Electron-Deficient Pyridylimines: Versatile Building Blocks for

Article pubs.acs.org/IC

Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Electron-Deficient Pyridylimines: Versatile Building Blocks for Functional Metallosupramolecular Chemistry Niklas Struch,‡ Filip Topić,§,† Gregor Schnakenburg,∥ Kari Rissanen,§ and Arne Lützen*,‡ ‡

Kekulé-Institut für Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Straße 1, D-53121 Bonn, Germany § University of Jyväskylä, Department of Chemistry, Nanoscience Center, P.O. Box 35, 40014 Jyväskylä, Finland ∥ Institut für Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Straße 1, D-53121 Bonn, Germany S Supporting Information *

ABSTRACT: Metallosupramolecular systems heavily rely on the correct choice of ligands to obtain materials with desired properties. Engaging this problem, we present three ligand systems and six of their mono- and dinuclear complexes, based on the subcomponent self-assembly approach using electrondeficient pyridylcarbaldehyde building blocks. The properties are examined in solution by NMR and UV−vis spectroscopy and CV measurements as well as in solid state by single crystal X-ray diffraction analysis. Ultimately, the choice of ligands allows for fine-tuning of the electronic properties of the metal centers, complex-to-complex transformations, as well as establishing distinct anion−π-interaction motifs.

■

or a Bruker Avance I 500 at 175.1 or 125.1 MHz, respectively. 19FNMR spectra were recorded on a Bruker Avance I 300 at 282.4 MHz. Chemical shifts δ are given in ppm relative to (residual) solvent signals (1H, 13C) or relative to CCl3F as an external standard (19F). Signal multiplicities are given as s (singlet), d (doublet), m (multiplet); b indicates a broad signal.36,37 ESI mass spectra were recorded on a Fischer Scientific LTQ Orbitrap XL or a Bruker micrOTOF-Q. UV− vis spectra were recorded on a Jena Scientific Specord 300 spectrometer. Cyclic voltammograms of 1[H](BF4)2, 1[F](BF4)2, 1[NO2](BF4)2, and 1[CF3](BF4)2 were recorded using a Gamry Instruments Interface 1000T potentiostat and Gamry Instruments software in a 20 mL glass cell using platinum electrodes against an Ag/ AgNO3 electrode. Therefore, a 1 mM solution of analyte in 5 mL of air-saturated acetonitrile with 100 mM tetrabutylammonium hexafluorophosphate was placed in a 20 mL glass cell open to air and measured at different scan rates. Sufficient results were found for scan rates of 200 mV/s. All cyclic voltammograms were calibrated against ferrocene in an external solution under the same conditions and scan rates. Synthesis of 1[H](BF4)2. A solution of 10.0 mg (0.068 mmol, 1.00 equiv) of tris(2-aminoethyl)amine, 22.0 mg (0.205 mmol, 3.01 equiv) of 2-pyridylcarbaldehyde, and 7.6 mg (0.068 mmol, 1.00 equiv) of iron(II) tetrafluoroborate hexahydrate in 1.0 mL of acetonitrile (hplc grade) was degassed by bubbling argon through the solution for 15 min and heated to 70 °C for 5 h to yield a purple solution. The product was precipitated by vapor diffusion of methyl tert-butyl ether overnight to yield purple crystals. The material was filtered off, washed with generous amounts of diethyl ether, and dried in a stream of air to

INTRODUCTION The implementation of functionality in supramolecular aggregates is one of the major challenges in modern metallosupramolecular chemistry.1−7 This may include novel functional ligands,8−13 new architectures and topologies,14−17 and utilizing cavities and voids in the supramolecular aggregates18−22 or even the whole supramolecular entity as functional unit.23,24 Electronic effects in the ligands can play a major role in the self-assembly of such systems25 or in their electronic behavior. For example, fine-tuning of spin-crossover properties by utilizing electron-withdrawing substituents has been demonstrated26−28 and the interplay of ligands and metal centers is acknowledged as of utmost importance.29 Pyridylimine-based iron(II) complexes have found major interest in the field of metallosupramolecular chemistry30,31 and are valuable building blocks in the synthesis of sophisticated supramolecular aggregates.32−35 Here, we describe and characterize the implementation of electron-deficient pyridylimine building blocks in prototypical iron(II) complexes to modulate their electronic and spectroscopic properties and packing motifs in the solid state.

■

EXPERIMENTAL SECTION

General. All substances were purchased from Alfa Aesar, J.T. Baker, Fluorochem, Sigma-Aldrich, or VWR Chemicals and used without further purification. 1H NMR spectra were recorded at 700.1, 499.1, 400.1, or 300.1 MHz on a Bruker Avance III HD Ascend 700, Avance I 500, Avance I 400, or Avance I 300 spectrometer, respectively. 13C NMR spectra were recorded on a Bruker Avance III HD Ascend 700 © XXXX American Chemical Society

Received: September 21, 2017

A

DOI: 10.1021/acs.inorgchem.7b02412 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

