Photoreactivity of Ag(I) Complexes and Coordination Polymers of

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Photoreactivity of Ag(I) Complexes and Coordination Polymers of Pyridyl Acrylic Acids Goutam Kumar Kole,† Geok Kheng Tan,† and Jagadese J. Vittal*,†,‡ † ‡

Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543 Department of Chemistry, Gyeongsang National University, Jinju, South Korea 660-701

bS Supporting Information ABSTRACT: An attempt has been made to orient the CdC bonds in trans-3(30 -pyridyl)acrylic acid (3-PAH) and trans-3-(40 -pyridyl)acrylic acid (4-PAH) in the hydrogen-bonded coordination complexes and coordination polymers of Ag(I), utilizing the argentophilic interaction. Both neutral and deprotonated ligands were employed to synthesize the following compounds: [Ag(3-PAH)2](BF4) (1), [Ag(3-PAH)2](ClO4) (2), [Ag(4-PAH)2](ClO4) 3 H2O (3), [Ag(3PA)] 3 1.5H2O (4), and [Ag(4-PA)] (5). Of these, 1
2 are isotypical hydrogenbonded polymers of Ag(I) complexes and 3 is a hydrogen-bonded dimer, whereas 4 and 5 are coordination polymers. Compounds 1
4 undergo photodimerization in head-to-head fashion in the solid state. The photoreactivity of these compounds in solution was also investigated. The head-to-head photodimerized product of 4-PAH, namely, 3,4-bis(40 -pyridyl)cyclobutane-1,2-dicarboxylic acid (HH-4,4-BPCD), has been shown to be a potential ligand for synthesizing coordination polymers, by the isolation of [Ag2(HH-4,4-BPCD)(H2O)] 3 (2H2O)(1/2MeOH), which has a twodimensional polymeric structure in the solid state.

’ INTRODUCTION Covalent synthesis of strained cyclobutane derivatives utilizing supramolecular interactions has driven tremendous success in the past decade. Photodimerization reaction in the solid state, to synthesize cyclobutane derivatives, has drawn considerable attention of crystal engineers in the modern age because of its high yield, distinguished selectivity, environment friendliness, and access to molecules that are otherwise inaccessible in solution.1 Hydrogen bonded cocrystals2 and molecular salts,3 coordination compounds,4 host
guest compounds,5 and other various organized media6 have been explored for this purpose in the past. In this regard, metallophilic interactions are gaining much visibility. Of late, Puddephatt designed several diphosphine bridged gold(I) and silver(I) based macrocycles in which the linear olefin ligands have been aligned parallel via aurophilic7 and argentophilic8 interactions suitable for photodimerization reaction. MacGillivray reported the argentophilic interaction as a tool to preorganize a pair of 4-pyridylstyrenes in a Ag(I) complex which, upon photochemical cycloaddition reaction, transformed to a onedimensional polymer from a finite complex.9 Argentophilic interaction was later exploited to 4-vinylpyridine, a liquid and terminal olefin, for its solid state photoreactivity in Ag(I) complexes.10 A silver coordination polymer [Ag(μ-4,40 -bpe)(H2O)](CF3CO2) 3 CH3CN, investigated by us, was found to undergo a quantitative photodimerization reaction after desolvation.11 In many cases, argentophilic interactions are assisted by ligands or anions present in the solid. Angular bridging ligands or anions, such as carboxylate, bridge two Ag(I) atoms to bring the Ag(I) atoms closer, within a distance less than the sum of their van der Waals r 2011 American Chemical Society

radii, resulting in an argentophilic interaction, and this is known as an anion or ligand supported argentophilic interaction.11,12 When an argentophilic interaction results without any support from ligands or anions, it is termed as a ligand or anion unsupported argentophilic interaction.13 Biradha et al. has reported silver coordination compounds of trans-3-(40 -pyridyl)acrylic acid (4-PAH) and analogues that undergo photodimerization in head-to-head fashion via nitrate anion supported argentophilic interaction.12a Although the double bonds in the neutral 3-PAH are aligned parallel in head-to-head fashion in the solid state and undergo no,15 the photodimerization as reported by Schmidt14 and Brice~ conversion was only 66%. In addition, the head-to-tail parallel orientation of olefins has not been achieved in the solid state for 3-PAH. The coordination chemistry of 3-PA and 4-PA has been well explored in the past,16 but the silver(I) coordination chemistry of these ligands is relatively unexplored.12a In this contribution, we present our results on our attempts to preorganize the anionic and neutral 3-PA and 4-PA in several silver(I) coordination compounds using weakly coordinating anions.

