Coordination Polymers from Functionalized Bipyrimidine Ligands and

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Coordination Polymers from Functionalized Bipyrimidine Ligands and Silver(I) Salts Guillaume Beaulieu-Houle,† Nicholas G. White,†,‡ and Mark J. MacLachlan*,† †

Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, British Columbia V6T 1Z1, Canada Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 2601, Australia

‡

S Supporting Information *

ABSTRACT: Readily functionalizable bipyrimidine compounds were prepared for the first time, and their coordination chemistry with silver salts was explored. Solution 1H NMR spectroscopy experiments indicated that the ligands rapidly form complexes with silver(I) salts, and coordination at a first site inhibits coordination of a second cation to the ligand, thus favoring 1:1 complexes in solution. These 1:1 units self-assemble into one-dimensional chains in the solid state, even in the presence of excess Ag(I). Structurally diverse coordination polymers exhibiting different coordination numbers and geometry were characterized by single crystal X-ray crystallography. Our results demonstrate that a modification to the ligand, distal from the binding site, affects the coordination chemistry and supramolecular structure of these complexes.

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metal ions and a π-conjugated pathway that can mediate electronic or magnetic interactions between metal centers. One important difference between these three ligands is that 2,2′bipyridine generally only coordinates to a single metal ion, whereas 4,4′-bipyridine and 2,2′-bipyrimidine can bridge two metal centers. A recent important experiment demonstrated that bipyrimidine could link Co(II) centers to form a controllable spin system through switching of coupled spins in a single-molecule junction. In that work, the bipyrimidine moiety linked two Co(II) spin centers forming a combined controllable spin system.24 Despite the attractive properties of 2,2′-bipyrimidine as a bridging ligand, there are a limited number of reports of functionalized analogues, except for methylated derivatives. Therefore, developing a facile route to functionalized 2,2′bipyrimidine is attractive for exploring its use in supramolecular chemistry and may open a path to new families of coordination polymers with interesting properties. In this work, we describe the synthesis and characterization of four new ligands based on 2,2′-bipyrimidine. We demonstrate that these compounds are effective ligands for silver(I) cations to produce coordination polymers. The interesting coordination polymers obtained were studied by single crystal X-ray diffraction (SCXRD). This new route to coordination polymers containing bipyrimidine may lead to diverse new materials with interesting and tunable properties.

INTRODUCTION Bridging ligands have been central to the developments of inorganic chemistry in the last century and are now at the heart of supramolecular coordination chemistry.1 For example, pioneering work by Creutz and Taube on bimetallic compounds bridged by 1,4-pyrazine ligands demonstrated the principles of inner sphere electron transfer.2 In addition, 1,4benzenedicarboxylate is the key bridging ligand in the archetypical metal−organic framework, MOF-5.3 Other Nheterocyclic bridging ligands, such as pyrazolate4 and imidazole,5−9 have also been employed to create fibers10 and liquid crystals.11−14 Furthermore, metallosupramolecular structures, including coordination polymers15−20 and frameworks,21,22 all use bridging ligands for structural organization. Conjugated N-containing heterocycles are important bridging ligands. The coordination chemistry of 2,2′-bipyrimidine ligands, however, has been understudied and underdeveloped compared to its more prominent N-heterocyclic analogues, 2,2′-bipyridine and 4,4′-bipyridine (Figure 1).23 Nevertheless, 2,2′-bipyrimidine shares the key features of each of these ligands: preorganized nitrogen donor atoms that can chelate to

Received: November 28, 2017 Revised: February 14, 2018

Figure 1. Comparison between bipyridine and bipyrimidine ligands. © XXXX American Chemical Society

