Metallo-Organic Ligand Designing Road for Constructing the First

Mar 23, 2017 - High-resolution ESI-MS coupled with a traveling-wave ion-mobility cell(69-72) was further applied to verify the exact composition of 11...
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Metallo-Organic Ligand Designing Road for Constructing the FirstGeneration Dendritic Metallotriangle Tun Wu,† Yu-Sheng Chen,‡ Mingzhao Chen,† Qianqian Liu,† Xiaobo Xue,† Yixian Shen,† Jun Wang,† Han Huang,§ Yi-Tsu Chan,*,‡ and Pingshan Wang*,† †

Department of Organic and Polymer Chemistry, College of Chemistry and Chemical Engineering and §Institute of Super-microstructure and Ultrafast Process in Advanced Materials, School of Physics and Electronics, Central South University, Changsha, Hunan 410083, People’s Republic of China ‡ Department of Chemistry, National Taiwan University, Number 1, Section 4, Roosevelt Road, Taipei 10617, Taiwan S Supporting Information *

ABSTRACT: Three approaches have been carefully examined in order to develop a terpyridine-based dendritic metallotriangle: (1) direct selfassembly of two types of organic polyterpyridines with metal ions; (2) assembly of flexible metallo-organic ligands containing two uncomplexed free terpyridines with a possible 60°-V-shaped orientation; (3) assembly of functionalized metallotriangles possessing a fixed 60°-bent uncoordinated bisterpyridine. Only the third approach has successfully given rise to the desired first-generation dendritic metallotriangle. Structural characterization was accomplished by NMR, ESI-TWIM-MS, and AFM.

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or heterometallic triangles 2a−c has been documented52 and regarded as the zero-generation metallotriangle (Figure 1).

INTRODUCTION Currently, coordination-driven supramolecular chemistry has received considerable interest and experienced remarkable developments1 and been utilized as an efficient strategy for construction of multidimensional architectures with predesigned ligands.2−15 Lehn,4,16,17 Stang,1−3 Fujita,6,18−20 and others21−23 reported numerous well-defined structures based on various pyridinyl and bipyridinyl coordination systems. Recently, 2,2′:6′,2″-terpyridine (tpy) has been widely used due to its tunable binding ability with diverse metal ions.24−26 Several examples of tpy-based supramolecular structures have been reported, such as metallopolymers,27−30 2D macrocycles,31−34 grid array,35−38 and other architectures.39−45 In these cases, only a few self-assemblies with heteroleptic bis(terpyridine) connections have been achieved because multicomponent self-assembly usually generates the undesired self-sorted products along with other structures with similar thermodynamic stability,46−48 and the equilibrium between the assembled species was mainly controlled by stoichiometry, ligand geometry, and reaction conditions.49−52 As a consequence, construction of desired supramolecular architechtures containing heteroleptic complexes still remains a reasonable synthetic challenge.32,43,47 Dendritic patterns universally exist in nature, e.g., trees, flowers, snowflakes, and nervous systems. Inspired by the unique structure of the 1 → 3 branched dendrimers,53−56 a novel dendritic metallotriangle structure is envisioned to have specific photo- and electrochemical properties. To this end, a series of terpyridine-based homo© 2017 American Chemical Society

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RESULTS AND DISCUSSION Usually a homometallic triangle can be prepared through a onepot reaction; on the other hand, the heterometallic triangle can be only isolated from a stepwise assembly.52 In the beginning our endeavor to prepare the first-generation dendritic homometallic triangle was executed by mixing ligands 5 and 1 and Zn2+ ions (Figure 1, Scheme 1, and SI) in a precisely molar ratio of 1:2:4. Unfortunately the assembly only generated a mixture of unidentified insoluble polymers and metallotriangles. The 1H NMR and ESI-MS spectra revealed that metallotriangle 2a is the major component (Figure 2 and Figure S23 in the SI), which also confirmed that the multiple polyterpyridine assembly could not be realized by only controlling stoichiometry. Building on the previous results,39,51,52 it is worth noting that the complex of ⟨tpy− Ru2+−tpy⟩ connection is extremely kinetically inert and therefore does not exchange their ligands. In order to suppress the formation of unwanted byproducts, an effective stepwise method to construct a free terpyridine-functionalized metalloligand 7 was designed, which is expected to complex with metal ions to form a first-generation dendritic metallotriangle 9. With the advantage that a single molecular assembly is more Received: January 4, 2017 Published: March 23, 2017 4065

