Unique Ruthenium Bimetallic Supramolecular Cages From C4

Apr 18, 2017 - Synopsis. The self-assembly of C4-symmetric tetrapyridyl metalloligands containing Fe or Co and diruthenium electron acceptors led to t...
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Unique Ruthenium Bimetallic Supramolecular Cages From C4‑Symmetric Tetrapyridyl Metalloligands Ji Yeon Ryu,† Eun Hye Wi,† Moumita Pait,† Sunwoo Lee,† Peter J. Stang,*,‡ and Junseong Lee*,†,‡ †

Department of Chemistry, Chonnam National University, Gwangju 61186, Republic of Korea Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, Utah 84112, United States

‡

S Supporting Information *

ABSTRACT: The self-assembly of C4-symmetric tetrapyridyl metalloligands containing Fe or Co and diruthenium electron acceptors by means of dative coordination bonding led to the formation of six different heterobimetallic supramolecules. All complexes were characterized by X-ray crystallography, ESI mass spectrometry, and 1H NMR (in the case of diamagnetic systems) spectroscopy. The bridging units in the diruthenium complexes greatly influenced the geometrical preference of the supramolecular structures, resulting in the formation of different architectures, namely A4D2 or A6D3 (A = acceptor, D = donor). Depending on the bridging unit, A4D2 tetragonal prism, A4D2 molecular tweezer, or A6D3 triple-decker complexes were obtained selectively. The self-assembly of an unexpected triple-decker type Ru12Fe3 heterobimetallic species was also observed.

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INTRODUCTION The successful synthesis of supramolecular cages via coordination-driven self-assembly1−17 opens a new path for the synthesis of coordination cage complexes with aesthetically appealing supramolecular architectures of various shapes, sizes, and functionalities.2 This class of materials not only has structural beauty but also has applications across a breadth of areas, such as gas separation and storage, molecular recognition, host−guest chemistry, modulation of the chemical reactivity of guest molecules, enzyme-mimicking supramolecular catalysis, and biomedical applications.18 Straightforward, self-assembly approaches for the synthesis of supramolecular architectures generally involve organic linkers, pyridyl-based acceptors with specific geometries, and metal precursors (multicomponent self-assembly). Such strategies have resulted in a large number of molecular architectures reported by many research groups.19,20 An alternative approach involving multitopic donor ligands containing metal ions (“metalloligands”) and metallo-organic linkers instead of simple organic linkers may be useful for the synthesis of heterobimetallic supramolecular assemblies.21−26 Recently, there has been a growing interest in metalloligandbased heterometallic supramolecular assemblies, which comprise multiple metal ions and are based on the ‘“complex-as-aligand”’ concept.8,27,28 Among various reported metalloligand systems, symmetrical metal complexes possessing four pyridyl groups are considered the most promising system for the synthesis of solid tetragonal prismatic cages.24−26,28 On the other hand, the self-assembly of lower-symmetry supramolecules has not received much attention because their © 2017 American Chemical Society

synthesis and characterization is difficult and high-symmetry systems are thermodynamically favored.8,27 Hence, to generate less symmetrical supramolecules, Cssymmetric a CpCo-tetrakis(4-pyridyl)cyclopentadienone metallocene metalloligand (CpCoC5(O)Py4; 1)29 was used in complexation with three diruthenium complexes with naphthalene (Ru2Np; 6), benzene (Ru2Bz; 5), or oxalate (Ru2Ox; 4) to result in the formation of supramolecules with different shapes (Chart 1). It was found that the length or thickness of the bridging unit could influence the shape of self-assembled supramolecules. Specifically, we have focused on a C4symmetric Cp*Fe-tetrakis(4- pyridyl)cyclobutadienyl metallocene complex (Cp*FeC4Py4; 2) and a CpCo-tetrakis(4pyridyl)cyclobutadienyl metallocene complex (CpCoC4Py4; 3), in the self-assembly with diruthenium complexes 4−6. The cyclobutadiene-type tetratopic metalloligands 2 and 330 have symmetry higher than that of 1 and geometrical properties different from those of the analogue 1 (Chart 2); the four pyridyl groups are identical, and therefore, the same coordination modes (inter or intra) are expected. In comparison to cyclopentadienone analogue 1, metalloligands 2 and 3 have longer distances and higher dihedral angles between the pyridyl groups. Thus, if they are reacted with diruthenium electron acceptors, C4-symmetric A4D2 (A = acceptor, D = donor) tetragonal-prismatic cages could be formed by the intermolecular coordination of the di-Ru complexes. We recently reported on the Ru-Fe heterobimetallic Received: March 3, 2017 Published: April 18, 2017 5471