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DOI: 10.1021/acs.cgd.7b01657 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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RESULTS AND DISCUSSION Synthesis of the Ligands. Our approach to monofunctionalized 2,2′-bipyrimidine ligands was inspired by a method described in a patent, where the synthesis of bipyrimidine ethyl ester 3 was first reported.25 We found, however, that the one-pot procedure described therein was unable to yield the desired compound due to an error in the procedure (the 1,3-dicarbonyl used is not a dialdehyde but an aldehyde and a methyl ketone, resulting in a methyl substituted ring). Consequently, it was necessary to independently establish a synthetic route to compound 3. Scheme 1 shows our route to monofunctionalized bipyrimidine derivatives. Reaction of the amidinium 1 with Scheme 1. Synthesis of Functionalized 2,2′-Bipyrimidine Ligands

Figure 2. Downfield region of the 1H NMR spectra of top, L1; middle, ligand after addition of one equivalent of AgPF6; bottom, ligand after the addition of four equivalents of AgPF6 (CD3CN, r.t., 400 MHz).

exchange. The 1H NMR spectrum of the solution cooled to −35 °C also showed only three signals for the aromatic protons, signifying that even at this low temperature the ligand and metal are still in fast exchange. We then studied Ag(I) complexation in more detail using quantitative 1H NMR titration experiments. As can be seen in Figure 3, a sigmoidal binding curve is obtained, suggesting the

dialdehyde 2 results in the formation of the para-substituted pyrimidine ring 3 in 58% yield. The structure of this compound was verified by 1H and 13C NMR spectroscopy, mass spectrometry, and elemental analysis. Alkaline hydrolysis of ester 3 gave compound 4 with a readily functionalizable carboxylic acid group at the 5-position in 89% yield. We found that the amide coupling reagent pair EDCI·HCl and hydroxybenzotriazole (HOBt) worked well to provide ligands L1−L4. Conveniently, the pure product precipitated out of solution as the reaction proceeded or upon the addition of water, and column chromatography was unnecessary to purify the products. New compounds L1−L4 were characterized by mass spectrometry, 1H NMR, 13C NMR, and IR spectroscopy. In addition, compounds L3 and L4 were characterized by SCXRD. The molecular structures of L1−L4 are shown in Figure S1. Binding of Metal Salts in Solution. To begin our studies of the coordination chemistry of L1−L4, we turned to silver(I) because it has been used extensively with N-containing heterocycles. Silver(I) has a flexible geometry owing to a d10 electron configuration,26 and coordination polymers of silver are of interest for antimicrobial agents,27 catalyst precursors,28 and electronic materials. In fact, Ag(I) has been previously shown to form one-dimensional chains with the parent 2,2′bipyrimidine molecule.29,30 The diamagnetism of Ag(I) would also facilitate solution studies by 1H NMR spectroscopy. The complexation of AgPF6 by L1 was investigated using 1H NMR spectroscopy. Addition of silver salt to the ligand in CD3CN causes downfield shifts in the protons of the bipyrimidine group and the amide hydrogen (Figure 2). Upon addition of the AgPF6 solution to the free ligand, the symmetry of the molecule is preserved; even when less than one equivalent is added, only three aromatic signals are observed, indicating that free and complexed ligand are in fast

Figure 3. (a) Species present in solution with varying equivalents of silver cation and (b) titration binding curve of L1 with AgPF6 showing the shift in signal of the bipyrimidine triplet. Inset shows the sigmoidal behavior of the signal in the region 0−1 equiv.

formation of AgL2, AgL, and Ag2L species in solution depending on the stoichiometry present. Given that saturation is not reached even after 12 equivaents of silver cation, it appears that binding of a second silver(I) ion to AgL is very weak; i.e., even in the presence of excess silver, there is a minimal amount of Ag2L complex present in solution. B

