P21/c 0.777 8.202(2) 23.559(7) 19.614(6) 90 92.100(4) 90 3787.4(19) 4 1.500 296(2) 1728 2.86 to 26.00 0.0591, 0.1131 0.0925, 0.1275

C29H12.9AgF3N4O3.45S7 861.87 orthorhombic Fddd 1.138 12.7731(13) 29.872(3) 33.792(4) 90 90 90 12894(2) 16 1.774 200(2) 6842 3.16 to 26.00 0.0674, 0.1452 0.0816, 0.1489

22911 4220 3042

16928 6512 5115

21469 16221 14862

39037 7420 5158

3163 3163 2343

Figure 2. Single-crystal structure of 4•AgBF4•1-2/3PhH, showing the anti orientation of the bithiophene core; H atoms and the solvent molecules (which are noncoordinating) are hidden for clarity. Colors are the same as in Figure 1, phosphorus atoms are orange.

the 1:1 salt 3•AgCF3SO3•PhH was isolated from benzene while a 2:1 salt 32•AgCF3SO3 was isolated from nitrobenzene. As can be seen in Figure 3, the 3-D structures of the two 2:1 species 22•AgClO4 and 32•AgCF3SO3 are similar, with a “squashed diamondoid” gross structure, although the two space groups are different (32•AgCF3SO3 is in Fddd, 22•AgClO4 is in P4/n). Both structures have a pseudotetrahedral silver(I), which means that the ligand framework contains pockets; the counterions sit in the pocket and do not form any interactions with the rest of the structure.51 This gives rise to anion disorder, since there is no preferred anion geometry based on short contacts. The solved crystal structure of 32•AgCF3SO3 has 0.45 water molecules scattered through the structure (modeled as disordered solvent molecules), but the combustion analysis on the bulk is consistent with a stoichiometry containing no solvent. Another 2:1 structure with ligand 3 is formed with silver(I) hexafluoroantimonate because the SbF6− anion is also large enough to induce the three-dimensional

interactions between the ligand and the triflate counterions. To further verify this hypothesis, we have now prepared the sterically bulky ligand 4; the diphenylphosphines serve to sequester the backbone hydrogen atoms. As expected, the coordination compound 4•AgBF4•1-2/3PhH does contain anti thiophene rings (Figure 2). Three-Dimensional Network Structures with Ligands 2 and 3. As a part of our preliminary screening process, we try a variety of ligand:cation ratios, such as 1:2, 1:1, and 2:1. In almost every case, only one structure is formed, regardless of the stoichiometry added. Thus, for ligand 2 we found that silver triflate only formed a 1:1 salt37 while crystals isolated from all reactions between 2 and silver borate or silver perchlorate were three-dimensional networks with four-coordinate silver cations and a 2:1 ligand:cation ratio.38 The structure of 22•AgClO4 is shown in Figure 3; 22•AgBF4 is isostructural. The lone exception of this rule of stoichiometric indifference is the combination of 3 with silver triflate. More than one crystal morphology appeared in these reactions, and ultimately D




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Figure 3. Single-crystal structures, showing the three-dimensional silver(I)-dinitrile coordination polymers, of (a) the previously published 22•AgClO438 and (b) 32•AgCF3SO3; all H atoms have been removed for clarity and in both cases the anion is rotationally disordered within the structural pocket. Chlorine atoms are green, other colors are the same as in Figure 1.

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network. Details on the structure 32•AgSbF6 are given in the Supporting Information. The local bonding environments of the silver(I) cations for the two compounds formed from the ligand 3 and silver triflate are shown in Figure 4. There are three crystallographically independent silver(I) cations and triflates in the 1:1 structure 3•AgCF3SO3•PhH, giving different coordination environments to the cations, but all have at least one short silver(I)−oxygen contact. There are no such contacts in the structure with 2:1 stoichiometry, 32•AgCF3SO3, resulting in a disordered triflate anion as discussed above.

