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Daito, Osaka 574-8530, Japan. ‡Department of Chemistry, Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan. Supporting Informatio...
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Mixed-Metal Coordination Polymers and Molecular Squares Based on a Ferrocene-Containing Multidentate Ligand 1,2-Di(4-Pyridylthio)ferrocene Ryo Horikoshi, Takumi Tominaga, and Tomoyuki Mochida Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b00538 • Publication Date (Web): 12 Jul 2018 Downloaded from http://pubs.acs.org on July 13, 2018

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Crystal Growth & Design

Mixed-Metal Coordination Polymers and Molecular Squares Based on a Ferrocene-Containing Multidentate Ligand 1,2-Di(4-Pyridylthio)ferrocene Ryo Horikoshi,*,† Takumi Tominaga,‡ and Tomoyuki Mochida‡ †Department of Environmental Science and Technology, Faculty of Design Technology, Osaka Sangyo University, Daito, Osaka 574-8530, Japan ‡Department of Chemistry, Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan

Supporting Information

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ABSTRACT: Various metalloligands and inorganic-organic hybrid bridging ligands have been incorporated in polynuclear complexes and bimetallic coordination polymers. Ferrocene, exhibiting redox activity and facile chemical modification, is a versatile metalloligand component. However most metal complexes with ferrocene-containing ligands form discrete low-dimensional chelate complexes or coordination polymers. Thus, we designed and synthesized ferrocene-based multidentate ligands, 1,2-di(4-pyridylthio)ferrocene (L1) and 1,2-di(2-pyridylthio)ferrocene (L2). Here we report the synthesis and structures of molecular square complexes and coordination polymers

containing

L1,

which

reacted

with

M(hfac)2

(hfac

=

1,1,1,5,5,5-hexafluoroacetylacetonate) and AgCF3SO3 to yield molecular square complexes [M(hfac)2(L1)]2·2C6H5CH3 [M = Ni (1) and Co (2)] and [Ag(CF3SO3)(L1)(H2O)0.5]2·2CH2Cl2·H2O (3). The molecular square units comprise two metal ions bridged by two ligands. Isomorphic complexes 1 and 2 accommodate two toluene molecules above and below the molecular square. L1 reacted with Cu(hfac)2 and CuI to yield zigzag, {[Cu(hfac)2(L1)]}n·0.25n(CH2Cl2) (4), and ribbon-shaped, {[Cu4I4(L1)2]}n (5) coordination polymers. In 4, L1 behaves as a bidentate N,N-ligand bridging the CuII ions, while in 5, it acts as a tridentate S,N,N-ligand linking the stepped-cubane Cu4I4 units. L1 reacted with AgX to form 2D coordination polymers {[Ag(ClO4)(L1)]}n (6) and {[Ag(L1)]PF6}n (7), in which it acted as a tetradentate S,S,N,N-ligand. These complexes have topologies based on multidentate coordination of 1,2-substituted L1.

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Crystal Growth & Design

■ INTRODUCTION Macrocyclic complexes and coordination polymers formed by self-assembly of metal ions with organic linkers have been extensively reported over the years.1–4 The rational design of assembled structures and the functions of metal complexes have been widely investigated, based on an appropriate choice of ligands and metal ions.5–12 Meanwhile, the design of metalloligands, which are metal-containing organic linkers, is becoming important, because they produce mixed-metal complexes with different topologies.13–15 The design of their assembled structures is intriguing from a crystal engineering viewpoint. Ferrocene, comprising an FeII ion coordinated by two cyclopentadienyl (Cp) rings, is a versatile metalloligand precursor because of its reactivity and chemical stability.16–18 Introducing donor substituents to the Cp ring is a rational approach to obtaining functional metalloligands.19–38 For example, 1,1′-disubstituted ferrocenes such as 1,1′-ferrocenedicarboxylic acid and 1,1′-bis(diphenylphosphino)ferrocene are representative metalloligands that have yielded many discrete mixed-metal complexes and 1D coordination polymers.39–42 We previously reported 1,1′-disubstituted ferrocenes bearing two thiopyridine moieties, 1,1′-di(4-pyridylthio)ferrocene and 1,1′-di(2-pyridylthio)ferrocene (Figures 1a and 1b), which act as bridging ligands to produce redox-active 1D coordination polymers.42 However, 1,2-disubstituted ferrocenes have rarely been employed as bridging ligands, although many studies investigated their use as chiral ligands for asymmetric synthesis.43–46 We expected 1,2-disubstituted ferrocenes to produce more topologically diverse complexes than 1,1′-disubstituted ferrocenes due to their lower symmetry and additional chelating ability. Thus, we designed ferrocene-based ligands, 1,2-di(4-pyridylthio)ferrocene (L1) and 1,2-di(2-pyridylthio)ferrocene (L2) (Figures 1c and 1d), which are isomers of the corresponding 1,1′-disubstituted ferrocenes (Figures 1a and 1b). These ligands possess four donor atoms and consequently function as bidentate, tridentate, or tetradentate ligands, which allow formation of mixed-metal complexes with extended network structures. Additionally, the thiopyridine moieties of the ligands are expected to form π–π47,48 and/or C–H···S49,50 interactions to 2

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create extended network structures. This paper reports the preparation and crystal structures of the ligands and mixed-metal complexes containing L1. The variety of coordination geometries and assembled structures of these complexes contrasts with those of complexes formed from the corresponding 1,1′-disubstituted ferrocene ligands.