DOI: 10.1021/acs.cgd.7b01657 Cryst. Growth Des. XXXX, XXX, XXX−XXX

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Synthesis and Structures of the Metal Complexes. Two different silver salts, silver(I) hexafluorophosphate (AgPF6) and silver(I) triflate (AgOTf), were used to obtain solid-state structures of the complexes of ligands L1−L4. In general, the ligand was dissolved in boiling acetonitrile, and then a warm solution of the silver salt was added. The resulting yellow liquid was filtered through glass wool and left standing for 48−72 h to yield a crystalline precipitate. In the case of L4, it was found that a mixture of ethanol and acetonitrile was required to produce crystals of a size suitable for SCXRD. The solid complexes isolated from L1−L4 and silver(I) salts are all 1D coordination polymers as shown by SCXRD. In these complexes, the silver atoms are either all four-coordinate, all five-coordinate, or alternate between the two coordination numbers along the chain. Despite this change in coordination number, the N−Ag−N bond angle of each bipyrimidine is always in the narrow range of 70 ± 2°. The four-coordinate silver cations bind to four bipyrimidine nitrogen atoms, while the five-coordinate ones also add a solvent molecule to their coordination sphere. Significantly, the amide group never participates in the coordination to the silver ion. In all cases presented here, the four-coordinate silver ions are best described as having a pseudo-tetrahedral geometry. As well, very little torsion is seen between the two pyrimidine rings, in contrast to Train’s bipyrimidine-silver chain where a 27° torsion angle is observed in the presence of a perchlorate anion.30 In {[Ag(L1)(CH3CN)0.5]PF6}n the amide proton and carbonyl oxygen participate in interchain hydrogen bonding, resulting in closely packed wires; only 8.56 Å separate metal atoms on adjacent chains. The five-coordinate metal nodes present in the coordination polymer are of particular interest since they impart chirality to the structure. The space group of the crystal, P1, indicates the separation of the constituents into the two enantiomers during crystallization. The resulting supramolecular structure is thus of a bipyrimidine-silver wire with decorating chains alternating in two opposite orientations as seen in Figure 4.

surprise, the weak forces at play favored a different arrangement of the appended chains. As shown in Figure 5, the silver ions in this complex are all chemically equivalent and have a distorted square pyramidal

Figure 5. Solid-state structure of complex {[Ag(L2)CH3CN]OTf}n as determined by SCXRD. Noncoordinated anions and most hydrogen atoms are omitted for clarity.

geometry, with the cation resting slightly above the equatorial plane toward the axial acetonitrile ligand. The main difference from the previous example is the relative orientation of neighboring bipyrimidine moieties; rather than straddling the metal node, the alkyl groups of each chain only project on one side. It is interesting to note that the intermolecular interactions resulting from the addition of these 10 carbon atoms are sufficient to modify the coordination behavior of the distant bipyrimidine moiety. As well, no hydrogen bonding is observed between the amides of neighboring bipyrimidine units. Similar to the previous structure, the presence of five-coordinate silver ions imparts chirality on the structure; the two enantiomeric chiral ribbons cocrystallize as a racemate in the space group P1̅. In the next step of our investigation, a different substituent was selected to disrupt the interalkyl interactions of the previous systems. tert-Butylphenyl has a similar length to the hexyl chain but is more rigid and offers different potential intermolecular interactions to influence the assembly of the supramolecular structure. The complexation of L3 with AgPF6 resulted in the formation of {[Ag(L3)(H2O)0.5]PF6}n, whose structure is shown in Figure 6. Rather than the previously observed two chain positions, the substituents along the coordination polymer orient themselves in four distinct directions, resulting in an overall helical arrangement. Two chemically distinct metal centers, with different coordination numbers, are also present in this structure. A water molecule occupies the fifth coordination site of every other silver ion. This helix crystallizes as separate enantiomers in the chiral space group C2. By replacing the tert-butyl group at the para position of the phenylamide with the bulkier trityl group and reacting with silver triflate, {[Ag(L4)](EtOH)OTf}n was obtained (Figure 7). This time, all of the Ag(I) cations have the same coordination environment, a four-coordinate metal node with pseudo-tetrahedral geometry, where adjacent bipyrimidine planes sit almost at right angles from one another. In contrast to the previous examples, this supramolecular structure is achiral. Interestingly again, by increasing the steric demand of the ligand as was observed when going from hexyl to hexadecyl, the angle between adjacent bipyrimidines is decreased. Of all the examples shown here, it is the least sterically demanding hexyl chains that orient themselves farthest away from each other.