’ RESULTS AND DISCUSSION When neutral 3-PAH or 4-PAH was mixed with AgBF4 or AgClO4 in a 1:2 molar ratio, the hydrogen-bonded coordination complexes [Ag(3-PAH)2](BF4) (1), [Ag(3-PAH)2](ClO4) (2), Received: August 26, 2011 Revised: November 1, 2011 Published: November 23, 2011 326

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Figure 1. Hydrogen bonded 1D zigzag chain and various hydrogen bonded interactions in 1.

Figure 2. The cationic complexes are stacked parallel in 1 by an “anion unsupported” argentophilic interaction. Figure 3. The cationic complexes are stacked parallel in 2 by an anion unsupported argentophilic interaction.

and [Ag(4-PAH)2](ClO4) 3 H2O (3) were obtained in almost quantitative yield. When anionic ligands were used, neutral coordination polymers [Ag(3-PA)] 3 1.5H2O (4) and [Ag(4-PA)] (5) were isolated. The crystal structures of 1
5 were undertaken to investigate the influence of various supramolecular forces on the packing of the olefin bonds. Crystal Structure and Photoreactivity of Complex [Ag(3-PAH)2](BF4) (1). A single crystal X-ray diffraction experiment reveals that the pyridyl N atoms of the two 3-PAH ligands coordinate to Ag(I) in a linear fashion (with N
Ag
N angle 173.66(6)°) to furnish a cationic monomeric complex. No significant interaction with Ag(I) has been found, as seen from the shortest Ag 3 3 3 F distance of 3.09 Å, and hence, the role of BFh4 anions appears just to balance the charge. The carboxylic acid groups are involved in H-bonding to form the classical carboxylic acid dimer that yields a zigzag H-bonded polymeric structure (Figure 1). Two such [Ag(3-PAH)2]+ cations stack in parallel orientation, which may be attributed to the weak argentophilic interaction, as shown in Figure 2. The Ag 3 3 3 Ag distance of 3.34 Å is close to the sum of the van der Waals radii of two Ag(I) atoms, 3.44 Å.17 The 3-PAH ligands are aligned in head-to-head fashion, and the distance between the CdC bond pairs, 3.75 Å, is close enough to be photoreactive. Indeed 1 was found to undergo quantitative photodimerization under UV light for 15 h, as was followed by 1 H NMR spectroscopy by the disappearance of two peaks for ethylenic protons at δ = 7.63 and 6.69 ppm and the appearance of two peaks for cyclobutane protons at δ = 4.31 and 3.93 ppm (see the Supporting Information (SI)). Crystal Structure and Photoreactivity of Complex [Ag(3-PAH)2](ClO4) (2). Single crystal X-ray diffraction study reveals that 2 is isomorphous and isostructural to 1, and the two pyridyl

N atoms coordinate to Ag(I) with an angle of 173.48(7)° in the coordination complex cation, and the charge is balanced by the presence of ClOh4 anion which interacts very weakly with Ag(I) centers, as indicated by the closest Ag 3 3 3 OClO3 distance, 2.97 Å. The carboxylic acid groups are involved in H-bonding to form the classical carboxylic acid dimer. The [Ag(3-PAH)2]+ cationic pairs are again stacked by an anion unsupported argentophilic interaction with a Ag 3 3 3 Ag distance of 3.44 Å (Figure 3), which is equal to the sum of the van der Waals radii of two Ag atoms (3.44 Å).17 The distance between the well-aligned CdC bond pairs of 3-PAH molecules in a “head-to-head” manner is 3.74 Å. As expected, 2 was also found to undergo quantitative photodimerization upon irradiation under UV light for 16 h, as was witnessed by the disappearance of two peaks for ethylenic protons at δ = 7.63 and 6.69 ppm and the appearance of two peaks for the cyclobutane protons at δ = 4.32 and 3.94 ppm in 1H NMR spectroscopy (see the SI). Crystal Structure and Photoreactivity of Complex [Ag(4PAH)2](ClO4) 3 H2O (3). X-ray diffraction study reveals that there are two independent formula units in the asymmetric unit of the unit cell. Of the four 4-PA ligands in the asymmetric unit, the “acrylic acid” fragments in two bearing oxygen atoms O1, O2, O7, and O8 were found to be disordered. It is interesting to note that all the atoms in the two [Ag(4-PAH)2]+ cations, the chlorine atoms of the two ClOh4 anions, and the oxygen atoms of the two water molecules occupy the crystallographic ac-mirror plane. This imposes crystallographic disorder on the oxygen atoms of the two perchlorate anions. In the cation, the two crystallographically independent Ag(I) are bonded to the N atoms of the two 327