of the desired complex as a purple powder. Crystals suitable for single crystal X-ray diffraction were obtained by slow vapor diffusion of methyl tert-butyl ether to a concentrated solution in acetonitrile over several days. 1H NMR (acetonitrile-d3, 298 K, 300.1 MHz): δ [ppm] = 11.48 (bs, H-6), 9.19 (bs, H-1), 8.99 (s, H-3), 8.93 (s, H-4), 5.33 (bs, H-7), 3.39 (bs, H-8); due to the inherent paramagnetism of the sample no sufficient 13C NMR could be recorded even when accumulating 5k scans at 176.1 MHz, furthermore the paramagnetic character reduces the relaxation times significantly, effectively inhibiting the detection of H−H-couplings in regular 1H NMR experiments;40,41 19F-NMR (acetonitrile-d3, 298 K, 282.4 MHz): δ [ppm] = −151.3 (BF4−); high resolution ESI-MS (acetonitrile): m/z = 302.0603 ([M]2+, calcd for ([C24H24FeN10O6])2+ 302.0609), 623.120 ([M+F]+, calcd for ([C24H24FeN10O6]F)+ 623.1214), 691.1252 ([M+BF4]+, calcd for ([C24H24FeN10O6](BF4))+ 691.1253); UV−vis (acetonitrile, 200 μM, 298 K): λ [nm] = 246, 282, 364, 566, 624. Synthesis of 2[F](BF4)4. A degassed solution of 10.0 mg (0.051 mmol, 3.00 equiv) of 4,4′methylenedianiline, 13.0 mg (0.103 mmol, 6.02 equiv) of 5-fluoropyridyl-2-carbaldehyde, and 11.0 mg (0.0337 mmol, 2.00 equiv) of iron(II) tetrafluoroborate hexahydrate in 1.0 mL of acetonitrile (hplc grade) was heated to 60 °C for 18 h under an argon atmosphere to yield a pink solution. The product was precipitated by addition of 25 mL diethyl ether, filtered off, washed with generous amounts of diethyl ether and dried in a stream of air to yield 22.3 mg (0.013 mmol, 76%) of the desired complex as a pink powder. Single crystals suitable for single crystal X-ray diffraction were obtained by slow vapor diffusion of methyl tert-butyl ether to a concentrated solution of 2[F](BF4)4 in acetonitrile over several weeks. 1 H NMR (acetonitrile-d3, 298 K, 700.1 MHz): δ [ppm] = 9.12 (s, 1 H, H-6), 8.75−8.79 (m, 1 H, H-3), 8.19−8.22 (m, 1 H, H-4), 7.58 (s, 1 H, H-1), 6.97 (brs, 2 H, H-8), 5.53 (brs, 2 H, H-9), 4.08 (s, 1 H, H11); 13C NMR (acetonitrile-d3, 298 K, 176.1 MHz): δ [ppm] = 173.0 (C-6), 163.7 (d, 1JF,C‑2 = 289.9 Hz, C-2), 154.9 (C-5), 149.5 (C-10), 146.3 (d, 2JF,C‑1 = 33.8 Hz, C-1), 142.0 (C-8/9), 133.4 (d,3JF,C‑4 = 8.3 Hz, C-4), 130.1 (C-7), 127.0 (d, 2JF,C‑3 = 19.3 Hz, C-3), 121.0 (C-8/ 9), 39.1 (C-11); 19F (acetonitrile-d3, 298 K, 282.4 MHz): δ [ppm] = −121.3 MHz (FAr), − 154.3 (BF4−); high resolution ESI-MS (acetonitrile): m/z = 337.0776 ([M]4+, calcd for [(C25H18F2N4)3Fe2]4+ 337.0795), 455.7735 ([M+F]3+, calcd for [(C25H18F2N4)3Fe2F]3+ 455.7727), 761.1594 ([M+2 BF4]2+ calcd. for [(C25H18F2N4)3Fe2(BF4)2]2+ 761.1635); UV−vis (acetonitrile, 200 μM, 298 K): λ [nm] = 234, 280, 368, 492, 542. Synthesis of 2[CF3](BF4)4. A degassed solution of 10.0 mg (0.051 mmol, 3.00 equiv) of 4,4′methylenedianiline, 18.0 mg (0.101 mmol, 6.02 equiv) of 5-trifluoromethylpyridyl-2-carbaldehyde, and 11.0 mg (0.0337 mmol, 2.00 equiv) of iron(II) tetrafluoroborate hexahydrate in 1.0 mL of acetonitrile (hplc grade) was heated to 60 °C for 18 h under an argon atmosphere to yield a purple solution. The product was crystallized by vapor diffusion of methyl tert-butyl ether to the solution to yield X-ray quality single crystals. The material was filtered off, washed with generous amounts of diethyl ether and dried in a stream of air to yield 30.0 mg (0.015 mmol, 89%) of the desired complex as a purple powder. 1H NMR (acetonitrile-d3, 298 K, 700.1 MHz): δ [ppm] = 9.84 (s, 1 H, H-6), 9.19 (d, 3JH‑3,H‑4 = 8.1 Hz, 1 H, H-3), 9.11(d, 3JH‑3,H‑4 = 8.1 Hz, 1 H, H-4), 8.60 (s, 1 H, H-1), 7.04 (bs, 2 H, H-8), 5.59 (bs, 2 H, H-9), 4.17 (s, 1 H, H-11); 13C NMR (acetonitriled3, 298 K, 176.1 MHz): δ [ppm] = 173.4 (C-6), 160.1 (C-2), 153.2 (C-5), 150.0 (C-10), 142.9 (C-1), 136.1 (C-8/9), 133.2 (C-4), 132.0 (bs, CF3) 130.2 (C-7), 125.0 (C-3), 122.4 (C-8/9),39.0 (C-11); 19F (acetonitrile-d3, 298 K, 282.4 MHz): δ [ppm] = −62.4 MHz (CF3), − 154.5 (BF4−); high resolution ESI-MS (acetonitrile): m/z = 412.0753 ([M]4+, calcd for [(C27H18F6N4)3Fe2]4+ 412.0745), 549.098 ([M-H]3+, calcd for [(C27H18F6N4)2(C27H17F6N4)Fe2]3+ 549.098), 555.766 ([M +F]3+, calcd for [(C27H18F6N4)3FeF]3+ 555.766); UV−vis (acetonitrile, 200 μM, 298 K): λ [nm] = 234, 278, 284, 368, 526, 576. Synthesis of 2[NO2](BF4)4. A degassed solution of 10.0 mg (0.051 mmol, 3.00 equiv) of 4,4′methylenedianiline, 16.0 mg (0.101 mmol, 6.02 equiv) of 5-nitropyridyl-2-carbaldehyde, and 11.0 mg (0.0337 mmol, 2.00 equiv) of iron(II) tetrafluoroborate hexahydrate in 1.0 mL of acetonitrile (hplc grade) was heated to 60 °C for 18 h under an