Figure 1. Structural formulae of (a) 1,1′-di(4-pyridylthio)ferrocene,42 (b) 1,1′-di(2-pyridylthio)ferrocene,42 (c) 1,2-di(4-pyridylthio)ferrocene (L1), and (d) 1,2-di(2-pyridylthio)ferrocene (L2).

■ EXPERIMENTAL SECTION General. All reagents and solvents employed were commercially available and were used as supplied without further purification. Infrared spectra were recorded using attenuated total reflectance (ATR) with a Thermo Scientific Nicolet iS5 spectrometer (Figures S1-S3). 1H NMR were recorded on a Bruker AVANCE 400 spectrometer (400 MHz) (Figure S4). Elemental analysis was performed with a Perkin Elmer 2400 II elemental analyzer. Solid-state cyclic voltammograms were recorded with an ALS/chi electrochemical analyzer model 600A by following a literature procedure.42 Syntheses of the Ligand and Complexes. 1-Bromo-2-(4-pyridylthio)ferrocene. A 3

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Crystal Growth & Design

synthetic route for L1 is depicted in Figure 2. At −78ºC, 1.6 M n-butyllithium in hexane (2.5 mL) was added dropwise to a solution of 1,1′-dibromoferrocene (1.37 g, 4.0 mmol) in 20 mL THF. The reaction mixture was stirred at −78ºC for 0.5 h before adding 2,2,6,6-tetramethylpiperidide (0.75 mL, 4.4 mmol) in one portion. The reaction mixture was warmed to −40ºC and stirred for 3 h. After cooling to –78ºC, a solution of 4,4′-dipyridyl disulfide (0.88 g, 4.0 mmol) in 20 mL THF was added, and then the reaction mixture was slowly warmed to room temperature. After addition of water (10 mL), the reaction mixture was extracted with dichloromethane (2 × 50 mL). The collected organic layers were washed with water (2 × 20 mL) and dried with anhydrous sodium sulfate. After removing the solvent under reduced pressure, the crude product was purified by column chromatography (silica gel, dichloromethane/ethanol 9:1) to give the desired compound as a yellow solid (0.61 g, 41%). 1H NMR (400 MHz, CDCl3): δ = 4.33 (s, 5H), 4.41 (t, J = 2.72 Hz, H), 4.44 (dd, J = 1.16 Hz, H), 4.75 (dd, J = 1.24, H), 6.87 (m, 2H), 8.31 (m, 2H).

1,2-Di(4-pyridylthio)ferrocene (L1). At −78ºC, 1.6 M n-butyllithium in hexane (2.0 mL) was added dropwise to the solution of 1-bromo-2-(4-pyridylthio)ferrocene (1.18 g, 3.0 mmol) in 20 mL THF. The reaction mixture was stirred at −78ºC for 0.5 h. A solution of 4,4′-dipyridyl disulfide (0.66 g, 3.0 mmol) in 20 mL THF was added, and the reaction mixture was slowly warmed to room temperature. After adding water (10 mL), the reaction mixture was extracted with dichloromethane (2 × 50 mL). The collected organic layers were washed with water (2 × 20 mL) and dried with anhydrous sodium sulfate. After removing the solvent under reduced pressure, the crude product was purified by column chromatography (silica gel, dichloromethane/ethanol 8:2) to give L1 as a yellow solid (0.37 g, 30%). IR (ATR, cm−1): 1570, 1475, 1406, 833, 804, 700, 528, 492, 465, 447, 432. 1H NMR (400 MHz, CDCl3): δ 4.39 (s, 5H), 4.71 (t, J = 2.68 Hz, 2H), 4.81 (d, J = 2.68 Hz, 1H), 6.82 (m, 4H), 8.15 (m, 4H). Anal. Calcd for C20H16FeN2S2: C, 59.41; H, 3.99; N, 6.93%. Found: C, 59.12; H, 3.86; N, 6.92%. L1 showed polymorphism. Single crystals of α-L1 suitable for X-ray diffraction were obtained from chloroform solution by slow evaporation, while those of β-L1 were obtained unintentionally as precipitates from an attempted reaction between L1 and AgNO3. 4

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1-Bromo-2-(2-pyridylthio)ferrocene. The synthesis procedure was the same as that for 1-bromo-2-(4-pyridylthio)ferrocene, except that 2,2′-dipyridyl disulfide was used (0.67 g, 45%). IR (ATR, cm−1): 1574, 1558, 1449, 1416, 1121, 932, 835, 802, 760, 719, 501, 465.

1,2-Di(2-pyridylthio)ferrocene (L2). The synthesis procedure was the same as that for L1, except that 2,2′-dipyridyl disulfide was used (1.06 g, 88%). IR (ATR, cm−1): 1572, 1557, 1447, 1410, 1117, 997, 984, 835, 820, 758, 719, 525, 464, 453, 403. 1H NMR (400 MHz, CDCl3): δ = 4.36 (s, 5H), 4.62 (t, J = 2.80 Hz, H), 4.78 (d, J = 2.80 Hz, 2H), 6.79 (m, 2H), 6.91 (m, 2H), 7.21 (m, 2H), 8.21 (m, 2H). Anal. Calcd for C20H16FeN2S2: C, 59.41; H, 3.99; N, 6.93%. Found: C, 59.14; H, 3.83; N, 6.94%. Single crystals of L2 suitable for X-ray diffraction were obtained from chloroform solution by slow evaporation.