Figure 4. Solid-state structure of the complex {[Ag(L1)(CH3CN)0.5]PF6}n as determined by SCXRD. Noncoordinated anions and most hydrogen atoms are omitted for clarity.

In an effort to separate the wires from one another in the solid-state structure, and potentially make them solutionprocessable, we elongated the alkyl chain from C6 to C16 and synthesized L2. We anticipated this would yield an insulated, soluble bipyrimidine-silver wire after coordination with silver(I) triflate, where the core structure of the L1 complex would be retained, but with longer alkyl chains on both sides. To our C

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proportions of silver triflate in pure acetonitrile, an interesting behavior is observed; the precipitated product of L3 with 1 equiv of silver cation is the discrete {[Ag(L3)2]OTf·CH3CN} complex. When three or more equivalents are used, then the crystalline polymer {[Ag(L3)CH3CN]OTf}n is obtained. On the other hand, when L4 is reacted with the same cation in acetonitrile, the monometallic {[Ag(L4) 2 CH 3 CN]OTf· CH3CN} complex rapidly crystallizes out of solution, even when 12-fold excess silver is added (Figure 8).

Figure 6. Solid-state structure of the complex {[Ag(L3)(H2O)0.5]PF6}n as determined by SCXRD. Top: side-on view of the polymeric chain. Bottom: end on view showing the four different orientations of the substituents. Noncoordinated anions and most hydrogen atoms are omitted for clarity.

Figure 8. Solid-state structure of the complexes (a) {[Ag(L3)2]OTf· CH3CN}, (b) {[Ag(L4)2CH3CN]OTf·CH3CN}, and (c) {[Ag(L3)CH3CN]OTf}n as determined by SCXRD. Noncoordinated anions and most hydrogen atoms are omitted for clarity.

A larger scale preparation of two of these complexes, the polymeric material {[Ag(L3)CH3CN]OTf}n and the dimer {[Ag(L4)2CH3CN]OTf·CH3CN} was carried out and analyzed by IR and Raman spectroscopy (Figures S17−18), and powder X-ray diffraction (PXRD) to show the homogeneity of the material obtained. Figure 9 shows the PXRD traces of the

Figure 7. Solid-state structure of complex {[Ag(L4)](EtOH)OTf}n as determined by SCXRD. Noncoordinated anions and most hydrogen atoms are omitted for clarity.

Investigation of the Self-Assembly Process. The fact that 1:1 Ag(I):ligand coordination polymers are formed even in the presence of a large excess of silver hints strongly toward a self-sorting mechanism. Our titration experiment shows that the complexation of a silver ion in one of the two nitrogen pockets significantly inhibits the binding of a second ion in the adjacent pocket; a bipyrimidine ligand cannot easily satisfy two silver(I) atoms by itself. Thus, even in the presence of excess silver, the polymerization of the monomer AgL through preferential self-selection into (AgL)n is favored over the addition of a “bare silver” to the second binding site, i.e., formation of Ag2L. When L3 and L4 are treated with different

Figure 9. (a) PXRD trace of {[Ag(L4)2CH3CN]OTf·CH3CN} and (b) the simulation from SCXRD. (c) PXRD trace of {[Ag(L3)CH3CN]OTf}n and (d) the simulation from SCXRD. D