yield 36.2 mg (0.057 mmol, 84%) of the desired product as a purple powder. The analytical data match those presented in the literature.38,39 Crystals suitable for single crystal XRD were obtained by slow vapor diffusion of methyl tert-butyl ether into a concentrated solution of 1[H](BF4)2 in acetonitrile over several days. Synthesis of 1[F](BF4)2. A solution of 10.0 mg (0.068 mmol, 1.00 equiv) of tris(2-aminoethyl)amine, 26.0 mg (0.205 mmol, 3.01 equiv) of 5-fluoro-2-pyridylcarbaldehyde, and 7.6 mg (0.068 mmol, 1.00 equiv) of iron(II) tetrafluoroborate hexahydrate in 1 mL of acetonitrile (hplc grade) was degassed by bubbling argon through the solution for 15 min and heated to 70 °C for 5 h to yield a pink solution. The product was precipitated by vapor diffusion of methyl tert-butyl ether overnight to yield pink crystals suitable for single crystal XRD. The material was filtered off, washed with generous amounts of diethyl ether, and dried in a stream of air to yield 29.8 mg (0.044 mmol, 65%) of the desired product as a pink powder. 1H NMR (acetonitrile-d3, 298 K, 700.1 MHz): δ [ppm] = 9.81 (s, 1 H, H-6), 8.50 (dd, 3JH‑3,H‑4 = 8.3 Hz, 3JF,H‑3 = 5.3 Hz, 1 H, H-3), 7.99 (m, 1 H, H-4), 7.69 (brs, 1 H, H1), 4.13 (m, 2 H, H-7), 3.18 (m, 2 H, H-8); 13C NMR (acetonitrile-d3, 298 K, 176.1 MHz): δ [ppm] = 169.51 (C-6), 152.9 (C-5), 144.5 (d, 2 JC‑1,F = 31.1 Hz, C-1), 131.4 (C-4), 125.9 (d, 2JC‑3,F = 18.9 Hz, C-3), 58.3 (C-7), 53.1 (C-8), due to the paramagnetic character of the sample and the coupling to the fluorine, the quaternary carbon C-2 cannot be detected; 19F (acetonitrile-d3, 298 K, 282.4 MHz): δ [ppm] = −121.3 (FAr), −154.3 (BF4−); high resolution ESI-MS (acetonitrile): m/z = 261.5687 ([M]2+, calcd for [(C24H24F3FeN7)]2+ 261.5692), 610.1417 ([M+BF4]+, calcd for [(C24H24F3FeN7)(BF4)]+ 610.1418), 720.1346 ([M+(BF4)2Na]+, calcd for [(C24H24F3FeN7)(BF4)2Na]+ 720.1345); UV−vis (acetonitrile, 298 K, 200 mM): λ [nm] = 244, 272, 320, 508, 556. Synthesis of 1[CF3](BF4)2. A solution of 10.0 mg (0.068 mmol, 1.00 equiv) of tris(2-aminoethyl)amine, 36.0 mg (0.205 mmol, 3.01 equiv) of 5-trifluoromethyl-2-pyridylcarbaldehyde, and 7.6 mg (0.068 mmol, 1.00 equiv) of iron(II) tetrafluoroborate hexahydrate in 1.0 mL of acetonitrile (hplc grade) was degassed by bubbling argon through the solution for 15 min and heated to 70 °C for 5 h to yield a purple solution. The product was precipitated by vapor diffusion of methyl tert-butyl ether overnight as purple block-shaped crystals suitable for single crystal XRD. The material was filtered off, washed with generous amounts of diethyl ether, and dried in a stream of air to yield 49.6 mg (0.059 mmol, 87%) of the desired product as a purple powder. 1H NMR (acetonitrile-d3, 298 K, 500.1 MHz): δ [ppm] = 10.37 (bs, 1 H, H-6), 8.68, (d, 3JH‑3,H‑4 = 7.6 Hz, 1 H, H-3), 8.57 (3JH‑3,H‑4 = 7.6 Hz, 1 H, H-4), 8.03 (bs, 1 H, H-1), 4.49 (bs, 2 H, H-7), 3.30 (bs, 2 H, H-8); 13 C NMR (acetonitrile-d3, 298 K, 125.8 MHz) δ [ppm] = 169.8 (C-6), 157.8 (C-5), 152.4 (C-1), 137.1 (C-4), 132.9 (bs, CF3), 130.1 (C-3), 58.9 (C-7), 52.5 (C-8); 19F-NMR (acetonitrile-d3, 298 K, 282.4 MHz) δ [ppm] = −63.5 (CF3), −151.5 (BF4−); high resolution ESI-MS (acetonitrile): m/z = 336.564 ([M]2+, calcd for [(C27H24F9FeN7)]2+ 336.565), 760.1320 ([M+(BF4)]+, calcd for [(C27H24F9FeN7)(BF4)]+ 760.1328); UV−vis (acetonitrile, 298 K, 200 mM): λ [nm] = 226, 270, 344, 540, 590. Synthesis of 1[NO2](BF4)2. A solution of 10.0 mg (0.068 mmol, 1.00 equiv) of tris(2-aminoethyl)amine, 31.0 mg (0.205 mmol, 3.01 equiv) of 5-nitro-2-pyridylcarbaldehyde, and 7.6 mg (0.068 mmol, 1.00 equiv) of iron(II) tetrafluoroborate hexahydrate in 1.0 mL of acetonitrile (hplc grade) was degassed by bubbling argon through the solution for 15 min and heated to 70 °C for 5 h to yield a blue solution. The product was precipitated by vapor diffusion of methyl tert-butyl ether overnight to yield blue polycrystalline material. The material was filtered off, washed with generous amounts of diethyl ether and dried in a stream of air to yield 33.4 mg (0.039 mmol, 58%) B


1[H](BF4)2

1573410 C24H27B2F8FeN7 643.0 100(1) 1.54178 monoclinic P21/c 10.4840(4) 15.4588(6) 16.8333(6) 90 97.040(2) 90 2707.81(18) 4 1.577 empirical 5.238 0.753/0.211 1312.0 clear dark red blocks 0.25 × 0.12 × 0.11 3.896−67.491 28084 [0.0778] 4318 98.2 4827/380/0 1.024 0.0717, 0.1944 0.0799, 0.2047 0.77/−1.03