DOI: 10.1021/acs.inorgchem.7b00025 Inorg. Chem. 2017, 56, 4065−4071

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Figure 2. Stacked 1H NMR spectra of the product from the complexation reaction of 5, 1, and Zn2+ in 1:2:4 stoichiometry (top) and triangle 2a (bottom) in CD3CN.

uncomplexed terpyridine units in 7 is close to 60° when it is folded in a stacking fashion. From the geometrical point of view, the dendritic metallotriangle 9 could be formed by the combination of metal ions and 7 in 1:1 stoichiometry, in which a multicomponent assembly58−62 with heteroleptic connections might be achieved through a homoleptic self-assembly process. The organic polyterpyridine ligands and precursor 3 were prepared through the literature methods.32,63,64 The bisRuCl3 adduct was reacted with 180°-stretched bisterpyridine 4 in a 1:2.2 molar ratio in a mixed solvent of CHCl3 and MeOH (1:1, v/v) containing N-ethylmorpholine to produce a reddish solution. The metalloligand 7 with Cl− as the counterion was isolated in 39% yield by column chromatography (Al2O3, CH2Cl2/MeOH = 100:2). 1H NMR characterization of metalloligand 7 (Figure 3A) displayed three singlets at 9.30− 9.35 ppm for the complexed tpyH3′,5′, along with a singlet at 8.70 ppm for the uncomplexed tpyH3′,5′ in an expected integration ratio of 1:1:1:1 (each kind of tpyH unit is marked with different colors in Scheme 1). The signals for the complexed tpyH6,6′′ were shifted upfield dramatically in comparison to its precursor 4 due to the electron-shielding

Figure 1. (A) Conceptual progression of dendritic triangles and 1 → 3 branched dendrimers. (B) Synthetic route of the zero-generation dendritic metallotriangle.

constructive to form the thermodynamically stable product,57 novel tpy-based metallo-organic ligand 7 was synthesized by utilizing a 60°-oriented ⟨tpy−Ru2+−tpy⟩ bisRuCl3 adduct 3 with two 180°-bistpys 4. Thus, the angle between two

Scheme 1. Synthesis of the First-Generation Dendritic Triangle 11

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DOI: 10.1021/acs.inorgchem.7b00025 Inorg. Chem. 2017, 56, 4065−4071

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Figure 3. (A) Stacked 1H NMR spectra (500 MHz) of ligand 7 (top) in CD3OD and complex 10 in CD3CN (bottom). (B) DOSY NMR of 10.

effect,65,66 while the uncomplexed tpyH6,6′′ in 7 did not show a significant shift, which was consistent with the structural assignments. The ESI-MS spectrum of 7 showed three distinct peaks at m/z = 552.38, 670.17, and 846.45 corresponding to the 6+, 5+, and 4+ ions generated by loss of 6, 5, and 4 Cl− counterions, respectively, further supporting the stucture of 7 (Figure S20 in the SI). The initial self-assembly of metalloligand 7 with 1 equiv of Zn2+ failed based on evidence of the ESI-MS spectrum which only showed peaks belonging to the unreacted metalloligand 7. Perhaps it is caused by the small coordination constant K of ⟨tpy−Zn2+−tpy⟩ and the two unfixed arms in 7 that are able to rotate freely in space. Since the ⟨tpy−Fe2+−tpy⟩ connection has a higher formation constant K than that of ⟨tpy−Zn2+−tpy⟩, metalloligand 7 was reacted with an equimolar amount of Fe2+ in a mixed CHCl3/MeOH (1:2, v/v) solvent. The mixture was stirred at 80 °C for 5 h followed by addition of excess NH4PF6 to afford a red precipitate, which was washed thoroughly with MeOH and deionized water and then dried in vacuo at 45 °C for 20 h to afford the product in 95% yield. The ESI-MS spectrum indicated that the isolated product was a twisted dimer 10 rather than complex 9. A series of ESI-MS peaks was assigned to the ions with the charge states ranging from 16+ to 6+. The experimental isotope patterns of all peaks agreed well with the corresponding simulated isotope patterns (Figure 4 and Figure S25 in the SI). The structure of 10 was also established by 1H NMR experiments. As compared to its precursor 7, the signal for the tpyH6,6′′ on the purple tpy moieties showed a significant upfield shift (Figure 3A, Δδ = −1.46 ppm). The other assignments were confirmed by 2D COSY and NOESY NMR experiments (SI). The diffusionordered spectroscopy (DOSY) NMR experiment67 of 10 was conducted in CD3CN at 25 °C, which unambiguously revealed there was only one single product in solution with a diffusion coefficient (D) of 1.82 × 10−10 m2 s−1 (Figure 3B). These results are fully consistent with the proposed structure of 10. The energy-minimized molecular model further demonstrated that 10 adopted an “eight”-shaped conformation (Figure 4C).68

Figure 4. (A) ESI-MS spectra of structure 10. (B) 2D ESI-TWIM-MS plot (m/z versus drift time) for complex 10. Charge states of intact assemblies are marked. (C) Energy-minimized structure of 10.