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Preparation of Bipyrimidine Ethyl Ester (3). Compound 1 (4.7 g, 26 mmol) and pyridine (50 mL) were added to crude ethyl 2,2diformylacetate (4.8 g, 33 mmol). The mixture was warmed to 70 °C under a nitrogen atmosphere and stirred overnight. Pyridine was then evaporated under reduced pressure to give a dark brown sticky solid. The solid was washed multiple times with cold acetone to obtain bipyrimidine ethylester as a beige powder in 58% yield (4.3 g, 19 mmol). 1 H NMR (300 MHz, CDCl3) δ = 9.52 (s, 2 H), 9.07 (d, J = 4.8 Hz, 2 H), 7.49 (t, J = 4.8 Hz, 1 H), 4.50 (q, J = 7.1 Hz, 2 H), 1.47 (t, J = 7.1 Hz, 3 H) ppm; 13C NMR (75 MHz, CD3CN) δ = 166.2, 164.7, 163.3, 159.5, 158.9, 125.1, 122.9, 62.9, 14.5; HRMS (ESI TOF) m/z [M + H]+ Calcd for C11H11N4O2: 231.0882. Found: 231.0878; Anal. Calcd for C11H10N4O2: C, 57.39; H, 4.38; N, 24.34. Found: C, 57.11; H, 4.37; N, 23.96; melting point range: 146−149 °C. Preparation of Bipyrimidine Carboxylic Acid (4). To a flask containing 3 (4.3 g, 19 mmol) was added sodium hydroxide (5.0 g, 125 mmol) and water (50 mL). The mixture was stirred at room temperature for 3 h and acidified with conc. HCl until a white precipitate formed. The solid was filtered off and washed with cold water to give bipyrimidine carboxylic acid 4 as a white powder in 89% yield (3.5 g, 17 mmol). 1 H NMR (400 MHz, DMSO-d6) δ = 9.39 (s, 2 H), 9.05 (d, J = 4.8 Hz, 2 H), 7.70 (t, J = 4.8 Hz, 1 H) ppm; 13C NMR (101 MHz, DMSO-d6) δ = 164.8, 164.6, 162.0, 158.6, 158.0, 124.3, 122.2 ppm; HRMS (TOF ES-, m/z) Calcd for C9H5N4O2 [M − H]−: 201.0413. Found: 201.0415; Anal. Calcd for C9H7N4O2.5 (M+0.5H2O): C, 51.19; H, 3.34; N, 26.53. Found: C, 51.17; H, 3.36; N, 26.24; melting point > 260 °C. Preparation of Bipyrimidine-amide-C6 (L1). Compound 4 (202 mg, 1.0 mmol), HOBt (203 mg, 1.5 mmol), EDCI·HCl (287 mg, 1.5 mmol), dimethylacetamide (6 mL), and hexylamine (140 μL, 1.0 mmol) were combined in a round-bottomed flask. The mixture was sonicated until all reagents had dissolved and the solution turned yellow. The reaction was stirred at 65 °C under a nitrogen atmosphere for 16 h. The reaction mixture was then