Complex

CCDC Number Empirical formula Formula weight Temperature (K) λ/Å Crystal system Space group Unit cell dimensions: a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) Volume (Å3) Z Density (calculated) (g cm−3) Absorption correction Absorption coefficient (mm−1) Max. and min transmission F(000) Crystal color and shape Crystal size (mm3) θ range for data collection (deg) Reflections collected [R(int)] Reflections [I > 2σ(I)] Data completeness (%) Data/parameters/restraints Goodness-of-fit on F2 Final R indices [I > 2σ(I); R1, wR2] Final R indices [all data, R1, wR2] Largest diff. peak/hole (e Å−3) Flack parameter x

1573412 C24H24B2N7F11Fe 696.97 100(1) 1.54178 monoclinic P21/c 10.6585(7) 15.6322(10) 16.8717(11) 90 98.482(3) 90 2780.3(3) 4 1.665 empirical 5.315 0.7536/0.3077 1408.0 clear dark red plates 0.45 × 0.35 × 0.15 3.875−67.679 30652 [0.0755] 4581 99.5 5023/406/0 1.026 0.0764, 0.2077 0.082, 0.2162 1.24/−1.47

1[F](BF4)2 1573411 C26H27B2F8FeN11O6 819.05 100(1) 1.54178 orthorhombic Pbca 16.3511(6) 14.3608(6) 27.7246(11) 90 90 90 6510.1(4) 8 1.671 empirical 4.688 0.7528/0.2659 3328.0 clear black plates 0.30 × 0.15 × 0.04 3.188−66.743 42170 [0.0739] 4871 95.5 5507/507/42 1.053 0.0378, 0.0911 0.0446, 0.0949 0.36/−0.39

1[NO2](BF4)2

Table 1. Crystallographic Data for All Compounds Presented in This Work 1[CF3](BF4)2 1573312 C31H30B2F17FeN9 929.11 170.0(1) 0.71073 orthorhombic Pbca 17.6421(1) 14.0684(1) 31.5973(3) 90 90 90 7842.33(10) 8 1.574 multiscan 0.503 0.7457 and 0.6674 3744 violet blocks 0.533 × 0.413 × 0.275 1.960 to 28.496 145049 [0.0544] 8268 99.8 to θ = 25.25° 9915/685/1221 1.063 0.0392, 0.0909 0.0498, 0.0957 0.284/−0.312

2[F](BF4)4 1573413 C168H135B6F36Fe4N33 3588.34 100(1) 1.54178 monoclinic P2/n 22.9021(7) 13.5053(4) 28.6808(9) 90 107.9467(18) 90 8439.3(5) 2 1.412 empirical 3.580 1.000/0.4268 3664.0 clear dark red plates 0.50 × 0.11 × 0.11 2.170−67.495 39174 [0.1379] 9076 97.9 14885/1131/661 1.561 0.1711, 0.4405 0.2268, 0.4788 2.87/−1.56

2[NO2](BF4)4 1573414 C87H72B4F16Fe2N24O12 2104.62 100(1) 0.71073 monoclinic C2/c 27.342(3) 10.1484(11) 34.971(4) 90 106.923(2) 90 9283.3(17) 4 1.506 empirical 0.420 0.7460/0.6798 4296.0 clear blue blocks 0.22 × 0.20 × 0.10 2.152−28.0 83620 [0.0463] 8924 99.8 11205/827/355 1.089 0.0963, 0.2416 0.1150, 0.2531 1.83/−1.51

2[CF3](BF4)4 1573313 C93H72B4F34Fe2N18 2242.62 123.0(1) 1.54184 monoclinic I2 21.7929(6) 9.6802(2) 23.4967(5) 90 105.746(2) 90 4770.8(2) 2 1.561 Gaussian 3.542 0.961 and 0.701 2268 violet needles 0.149 × 0.037 × 0.035 3.909 to 74.160 28432 [0.041] 12052 99.7 to θ = 67.75° 16945/685/1 0.947 0.0501, 0.1169 0.0714, 0.1249 0.640/−0.464 0.018(4)