DOI: 10.1021/acs.inorgchem.7b00556 Inorg. Chem. 2017, 56, 5471−5477

Article

Inorganic Chemistry Chart 1. (a) Tetrapyridyl Electron Donor Molecules 1−3 and (b) Diruthenium Acceptor Units 4−6

Scheme 1. Coordination-Driven Self-Assembly of Heterobimetallic Supramolecules 8 and 9 from Tetratopic Metalloligand 2 and Diruthenium Acceptors 4−6a

a

electrometer ionization at the Korea Basic Science Institute (Seoul, Korea). Synthesis of Heterometallic Supramolecule 8. Compound 2 (3.0 mg, 5.43 μmol), diruthenium 5 (7.3 mg, 10.8 μmol), and AgOTf (5.6 mg, 21.7 μmol) were dissolved in methanol in a 5 mL vial, and the reaction solution was stirred with exclusion of light for 24 h at 50 °C. The precipitated AgCl was filtered off, and the solvent was removed by a rotary evaporator. For X-ray-quality crystals, slow diffusion of diethyl ether into methanol at −20 °C produced red crystals (yield 54%). IR (KBr disk, cm−1): 1605 (m), 1523 (s), 1376 (m), 1258 (s), 1158 (w), 1030 (m). ESI-MS (m/z): 2217.10 (calcd for [M − 3OTf]3+ 2218.09), 1624.89 (calcd for [M − 4OTf]4+ 1624.58), 1269.15 (calcd for [M − 5OTf]5+ 1269.88). Anal. Calcd for C270H273F36Fe3N12O60Ru12S12· 2CH2Cl2: C, 44.97; H, 3.84; N, 2.31. Found: C, 44.42; H, 3.73; N, 2.32. Synthesis of Heterometallic Supramolecule 9. Compound 2 (5.7 mg, 9.8 μmol), diruthenium 6 (14.8 mg, 19.6 μmol), and AgOTf (10.0 mg, 39.2 μmol) were dissolved in methanol in a 5 mL vial, and the reaction solution was stirred with exclusion of light for 24 h at 50 °C. The precipitated AgCl was filtered off, and the solvent was removed by a rotary evaporator. For X-ray-quality crystals, slow diffusion of diethyl ether into methanol at −20 °C produced deep green crystals (yield 55%). IR (KBr disk, cm−1): 1606 (m), 1535 (s), 1273 (s). ESI-MS (m/z): 1495.00 (calcd for [M − 3OTf]3+ 1495.70) 1083.88 (calcd for [M − 4OTf]4+ 1084.60). Anal. Calcd for C196H190F24Fe2N8O40Ru8S8: C, 47.75; H, 3.88; N, 2.27. Found: C, 48.25; H, 3.63; N, 2.35. Synthesis of Heterobimetallic Supramolecule 10. Compound 3 (5.0 mg, 10.3 μmol), diruthenium 4 (12.9 mg, 20.6 μmol), and AgOTf (10.6 mg, 41.2 μmol) were dissolved in a mixed solvent (CHCl3 + MeOH), and the reaction solution was stirred with exclusion of light for 24 h at 50 °C. The precipitated AgCl was filtered off, and the solvent was removed by a rotary evaporator. For X-rayquality crystals, slow diffusion of diethyl ether into chloroform and methanol at −20 °C produced orange-yellow crystals (yield 75%). IR (KBr disk, cm−1): 1634 (s), 1260 (m), 1163 (w), 1057 (m). 1H NMR (nitromethane-d3, 400 MHz): 1.44 (s, 48H, −CH(CH3)2), 2.30 (s, 24H, −CH3), 2.98 (sep, 4H, −CH(CH3)2), 4.73 (s, 10H, Cp), 5.83 (s, 16H, p-cymene), 5.98 (s, 16H, p-cymene), 7.37 (s, 16H, pyr), 8.06 (s, 16H, pyr). ESI-MS (m/z): 2049.72 (calcd for [M − 2OTf]2+ 2049.48), 1316.19 (calcd for [M − 3OTf]3+ 1316.66), 950.09 (calcd for [M − 4OTf]4+ 950.01). Anal. Calcd for C154H154Co2F24N8O40Ru8S8·7CD4O· CDCl3: C, 40.81; H, 3.26; N, 2.35. Found: C, 41.03; H, 3.05; N, 2.22.