poured into basic water (1 g of NaHCO3, 100 mL) and extracted three times with DCM (300 mL total). The combined organic phase was washed with water (2 × 150 mL) and dried under reduced pressure. To the yellow oil obtained, 50 mL of water was added and left in the freezer until a white precipitate formed. The white powder was isolated using a glass frit and washed with water (2 × 10 mL) before being dried under reduced pressure to obtain a white precipitate, L1 (135 mg, 0.47 mmol, 47% yield). 1 H NMR (300 MHz, CDCl3) δ = 9.34 (s, 2 H), 9.06 (d, J = 4.8 Hz, 2 H), 7.49 (t, J = 4.8 Hz, 1 H), 6.27 (br. s., 1 H), 3.53 (dd, J = 6.4, 13.6 Hz, 2 H), 1.77−1.63 (m, 2 H), 1.50−1.23 (m, 6 H), 0.91 (t, J = 6.9 Hz, 3 H) ppm; 13C NMR (75 MHz, CDCl3) δ = 163.3, 163.0, 161.5, 158.1, 156.8, 127.9, 121.9, 40.4, 31.3, 29.4, 26.6, 22.4, 13.9 ppm; HRMS (TOF ES+, m/z) Calcd for C15H19N5ONa [M + Na]+ 308.1487. Found 308.1483; melting point: 130−134 °C. Preparation of Bipyrimidine-amide-C16 (L2). To compound 4 (202 mg, 1.0 mmol), HOBt (203 mg, 1.5 mmol), and EDCI·HCl (287 mg, 1.5 mmol) in dimethylacetamide (6 mL) was added hexadecylamine (241 mg, 1.0 mmol). The mixture was sonicated until all reagents had dissolved and the solution turned a faint yellow. The reaction was stirred at 65 °C under nitrogen for 16 h then triturated in 100 mL of basic water (1 g NaHCO3), and the white precipitate was filtered and washed with cold water. L2 was isolated as a white powder (345 mg, 0.82 mmol, 82% yield). 1 H NMR (300 MHz, CDCl3) δ = 9.34 (s, 2 H), 9.06 (d, J = 4.9 Hz, 2 H), 7.49 (t, J = 4.9 Hz, 1 H), 6.26 (t, J = 4.9 Hz, 1 H), 3.53 (dd, J = 7.2, 13.1 Hz, 2 H), 1.73−1.66 (m, 2 H), 1.38 (br. s., 2 H), 1.26 (br. m., 24 H), 0.89 (t, J = 6.9 Hz, 3 H) ppm; 13C NMR (75 MHz, CD3OH) δ = 163.2, 162.8, 160.0, 159.4, 132.4, 123.7, 40.9, 33.2, 30.94, 30.91, 30.8, 30.64, 30.62, 30.4, 28.8, 27.6, 23.9, 14.6 ppm; HRMS (TOF ES+, m/z) Calcd for C25H39N5ONa [M + Na]+ 448.3052, found 448.3058; melting point: dec 197 °C. Preparation of Bipyrimidine-amide-t-butylphenyl (L3). 4-tertButylaniline (160 μL, 1.0 mmol) was added to a suspension of 4 (202 mg, 1.0 mmol), HOBt (203 mg, 1.5 mmol) and EDCI·HCl (287