DISCUSSION

The thiophene sulfur atoms are nonbinding spectators in the solid-state structure, which is consistent with what we observed previously in oligothiophene-based coordination chemistry.37,38 This is generally the case with thiophene ligands in d10 cation chemistry, i.e., the thiophene sulfur is less coordinating than a nitrogen in a heteroaromatic ring,52−58 unless there is some geometric ligand arrangement that brings the thiophene S and the metal into close proximity.54,59 The nitrile stretching frequency, as measured by infrared (IR) spectroscopy, increases upon coordination, as shown in Table 2. Since the nitrile lone pair is nominally a σ* (antibonding) orbital, this indicates that σ-donation from the E




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Figure 4. Silver(I) coordination sphere of the two different coordination compounds created by the reaction between ligand 3 and silver(I) triflate: (a) a 1:1 stoichiometry in benzene gives 3•AgCF3SO3•PhH and (b) a 2:1 stoichiometry in nitrobenzene gives 32•AgCF3SO3. All three of the crystallographically independent silver(I) cations for the 1:1 structure are shown. Colors are the same as in Figure 1.

lone pair to the silver(I), which leads to a decrease in electron density in the σ* orbital, is the dominant mode of binding in the coordination compound. Back-donation from the silver(I) to the LUMO π* level would give the opposite effect, i.e., a decrease in the stretching frequency. While the effect is obvious in the IR data, the crystallographic data do not show a significant change in the C−N bond lengths. In silver(I)-aromatic nitrile complexes, the bond distance between the cation and the nitrogen on the nitrile depends on the number of cation−ligand bonds. For example, when the ligand is 4,4′-dicyanobiphenyl,7 the 1-D coordination polymer with 1:1 ligand:cation stoichiometry and two cation−nitrile bonds has an average Ag+-N distance of 2.136 Å, while the tetragonal 3-D structure with 2:1 stoichiometry and four cation−nitrile bonds has an Ag+-N distance of 2.27 Å, a difference of 0.14 Å. Similarly, the Ag+-N bond distance in the 1-D structure 2•AgCF3SO3•PhH is 0.12 Å shorter than in the 3-D structure 22•AgClO4 (2.167 (average)37 versus 2.283 Å38). Unfortunately, these examples each contain different anions in the 1-D versus the 3-D structures. With the new compounds reported herein, however, we can directly compare species with the same ligand and anion, namely, 3•AgCF3SO3•PhH versus 32•AgCF3SO3. Once again, the difference is 0.14 Å, with bond lengths of 2.145 Å (average) for the 1-D coordination polymer and 2.284 Å for the 3-D network structure. In the node-and-spacer method of crystal engineering, rodlike ligand spacers are connected by transition metal nodes, like Tinkertoys. In this approximation, the length of the spacer determines the porosity of the structure. Naturally, the larger the void spaces, the less stable the structure, and the nitrile− silver interaction is not strong enough to support a porous metal−organic framework without something in the pore to prop it open. Thus, the potential pocket size is a key feature of the structures we report here, because three-dimensional structures are only formed when the physical volume of the anion5 is the same size as the potential pocket size, or, put another way, the anions act as templates upon which a 3-D structure forms.27 Thus, 3-D structures are not formed with ligand 1 because none of the anions used in this study are small

Table 2. IR and Bond Length Data for the Nitrile Moiety frequency/ cm−1

change from ligand

1 1•AgSbF6•PhCH3

2230 2255

+15

2 2•AgCF3SO3•PhHa

2220 2230

+10

22•AgClO4b 3

2231 2212

+11 -

3•AgBF4•PhNO2

2239

+27

3•AgBF4•PhCH3

2239

+27

3•AgCF3SO3•PhH

2235

+23

32•AgCF3SO3•0.45H2O

2227

+15

32•AgSbF6

2229

+17

compound

bond length /Å N/A 1.128(8), 1.129(6) 1.144(2)b 1.139(4), 1.143(4) 1.145(3) 1.102(15)c 1.124(16) 1.125(15) 1.131(17) 1.142(16) 1.134(4), 1.145(4) 1.127(8) 1.134(10) 1.145(9) 1.146(8) 1.150(8) 1.154(10) 1.133(7) 1.143(8) 1.133(7), 1.143(8) 1.124(7), 1.125(7), 1.139(7), 1.140(6)