Chart 2. Bond Distances and Angles in (a) Cs-Symmetric Complex 1 and (b) C4-Symmetric Complex 2

tetragonal prismatic cage 7 by the assembly of 2 and 4 (Scheme 1).23 However, the influence of the length or thickness of the bridging unit in the diruthenium electron acceptor have not been studied so far. Herein, we report the use of two C4-symmetric tetratopic metalloligands (2 and 3), which are perfectly planar and thus are ideal building blocks for the synthesis of supramolecular cages. To gain insight into the formation and structural aspects of those systems, the three diruthenium complexes 4−6 having different bridging units were used.

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7 was reported previously.23

EXPERIMENTAL DETAILS

General Information. All solvents and reagents were commercially purchased from Aldrich, Alfa Aesar, and TCI Co. and used without any further treatment. Trimethylamine was distilled with sodium hydroxide after it was purchased from Aldrich. Compounds 4−6 were prepared according to the reported procedures. 1H NMR spectra were measured on a Bruker AVANCE III HD 400 instrument (400 MHz) at ambient temperature. Chemical shifts are reported in ppm with reference to the residual peaks of CDCl3 (7.26 ppm), CD3OD (3.33 ppm), and CD3NO2 (4.33 ppm). FT-IR spectra using KBr pellets were measured on a Bruker ALPHA spectrometer and reported in cm−1. Elemental analyses (C, H, and N) were performed with an EA1110-FISONS (CE) machine. Mass spectra were obtained with a Finnigan TSQ Quantum Ultra EMR instrument using 5472

DOI: 10.1021/acs.inorgchem.7b00556 Inorg. Chem. 2017, 56, 5471−5477

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Inorganic Chemistry Synthesis of Heterometallic Supramolecule 11. Compound 3 (3.0 mg, 6.19 μmol), diruthenium 5 (8.4 mg, 12.3 μmol), and AgOTf (6.3 mg, 24.7 μmol) were dissolved in a mixed solvent (CHCl3/ MeOH = 1/1), and the reaction solution was stirred with exclusion of light for 24 h at 50 °C. The precipitated AgCl was filtered off, and the solvent was removed by a rotary evaporator. For X-ray-quality crystals, slow diffusion of diethyl ether into chloroform and methanol at −20 °C produced red crystals (yield 66%). IR (KBr disk, cm−1): 1608 (m), 1522 (s), 1424 (m), 1258 (s), 1030 (m), 638 (m). 1H NMR (nitromethane-d3, 400 MHz): 1.28 (q, 24H, −CH(CH3)2), 1.38 (dd, 24H, −CH(CH3)2), 2.23 (s, 12H, −CH3), 2.25 (s, 12H, −CH3), 2.83 (sep, 4H, −CH(CH3)2), 2.93 (sep, 4H, −CH(CH3)2), 5.06 (s, 10H, Cp), 5.77 (m, 12H, p-cymene), 5.92 (d, 4H, bq), 5.97 (m, 16H, bq + p-cymene), 6.19 (dd, 8H, p-cymene), 7.18 (d, 4H, pyr), 7.51 (d, 8H, pyr), 7.70 (d, 4H, pyr), 7.79 (d, 4H, pyr), 8.18 (d, 8H, pyr), 8.52 (d, 4H, pyr). ESI-MS (m/z): 2152.27 (calcd for [M − 2OTf]2+2151.01), 1382.70 (calcd for [M − 3OTf]3+ 1383.36), 1000.56 (calcd for [M − 4OTf]4+ 1000.28). Anal. Calcd for C170H162Co2F24N8O40Ru8S8· 2CHCl3·CD3NO2: C, 42.42; H, 3.50; N, 2.57. Found: C, 42.74; H, 3.52; N, 2.55. Synthesis of Heterometallic Supramolecule 12. Compound 3 (5.0 mg, 10.3 μmol), diruthenium 6 (15.0 mg, 20.6 μmol), and AgOTf (10.6 mg, 41.2 μmol) were dissolved in a mixed solvent (CHCl3/ MeOH = 1/1), and the reaction solution was stirred with exclusion of light for 24 h at 50 °C. The precipitated AgCl was filtered off, and the solvent was removed by a rotary evaporator. For X-ray-quality crystals, slow diffusion of diethyl ether into chloroform and methanol at −20 °C produced deep green crystals (yield 60%). IR (KBr disk, cm−1): 1535 (s), 1274 (s), 1147 (m), 1058 (m), 638 (w). 1H NMR (nitromethane-d3, 400 MHz): 1.38 (s, 48H, −CH(CH3)2), 2.21 (s, 24H, −CH3), 2.90 (sep, 4H, −CH(CH3)2), 4.81 (s, 10H, Cp), 5.64 (d, 16H, p-cymene), 5.83 (d, 16H, p-cymene), 7.13 (s, 16H, nq), 7.22 (dd, 16H, pyr), 8.21 (dd, 16H, pyr). ESI-MS (m/z): 2250.41 (calcd for [M − 2OTf]2+ 2250.04), 1049.77 (calcd for [M − 4OTf]4+ 1050.29). Anal. Calcd for C186H170Co2F24N8O40Ru8S8·9CD4O·4CDCl3: C, 42.67; H, 3.06; N, 2.00. Found: C, 42.94; H, 2.77; N, 2.27. X-ray Structure Determination. Reflection data for 8−12 were collected using a Bruker APEX-II CCD-based diffractometer with graphite-monochromated Mo Kα radiation (λ = 0.7107 Å). Hemispheres of reflection data were collected as ω scan frames with 0.5°/ frame and an exposure time of 10 s/frame. Cell parameters were determined and refined using the SMART program. Data reduction was performed using SAINT software. The data were corrected for Lorentz and polarization effects. An empirical absorption correction was applied using the SADABS program. The structures of the compounds were solved using direct methods and refined by fullmatrix least-squares methods using the SHELXTL program package with anisotropic thermal parameters for all non-hydrogen atoms. The crystals of 8−12 diffracted very weakly because of the large amounts of disordered solvents and anions. Geometrical restraints, i.e., DFIX, SADI, SIMU, and AFIX 66, 56, on part of the hexagonal and pentagonal aromatic rings were used in the refinements. Some A- and B-level alerts were found using the IUCR CheckCIF routine for complexes 8−12, all of which originated from the limited diffraction ability of this type of supramolecular compound in the crystal state.