The resultant structure could be formed, presumably because the extended arms in 7 are more flexible than expected, and then alleviate the strain caused by the 60°-bent bisterpyridines. Eventually we realized an enhanced rigidity would facilitate formation of the target molecule. Two fixed uncoordinated terpyridines were introduced to one corner of the Ru2+ metallotriangle through complexation of bisRuCl3 adduct 3 with X-shaped organic tetraterpyridine 5 to afford ligand 8 (35%). In this case, 8 possessed a triangular complex and two uncoordinated tpy uints with a fixed 60° angle, where the metallotriangle might not affect the subsequent self-assembly of two free tpys with metal ions (Scheme 1). Treatment of ligand 8 with 1 equiv of Zn2+ ions at room temperature gave rise to a reddish solid, which underwent counterion exchange with NH4PF6 to improve its solubility in CH3CN. The 1H NMR spectrum of 8 (Figure 5A) showed three singlets for tpyH3′,5′ with a 2:1:1 integration ratio, which was consistent with the proposed structure. The structure of 8 was also verified with ESI-MS by the observed peaks at m/z = 580.85 and 704.22 corresponding to the 6+ and 5+ ions, respectively (Figure S22 in the SI). The 1H NMR spectrum of dendritic metallotriangle 11 showed a characteristic upfield shift for tpyH6,6′′ on the blue tpy units (Figure 5A, Δδ = −1.30 ppm) as compared to its precursor 8, confirming the complexation of ⟨tpy−Zn2+−tpy⟩. 4067

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Figure 6. (A) ESI-MS spectra of the first-generation dendritic triangle 11. (B) 2D ESI-TWIM-MS plot (m/z versus drift time) for complex 11. Charge states of intact assemblies are marked.

revealed a significant increase in the experimental CCSs for higher charge states, especially between 9+ and 10+ ions, most likely as a result of the raised conformational flexibility originating from the larger cyclic structure (Table S1 in the SI).73 Finally, the individual structure of 11 on mica was depicted as uniform dots by atomic force microscopy (AFM) (Figure 7A). The average measured height of the features is about 0.7 nm, which matched well with the energy-minimized model (Figure 7B).39,74−76

Figure 5. Structure of the first-generation dendritic triangle 11. (A) Stacked 1H NMR spectra (500 MHz) of ligand 8 (top) in CD3OD and 11 in CD3CN (bottom). (B) DOSY NMR spectrum of 11.

In addition, there are two sets of resonances for tpyH3,3′′ with a 1:3 integration ratio, which were assigned to the central and outer tpys, respectively (Figure 5A). The assignments were also confirmed by 2D COSY and NOESY NMR spectroscopy (see the SI). The DOSY NMR experiment of 11 conducted in CD3CN at 25 °C clearly demonstrated that there was only a single product in solution with a diffusion coefficient of 1.51 × 10−10 m2 s−1 (Figure 5B). High-resolution ESI-MS coupled with a traveling-wave ionmobility cell69−72 was further applied to verify the exact composition of 11 and to acquire its structural information. The spectrum shown in Figure 6A exhibited a series of peaks derived from the 18+ to 8+ ions of [Zn3Ru91653·24PF6−, MW 14130.58], and the experimental isotope patterns were in good accord with the corresponding simulated isotope patterns (Figure 6A and Figure S26 in the SI). Moreover, the ESITWIM-MS spectrum (Figure 6B) showed narrow drift time distributions for each charge state, suggesting that there are no constitutional isomers.69 The average experimental collision cross-section (avg. CCS = 1801.1 ± 19.1 Å2) obtained from the calibration curve also agreed well with the computational results (Table S2 in the SI), and the small standard deviation reflected the high conformational rigidity. In contrast, the TWIM-MS spectrum of 10 (avg. CCS = 1354.5 ± 110.5 Å2)

Figure 7. (A) 2D and (B) 3D AFM images of the first-generation dendritic triangle 11 on mica.