Inorganic Chemistry Article

C


Article

Inorganic Chemistry argon atmosphere to yield a blue solution with blue precipitate. The product was precipitated by addition of 25 mL diethyl ether, filtered off, washed with generous amounts of diethyl ether and dried in a stream of air to yield 25 mg (0.013 mmol, 75%) of the desired complex as a blue powder. Single crystals suitable for single crystal Xray diffraction were obtained by slow vapor diffusion of methyl tertbutyl ether to a concentrated solution of 2[NO2](BF4)4 in acetonitrile over several weeks. 1H NMR (acetonitrile-d3, 298 K, 700.1 MHz): δ [ppm] = 9.82 (s, 1 H, H-6), 9.19 (d, 3JH‑3,H‑4 = 8.4 Hz, 1 H, H-3), 9.11 (d, 3JH‑3,H‑4 = 8.4 Hz, 1 H, H-4), 8.59 (s, 1 H, H-1), 7.03 (s, 2 H, H-8), 5.58 (bs, 2 H, H-9), 4.17 (s, 1 H, H-11):13C NMR (acetonitrile-d3, 298 K, 176.1 MHz):δ [ppm] = 173.5 (C-6), 160.0 (C-2), 153.1 (C-5), 149.9 (C-10), 149.3 (C-1), 142.8 (C-8/9), 136.1 (C-4), 133.1 (C-7), 130.2 (C-3), 122.4 (C-8/9),39.1 (C-11); 19F (acetonitrile-d3, 298 K, 282.4 MHz) δ [ppm] = −154.3 (BF4−); high resolution ESI-MS (acetonitrile): m/z = 344.5710 ([M]4+, calcd for [(C25H18N6O4)3Fe2]4+ 377.5713), 509.7606 ([M+F]3+, calcd for [(C25H18N6O4)3Fe2F]3+ 509.7613); UV−vis (acetonitrile, 200 μM, 298 K): λ [nm] = 250, 284, 394, 570, 612. Ligand exchange experiments. In a typical experiment, 0.012 mmol of dinuclear complex was treated with 0.084 mmol (7.00 equiv) of the respective pyridyl-2-carbaldehyde in 0.7 mL of acetonitrile-d3. An immediate color change indicated the reaction. To complete the reaction the solution was degassed and heated to 60 °C for 18 h and analyzed by 1H NMR to verify complete transformation of the complexes. The analytical data on the statistical complex mixture obtained upon treating 2[NO2](BF4)4 with 5-trifluoromethylpyridyl2-carbaldehyde is shown in the SI. X-ray crystallography. The X-ray data for 1[CF3](BF4)2 were collected on a Bruker-Nonius KappaCCD diffractometer with an APEX-II detector with graphite-monochromatized Mo−Kα (λ = 0.71073 Å) radiation. Data collection and reduction were performed using the program COLLECT and HKL DENZO AND SCALEPACK, respectively, and the semiempirical absorption correction was applied using SADABS. The X-ray data for 2[CF3](BF4)4 were collected on an Agilent SuperNova Dual diffractometer with an Atlas detector using mirrormonochromatized Cu-Kα (λ = 1.54184 Å) radiation. CrysAlisPro software42 was used for data collection and reduction as well as applying numerical absorption correction based on Gaussian integration. The crystal of 2[CF3](BF4)4 was found to be a nonmerohedric twin with two components which could be successfully indexed and integrated. The X-ray data for 1[H](BF4)2, 1[NO2](BF4)2, 1[F](BF4)2, 2[F](BF4)4, and 2[NO2](BF4)4 were collected on a Bruker D8Venture diffractometer with a Photon-100 detector using mirrormonochromatized Cu−Kα (λ = 1.54184 Å) or Mo- Kα (λ = 0.71073 Å) radiation. Apex3 software was used for data collection and reduction as well as applying an empirical absorption correction by using SADABS. The structures were solved using SHELXT-2014/543 and refined by full-matrix least-squares using SHELXL-2014/7 or SHELXL-2017/144 within Olex245 and WinGX46 packages (see data in Table 1). All nonhydrogen atoms were refined anisotropically. All carbon-bound hydrogen atoms were calculated to their optimal positions and treated as riding atoms using isotropic displacement parameters 1.2 (or 1.5 in case of methyl groups) times larger than the respective parent atoms. In 1[CF3](BF4)2, all the CF3 groups were found to be disordered and were modeled by three, two and two components, respectively, with respective occupancies 0.558(13)/0.256(11)/0.184(7), 0.61(3)/ 0.39(3) and 0.50(3)/0.50(3). Moreover, one of the acetonitrile molecules was also modeled as disordered over two components with occupancies 0.507(14)/0.493(14). In all the disordered moieties geometry restraints were applied to the 1,2- and 1,3-distances, while the rigid body and similarity restraints were applied to the atomic displacement parameters. For 2[CF3](BF4)2, both twin components were used in the refinement, with the batch scale factor converging to 0.2267(10).

PLATON’s squeeze module had to be applied to 2[F](BF4)4, as one BF4 anion and several acetonitrile solvent molecules were heavily disordered and could not be reasonably modeled.

■

RESULTS AND DISCUSSION All systems presented in this study were synthesized by the subcomponent self-assembly approach. The ligands were formed from the commercially available precursors in situ and under mutual Lewis acid catalysis and stabilization upon complex formation.47 Stochiometric amounts of amine backbone, either tris(2aminoethyl)amine for 1[H](BF4)2, 1[F](BF4)2, 1[NO2](BF4)2, and 1[CF3](BF4)2, or 4,4′-methylenedianiline for 2[H](BF4)4, 2[F](BF4)4, 2[NO2](BF4)4, and 2[CF3](BF4)4, the respective pyridyl carbaldehyde and iron(II) tetrafluoroborate hexahydrate were dissolved in acetonitrile (HPLC grade), degassed by bubbling dry argon through the solution for 15 min, and heated to 50 °C for 18 h under argon atmosphere. A brief workup procedure of precipitating the material by the addition of diethyl ether or vapor diffusion crystallization and filtration yielded the compounds in good yields of around 80% for all the presented examples (Figure 1).

Figure 1. Synthesis of complexes 1[X] and 2[X] presented in this study.

Although 1[H](BF4)238,48 and 2[H](BF4)449,50 were reported previously and were synthesized in a different two-step procedure, we adapted the one-pot subcomponent selfassembly approach to readily yield the desired materials in comparable yields to those presented in the literature. Identity and purity were proven by 1H and 13C NMR spectroscopy, mass spectrometry, UV−vis spectroscopy, and single crystal Xray diffraction for all substances. X-ray crystallographic studies and anion binding in solid state. 1[NO2](BF4)2 and 1[CF3](BF4)2 both crystallize as acetonitrile solvates in the orthorhombic space group Pbca while 1[F](BF4)2 crystallizes in the monoclinic space group P21/c, as the parent structure of 1[H](BF4)2, also crystallizes in space group P21/c (Table 1). The molecular structure in solution, as shown by NMR spectroscopy and high resolution mass spectrometry, is similar to that in the solid state. An iron(II) center is placed in the middle of a hexadentate ligand formed by three pyridylimine moieties, corroborated by the Fe−N6 chromophore observed in respective UV−vis spectra. D


Article

Inorganic Chemistry

Table 2. Averaged Bond Lengths and Chelating Angles of the Iron(II) Coordination Sphere in the Presented Complexes davg(Fe−Nimine) davg(Fe−Npyr) α(Nimine−Fe−Npyr)

1[H](BF4)2

1[F](BF4)2

1[CF3](BF4)2

1[NO2](BF4)2

2[F](BF4)4

2[CF3](BF4)4

2[NO2](BF4)4

1.968 Å 1.947 Å 81.4°

1.953 Å 1.977 Å 81.1°

1.955 Å 1.983 Å 81.0°

1.946 Å 1.991 Å 81.2°

1.986 Å 1.977 Å 80.9°

1.985 Å 1.976 Å 80.9°

1.970 Å 1.974 Å 81.1°

Upon introduction of electron-withdrawing groups, however, this changes dramatically. Beginning with the least electronwithdrawing substituenta single fluorine atomnumerous interactions can be observed. One tetrafluoroborate anion sits well in the roughly C3-symmetric “cavity” at the lower rim of the complex, stabilized by three anion−π-interactions, one to each of the pyridyl rings (Figure 3). Furthermore, it forms one

Although the ligand is, in theory, heptadentate, the seventh nitrogen atom does not bind to the iron center, a common sign of a low-spin configuration.51,52 Accompanied by the bond lengths of 1.947−1.984 Å (1[F](BF4)2), 1.944−2.000 Å (1[NO2](BF4)2), 1.946−1.987 Å (1[CF3](BF4)2) and the highly symmetric coordination geometries best described as octahedral (see Table 2, Figure 2, and SI), this indicates a low spin configuration at 100 K in the solid state. UV−vis and NMR spectroscopy in solution at 298 K both support the assignment as mainly low spin (vide infra).