reaction and confirmed that there was no reactant in the reaction mixture. Subsequent crystallization of the individual reaction mixtures using a vapor diffusion of diethyl ether into a methanolic solution yielded crystalline products 8 and 9 (Scheme 1). X-ray single-crystal structural analysis confirmed the molecular structures of the triple-decker type sandwich 8 and the twisted tetrahedral prism 9, as shown in Figures 1 and 2, respectively. They were also characterized by electrospray ionization mass spectrometry (ESI-MS), elemental analysis, and IR spectroscopy.

Figure 1. Wireframe representation of the X-ray structure of the heterometallic supramolecule 8: front (top left), side (top right), and different-color (bottom) views. Color code for top figures: green, Ru; red, O; blue, N. H atoms, counteranions, and i-Pr and methyl groups of cymene are omitted for clarity.

Triple-decker coordination cage 8 (Figure 1) is comprised of two Fe metalloligands bridged by diruthenium acceptors. The diruthenium acceptors showed differential coordination abilities to furnish the A6D3 cage structure. Among the six diruthenium linkers, four coordinated intermolecularly with the pyridyl

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RESULTS AND DISCUSSION Self-Assembly of Supramolecules 8 and 9 Using Tetratopic Fe Metalloligand 2. The cyclobutadiene-type Fe tetrapyridyl electron donor 2 was used in the supramolecular assembly with diruthenium electron acceptors with various spacer units. Metalloligand 3, diruthenium acceptors 5 and 6, and AgOTf were mixed in a molar ratio of 2:4:8 in methanol and stirred at 50 °C for 3 days. Because NMR analysis could not be used for the assembly containing paramagnetic 2, IR spectroscopy was used to shed light on the progress of the reaction. The spectra showed significant changes after the

Figure 2. Wireframe representation of the X-ray structure of the tetragonal-prismatic cage 9: front (left) and different-color (right) views. Color code for left figure: green, Ru; red, O; blue, N. H atoms, counteranions, and i-Pr and methyl groups of cymene are omitted for clarity. 5473