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CONCLUSIONS In summary, a first-generation dendritic metallotriangle and an unexpected twisted octagon have been achieved by selfassembly of the predesigned metallo-organic ligands. Their structures were unambiguously established by various NMR experiments, ESI-TWIM-MS, and AFM. Instead of going 4068

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CD3CN): δ (ppm) 9.31 (s, 8H, tpy-HB3′,5′), 9.13 (s, 8H, tpy-HB3′,5′), 9.09−9.07 (s, 16H, tpy-HA3′,5′), 8.73−8.68 (m, 32H, tpy-HA3,3′′, tpyHB3,3′′, tpy-HC3,3′′), 8.48−8.46 (d, 8H, ArHCk, J = 8 Hz), 8.37−8.35 (d, 8H, ArHBk, J = 8 Hz), 8.27−8.24 (d, 16H, ArHAk, J = 12 Hz), 8.15−8.13 (d, 8H, ArHCj, J = 8 Hz), 8.10−8.08 (d, 8H, ArHBj, J = 8 Hz), 7.99−7.93 (m, 32H, tpy-HA4,4′′, tpy-HB4,4′′, tpy-HB4,4′′), 7,76− 7.74 (d, 16H, ArHAk, J = 8 Hz), 7.50−7.46 (m, 24H, tpy-HA6,6′′, tpyHB6,6′′), 7.39−7.37 (s, 8H, c, d), 7.27−7.26 (s, 8H, a, b), 7.24−7.18 (m, 32H, tpy-HA6,6′′, tpy-HB6,6′′, tpy-HB6,6′′), 7.14−7.10 (t, 12H, tpyHB5,5′′, J = 16 Hz), 4.05 (s, 24H, −OCH3), and 4.02 (s, 24H, −OCH3). ESI-MS (calcd for C400H288O16N48Ru6Zn2 with PF6− counterions m/z): +14 (m/z = 502.40) (calcd m/z = 502.25), +13 (m/z = 552.12) (calcd m/z = 552.04), +12 (m/z = 610.13) (calcd m/z = 610.12), +11 (m/z = 678.87) (calcd m/z = 678.77), +10 (m/z = 761.16) (calcd m/z = 761.14), +9 (m/z = 861.74) (calcd m/z = 861.72), and +8 (m/z = 987.59) (calcd m/z = 987.67). Synthesis of the First-Generation Dendritic Metallotriangle 11. To a solution of ligand 8 (4.4 mg, 1.2 μmol) in a mixed solvent of CHCl3 and MeOH (6 mL, 1:2, v/v), Zn(NO3)2·6H2O (0.36 mg, 1.2 μmol) was added. The solution was stirred for 30 min at 25 °C. Then excess NH4PF6 was added to obtain a red precipitate, which was filtered and washed repeatedly with MeOH to afford 11 as a red solid: 4.6 mg (yield 97%), mp > 300 °C. 1H NMR (500 MHz, CD3CN): δ (ppm) 9.05−9.03 (s, 48H, tpy-HA3′,5′, tpy-HB3′,5′, tpy-HB3′,5′), 8.79− 8.77 (d, 12H, tpy-HC3,3′′, J = 10 Hz), 8.71−8.66 (m, 36H, tpy-HA3,3′′, tpy-HB3,3′′), 8.28−8.24 (m, 24H, ArHBk, ArHCk), 8.18−8.16 (d, 24H, ArHAk, J = 10 Hz), 8.14−8.11 (t, 24H, tpy-HC4,4′′, J = 15 Hz), 7.91−7.87 (m, 36H, tpy-HA4,4′′, tpy-HB4,4′′), 7.83−7.82 (d, 24H, ArHBj, ArHCj, J = 5 Hz), 7.67−7.65 (d, 24H, ArHAj, J = 10 Hz), 7.46−7.45 (d, 36H, tpy-HA4,4′′, tpy-HB6,6′′, J = 10 Hz), 7.44−7.42 (d, 12H, tpy-HB6,6′′, J = 10 Hz), 7.41−7.38 (t, 12H, tpy-HC5,5′′), 7.30 (s, 6H, HAa), 7.29 (s, 6H, HAa), 7.18−7.17 (m, 24H, tpy-HA5,5′′), 7.14− 7.11 (t, 12H, tpy-HB5,5′′), 4.06 (s, 36H, -OCH3), 3.30 (m, 12H, −OCH2), 1.16−0.69 (m, 120H, −C10H20−), and 0.56 (t, 18H, −CH3 ). ESI-MS (calcd for C 642 H 534 O 24N 72 Ru 9 Zn3 with PF 6 − counterions m/z): +8 (m/z = 1621.34) (calcd m/z = 1621.34), +9 (m/z = 1425.08) (calcd m/z = 1425.08), +10 (m/z = 1268.32) (calcd m/z = 1268.08), +11 (m/z = 1139.82) (calcd m/z = 1139.62), +12 (m/z = 1032.57) (calcd m/z = 1032.57), +13 (m/z = 942.20) (calcd m/z = 941.99), +14 (m/z = 864.46) (calcd m/z = 864.35), and +15 (m/z = 797.22) (calcd m/z = 797.06).