[Ni(hfac)2(L1)]2—2C6H5CH3

(1).

A

solution

of

Ni(hfac)2

(hfac

=

1,1,1,5,5,5-hexafluoroacetylacetonate) (24 mg, 5.0 × 10−5 mol) in chloroform (1 mL) was added dropwise to a solution of L1 (20 mg, 5.0 × 10−5 mol) in chloroform (2 mL) while stirring constantly. The resulting green precipitates were collected by filtration, washed with chloroform, and dried in a desiccator (35 mg, 80%). IR (ATR, cm−1): 1645, 1595, 1481, 1251, 1206, 1188, 1136, 1101, 814, 791, 719, 669, 584, 497, 463. Anal. Calcd for the desolvated [Ni(hfac)2(L1)]2 = C60H32F24Fe2N4Ni2O8S4: C, 41.08; H, 2.07; N, 3.19%. Found: C, 41.47; H, 2.02; N, 3.19%. Single crystals of 1 suitable for X-ray diffraction were obtained from toluene solution by slow evaporation.

[Co(hfac)2(L1)]2—2C6H5CH3 (2). The synthesis procedure was the same as that for 1, except that 24 mg (5.0 × 10−5 mol) of Co(hfac)2 was used (35 mg, 80%). IR (ATR, cm−1): 1643, 1593, 1483, 1252, 1188, 1140, 1098, 1063, 814, 791, 719, 667, 582, 498. Anal. Calcd for the desolvated [Co(hfac)2(L1)]2 = C60H32Co2F24Fe2N4O8S4: C, 41.07; H, 2.07; N, 3.19%. Found: C, 40.99; H, 1.47; N, 3.29%. Single crystals of 2 suitable for X-ray diffraction were obtained from toluene solution by slow evaporation. The crystal size of 2 was much larger than that of 1, with cubes of about 3 mm or larger.

[Ag(CF3SO3)(L1)(H2O)0.5]2—2CH2Cl2—H2O

(3).

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A

solution

of

silver

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Crystal Growth & Design

trifluoromethanesulfonate (13 mg, 5.0 × 10−5 mol) in acetonitrile (1 mL) was added dropwise to a solution of L1 (20 mg, 5.0 × 10−5 mol) in chloroform (2 mL) while stirring constantly. The resulting yellow precipitates were collected by filtration, washed with acetonitrile and chloroform, and dried in a desiccator (14 mg, 42%). IR (ATR, cm−1): 1593, 1488, 1422, 1269, 1244, 1221, 1161, 1024, 1001, 810, 633, 517, 498. Anal. Calcd for compound 3 without dichloromethane [Ag(CF3SO3)(L1)(H2O)0.5]2·H2O = C42H36Ag2F6Fe2N4O8S6: C, 37.13; H, 2.67; N, 4.12%. Found: C, 37.29; H, 2.41; N, 4.18%. Single crystals of 3 suitable for X-ray diffraction were obtained from dichloromethane solution by slow evaporation.

{[Cu(hfac)2(L1)]}n—0.25n(CH2Cl2) (4). A solution of Cu(hfac)2 (24 mg, 5.0 × 10−5 mol) in methanol (1 mL) was slowly diffused into a solution of L1 (20 mg, 5.0 × 10−5 mol) in dichloromethane (2 mL). Dark green crystals formed in two days, which were suitable for X-ray single crystal structure determination (40 mg, 89%). IR (ATR, cm−1): 1651, 1599, 1485, 1250, 1196, 1138, 1088, 1065, 812, 789, 665, 583, 520, 498, 459. Anal. Calcd for the desolvated {[Cu(hfac)2(L1)]}n = C30H16CuF12FeN2O4S2: C, 40.85; H, 2.06; N, 3.18%. Found: C, 40.90; H, 1.81; N, 3.24%.

{[Cu4I4(L1)2]}n (5). A solution of CuI (9.5 mg, 5.0 × 10−5 mol) in acetonitrile (1 mL) was slowly diffused into a solution of L1 (20 mg, 5.0 × 10−5 mol) in dichloromethane (2 mL). Yellow crystals formed in two days, which were suitable for X-ray single crystal structure determination (19 mg, 49%). IR (ATR, cm−1): 1580, 1479, 1414, 1265, 1250, 1217, 1157, 1107, 1062, 1016, 999, 816, 806, 714, 635, 563, 532, 517, 494, 469, 455, 441, 409. Anal. Calcd for C40H32Cu4Fe2I4N4S4: C, 30.59; H, 2.05; N, 3.57%. Found: C, 30.86; H, 1.86; N, 3.76%.

{[Ag(ClO4)(L1)]}n (6). The synthesis procedure was the same as that for 3, except that 10 mg (5.0 × 10−5 mol) of silver perchlorate was used (22 mg, 73%). IR (ATR, cm−1): 1589, 1483, 1422, 1053, 1020, 991, 949, 820, 806, 716, 619, 598, 561, 517, 498, 455. Anal. Calcd for C20H16AgClFeN2O4S2: C, 39.27; H, 2.64; N, 4.58%. Found: C, 39.22; H, 2.45; N, 4.58%. Single crystals of 6 suitable for X-ray diffraction were obtained from dichloromethane solution by slow 6

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evaporation. CAUTION. Note that perchlorate compounds are potentially explosive. Nevertheless, we observed no hazardous reactions in our experiments.