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Figure 4. Discrete cationic complexes are stacked parallel in 3 by an anion supported argentophilic interaction. One set of distances is shown.

Figure 6. 1D ribbon-like structure of 4, showing stronger argentophilic interactions.

motion of the crisscrossed 4-PA can account for the formation of the rctt-isomer as the only isomer from the pairs aligned in crisscross fashion (Figure 5b) during photodimerization. Crystal Structure and Photoreactivity of Coordination Polymer [Ag(3-PA)] 3 1.5H2O (4). Single crystal X-ray diffraction study revealed that all the donor sites in 4 are coordinated to Ag(I). The coordination number around each Ag(I) ion is three, and the geometry is T-shaped . The carboxylate groups bridge two Ag(I) ions in μ1,3 fashion, and the distance is 2.883 Å, reflecting a very strong ligand supported argentophilic interaction. For Z = 1 in the space group P1, there is a crystallographic inversion center present in the middle of the 8-membered Ag2(O2C)2 ring. The pyridyl N atoms are bonded to the neighboring [Ag(3-PA)] repeating units to form a 1D ribbon-like polymer which extends approximately along the [011] direction as shown in Figure 6. These 1D ribbons are further slipped-stacked in parallel arrangement (with Ag
Ag
Ag angle of 34°) via ligand unsupported argentophilic interactions. In this process, the photoreactive CdC bonds are aligned infinitely in parallel and in head-to-head fashion, and the distance between two CdC bonds is 3.61 Å. The distance between the two diagonally packed Ag(I) ions, 3.11 Å (Figure 7), is smaller than the sum of their van der Waals radii (3.44 Å),17 reflecting that significant argentophilic interaction prevails. Moreover, there is another Ag 3 3 3 Ag distance of 3.61 Å along the edge, as shown in Figure 7, which is slightly more than the sum of their van der Waals radii. Upon irradiation under UV light for 36 h, the powdered sample of 4 underwent quantitative photodimerization. To our disappointment, it was not an SCSC process. But we reckon that the dimerization process occurs randomly, which is more probable, and the resulting structure would probably be 2D (see the SI). There are three molecules of disordered water also in the crystal structure with 50% occupancy, whose hydrogen atoms were not located. Crystal Structure of Coordination Polymer [Ag(4-PA)] (5). Single crystal X-ray diffraction study revealed that all the donor sites are coordinated to Ag(I). The coordination number around each Ag(I) ion is 3, and the geometry is “Y”-shaped (Figure 8). The carboxylate groups are chelating to Ag(I), and the pyridyl N from the neighboring repeating unit is bonded to provide a linear 1D coordination polymer which propagates parallel to the b-axis. In fact, all the 1D chains are aligned parallel to the b-axis but not with perfect alignment of similar atoms from the neighboring chains. The distance between two nearest Ag(I) ions is 3.88 Å, indicating there is no significant argentophilic interaction. The relative orientation of 4-PAs is crisscrossed in a head-to-tail manner, with the distance between the centroids of CdC bonds of 5.20 Å. This polymer was found to be photostable. The structure is stabilized by the weak interchain Ag(I) 3 3 3 O interaction as shown in Figure 8. Comparative Study on Structures and Photoreactivity. Among the above five compounds investigated, four were found to be photoreactive; the photoreactive CdC bonds were

Figure 5. (a) The packing of cationic complex units of 3, and (b) a different view showing the crisscrossed arrangement of 4-PAH ligands. The ClOh4 anions are not shown for clarity.