change from ligandd N/A −0.003 +0.001 -

+0.015 +0.018

+0.013 +0.013 +0.007

Reference 37 reports +10 cm−1 upon coordination; in our hand the ligand 2 has a frequency of 2220 cm−1, therefore the coordination compound has a frequency of 2230 cm−1 bref 38 cref 36; note that this structure used sublimation-grown crystals dIn cases of multiple crystallographically independent CN bonds, this is the difference in the average (mean) values a

F




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enough. With ligand 2, we see that triflate is too large for the pocket, but BF4− and ClO4− are just the right size. Finally, the longest spacer ligand 3 forms pockets that are now too large for BF4− (and presumably also ClO4−, although we have been unable to grow crystals of this species), but triflate and SbF6− are able to hold the structure open if necessary. The size match between ligand 3 and the triflate salt is not quite “just right”, however, as evidenced by the fact that both a 1-D and a 3-D structure are possible when combining 3 with silver(I) triflate, and because the species 32•AgCF3SO3 does incorporate some water molecules to help fill in the space. The presence of water can be easily explained because nitrobenzene is notoriously hygroscopic. Even though we dried the solvent by distilling over P2O5, transfer of the solvent (which boils at 210 °C, precluding the possibility of simple vacuum transfer on a Schlenk line) and harvesting of crystals took place in the air. This transfer could allow for a small amount of water to be absorbed. Unfortunately, this means that the bulk material is not consistent with the chemical formula of the crystal structurethe combustion analysis is consistent with a 2:1 ligand-to-silver(I) ratio but without any water. We suggest that the water is absorbed postcrystallization since the time exposed to air is significantly longer when preparing the X-ray experiment than the combustion analysis, and because the water molecules are so disordered coupled with an unusual occupancy of 0.45. By comparison, the species 3•AgBF4•PhNO2, also grown from nitrobenzene, dried and transferred using the same techniques, does not incorporate water in the structure because the compound’s 1-D structure and its incorporation of the nitrobenzene solvent renders water inclusion unnecessary in its crystals.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone: 807-3438079. Fax: 807-346-7775. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Funding was provided by Lakehead University. N.R.A. acknowledges support from the Natural Sciences and Engineering Research Council (NSERC) of Canada in the form of an Undergraduate Summer Research Award.

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REFERENCES

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CONCLUSION In the generation of metal−organic structures containing silver(I) and oligothiophene dinitriles of various lengths, the characteristic that determines the type of structure formed is the size of the silver(I) counterion. The default structure is a one-dimensional coordination polymer with a 1:1 ratio, which forms no matter what the reaction stoichiometry is, if the anion is not the correct size. On the other hand, a three-dimensional structure with a 2:1 ligand:metal cation ratio will be formed if the anion is the correct size to fit into the pore size formed in the diamondoid network created by the tetrahedrally substituted silver(I) cation. Again, the ligand:metal ratio in the reaction mixture does not alter the composition of the metal−organic framework, the excess silver salt is simply left dissolved in solution. The chemical identity of the anion, i.e., its donor ability, does not seem to be as important as its physical size, although all the anions with which we have been able to successfully grow crystals have weak to nonexistent donor abilities. Finally, the presence of the sulfur heteroatom does not seem to impact the structure, as we see no indication of any silver(I)−sulfur interactions in any of the structures.

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structures, and tables of bond distances and angles for all new structures (PDF) Crystal data for compound 3•AgBF4•PhCH3; crystal data for compound 32•AgSbF6 (CIF)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.5b00698. Crystal structure and data for compound 3•AgBF4•PhCH3, crystal structure and data for compound 32•AgSbF6, and pictures of the asymmetric units (with thermal ellipsoids) for all the new crystal G




Article

(59) Li, X.-Y.; Liu, Q.-K.; Ma, J.-P.; Huang, R.-Q.; Dong, Y.-B. Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 2009, C65, m45.

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