{[Ag(L1)]PF6}n (7).The synthesis procedure was the same as that for 3, except that 13 mg (5.0 × 10−5 mol) of silver hexafluorophosphate was used (24 mg, 73%). IR (ATR, cm−1): 1585, 1485, 1418, 1227, 1192, 1067, 860, 822, 810, 738, 714, 662, 640, 598, 554, 517, 494, 455. Anal. Calcd for C20H16AgF6FeN2PS2: C, 36.55; H, 2.45; N, 4.26%. Found: C, 36.38; H, 2.36; N, 4.28%. Single crystals from 7, suitable for X-ray diffraction were obtained from dichloromethane solution by slow evaporation. X-Ray Crystallography. X-ray diffraction data were collected on a Bruker APEX II Ultra CCD diffractometer using Mo Kα radiation (λ = 0.71073 Å). Since a single crystal of 2 easily released solvent molecules to produce powder, it was coated with silicone grease. The coordinated water molecule in 3 was refined with occupancy 0.5. All calculations were performed using SHELXTL. Structures were solved by direct methods (SHELXS 97).51 The non-hydrogen atoms were refined anisotropically, and the hydrogen atoms were placed at calculated positions. Mercury 3.9 for Windows was used to produce molecular graphics.52 Crystallographic parameters are listed in Tables 1 and 2.

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Crystal Growth & Design

Table 1. Crystal Data and Structure Refinement for α-L1, β-L1, L2, and Complexes 1–3.

Empirical formula Formula mass T/K Crystal system Space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 Z ρ/g cm−3 µ/mm−1 F(000) GOF on F2 R indices a [I > 2σ(I)] R indices a (all data) a

α-L1

β-L1

L2

L1 (P21/m)

L1 (Pnma)

L2

C20H16FeN2S2

C20H16FeN2S2

C20H16FeN2S2

404.32 100 monoclinic P21/m 7.2325(6) 14.6297(13) 8.1423(7)

404.32 100 orthorhombic Pnma 13.927(4) 13.801(4) 9.173(2)

404.32 100 orthorhombic Pnm21 14.385(4) 7.2098(18) 8.469(2)

1 [Ni(hfac)2(L1)]2 ·2C6H5CH3 C74H52F24Fe2N4 Ni2O8S4 1938.56 100 triclinic Pī 11.5396(18) 13.198(2) 14.355(2) 81.806(2) 67.810(2) 75.135(2) 1954.0(5) 1 1.647 1.060 976.0 1.034 R1 = 0.0276 wR2 = 0.0321 R1 = 0.0680 wR2 = 0.0709

93.2170(10) 860.17(13) 2 1.561 1.124 416 1.066 R1 = 0.0289 wR2 = 0.0718 R1 = 0.0331 wR2 = 0.0746

1763.1(8) 4 1.523 1.096 832 1.062 R1 = 0.0218 wR2 = 0.0538 R1 = 0.0239 wR2 = 0.0552

878.3(4) 2 1.529 1.101 416 1.030 R1 = 0.0206 wR2 = 0.0208 R1 = 0.0589 wR2 = 0.0591

2 [Co(hfac)2(L1)]2 ·2C6H5CH3 C74H52Co2F24Fe2 N4O8S4 1938.99 100 triclinic Pī 11.612(4) 13.227(4) 14.369(5) 81.864(5) 67.859(5) 75.124(6) 1973.2(11) 1 1.632 0.993 974.0 1.067 R1 = 0.0245 wR2 = 0.0273 R1 = 0.0642 wR2 = 0.0656

3 [Ag(CF3SO3)(L1)(H2O)0.5]2 ·2CH2Cl2·H2O C44H40Ag2Cl4F6 Fe2N4O8S6 1532.42 100 monoclinic C2/c 29.86(3) 9.109(9) 19.736(19) 93.327(16) 5359.(9) 8 1.900 1.761 3056 1.041 R1 = 0.0429 wR2 = 0.0988 R1 = 0.0576 wR2 = 0.1052

R1 = ∑||FO|−|FC||/∑|FO|, wR2 = [∑w(FO2−FC2)2/∑w(FO2)2]1/2

Table 2. Crystal Data and Structure Refinement for Complexes 4-7. Empirical formula Formula mass T/K Crystal system Space group a/Å b/Å c/Å α/° β/° γ/° V/Å3 Z ρ/g cm−3 µ/mm−1 F(000) GOF on F2 R indices a [I > 2σ(I)] R indices a (all data) a

4 {[Cu(hfac)2(L1)]}n·0.25n(CH2Cl2) C121H74Cl2Cu4F48Fe4N8O16S8 3612.82 100 Triclinic Pī 15.282(9) 15.593(9) 15.968(9) 106.357(7) 104.843(12) 90.395(7) 3516(4) 1 1.706 1.276 1798.0 1.098 R1 = 0.0757 wR2 = 0.0826 R1 = 0.2152 wR2 = 0.2207

5 {[Cu4I4(L1)2]}n C40H32Cu4Fe2I4N4S4 1750.44 100 monoclinic P21/n 10.936(3) 9.601(3) 21.559(6)

6 {[Ag(ClO4)(L1)]}n C20H16AgClFeN2O4S2 611.64 100 orthorhombic Pbca 14.2992(10) 14.8911(11) 20.6159(15)

96.782(4) 2247.8(10) 2 2.320 5.455 1488.0 1.057 R1 = 0.0352 wR2 = 0.0443 R1 = 0.0893 wR2 = 0.0979