DOI: 10.1021/acs.inorgchem.7b00556 Inorg. Chem. 2017, 56, 5471−5477

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Inorganic Chemistry groups of three coparallel metalloligands and two connected intramolecularly with the metalloligand. The three metalloligands were connected in a head-to-tail fashion and separated by a distance of 7.68−8.14 Å. The crystal structure of compound 9 showed a similar, yet more twisted, structure than complex 7 (Figure 2). Compound 9 crystallized in the triclinic space group P1̅, where the asymmetric unit contained the entire cluster as well as 12 triflate anions and eight methanol molecules. The structure consisted of two tetratopic metalloligands connected by four diruthenium linkers 6, which resulted in a twisted-tetrahedralprismatic structure. The two iron tetrapyridyl linkers were located in a head-to-head fashion. Due to the relatively long Ru−Ru distance, complex 9 was twisted by about 25°. Because of this distortion, the Ru acceptors were linked diagonally to the pyridyl rings. The size of the inside cavity, which could be estimated using the eight Ru vertices, is about 8.4 × 10.5× 14.8 Å3. The distance between the two Ru centers in the dimeric linkers is ca. 8.4 Å, with an Fe···Fe separation between the two Cp*Fe moieties of ca. 10.6 Å. ESI-MS analysis confirmed the stoichiometry of heterobimetallic Ru-Fe supramolecules 8 and 9 in solution. The mass spectrum of 8 exhibited peaks at m/z 2217.10, 1624.89, and 1269.15, corresponding to [8 − 3OTf]3+, [8 − 4OTf]4+ and [8 − 5OTf]5+, respectively (Figure S9 in the Supporting Information). Similarly, compound 9 exhibited peaks at m/z 1255 and 1000, corresponding to [9 − 4OTf]4+ and [9 − 5OTf] 5+ , respectively (Figure S10 in the Supporting Information). All peaks were isotopically resolved and agreed very well with the requisite theoretical distributions. Self-Assembly of Supramolecules 10−12 Using Tetratopic Co Metalloligand 3. Tetratopic metalloligand 3 was also used in the self-assembly with diruthenium acceptors 4−6. Compound 3, diruthenium complexes 4−6, and AgOTf were mixed in molar ratios of 2:4:8, respectively, in methanol and stirred at 50 °C for 3 days. The initial reaction mixtures exhibited complicated 1H NMR spectra due to the uncontrolled kinetic mixtures. Subsequent crystallization of the individual initial reaction mixtures using a vapor diffusion of diethyl ether into methanolic solution yielded the pure crystalline thermodynamic products 10−12 (Scheme 2), as evidenced by electrospray ionization mass spectrometry (ESI-MS), 1H NMR spectroscopy, and X-ray crystallography. ESI-MS data for 10−12 confirmed that, in all cases, the A4D2 compositions were present in solution (Figures S11−S13 in the Supporting Information). For example, the mass spectrum of 10 exhibited peaks at m/z 2049.72, 1316.19, and 950.09 corresponding to [10 − 2OTf]2+, [10 − 3OTf]3+, and [10 − 4OTf]4+ (where M = intact assembly), respectively, clearly supporting the self-assembly of an A4D2 type supramolecule. Similarly, three peaks were observed at m/z 2152.27, 1382.70, and 1000.54, which corresponded to [11 − 2OTf]2+, [11 − 3OTf]3+, and [11 − 4OTf]4+, respectively, for 11. In addition, the peaks at m/z 2250.41 and 1049.77, which corresponded to [12 − 2OTf]2+ and [12 − 4OTf]4+, confirmed the A4D2 assembly of 12. All peaks were resolved isotopically and matched well with their calculated theoretical distributions. 1 H NMR spectroscopy also supported the formation of A4D2 type supramolecules. The spectra of 10−12 confirmed their formation without concomitant formation of any impurities. Comparison of the 1H NMR spectra of 3, 6, and 12 (Figure 3) revealed that the resonances of complex 12 were different from those of 2 and 6. The 1H NMR spectra showed a diagnostic

Scheme 2. Coordination-Driven Self-Assembly of Heterobimetallic Supramolecules 10−12 from Tetratopic Metalloligand 3 and Diruthenium Acceptors 4−6

Figure 3. Partial 1H NMR spectra of (a) metalloligand 3, (b) diruthenium 6, and (c) supramolecule 12.