4-PA ligands almost linearly with N
Ag
N angles of 169.4(4) and 172.1(5)°. The ClOh4 anions interact with Ag(I) weakly in bridging fashion to bring the two Ag(I) centers closer (Figure 4). This influence is clearly noted from the shorter Ag 3 3 3 Ag distances of 3.32 and 3.43 Å as compared to the distances found in 1 and 2. The [Ag(4-PAH)2]+ complex cations are further involved in hydrogen-bonding with water molecules on one side and with a carboxylic acid group of another complex unit on another side, forming a dicarboxylic acid dimer synthon. The hydrogen bonding interactions result in a finite “dimer” consisting of two complex units and two water molecules terminating the formation of an infinite array. This is inferred from the fact that the closest distance is 3.21 Å between the carboxylic acid groups. The 4-PAH ligands are found to stack infinitely in head-to-head fashion with a distance of 3.72 and 3.81 Å (Figure 5a) along the b-axis with alternative crisscross pairs. This compound was found to undergo photodimerization (∼90%) to rctt-HH-4,4-BPCD, as was observed by the disappearance of two peaks for ethylenic protons at δ = 7.57 and 6.80 ppm and the appearance of two peaks for cyclobutane protons at δ = 4.30 and 3.92 ppm in 1H NMR spectroscopy. At the same time, this compound also underwent about 3% trans
cis isomerization. The formation of the rctt-isomer as the sole isomer from crisscross aligned pairs is the result of pedal-like motion of monomeric units with respect to each other (see the SI).3c,9,18 A thorough perusal of the crystal structure reveals that one side of the CdC
CO2H unit in each independent [Ag(4-PA)2]+ is disordered with two different orientations by 62:38. In both [Ag(4-PA)2]+ cations in the asymmetric unit, the disorder fragment is paired with the undisordered 4-PA. If we consider only the major component, it is crisscrossed by 62%, and for the minor component, 38% has parallel orientation. Therefore, a pedal-like 328

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Figure 7. View showing the slip-stacked arrangement of 3-PA as a ribbon in 4. The argentophilic interaction is between two diagonal Ag(I) centers.

Figure 8. Packing of 1D chains in 5.

preorganized by an argentophilic interaction along with other supramolecular interactions. In isostructural 1 and 2, BFh4 and ClOh4 anions have little contribution in assisting the argentophilic interaction. But in 3, ClOh4 anions are found to bridge the Ag(I) atoms and, therefore, have some role in assisting the argentophilic interaction. 1 and 2 form hydrogen-bonded infinite 1D zigzag chains through the classical carboxylic acid dimer synthon. On the other hand, 3 forms a hydrogen-bonded dimer in which the two molecules are interacting through a carboxylic acid dimer with two terminal water molecules. In 1 and 2, the observed N
Ag
N angles along with the shorter Ag 3 3 3 Ag distances compared to the distances between CdC bonds indicate that two Ag(I) centers are leaning toward each other, reflecting the presence of argentophilic interactions. In 4, there is no anion present, and thus, the argentophilic interaction is absolutely free of any anion effect. Between 4 and 5, the difference in the molecular packing and the photoreactivity arises from the position of the “N” atoms in the pyridyl groups that make 3-PA an angular spacer and 4-PA a linear spacer ligand. Being an angular spacer, 3-PA can form a 16 member ring structure comprising a μ1,3bridging mode of carboxylate and monodentate pyridyl groups. These ring structures extend to form a 1D polymer, and a parallel orientation results exclusively, due to argentophilic interaction. On the other hand, the 1D polymer resulted from the chelating carboxylate and monodentate pyridyl groups has no scope of exerting an argentophilic interaction and, thus, no alignment of CdC bonds in the solid state structure of 5.

The above compounds were irradiated under UV light in d6-DMSO solution for 12 h, and 1H NMR spectra were acquired to study their photoreactivity in solution (see the SI). 3-PAH and 4-PAH were observed to isomerize in solutions of compounds 1
3 under the same conditions, indicating the absence of any argentophilic interaction in the solution phase. Coordination polymer 4 underwent incomplete photodimerization along with trans
cis isomerization, which reflects that the parallel arrangement of 1D ribbons still partially exists in the solution. In addition, the compound still maintains the stereoselectivity during the solution phase dimerization, as it results only in an rctt-HHdimer among all possible dimers of 3-PA. The observed isomerization is the result of the dissociation and scrambling of 3-PA in solution. Coordination polymer 5 underwent only trans
cis isomerization and no dimerization, which indicates that the 1D chains, although in random motion in solution, cannot come closer within the distance limit to be reactive. Generally, the compounds that are photostable in the solid state are observed to furnish a mixture of products in the solution phase due to the Brownian motion. We also observed some molecular salts of 4-PA that underwent quantitative photodimerization in the solid state but were observed not to furnish any dimerization in the solution phase despite higher freedom of molecular movements.3g Here we observed a similar phenomenon for 1
3. Compounds 1
4 undergo quantitative dimerization in the solid state. It is surprising to observe that the 3-PA molecule alone does not undergo photodimerization in solution phase but dimerizes in the solid state. 329