7 {[Ag(L1)]PF6}n C20H16AgFeN2S2F6P 657.16 100 monoclinic P21/c 11.4773(14) 13.7497(16) 13.8114(16) 92.340(2)

4389.8(5) 8 1.851 1.896 2432 1.041 R1 = 0.0254 wR2 = 0.0577 R1 = 0.0318 wR2 = 0.0602

R1 = ∑||FO|−|FC||/∑|FO|, wR2 = [∑w(FO2−FC2)2/∑w(FO2)2]1/2

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2177.8(4) 4 2.004 1.894 1296 1.068 R1 = 0.0259 wR2 = 0.0638 R1 = 0.0302 wR2 = 0.0657

Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

■ RESULTS AND DISCUSSION

Synthesis and Structures of L1 and L2. L1 and L2 were synthesized from a racemic mixture of 1-bromo-2-(pyridylthio)ferrocene using 1,1′-dibromoferrocene as the starting material (Figure 2). The total yield of L1 (12%) was lower than that of L2 (40%). The crystallographic structures of the ligands were determined. L1 has two polymorphs (α-L1 and β-L1). These crystallized in monoclinic (P21/m) and orthorhombic (Pnma) systems respectively, and their packing diagrams are depicted in Figure S5. The pyridine rings of α-L1 formed intermolecular π–π interactions (centroid-centroid distance = 3.8 Å), while β-L1 showed no π–π interactions. The density of α-L1 was slightly higher than that of β-L1, indicating that the former is more stable than the latter, probably due to the π–π interactions. The packing arrangement of L2 (space group Pnm21) was similar to that of β-L1, although their unit cells and space groups were different (Figure S6). L2 showed no significant π–π interactions in the crystal. The molecular structures of α-L1, β-L1, and L2 are shown in Figure 3. Although their packing arrangements are different, their molecular structures are similar. Each molecule is located on a mirror plane that passes through the FeII ion. The substituted Cp ring and the two pyridine rings are almost perpendicular. The C–S–C bond angles and C–S–C–C torsion angles of L are designated as θ1, θ2, τ1, and τ2, respectively, in this article (Figure 4). The C–S–C bond angles for the ligands are around 100º, which is typical for thioethers.36–38,42,49,50,53,54 The C–S–C–C torsion angles, which differ in α-L1, β-L1, and L2, are 2.9º, 9.8º, and 0.2º, respectively.

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Crystal Growth & Design

Figure 2. Synthetic routes for L1 and L2. TMP, 4-DPDS, and 2-DPDS are 2,2,6,6-tetramethylpiperidine, 4,4′-dipyridyl disulfide, and 2,2′-dipyridyl disulfide, respectively.

Figure 3. Solid-state structures of (a) α-L1, (b) β-L1, and (c) L2. Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted for clarity.

Figure 4. Definitions of torsion angles τ1–τ2 and bond angles θ1–θ2. 10

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Coordination Structures of Metal Complexes with L1. A general reaction scheme of L1 with metal complexes or salts (M(hfac)2, CuI, and AgX) is shown in Figure 5. The reactions resulted in molecular squares (1–3), 1D coordination polymers (4, 5), and 2D coordination polymers (6, 7). Schematic illustrations of their assembled structures are depicted in Figure 6. Ligands L1 and L2 are soluble in common organic solvents. Their chloroform and dichloromethane solutions, from which L1 and L2 can be recovered unchanged, are stable in air at room temperature. However, their methanol, acetone, and acetonitrile solutions gradually change from yellow to brown, to eventually afford black precipitates. The methanol solution of L1 decomposes after two days of exposure to air, whereas that of L2 decomposes after several hours. Since L2 is far less stable than L1, attempts at complexing metal salts with L2 in relatively polar solvents were unsuccessful. In addition, attempts at obtaining M(hfac)2 complexes with L2 in chloroform or dichloromethane failed. The coordination modes of L1 in its metal complexes are shown in Figure 7. L1 adopted

N,N-bidentate, S,N,N-tridentate, or S,S,N,N-tetradentate coordination modes. The topology of metal complexes is determined by the number of coordination sites of the metal species. M(hfac)2 possesses two coordination sites and consequently forms only low-dimensional structures (molecular squares 1, 2, and 1D coordination polymer 4), in which the ligand exhibits N,N-bidentate coordination. However, the AgI ion possesses four or more coordination sites and therefore forms high-dimensional structures (2D coordination polymers 6 and 7), in which the ligand adopts

S,S,N,N-tetradentate coordination, or a low-dimensional structure (molecular square 3) with anion coordination. CuI forms polynuclear clusters with multiple coordination sites and hence a network structure is formed (1D ribbon coordination polymer 5), in which the ligand adopts S,N,N-tridentate coordination. Furthermore, the coordination modes are consistent with the hard soft acids and bases (HSAB) theory.55,56 NiII, CoII, and CuII ions coordinated with only pyridine moieties (complexes 1, 2, and 4), while AgI and CuI ions, which are soft acids, also coordinated with the soft base thioether 11

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moiety (complexes 5–7). Complex 3 is exceptional in that it has no Ag–S bonds despite containing the AgI ion. Therefore, L1, having both soft and hard donor atoms, is a flexible ligand that can change its coordination mode depending on the metal species, which led to structural variation in its complexes. Conversely, the isomer 1,1′-di(4-pyridylthio)ferrocene produced only 1D coordination polymers. The topological diversity of complexes from L1 stems from its lower symmetry and additional intramolecular chelating ability. As with uncoordinated L1, the C–S–C bond angles for the ligand in complexes 1–7 are around 100º. The C–S–C–C torsion angles in the complexes range from 0º to 40º (Table S1). Parameters τ1 and τ2 for the molecular squares (1–3) and 1D coordination polymer (4) are similar, while those for the 2D coordination polymers (6, 7) differ significantly. Most of the dihedral angles between pyridine and Cp for the complexes are around 80º, although one of the two dihedral angles in the molecular squares (1, 2) is approximately 60º (Figure 8). Assembled structures of each complex are discussed in detail in the following sections, in order of increasing dimensionality.