upfield shift of the α-protons in 10−12 in comparison to those in free 3 (δ 8.55 and 7.23 ppm, Figure 3a). For example, in complex 12 (Figure 3c), the two signals appeared at δ 8.10 and 7.20 ppm; these were shifted upfield in comparison to those of the free ligand 3. The significant upfield shifts of the α-protons of 12 were similar to those in our recent report on supramolecular cages that were assembled from complex 1 and half-sandwich diruthenium acceptors 4−6.29 In addition, significant downfield shifts in cymene in the self-assembly of complexes 10−12 were observed, indicating Ru−py bond formation. X-ray single-crystal structural analysis confirmed the molecular structures of complexes 10−12, as shown in Figures 4−6, respectively. Compounds 10 and 12 are isostructural, and they feature a discrete tetragonal prismatic A2D2 cage, which crystallized in the monoclinic space groups P21/c and P21/n, respectively. Both metallocages consist of two parallel tetratrapyridyl metalloligands linked by four dinuclear Ru acceptors connected in a head-to-head fashion. Moreover, the length of the acceptor unit played a very significant role in the molecular packing of the metallocages. In the case of 10, the four pyridine rings of the “star” connector twisted out of the plane of the central cyclobutadiene ring due to the short Ru··· Ru distance of the oxalate linker (5.5 Å) and formed a distorted-tetragonal prism with separation among the pyridyl rings ranging from 4.54 to 4.74 Å (Figure 4). The dimensions of the cavity are 5.48 × 10.9× 10.5 Å3, with a distance of ∼7.16 5474

DOI: 10.1021/acs.inorgchem.7b00556 Inorg. Chem. 2017, 56, 5471−5477

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Inorganic Chemistry

adjacent pyridyl units of the metalloligand molecule. The two metalloligands were separated in a parallel way with a distance of 11.8 Å. Structural Comparison of Supramolecules 8−12. As shown in Schemes 1 and 2, the combination of C4-symmetric tetrapyridyl metalloligands 2 and 3 and the different diruthenium acceptors 4−6 (Chart 1), in molar ratios of 1:2, respectively, resulted in the selective formation of A4D2 tetragonal prisms (7, 9, 10, and 12) and an A4D2 molecular tweezer (8), as well as an A6D3 triple-decker Ru12Fe3-type complex (11). On the basis of this crystallographic study, different bridging units led to the formation of different architectures in the self-assembly of heterobimetallic supramolecules. Although complex 5 is not the longest bridging unit among complexes 4−6, it provided the significantly different assemblies 8 and 11 from supramolecules prepared by complexes 4 and 6. Thus, we need to consider structural factors other than just length, such as the width of the bridging unit.31 As mentioned already, the distances between the ruthenium metal centers in the diruthenium electron acceptor units are 5.5, 7.8, and 8.2 Å and the widths of the bridging units are 2.65, 2.9, and 4.9 Å for complexes 4−6, respectively (Chart 3),

Figure 4. Wireframe representation of the X-ray structure of the tetragonal-prismatic cage 10: front (left) and different-color (right) views. Color code for left figure: green, Ru; red, O; blue, N. H atoms, counteranions, and i-Pr and methyl groups of cymene are omitted for clarity.

Figure 5. Wireframe representation of the X-ray structure of the molecular tweezer 11: front (left) and different-color (right) views. Color code for left figure: green, Ru; red, O; blue, N. H atoms, counteranions, and i-Pr and methyl groups of cymene are omitted for clarity.

Chart 3. Bond Distances and Angles and Length/Width Ratios in Complexes 4−6

Figure 6. Wireframe representation of the X-ray structure of the tetragonal-prismatic cage 12: front (left) and different-color (right) views. Color code for left figure: green, Ru; red, O; blue, N. H atoms, counteranions, and i-Pr and methyl groups of cymene are omitted for clarity.

Complex 5 showed the highest aspect ratio (length/width ratio), indicating that this complex is the thinnest among diruthenium complexes 4−6. This suggests that complex 5 is the sterically most flexible bridging unit and can form inter- or intramolecular interactions with tetrapyridyl electron donors 2 and 3. In accordance with this idea, two complexes 8 and 11, synthesized from diruthenium complex 5, only exhibited interand intramolecular coordination. It seems that different aspect ratios of the bridging units in the diruthenium electron acceptors are critical to the formation of these molecules.