Figure 3. Interactions between anions and the cationic unit as found in the crystal structure of 1[F](BF4)2. Close contacts between the cationic unit and fluorine atoms from the tetrafluoroborate anions are marked in red. Other counteranions, solvent molecules, and disordered atoms are omitted for clarity, color code: gray−carbon, blue−nitrogen, orange−iron, yellow−fluorine, pink−boron.

Figure 2. Cationic unit of 1[CF3](BF4)2 as found by single crystal XRD; for 1[H](BF4)2, 1[F](BF4)2, and 1[NO2](BF4)2; see SI. Selected atoms are labeled. Ellipsoids set to 50% probability level, hydrogen atoms, counteranions, solvent molecules, and disordered atoms are omitted for clarity, color code: gray−carbon, blue−nitrogen, orange−iron, yellow−fluorine.

hydrogen bond to the ligand and hydrogen bonds to other cationic units. The TREN moiety of the ligand also forms hydrogen bonds to the counteranions. It is noteworthy that, in the case of 1[H](BF4)2, the BF4− ion cannot be found in the “lower” cavity of the complexes, highlighting the importance of the anion−π-interactions for the packing. In 1[NO2](BF4)2 (Figure 4), again, numerous interactions can be found. While hydrogen bonds play a major role, anion−π interactions can also be identified. These interactions are directed toward both the carbon atoms and the nitrogen atoms of the nitro groups. Here, we can observe one tetrafluoroborate anion sitting in the cavity, interacting with two ligands, and another one placed close to it. The dimeric complexes 2[H](BF4)4 (see ref 44), 2[F](BF4)4, 2[NO2](BF4)4, and 2[CF3](BF4)4 exhibit more differences in packing. 2[F](BF4)4 crystallizes in the monoclinic space group P2/n with one helicate in the asymmetric unit. 2[NO2](BF4)4 crystallizes in the monoclinic space group C2/c with half a helicate and two counter-anions in the asymmetric unit. 2[CF3](BF4)4, however, crystallizes in monoclinic space group I2, again with half a helicate and two counteranions in the asymmetric unit (Table 1). 2[H](BF4)4 is described in literature49 as crystallizing in the monoclinic space group P21/n when using similar conditions as used in our study. Despite our efforts, the crystal structures of 2[NO2](BF4)4 and 2[F](BF4)4 are only of mediocre quality and are thus not discussed in detail (see SI). Nevertheless, they unambiguously prove the connectivity, the general packing motifs, and the key

The packing of the cationic units itself is quite regular and, hence, will not be discussed in great detail here. Nonetheless, some intriguing features become apparent upon comparing the crystal structures, such as the anion−π interactions. While these must be evaluated with caution,53−56 numerous distinct anion−π interactions can be observed in the structures of the materials presented in this work. Anion−π interactions rely on the interaction between the electron-rich anions and the electron-poor aromatic systems. Since the pyridylimines in this study are on the one hand bound to metal cations and on the other hand contain electron-withdrawing groups, their aromatic systems readily form anion−π interactions in the solid state.57,58 We re-evaluated the structure of 1[H](BF4)2 (see SI) as well to compare the “neutral” state to those interactions found in our systems. Hydrogen bonds (C−H···F−B) to the anions are the dominant interactions between the cationic units and the anions (see SI). Only one possible anion−π interaction is found in the crystal structure with a distance of 3.164 Å between the fluorine atom of a tetrafluoroborate anion and the associated sp2-carbon atom. The respective anion sits well below the C3symmetric cavity of the lower rim of the structure (vide infra). While this is well within the range observed for other anion−π interactions, it is the only one present in this structure (see SI). E


Article

Inorganic Chemistry

Figure 4. Interactions between the anions and the cationic unit as found in the crystal structure of 1[NO2](BF4)2 (left) and 1[CF3](BF4)2 (right). Close contacts between the cationic unit and fluorine atoms from the tetrafluoroborate anions are marked in red. Other counteranions, solvent molecules, and disordered atoms are omitted for clarity, color code: gray−carbon, blue−nitrogen, orange−iron, yellow−fluorine, red−oxygen, pink− boron.

Figure 5. Cationic unit of 2[CF3](BF4)4 as observed in the crystal structure exemplary for the dinuclear complexes (for 2[F](BF4)4 and 2[NO2](BF4)4; see SI). Selected atoms are labeled. Ellipsoids set to 50% probability level, hydrogen atoms, counteranions, and solvate molecules are omitted for clarity, color code: gray−carbon, blue−nitrogen, orange−iron, yellow−fluorine.

dinuclear complexes respectively adopt the expected C3symmetric and D3d-symmetric conformations. Notably, however, the signals are significantly broadened. This is due to the fact that iron(II) has two different possible electronic states, the diamagnetic S = 0 low-spin state and the paramagnetic S = 2 high-spin state. While in pure pyridylimine complexes of iron(II) only the low-spin state is stabilized, changing the ligand field can stabilize the high-spin state in a way that makes it possible to (partly) occupy it, even around room temperature. This is often observed for electron-deficient ligands such as imidazolylimines60 or sterically strained metal centers with an artificially widened ligand sphere.48,61,62 Since our systems are, with respect to their sterical properties and the bite angle, nearly identical to the low-spin stabilizing pyridylimines (Table 2), the NMR signal broadening clearly arises due to the presence of the electron-withdrawing groups.26 To examine this we conducted temperature-dependent NMR spectroscopy (Figure 6). We focused on the imine protons to probe the spin state, as they are only slightly affected by temperature-induced dynamics (vide infra) of the system and, because of the quite strong Fermi contact interaction, they show the strongest shifts due to the partly occupied high-spin states.63,64 Two trends could be observed. First, the sharpening of the imine signals and their convergence to the shifts of the pure low-spin pyridylimine complexes upon cooling, indicating the