Figure 5. General reaction scheme for the syntheses of molecular squares and coordination polymers with L1.

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Figure 6. Schematic illustrations of metal complexes with L1: (a) Molecular squares (1–3), (b) 1D zigzag chain (4), (c) 1D ribbon (5), and (d) 2D sheets (6, 7).

Figure 7. Coordination modes of L1 observed in the metal complexes.

Structures of Molecular Squares Complexes 1–3. The reactions of L1 with M(hfac)2 and AgCF3SO3 yielded molecular square complexes [M(hfac)2(L1)]2·2C6H5CH3 (M = Ni (1) and M = Co (2)) and [Ag(CF3SO3)(L1)(H2O)0.5]2·2CH2Cl2·H2O (3), respectively. These complexes have a structure consisting of two metal ions and two ligands, in which L1 acts as a bidentate N,N-ligand. The molecular squares in 1 and 2 are square and open, while that in 3 is rectangular and closed. These structures are shown in Figure 6a. The molecular squares structures in 1 and 2 are shown in Figures 9 and S6, respectively. Complexes 1 and 2 are isomorphic and thus only the crystal structure of 1 is discussed in detail. The 13

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molecular square has a crystallographic two-fold rotation axis that passes through the two FeII ions. The molecular square cavity size is ca. 131 Å2 as estimated from the NiII···NiII (10.9 Å) and S1···S1 (12.0 Å) distances. Two toluene molecules are accommodated above and below the cavity. The molecular squares are arranged in slip-stacks along the c-axis, hence no channels are formed. The slip-stack arrangement is supported by four intermolecular C–H···S interactions (H···S distances = 3.0 Å, Figure S7). The torsion angles (τ1 and τ2) of L1 in 1 are 4.6º and 6.1º, respectively. One of the two pyridine rings (Py1) in L1 is almost perpendicular to the substituted Cp ring (torsion angle: 80.5º), while the other (Py2) is largely tilted (torsion angle: 59.1º), as shown in Figure 8a. The large tilt angle of the latter is correlated with the C–H···S interaction involving the – S–Py2 moiety. The coordination geometry around the metal center is a distorted tetragonal bipyramid with a cis conformation. A molecular square structure similar to 1 can be found in [Ni(hfac)2(4,4′-dipyridlydisulfide)]2·4(CHCl3), which is a molecular square with 4,4′-dipyridyl disulfide.57,58 The molecular square cavity size is ca. 99 Å2 as estimated from the NiII···NiII (10.8 Å) and S···S (9.2 Å) distances. The cavity size in 1 is larger than this and can therefore accommodate larger solvated molecules. The dihedral angles between the two pyridine rings in the ligand in 1 and [Ni(hfac)2(4,4′-dipyridyl disulfide)]2·4(CHCl3) are close to right angles at 83.6º and 85.0º, respectively.

Figure 8. Comparison of dihedral angles between pyridine rings and the Cp ring in (a) 1, (b) 3, and (c) 4. Hydrogen atoms are omitted for clarity.

The molecular square structure of [Ag(CF3SO3)(L1)(H2O)0.5]2·2CH2Cl2·H2O (3) is shown 14

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in Figure 10. Adjacent molecular squares are rotated by approximately 90º to each other, and solvated molecules (CH2Cl2 and H2O) are located in the interstices between them. The solvated CH2Cl2 molecules form C–H···S interactions with L1 (H···S distance = 2.8 Å, Figure S8). The pyridine rings in the molecular square form intramolecular π–π interactions (centroid-centroid distance = 3.6 Å), which constrain the two pyridine rings in a parallel arrangement. The two AgI ions are crystallographically equivalent and exhibit a distorted tetrahedral N2O2-coordination geometry, which is occupied by two nitrogen atoms from two L1 ligands, an oxygen atom from CF3SO3, and an oxygen atom from coordinated water. The coordinated water has an occupancy of 0.5. The AgI···AgI distance in the molecular square is 3.6 Å, which indicates no significant interaction.59 The torsion angles (τ1 and τ2) of L1 are 30.0º and 28.4º, respectively, which are larger than those in other complexes due to the intramolecular π–π interactions. Structures analogous to 3 can

be

found

in

AgI

complexes

with

a

thiopyridine

derivative

[AgX(1,2-bis[(pyridin-4-ylthio)methyl]benzene)]2 (X = CF3SO3 and ClO4).60,61 The intramolecular centroid-centroid distances between the two pyridines and AgI···AgI separations in these molecular squares are 3.7–3.9 Å and 3.2–3.4 Å, respectively, which are comparable to the corresponding distances in 3.

Figure 9. Solid-state structure of [Ni(hfac)2(L1)]2·2C6H5CH3 (1). Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted for clarity.