ground material and models obtained from the SCXRD structure (after correction to account for the difference in temperature between the two experimental techniques). Efforts to scale up the other complexation reactions did not yield sufficient material for PXRD or showed a mixture of phases.

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CONCLUSIONS In summary, we have developed the synthesis of 5-substituted bipyrimidines. To demonstrate the utility of these functionalized compounds, four new derivatives were synthesized and used as ligands. When combined with silver(I) salts, these bipyrimidine ligands rapidly bind to the metal ion and crystallize into coordination polymers with diverse 1-D chain structures. This new family of bridging ligands is promising for the development of coordination polymers. We are now investigating the coordination chemistry of related ligands to form complex metallosupramolecular assemblies.

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EXPERIMENTAL SECTION

General Remarks. All reagents were purchased from SigmaAldrich or AK Scientific and used without further purification. 4Tritylaniline was synthesized according to a literature procedure.31 1H and 13C NMR spectra were recorded on a Bruker AV-300 or AV-400 spectrometer and referenced to residual solvent signals. 13C NMR spectra were recorded using a proton decoupled pulse sequence. Electrospray ionization mass spectra (ESI-MS) were obtained on a Waters/Micromass LCT-TOF instrument. Melting points were recorded on a Stanford Research Systems Digimelt. Elemental analyses were performed at the UBC Microanalytical Services Laboratory. PXRD patterns were collected on a Bruker D8 Discover diffractometer at room temperature. Single-crystal X-ray data were collected on a Bruker APEX DUO diffractometer using graphite monochromated Mo Kα radiation (λ = 0.71073 Å). All data were collected at 90 K to a resolution of 0.77 Å. Raw frame data (including data reduction, interframe scaling, unit cell refinement, and absorption corrections) for all structures were processed using APEX2.32 Structures were solved using SUPERFLIP33 and refined using full-matrix least-squares on F2 within the CRYSTALS suite.34 All non-hydrogen atoms were refined with anisotropic displacement parameters. Hydrogen atoms were generally visible in the Fourier difference map and were initially refined with restraints on bond lengths and angles, after which the positions were used as the basis for a riding model.35 The structure of {[Ag(L3)(H2O)0.5]PF6}n is of relatively low quality and so is provided as an indication of structural connectivity only; in this structure it was not possible to resolve an area of diffuse electron density (believed to arise from disordered solvent molecules), and so PLATON-SQUEEZE was used to account for this electron density in the model.36 Individual structures are shown in more detail in the CIFs, which have been deposited with the CCDC (CCDC numbers: 1586467−1586475). Synthesis of Ligands. Compound 2 was synthesized using a reported procedure and used without further purification.37 1 had been reported previously, but we developed a new synthesis that does not involve the use of ammonia.38 Preparation of 2-Amidinopyrimidine Acetate (1). 2-Cyanopyrimidine (5.0 g, 48 mmol) and ammonium acetate (7.0 g, 91 mmol) were mixed in 50 mL of methanol and heated to 80 °C for 16 h. After being cooled down to room temperature, the yellow solution containing a pale precipitate was taken to dryness under reduced pressure. The solid was washed with a small amount of cold methanol to give pure 2-amidinopyrimidine acetate as a white solid (3.5 g, 19 mmol, 40% yield). 1 H NMR (400 MHz, D2O) δ = 8.95 (d, J = 5.0 Hz, 2 H), 7.72 (t, J = 5.0 Hz, 1 H), 1.84 (s, 3 H) ppm; 13C NMR (101 MHz, D2O) δ = 181.4, 159.8, 158.3, 152.3, 124.8, 23.4 ppm; HRMS (ESI TOF) m/z [M − CH3COO]+ Calcd for C5H7N4 123.0671. Found 123.0673; Anal. calcd for C7H10N4O2: C, 46.15; H, 5.53; N, 30.75. Found: C, 46.48; H, 5.54; N, 30.71; melting point: dec > 205 °C. E