interactions as described. On the other hand, 2[CF3](BF4)4 crystallizes very nicely, giving a well-ordered structure and a good quality model (Figure 5). The observed packing features, especially the anion binding motifs, are strikingly similar to those observed in the mononuclear structures. Namely, in 2[F](BF4)4 one tetrafluoroborate is encapsulated in the “cavity”, as already observed in 1[F](BF4)2. In 2[NO2](BF4)4 we observe binding of the anion to the nitro groups and in 2[CF3](BF4)4 we observe interactions to the imine carbon atoms, as observed in the mononuclear counterparts. In 1[H](BF4)2 such interactions are not observed at all. Hence, we can deduce that these interactions hail from and are directed by the electronwithdrawing groups. It is noteworthy that, while crystals of 2[F](BF4)4 and 2[NO2](BF4)4 are quite difficult to grow and are only of poor quality, 2[CF3](BF4)4 readily forms good quality crystals,59 also suggesting a great importance of the substituents on the efficient packing in the respective crystals. Spectroscopic and solution properties. Both the mononuclear and the dinuclear complexes are also stable in solution as shown by NMR and UV−vis spectroscopy as well as mass spectrometry. The mass spectra respectively show the presence of intact ML (1) and M2L′3 (2) aggregates, which is also corroborated by NMR spectroscopy (see SI). As indicated by the highly symmetric NMR spectra, the mononuclear and F


Article

Inorganic Chemistry

decrease the σ-donating character of the ligand, hence decreasing the ligand-field splitting and changing the colors compared to the neutral pyridyl system.61 We were also interested in the electrochemical properties of these systems. Cyclic voltammetry measurements can provide interesting insights into the (supramolecular) properties of materials.70 Hence, we conducted CV experiments on the mononuclear complexes to examine the influence of the ligands on the electrochemical stability of the presented complexes.71 While 1[H](BF4)2 and 1[F](BF4)2 show quite regular cyclic voltammograms and respective E1/2 values of 0.688 V (1[H](BF4)2) and 0.732 V (1[F](BF4)2), 1[CF3](BF4)2 (E1/2 = 0.871 V) and especially 1[NO2](BF4)2 (E1/2 = 0.917 V) were quite difficult to study (see SI).65 Relatively high potentials were needed to oxidize the iron(II), and high sweep rates were required due to the instability of the formed iron(III) species. Even at 200 mV/s, the products were not stable and decomposition was observed.57,58 We can conclude that the oxidation of the complexes with increasingly stronger electron-withdrawing substituents gets more difficult and the ligands are even less suited to stabilizing the iron(III) cations. To gain more insight into the chemistry of the complexes and showcase some possible applications of the new systems, we performed complex-to-complex transformation experiments (Figure 8). While it is well-known that more electron-rich ligands form more stable complexes with iron(II),72 35 previous reports have mostly focused on varying the aniline subcomponents rather than the pyridylcarbaldehyde components. Starting from the most electron-deficient nitro ligands we can obtain a library of nitro and trifluoromethylene substituted complexes in a nearly statistical mixture upon addition of 7.00 equiv (1.17 equiv per exchanged aldehyde) of 5-(trifluoromethyl)-pyridyl-2-carbaldehyde and subsequent heating to 50 °C for 1 h. In this case, we cannot confidently deduce any selectivity or self-sorting from the NMR and mass spectra. A slight preference for the trifluoromethyl-substituted ligand might be deduced from the fact that the mass spectra show no species with exclusively nitro groups in the mixture, but this might also be due to a different ESI response factor (see SI). However, this mixture or pure 2[NO2](BF4)4 or pure 2[CF3](BF4)4 can all be selectively transformed to 2[F](BF4)4 upon addition of 7.00 equiv (1.17 equiv per exchanged aldehyde) of 5-fluoropyridyl-2-carbaldehyde and subsequent heating. This step is completely selective, yielding pure 2[F](BF4)4. Next, after purification by one precipitation cycle, this complex can finally be transformed into 2[H](BF4)4 upon addition of 7.00 equiv (1.17 equiv per exchanged aldehyde) of pyridyl-2-carbaldehyde and heating. Altogether, the selectivity follows the trends established by NMR- and UV−vis-spectroscopy and CV measurements.

Figure 6. Chemical shifts of the imine protons in 1[F](BF4)2 (red triangles), 1[NO2](BF4)2 (blue triangles), 1[CF3](BF4)2 (purple triangles), 2[F](BF4)4 (red squares), 2[NO2](BF4)4 (blue squares), and 2[CF3](BF4)4 (purple squares) plotted against the temperature (with lines to guide the eye).

presence of purely low-spin configurated complexes at around 270 K. With increasing temperature, all complexes show increasing shifts, especially so in the case of the mononuclear complexes: The stronger the electron-withdrawing effect in the used ligands, the stronger the effect on the observed shifts.65 This results in a maximum chemical shift of 24.4 ppm for the imine proton in 1[NO2](BF4)2 at 70 °C.48 A second effect is that, while the overall trend is maintained, the dinuclear complexes show significantly smaller shifts in the NMR spectrum upon heating.66−69 Most apparently, the structures, although closely related, show an intriguing range of colors, mirroring the different electronic properties of the ligands. 1[H](BF4)2 and 2[H](BF4)4 are purple, 1[CF3](BF4)2 and 2[CF3](BF4)4 have a similar, but darker color, whereas the nitro-derivatives are deep blue and the fluoro-derivatives are bright pink. All colors can be observed in solid state and in solution, and the absorbance was investigated by UV−vis spectroscopy as well (Figure 7). The color of the presented complexes is governed by the MLCTtransitions around 350 nm and the 1A1 → 1T1 transitions between 500 and 650 nm, directly reflecting the ligands electronic structures. More electron-withdrawing substituents