Å between the two cobalt ions, the longer naphthalene-1,4,5,8tetrakis(olate) spacer, or acceptor 6 (8.2 Å) linked with the pyridyl groups of the connector and furnished a square-barrel topology.(Figure 6) The CpCo moieties in 10 and 12 were equivalent and appeared to be outside of the square faces of the self-assembled cage. Surprisingly, X-ray structure analysis of the heterobimetallic supramolecular architecture 11 revealed a molecular tweezerlike shape containing diruthenium electron acceptor 5, with a benzene-1,2,4,5-tetrakis(olate) spacer unit and “star” connector in a very distorted geometry (Figure 5). Although the composition of the building units in the resulting complex was identical with that of the expected tetragonal prism, the structure was similar to that of a previously reported complex containing “star” connector 1. Structural refinements revealed that complex 11 crystallized in a triclinic system with space group P1̅. In this structure, two Ru linkers were connected intermolecularly to the two metalloligand molecules, while the other two linkers were intramolecularly coordinated to two

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CONCLUSIONS We prepared and characterized three A4D2 tetragonal-prismatic supramolecular architectures (9, 10, and 12) as well as an A4D2 molecular tweezer (8) and an A6D3 triple-decker complex (11) from C4-symmetric tetratopic pyridyl metalloligands 2 and 3 and diruthenium acceptors 4−6. In spite of the high symmetry of the tetratopic pyridyl metalloligands, the product supramolecules had different symmetries, affected by the linker units in the diruthenium acceptors. Consequently, diruthenium acceptor 5 provided the less symmetric supramolcules 8 and 11, significantly different from other C 4 -symmetrically assembled supramolcules. The aspect ratios of the diruthenium complexes are critical factors for the observed structural differences. This report shows that the symmetry of the 5475

DOI: 10.1021/acs.inorgchem.7b00556 Inorg. Chem. 2017, 56, 5471−5477

Article

Inorganic Chemistry

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assembled supramolecules can be controlled by the linker units in the diruthenium acceptors.

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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.inorgchem.7b00556. Experimental procedures, analytical data of the cages with 1H NMR, mass spectra, and X-ray data and structures of 8−12 (PDF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF) Crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail for P.J.S.: [email protected]. *E-mail for J.L.: [email protected]. ORCID

Ji Yeon Ryu: 0000-0001-6321-5576 Eun Hye Wi: 0000-0002-6524-0713 Moumita Pait: 0000-0001-7215-7048 Sunwoo Lee: 0000-0001-5079-3860 Peter J. Stang: 0000-0002-2307-0576 Junseong Lee: 0000-0002-5004-7865 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS P.J.S. thanks the NSF (1212799) for financial support. J.L. acknowledges financial support from the Basic Science Research Program (2016R1D1A1B03930507) and BRL Program (2015R1A4A1041036) through the National Research Foundation of Korea (NRF), funded by the Ministry of Science, ICT & Future Planning and Education.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.7b00556 Inorg. Chem. 2017, 56, 5471−5477

Article

Inorganic Chemistry (28) Cecot, G.; Alameddine, B.; Prior, S.; Zorzi, R. D.; Geremia, S.; Scopelliti, R.; Fadaei, F. T.; Solari, E.; Severin, K. Large heterometallic coordination cages with gyrobifastigium-like geometry. Chem. Commun. 2016, 52, 11243−11246. (29) Ryu, J. Y.; Park, Y. J.; Park, H. R.; Saha, M. L.; Stang, P. J.; Lee, J. Ruthenium-Cobalt Bimetallic Supramolecular Cages via a Less Symmetric Tetrapyridyl Metalloligand and the Effect of Spacer Units. J. Am. Chem. Soc. 2015, 137, 13018−13023. (30) Harrison, R. M.; Brotin, T.; Noll, B. C.; Michl, J. Toward a square-grid polymer: Synthesis and structure of pedestal-mounted tetragonal star connectors, C4R4-Co-C5Y5. Organometallics 1997, 16, 3401−3412. (31) Jansze, S. M.; Cecot, G.; Wise, M. D.; Zhurov, K. O.; Ronson, T. K.; Castilla, A. M.; Finelli, A.; Pattison, P.; Solari, E.; Scopelliti, R.; Zelinskii, G. E.; Vologzhanina, A. V.; Voloshin, Y. Z.; Nitschke, J. R.; Severin, K. Ligand Aspect Ratio as a Decisive Factor for the SelfAssembly of Coordination Cages. J. Am. Chem. Soc. 2016, 138, 2046− 2054.

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DOI: 10.1021/acs.inorgchem.7b00556 Inorg. Chem. 2017, 56, 5471−5477