through a multicomponent self-assembly process, the kinetically inert Ru2+ building blocks provided facile access to preparation of hierarchical supramolecular architectures. Applications of this methodology in fabricating more sophisticated structures are currently in process.

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EXPERIMENTAL SECTION

Synthesis of Ligand 7. A round-bottom flask was charged with 60°-based ⟨tpy−Ru2+−tpy⟩ capping component 3 (29 mg, 14 μmol), ligand 4 (22 mg, 28 μmol), and a mixed solvent of CHCl3:MeOH (100 mL, 2:3, v/v). Then N-ethylmorpholine (4 drops) was added. After refluxing for 48 h, the deep red solution was filtered through a Celite pad. The solution was concentrated in vacuo to give a red solid that was chromatographed (Al2O3), eluting with a solvent mixture of CH2Cl2:MeOH (100:3) to generate 7 as a red powder: 20 mg (yield 39%); mp > 300 °C. 1H NMR (500 MHz, CD3OD): δ (ppm) 9.40 (s, 4H, tpy-HB3′,5′), 9.38 (s, 8H, tpy-HA3′,5′), 8.99−8.96 (m, 12H, tpyHA3,3′′, tpy-HB3′,5′), 8.77 (s, 4H, tpy-HC3′,5′), 8.76−8.74 (m, 8H, tpyHC6,6′′, tpy-HC3,3′′), 8.44−8.41 (m, 12H, ArHAk, ArHBk), 8.10−8.07 (m, 16H, tpy-HA4,4′′, tpy-HB4,4′′, tpy-HC4,4′′), 8.05−8.02 (m, 20H, ArHCk, ArHAj, ArHBj), 7.90−7.88 (d, 4H, ArHCj, J = 10 Hz) 7.65− 7.62 (m, 12H, tpy-HA6,6′′, tpy-HB6,6′′), 7.57−7.54 (t, 4H, tpy-HC5,5′′, J = 15 Hz), 7.48−7.46 (m, 2H, Hc), 7.28−7.27 (d, 4H, HAa,b), 7.25− 7.23 (m, 2H, Hd), 4.09 (s, 12H, A-OCH3), 3.97 (s, 6H, B-OCH3), and 3.95 (s, 6H, C-OCH3). 13C NMR (126 MHz, MeOD) δ (ppm) 158.23, 155.45, 152.00, 151.19, 151.01, 149.26, 148.68, 144.09, 138.08, 132.37, 131.19, 130.52, 130.02, 127.67, 127.56, 127.40, 127.16, 127.09, 126.72, 126.66, 124.88, 124.75, 124.72, 124.63, 124.19, 121.77, 121.47, 121.05, 120.75, 118.39, 118.34, 114.71, 114.58, 114.49, 114.14, 114.12, 99.97, 55.81, 55.78, and 55.46. ESI-MS (calcd for C200H144O8N24Ru3 with Cl− counterions m/z): +6 (m/z = 552.38) (calcd m/z = 552.48), +5 (m/z = 670.17) (calcd m/z = 670.17), +5 (m/z = 662.60) ([M − H+]5+, calcd m/z = 662.77), and +4 (m/z = 846.45) (calcd m/z = 846.45). Synthesis of Ligand 8. A round-bottom flask was charged with 60°-based ⟨tpy−Ru2+−tpy⟩ capping component 3 (58 mg, 28 μmol), ligand 5 (50 mg, 30 μmol), and a solvent mixture of CHCl3:MeOH (100 mL, 2:3, v/v). Then N-ethylmorpholine (4 drops) was added. After refluxing for 48 h, the deep red solution was filtered through a Celite pad. The solution was concentrated in vacuo to give a red solid that was chromatographed (Al2O3), eluting with a solvent mixture of CH2Cl2:MeOH (100:2.5) to afford 8 as a red solid: 30.2 mg (yield 28%); mp > 300 °C. 1H NMR (500 MHz, CD3OD): δ (ppm) 9.31 (s, 8H, tpy-HA3′,5′), 9.30 (s, 4H, tpy-HB3′,5′), 8.92−8.89 (m, 12H, tpyHA3,3′′, tpy-HB3,3′′), 8.75 (s, 4H, tpy-HC3′,5′), 