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Figure 10. Solid-state structure of [Ag(CF3SO3)(L1)(H2O)0.5]2·2CH2Cl2·H2O (3). Displacement ellipsoids are drawn at the 30% probability level. Counter anions and coordinated solvents are shown as ball-and-stick models. Uncoordinated solvated molecules and hydrogen atoms are omitted for clarity. The dashed line indicates an intermolecular π–π interaction.

Structures of 1D Coordination Polymers 4–5. The reaction of L1 with Cu(hfac)2 and CuI yielded a zigzag coordination polymer {[Cu(hfac)2(L1)]}n·0.25n(CH2Cl2) (4) and a ribbon-shaped coordination polymer {[Cu4I4(L1)2]}n (5) containing polynuclear Cu4I4 units. This structure is shown in Figure 6b. The assembled structure of {[Cu(hfac)2(L1)]}n·0.25n(CH2Cl2) (4) is shown in Figure 11. The structure consists of two crystallographically independent Cu(hfac)2L1 units, linked alternately along the a-axis. Two adjacent 1D chains are linked by interchain C–H···S interactions (H···S distance is ca. 3.0 Å) to form a ribbon-like structure (Figure S9). The intrachain and interchain CuII···CuII separations in 4 are 8.8 and 9.0 Å, respectively, indicating an absence of significant interactions between the CuII ions. Both Cu(hfac)2 units adopt the cis-configuration. The solvated dichloromethane molecules, disordered in two positions with an occupancy of 0.5, are located in the interstice between two zigzag chains and are surrounded by four pyridine rings from two L1 ligands. Both the crystallographically independent L1 units function as bidentate N,N-ligands. They exhibit different conformations, with torsion angles (τ1, and τ2) of 28.4º and 8.8º for one, and 10.6º and 0.8º for the other. The arrangements of the two pyridine rings in 4 are similar to those observed in 1; however, the dihedral angles between the pyridine and Cp rings in 4 are larger than those in 1 (Figure 8). The bent structure of L1 yielded zigzag structures, contrasting with the isomer 1,1′-di(4-pyridylthio)ferrocene (Figure 1a), which produced a linear 1D complex with Cu(hfac)2.42 The ribbon-shaped 1D structure of {[Cu4I4(L1)2]}n (5) is shown in Figure 12. This 16

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structure corresponds to that shown in Figure 6c. The ribbon expands along the b-axis with no remarkable interchain interactions. The structure consists of a stepped-cubane Cu4I4 unit and two L1 ligands, which are further linked via Cu–S bonds with lengths of 2.4 Å to form a ribbon structure, in which four pyridine rings from the two L1 ligands are aligned to bridge the Cu4I4 units, forming intramolecular π–π interactions (centroid-centroid distance = 3.8 Å). In the Cu4I4(L1)2 unit, each CuI ion exhibits a distorted tetrahedral coordination geometry. Two of the four CuI ions are surrounded by a nitrogen atom and a sulfur atom from L1 and two iodine anions, while the other two are coordinated by a nitrogen atom and three iodine anions. Thus, the ligand acts as a tridentate S,N,N-ligand, and the torsion angles (τ1 and τ2) are 19.2º and 25.1º, respectively. Only a few examples of stepped-cubane Cu4I4 substructures similar to that in 5 have been reported, such as [(CuI)4(2-methylpyridine)6],62

[(CuI)4(4-cyanopyridine)],63

and

[(CuI)4(1,1′-di(pyrazinyl)ferrocene)2].32

Figure 11. Solid-state structure of {[Cu(hfac)2(L1)]}n·0.25n(CH2Cl2) (4). Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms and solvent molecules are omitted for clarity. 17

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Figure 12. Solid-state structure of {[Cu4I4(L1)2]}n (5). Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms and solvent molecules are omitted for clarity. The dashed line indicates π–π interactions.

Structures of 2D Coordination Polymers 6–7. The reactions of L1 and AgX (X = ClO4 and PF6) lead to 2D coordination polymers {[Ag(ClO4)(L1)]}n (6) and {[Ag(L1)]PF6}n (7). The polymers exhibit similar structures with the 63-hcb topology (Figure S10),64–66 though their local coordination structures are slightly different due to the coordination ability of the anion in 6. These structures correspond to those shown in Figure 6d. The 2D sheet structure of 6 is shown in Figure 13a. The sheet contains a substructure of 1D zigzag chains formed by AgI ions and L1 ligands alternately linked through two nitrogen atoms, and the chains are cross-linked via the chelation of two sulfur atoms in L1 to the AgI ion in the neighboring chain. Thus, L1 acts as a tetradentate S,S,N,N-ligand. One of the pyridine rings (Py2) forms intermolecular π–π interactions (centroid-centroid distance = 3.5 Å). The AgI ion adopts a distorted tetragonal pyramidal N2S2O-coordination geometry, coordinated by two pyridine and two thioether moieties from two L1 ligands, and an oxygen atom from the ClO4 anion (Figures 13b and 13c). The structure of complex 7 is topologically similar to that of 6 (Figure 14a), though the 18

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intramolecular angles are slightly different, as seen by comparing Figures 13b and 14b. The torsion angles (τ1 and τ2) in the ligand are different; these are 5.1º and 38.9º in 6 and 11.8º and 0.5º in 7. This complex also contains π–π interactions (centroid-centroid distance = 3.5 Å). The coordination geometry around the metal center differs from that in 7, in that the anion is uncoordinated in this complex (Figure 14c). The coordination geometry is a distorted tetrahedron with two nitrogen and two sulfur atoms from two L1 ligands. The bent structure and additional coordination ability of the thioether moieties in L1 yielded higher dimensional structures than the isomer 1,1′-di(4-pyridylthio)ferrocene, which reacted with AgPF6 to form a linear 1D complex {[Ag{1,1′-di(4-pyridylthio)ferrocene}(PF6)]}n.42

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Figure 13. Solid-state structure of {[Ag(ClO4)(L1)]}n (6): (a) view of the 2D sheet, (b) view of the coordination geometry around the AgI center, and (c) corresponding schematic. Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted for clarity. The dashed line indicates π–π interactions.