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Figure 9. Two-dimensional polymeric network of 6.

Figure 10. Stacking of the two-dimensional sheets by argentophilic interactions in 6. The noncoordinated solvents are removed for clarity, and the H atoms of the coordinated water molecules are only shown. Figure 11. (a) Various metallomacrocycles formed by argentophilic interaction and (b) a 12-membered water cluster ring inside the macrocycles.

Therefore, it can be concluded that the hydrogen bonded coordination complexes 1
3 behave like free ligand in the solution phase. The two cyclobutane compounds, viz., 3,4-bis(30 -pyridyl)cyclobutane-1,2-dicarboxylic acid and 3,4-bis(40 -pyridyl)cyclobutane1,2-dicarboxylic acid (head-to-head dimers of 3-PA and 4-PA, respectively) are abbreviated here as HH-3,3-BPCD and HH4,4-BPCD, respectively. One can utilize these cyclobutane compounds as potential ligands to synthesize coordination polymers. One such coordination polymer of Ag(I) with HH-4,4-BPCD is described here. Coordination Polymer of HH-4,4-BPCD with Ag(I). The compound [Ag2(HH-4,4-BPCD)(H2O)] 3 (2H2O)(1/2MeOH) (6) was synthesized by reacting AgBF4 with the Na-salt of HH4,4-BPCD19 in water, MeOH, and CH3CN. The asymmetric unit contains the formula unit of the complex. There are two types Ag(I) ions present in 6, of which the Ag1 has a linear coordination geometry comprising one N from a pyridyl group and one O from the carboxylate group of another ligand with an N
Ag
O angle of 178.3°. The Ag2 has a distorted trigonal geometry with a N from a pyridyl group, one O from the carboxylate group of the neighboring ligand, and one O from a coordinated water molecule (aqua ligand) where Ag(I) occupies 0.401 Å above the O2N

plane. Since each HH-4,4-BPCD ligand is bonded to four different Ag(I) ions, this gives rise to a two-dimensional polymeric structure, as shown in Figure 9. Apart from a coordinated water molecule, two noncoordinated water molecules and half a MeOH are also present in the lattice to fill in the void. The coordinated and noncoordinated water molecules form hydrogen bonds with the O atoms of the carboxylate group of the ligand, as shown in Figure 9. The MeOH molecule is situated closer to a crystallographic inversion and not involved in any hydrogen bonds. The connectivity of the twodimensional polymeric sheets consists of rhomboids (considering the center of the cyclobutane rings), and this is commonly known as (4,4) grids.20 Two such (4,4) sheets are further assembled through argentophilic interactions with a distance between Ag1 and Ag2 of 3.11 Å, as shown in Figure 10. In this assembly, the pyridyl rings of this cylclobutane are found to stack parallel with a distance of 3.83 Å. Interestingly, the Ag 3 3 3 Ag contacts create 16-, 20-, and 24-membered metallomacrocycle rings, as shown in Figure 11a. 330

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It appears that such an argentophilic interaction assisted metallomacrocyclic ring is very rare.21 Each 16-membered macrocyclic ring contains four carbonyl oxygen atoms, and all these oxygen atoms are hydrogen bonded to the water molecules. A thorough perusal of the structure reveals that these coordinated and noncoordinated water molecules form a hydrogen bonded water cluster ring along with the keto oxygen of HH-4,4-BPCD. The graph set notation of such rings can be denoted as R64(12), as shown in Figure 11b.