8.72−8.70 (d, 4H, tpyHC6,6′′, J = 10 Hz), 8.68−8.67 (d, 4H, tpy-HC3,3′′, J = 5 Hz), 8.35− 8.34 (d, 4H, ArHBk, J = 5 Hz), 8.29−8.27 (d, 8H, ArHAk, J = 10 Hz), 7.98−7.95 (t, 4H, tpy-HC5,5′′, J = 15 Hz) 7.94−7.90 (m, 12H, tpyHA4,4′′, tpy-HC4,4′′), 7.82−7.81 (d, 4H, ArHBj, J = 5 Hz), 7.69−7.68 (d, 4H, ArHCk, J = 5 Hz), 7.65−7.63 (d, 8H, ArHAk, J = 10 Hz), 7.54−7.48 (m, 16H, tpy-HA6,6′′, tpy-HB6,6′′, tpy-HC4,4′′), 7.28−7.21 (m, 12H, a, b, tpy-HA5,5′′, tpy-HB5,5′′), 7.19−7.17 (d, 4H, ArHCj), 4.06 (s, 12H, A-OCH3), 3.65 (m, 4H, −OCH2), 1.26−1.22 (m, 40H, alkylCH2), and 0.72−0.69 (t, 6H, alkylCH3). 13C NMR (126 MHz, CD3OD:CDCl3 = 2:1) δ (ppm) 158.23, 158.16, 157.27, 156.00, 155.84, 155.38, 155.34, 151.83, 151.72, 149.12, 148.71, 148.63, 148.47, 146.76, 142.65, 138.21, 137.41, 132.39, 131.21, 129.58, 127.80, 127.75, 127.71, 127.49, 127.42, 127.37, 127.31, 126.59, 125.79, 125.72, 125.08, 125.05, 124.09, 121.78, 121.42, 121.34, 69.90, 55.84, 35.35, 31.71, 29.52, 29.44, 29.39, 29.31, 29.02, 26.88, 25.57, 22.41, and 13.39. ESIMS (C214H178O6N24Ru3 with Cl− counterions m/z): +6 (m/z = 580.85) (calcd m/z = 580.86), +5 (m/z = 704.22) (calcd m/z = 704.22). Synthesis of 10. To a solution of ligand 7 (3.5 mg, 1 μmol) in a mixed solvent of CHCl3 and MeOH (6 mL, 1:2, v/v), FeSO4·7H2O (0.28 mg, 1 μmol) was added. The solution was stirred for 30 min at 25 °C. Then excess NH4PF6 was added to obtain a red precipitate, which was filtered and washed repeatedly with MeOH to afford 10 as a red solid: 4.3 mg (yield 95%), mp > 300 °C. 1H NMR (400 MHz,

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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.7b00025. Synthesis protocols, product characterization data, mass spectrometry, collision cross sections calibration, molecular modeling, and optical spectroscopic data (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. ORCID

Han Huang: 0000-0003-0641-1962 Yi-Tsu Chan: 0000-0001-9658-2188 Pingshan Wang: 0000-0002-1988-7604 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the National Natural Science Foundation of China (21274165), the Distinguished Professor 4069

DOI: 10.1021/acs.inorgchem.7b00025 Inorg. Chem. 2017, 56, 4065−4071

Article

Inorganic Chemistry

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Research Fund from Central South University of China. Y.-T.C. acknowledges the support from the Ministry of Science and Technology of Taiwan (MOST105-2119M-002-029). Authors acknowledge the NMR measurements from The Modern Analysis and Testing Center of CSU.

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DOI: 10.1021/acs.inorgchem.7b00025 Inorg. Chem. 2017, 56, 4065−4071

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DOI: 10.1021/acs.inorgchem.7b00025 Inorg. Chem. 2017, 56, 4065−4071