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Figure 14. Solid-state structure of {[Ag(L1)]PF6}n (7): (a) view of the 2D sheet, (b) view of coordination geometry around the AgI center, and (c) corresponding schematic. Displacement ellipsoids are drawn at the 30% probability level. Hydrogen atoms and the counter anion are omitted for clarity. The dashed lines indicate π–π stacking interactions.

Solid-State

Redox

Properties

of

the

Ligands

and

Complexes.

The

electrochemical properties of ligands L1 and L2 and complexes 1–7 were investigated using solid-state cyclic voltammetry. Their redox potentials are listed in Table 3, and cyclic voltammograms of L1, 1, and 3–6 are shown in Figure 15. The voltammogram of 2 is similar to that of 1, and those of 6 and 7 are similar. All the compounds showed oxidation potentials (Epa) around 21

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0.5 V (vs. solid-state FeCp2/FeCp2+), which corresponded to the oxidation of the ferrocene moieties. Although L1 and 3 showed reduction potentials (Epc) around 0.4 V, the others showed no clear peaks around 0.4 V. Contrary to our expectations, there were no significant differences in redox potentials between free L1 and complex 3.

Table 3. Solid-State Redox Potentials from Cyclic Voltammetry (in V vs. FeCp2/FeCp2+). Compound L1 L2 1 2 3 4 5 6 7 1,1′-di(4-pyridylthio)ferrocene42 1,1′-di(2-pyridylthio)ferrocene42

Epa 0.50 (sh) 0.30, 0.45 (sh) 0.49 0.52 0.52 (sh) 0.50 0.57 (sh) 0.40 (sh), 0.51 0.40 (sh), 0.51 0.56 0.61

Epc 0.40 – – – 0.40 – – – – 0.45 0.40

E1/2 0.45 – – – 0.46 – – – – 0.50 0.51

The term sh indicates shoulder.

Figure 15. Solid-state cyclic voltammograms of L1, 1, and 3–6.

■ CONCLUSIONS In this report, we have described mixed-metal molecular square and coordination polymer complexes using ferrocene-based multidentate ligand L1. The mixed-metal complexes show extended network structures with characteristic topologies, due to the bulkiness of the ferrocene moiety and bent structure of the thioether moiety in L1. The network structures extend as the coordination number of L1 is increased. Although L1 possesses a redox-active ferrocene backbone, most of the complexes with L1 show no clear redox peaks. Although 1,1′-disubstituted ferrocenes have been used so far, this study has shown that the 1,2-disubstituted ferrocene derivative L1 is also 22

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a useful building block for constructing mixed-metal complexes.

■ ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: IR Spectra 1

H NMR Spectra

Additional Solid-State Structures Selected Bond Lengths, Bond Angles, Torsion Angles, and Dihedral Angles

Accession Codes CCDC 1556470−1556478 and 1573940 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 Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, U.K.; fax: +44 1223 336033.

■ AUTHOR INFORMATION Corresponding Author *Email: [email protected] ORCID Ryo Horikoshi: 0000-0002-8609-9173 Tomoyuki Mochida: 0000-0002-3446-2145 Notes The authors declare no competing financial interest.

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■ ACKNOWLEDGMENTS This work was supported by KAKENHI (16H04132) from the Japan Society for the Promotion of Science, and by the Report on the Focused Researchers of Osaka Sangyo University. The authors are grateful to Dr. Y. Funasako (Tokyo University of Science, Yamaguchi) for his helpful discussions. R. H. thanks Prof. Dr. I. Fujihara (Osaka Sangyo University) for his continued encouragement and Enago (www.enago.jp) for the English language review.

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Inorg. Organomet. Polym. 2017, 27, 1501–1513. (23) Scottwell, S. Ø.; Crowley J. D. Ferrocene-Containing Non-Interlocked Molecular Machines. Chem. Commun. 2016, 52, 2451–2464. (24) Shekurov, R.; Miluykov, V.; Kataeva, O.; Krivolapov, D.; Sinyashin, O.; Gerasimova, T.; Katsyuba, S.; Kovalenko, V.; Krupskaya, Y.; Kataev, V.; Büchner, V.; Senkovska, I.; Kaskel, S. Reversible Water-Induced Structural and Magnetic

Transformations

and

Selective

Water

Adsorption

Properties

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Poly(manganese

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Mixed-Metal Coordination Polymers and Molecular Squares Based on a Ferrocene-Containing Multidentate Ligand 1,2-Di(4-Pyridylthio)ferrocene

Ryo Horikoshi, Takumi Tominaga, and Tomoyuki Mochida

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Synopsis The reaction of a ferrocene-based multidentate ligand, 1,2-di(4-pyridylthio)ferrocene, with M(hfac)2, CuI, and AgX resulted in the formation of mixed-metal complexes with molecular square, 1D zigzag, 1D ribbon, and 2D sheet structures due to the flexible coordination modes of the ligand.

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