’ CONCLUSION We have presented the syntheses and structures of three hydrogen-bonded silver(I) coordination complexes and two coordination polymers. All these compounds except one have been found to be photoreactive and undergo a photodimerization reaction in the solid state under UV light. The overall packing, including the preorganization of olefin ligands with global minimum energy, is a balance between various supramolecular interactions including argentophilic association. Further, we have shown that the cyclobutane compounds can be used as a potential ligand to synthesize coordination polymers. This is the first report of any Ag(I) coordination compounds of neutral 3-PA ligand. All these coordination compounds and neutral 3-PAH undergo photodimerization in head-to-head fashion, which motivates us to design photoreactive solids where 3-PA can be aligned in a head-to-tail fashion. We have accomplished this as organic salts exploiting ionic interaction as template, and the results will be published elsewhere.

Crystal data for 4 at 100 K: C16H12Ag2N2O7, M = 560.02, triclinic, space group P1, a = 3.608(7), b = 9.937(2), c = 12.728(2) Å, α = 73.32(3)°, β = 87.94(3)°, γ = 84.00(3)°, V = 434.8(1) Å3, Z = 1, Dcalcd = 2.139 g cm
3, μ = 2.295 mm
1, Gof on F2 = 1.151, final R1 = 0.0337, wR2 = 0.0916 [for 1856 data I > 2σ(I)]. Anal. Found: C, 34.50; H, 2.29; N, 5.09. Ag2C16H12N2O7 requires C, 34.23; H, 2.16; N, 5.00%. Synthesis of 5: Similar method as for 4, except 4-PAH was used instead of 3-PAH. Yield: 75%. Crystal data for 5 at 223 K: C8H6AgNO2, M = 256.01, monoclinic, space group P21/c, a = 9.855(9), b = 11.472(1), c = 6.916(6) Å, β = 109.35(2)°, V = 737.8(1) Å3, Z = 4, Dcalcd = 2.305 g cm
3, μ = 2.679 mm
1, Gof on F2 = 1.042, final R1 = 0.0425, wR2 = 0.1027 [for 1433 data I > 2σ(I)]. Anal. Found: C, 37.05; H, 2.08; N, 5.35. C8H6AgNO2 requires C, 37.53; H, 2.36; N, 5.47%. Synthesis of 6: 15 mg of the ligand HH-4,4-BPCD was neutralized by NaOH (aq) in 3 mL of water. AgBF4 (19 mg, 0.1 mmol) in 2 mL of MeOH was carefully layered over it, keeping 3 mL of CH3CN as buffer layer in the middle in a test tube. The product was crystallized out after a few days. Yield: 72%. Crystal data for 6 at 293 K: C16.5H18Ag2N2O7.5, M = 1160.13, triclinic, space group P1, a = 9.116(8), b = 9.626(8), c = 12.316(1) Å; α = 106.13(2)°, β = 106.55(2)°, γ = 99.87(2)°, V = 957.7(1) Å3, Z = 2, Dcalcd = 2.012 g cm
3, μ = 2.089 mm
1, Gof on F2 = 1.049, final R1 = 0.0363, wR2 = 0.0882 [for 4133 data I > 2σ(I)]. Anal. Found: C, 34.50; H, 3.19; N, 5.09. Calcd for C33H36Ag4N4O15: C, 34.16; H, 3.13; N, 4.83%.

’ ASSOCIATED CONTENT

bS

Supporting Information. Additional structural diagrams, hydrogen bonding parameters, 1H NMR spectra, TGA plots, and cif files (CCDC 841568
841572). This material is available free of charge via the Internet at http://pubs.acs.org.