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mg, 1.5 mmol) in dimethylacetamide (6 mL). The reaction was stirred at 65 °C under nitrogen for 16 h, then triturated in 100 mL basic water (1 g NaHCO3), the white precipitate was filtered and washed with cold water. L3 was isolated as a white powder (280 mg, 0.84 mmol, 84% yield). 1 H NMR (400 MHz,CDCl3) δ = 9.49 (s, 2 H), 9.04 (d, J = 5.1 Hz, 2 H), 8.29 (br. s., 1 H), 7.59 (d, J = 7.6 Hz, 2 H), 7.48 (t, J = 4.8 Hz, 1 H), 7.41 (d, J = 8.9 Hz, 2 H), 1.33 (s, 9 H) ppm; 13C NMR (75 MHz, CDCl3) δ = 163.5, 161.4, 161.2, 158.1, 157.0, 148.6, 134.4, 128.4, 126.0, 122.0, 120.4, 34.5, 31.3 ppm; HRMS (TOF ES+, m/z) Calcd for C19H20N5O [M + H]+ 334.1670, found 334.1668; anal. calcd for C19H19N5O: C, 68.45; H, 5.74; N, 21.01. Found: C, 68.19; H, 5.76; N, 20.74; melting point > 260 °C. Preparation of Bipyrimidine-amide-tritylphenyl (L4). Compound 4 (202 mg, 1.0 mmol), HOBt (203 mg, 1.5 mmol), EDCI·HCl (287 mg, 1.5 mmol), 6 mL of dimethylacetamide, and 4-trityl aniline (335 mg, 1.0 mmol) were combined in a round-bottomed flask. The mixture was sonicated until all reagents had dissolved and the solution turned gray. The reaction was stirred at 65 °C under a nitrogen atmosphere for 16 h. The product was triturated with 100 mL of basic water (1 g NaHCO3), the off-gray precipitate was filtered and washed with cold water. L4 was isolated as a powder (317 mg, 0.61 mmol, 61% yield). 1 H NMR (400 MHz, CD3CN) δ = 9.37 (s, 2 H), 9.02 (s, 1 H), 8.99 (d, J = 5.1 Hz, 2 H), 7.66 (d, J = 8.9 Hz, 2 H), 7.55 (t, J = 5.1 Hz, 1 H), 7.33−7.18 (m, 17 H) ppm; HRMS (TOF ES+, m/z) Calcd for C34H25N5ONa [M + Na]+ 542.1957. Found 542.1949; melting point > 260 °C. Preparation of Single Crystals of Silver Coordination Polymers. Typically, 5 mg of ligand and at least 3 equiv of silver triflate or hexafluorophosphate were dissolved in 5 mL of warm acetonitrile. The solution was filtered through glass wool and left to stand until yellow needles of a suitable size could be observed. In the case of L4, it was found that 5 mL of 50/50 v/v ethanol/acetonitrile mixture was required to produce crystals of size suitable for SCXRD. Preparation of {[Ag(L3)CH3CN]OTf}n. Silver triflate (150 mg, 0.60 mmol), and ligand L3 (66 mg, 0.20 mmol), were dissolved in 25 mL of boiling acetonitrile. The solution was filtered through glass wool. The solution was let to stand for 1 week at room temperature as a yellow sparkly precipitate formed. The crystalline precipitate was filtered and dried to obtain the coordination polymer (72 mg, 0.11 mmol, 55% yield). Anal. calcd for C22H22N6O4 AgSF3: C, 41.85; H, 3.51; N, 13.31; S, 5.04. Found: C, 41.60; H, 3.49; N, 13.01; S, 4.84. FT-IR 1678 s (amide CO), 1238 vs, 1156 s, 1026 vs cm−1. Preparation of {[Ag(L4)2CH3CN]OTf·CH3CN}. Silver triflate (150 mg, 0.60 mmol), and ligand L4 (52 mg, 0.20 mmol), were dissolved in 25 mL of boiling acetonitrile. The solution was filtered through glass wool. The solution was let to stand for 1 week at room temperature as a yellow sparkly precipitate formed. The crystalline precipitate was filtered and dried to obtain the discrete complex (38 mg, 0.028 mmol, 28% yield). Anal. Calcd for C73H56N12O5 AgSF3: C, 63.62; H, 4.10; N, 12.20; S, 2.33. Found: C, 61.89; H, 3.81; N, 10.41; S, 2.69. FT-IR 1663 s (amide CO), 1282 s, 1223 s, 1023 s, cm−1.

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Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*Dr. Mark MacLachlan, Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC V6T 1Z1, Canada. E-mail: [email protected]. ORCID

Nicholas G. White: 0000-0003-2975-0887 Mark J. MacLachlan: 0000-0002-3546-7132 Funding

Natural Sciences and Engineering Research Council (NSERC) of Canada; Killam Trust. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank NSERC for funding (Discovery Grant, Scholarship to G.B.H.) and the Killam Trust for a Postdoctoral Fellowship for NGW. G.B.H. would like to thank Veronica Carta for her help with SCXRD data acquisition of one structure.

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REFERENCES

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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.7b01657. Crystal data and structure refinement as well as structures of the ligands, their IR and NMR spectra, and Raman and IR spectra of selected complexes (PDF) Accession Codes

CCDC 1586467−1586475 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 F

DOI: 10.1021/acs.cgd.7b01657 Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

Article

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DOI: 10.1021/acs.cgd.7b01657 Cryst. Growth Des. XXXX, XXX, XXX−XXX