’ EXPERIMENTAL SECTION Synthesis of 1 and 2: 3-PAH (15 mg, 0.1 mmol) was dissolved 3 mL of methanol; then AgBF4 (19 mg, 0.1 mmol) for 1 and AgClO4 (21 mg, 0.1 mmol) for 2 in 2 mL of CH3CN were added. The resulting white precipitate was dissolved by adding 2 mL of water. Single crystalline products were obtained by slow evaporation. Yield: 90%. Crystal data for 1 at 100 K: C16H14AgBF4N2O4, M = 492.97, triclinic, space group P1, a = 8.075(2), b = 10.153(3), c = 11.524(3) Å, α = 74.68(5)°, β = 77.78(5)°, γ = 70.74(5)°, V = 852.1(4) Å3, Z = 2, Dcalcd = 1.921 g cm
3, μ = 1.252 mm
1, Gof on F2 = 1.131, final R1 = 0.0253, wR2 = 0.0675 [for 3847 data I > 2σ(I)]. Anal. Found: C, 38.58; H, 2.93; N, 5.64. C16H14AgBF4N2O4 requires C, 38.98; H, 2.86; N, 5.68%. Crystal data for 2 at 100 K: C16H14AgClN2O8, M = 505.61, triclinic, space group P1, a = 8.198(6), b = 10.145(8), c = 11.575(9) Å, α = 74.89(2)°, β = 77.20(2)°, γ = 70.62(2)°, V = 867.01(1) Å3, Z = 2, Dcalcd = 1.937 g cm
3, μ = 1.368 mm
1, Gof on F2 = 1.092, final R1 = 0.0264, wR2 = 0.0657 [for 3782 data I > 2σ(I)]. Anal. Found: C, 38.21; H, 2.78; N, 5.85. C16H14AgClN2O8 requires C, 38.01; H, 2.79; N, 5.54%. Synthesis of 3: 4-PAH (15 mg, 0.1 mmol) was dissolved in 4 mL of hot water; then AgClO4 (21 mg, 0.1 mmol) in 2 mL of CH3CN was added. Single crystalline products were obtained by slow evaporation. Yield: 85%. Crystal data for 3 at 100 K: C16H16AgClN2O9, M = 523.63, monoclinic, space group P21/m, a = 16.371(2), b = 6.413(7), c = 18.820(2) Å, β = 109.45(3)°, V = 1863.2(4) Å3, Z = 4, Dcalcd = 1.867 g cm
3, μ = 1.280 mm
1, Gof on F2 = 1.054, final R1 = 0.0654, wR2 = 0.1534 [for 2853 data I > 2σ(I)]. Anal. Found: C, 36.71; H, 2.94; N, 5.48. C16H16AgClN2O9 requires: C, 36.70; H, 3.08; N, 5.35%. Synthesis of 4: AgBF4 (19 mg, 0.1 mmol) in 2 mL of methanol was carefully layered over the Na-salt of 3-PAH (15 mg of 3-PAH was neutralized by NaOH (aq)) in 3 mL of water, keeping 3 mL of CH3CN as buffer layer in the middle in a test tube. The product was crystallized out after a few days. Yield: 78%.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected]. Fax: +65 6779 1691. Telephone: +65 6516 2975.

’ ACKNOWLEDGMENT We gratefully acknowledge the Ministry of Education, Singapore, for financial support through NUS FRC Grant R-143-000-439-112. We sincerely thank Hong Yimian for her kind help with the X-ray crystallography. We also thank R. Arvindren, DAR Salomone of Raffles Junior College, and Chew Wen Xiang and Alister Jan Uy Lussuan from NUS High School, Singapore, for being associated with this project at the beginning. J.J.V. thanks the Ministry of Education, Science & Technology (S. Korea) for the World Class University Chair Professorship through Grant No. R32-2008-000-2003-0. ’ REFERENCES (1) (a) MacGillivray, L. R.; Papaefstathiou, G. S.; Friscic, T.; Hamilton, T. D.; Bucar, D.-K.; Chu, Q.; Varshney, D. B.; Georgiev, I. G. Acc. Chem. Res. 2008, 41, 280–291. (b) MacGillivray, L. R. J. Org. Chem. 2008, 73, 3311–3317. (c) Nagarathinam, M.; Vittal, J. J. Macromol. Rapid Commun. 2006, 27, 1091–1099. (d) Nagarathinam, M.; Peedikakkal, A. M. P.; Vittal, J. J. Chem. Commun. 2008, 5277–5288. (2) (a) Friscic, T.; Drab, D. M.; MacGillivray, L. R. Org. Lett. 2004, 6, 4647–4650. (b) Mei, X.; Liu, S.; Wolf, C. Org. Lett. 2007, 9, 2729–2732. (c) Dutta, S.; Bucar, D. K.; Macgillivray, L. R. Org. Lett. 2011, 13, 2260–2262. (d) Bhogala, B. R.; Captain, B.; Parthasarathy, A.; Ramamurthy, V. J. Am. Chem. Soc. 2010, 132, 13434–13442. 331

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Crystal Growth & Design

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dx.doi.org/10.1021/cg201119c |Cryst. Growth Des. 2012, 12, 326–332