■

CONCLUSIONS We have synthesized and characterized a series of mononuclear and dinuclear complexes starting from commercially available amine backbones and pyridylcarbaldehydes with electronwithdrawing substituents. We have characterized the complexes in solid state by single crystal X-ray diffraction, in solution by (temperature dependent) NMR-spectroscopy, UV−vis spectroscopy, and CV measurements, and in gas phase by mass spectrometry. We have successfully correlated the properties of these complexes with the electronic properties of their constituent ligands. This enables the tuning of the oxidation

Figure 7. UV−vis spectra of 2[H](BF4)4 (black), 2[F](BF4)4 (red), 2[NO2](BF4)4 (blue), and 2[CF3](BF4)4 (purple) in acetonitrile, 200 μM, 298 K. Inset shows the region from 450 to 750 nm. G


Article

Inorganic Chemistry

Figure 8. Schematic representation of the complex to complex transformations.

potentials of those complexes, the adjustment of the ligand field splitting for possible applications as building blocks for spincrossover compounds, and their thermodynamic stability, allowing for complex-to-complex transitions. Finally, depending on the substituent, we observed reproducible anion−π interaction motifs in the solid state.

■

(3) Caulder, D. L.; Raymond, K. N. Supramolecules by design. Acc. Chem. Res. 1999, 32, 975−982. (4) Leininger, S.; Olenyuk, B.; Stang, P. J. Self-assembly of discrete cyclic nanostructures mediated by transition metals. Chem. Rev. 2000, 100, 853−908. (5) Seidel, S. R.; Stang, P. J. High-symmetry coordination cages via self-assembly. Acc. Chem. Res. 2002, 35, 972−983. (6) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Coordination assemblies from a Pd(II)-cornered square complex. Acc. Chem. Res. 2005, 38, 369−78. (7) McConnell, A.; Wood, C. R.; Neelakandan, P. P.; Nitschke, J. R. Stimuli responsive metal-ligand assemblies. Chem. Rev. 2015, 115, 7729−7793. (8) Moussa, J.; Amouri, H. Supramolecular assemblies based on organometallic Quinoid linkers: A new class of coordination networks. Angew. Chem., Int. Ed. 2008, 47, 1372−1380. (9) Oliveri, C. G.; Ulmann, P. A.; Wiester, M. J.; Mirkin, C. A. Heteroligated supramolecular coordination complexes formed via the halide-induced ligand rearrangement reaction. Acc. Chem. Res. 2008, 41, 1618−1629. (10) Amouri, H.; Desmarets, C.; Moussa, J. Confined nanospaces in metallocages: Guest molecules, encapsulated anions, and catalyst sequestration. Chem. Rev. 2012, 112, 2015−2041. (11) Ward, M. D.; Raithby, P. R. Functional behaviour from controlled self-assembly: Challenges and prospects. Chem. Soc. Rev. 2013, 42, 1619−1636. (12) Han, M.; Engelhard, D. M.; Clever, G. H. Self-assembled coordination cages based on banana-shaped ligands. Chem. Soc. Rev. 2014, 43, 1848−1860. (13) Pochorovski, I.; Diedrich, F. Development of redox-switchable Resorcin[4]arene cavitands. Acc. Chem. Res. 2014, 47, 2096−2105. (14) Cook, T. R.; Zheng, Y.-R.; Stang, P. J. Metal-organic frameworks and self-assembled supramolecular coordination complexes: Comparing and contrasting the design, synthesis, and functionality of metalorganic materials. Chem. Rev. 2013, 113, 734−777. (15) Harris, K.; Fujita, D.; Fujita, M. Giant hollow MnL2n spherical complexes: Structure, functionalisation and applications. Chem. Commun. 2013, 49, 6703−6712. (16) Chen, L.-J.; Yang, H.-B.; Shinoya, M. Chiral metallosupramolecular architectures. Chem. Soc. Rev. 2017, 46, 2555−2576. (17) Brock, A. J.; Al-Fayaad, H.; Pfrunder, M. C.; Clegg, J. K. In Functional Supramolecular Materials: From Surfaces to MOFs; Banerjee, R., Ed.; Royal Society of Chemistry: London, 2017. (18) Fiedler, D.; Leung, D. H.; Bergman, R. G.; Raymond, K. N. Selective molecular recognition, C-H bond activation, and catalysis in nanoscale reaction vessels. Acc. Chem. Res. 2005, 38, 349−358. (19) Yoshizawa, M.; Klosterman, J. K.; Fujita, M. Functional molecular flasks: New properties and reactions within discrete, selfassembled hosts. Angew. Chem., Int. Ed. 2009, 48, 3418−3438. (20) Leenders, S. H. A. M.; Gramaga-Doria, R.; de Bruin, B.; Reek, J. N. H. Transition metal catalysis in confined spaces. Chem. Soc. Rev. 2015, 44, 433−448. (21) Zarra, S.; Wood, D. M.; Roberts, D. A.; Nitschke, J. R. Molecular containers in complex chemical systems. Chem. Soc. Rev. 2015, 44, 419−432.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02412. Additional figures, experimental data and spectra (PDF) Accession Codes

CCDC 1573312−1573313 and 1573410−1573414 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]. uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Kari Rissanen: 0000-0002-7282-8419 Arne Lützen: 0000-0003-4429-0823 Present Address †

Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montréal, Québec H3A 0B8, Canada. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial support by Deutsche Forschungsgemeinschaft (DFG SFB 813) and the Academy of Finland (K.R.: project no’s. 263256, 265328, and 292746) is gratefully acknowledged. N.S. thanks Evonik Foundation for a doctoral scholarship and German Academic Exchange Service DAAD for a travel grant. J. A. Wilms and M. Engeser are acknowledged for providing CV equipment.

■

REFERENCES

(1) Lehn, J. M. Supramolecular Chemistry: Concepts and perspectives; VCH: Weinheim, 1995. (2) Steed, J. W.; Atwood, J. L. Supramolecular Chemistry: A Concise Introduction; Wiley: Chichester, 2000. H


Article

Inorganic Chemistry (22) Brown, C. J.; Toste, F. D.; Bergman, R. G.; Raymond, K. N. Supramolecular catalysis in metal-ligand cluster hosts. Chem. Rev. 2015, 115, 3012−3035. (23) Hannon, M. J. Supramolecular DNA-recognition. Chem. Soc. Rev. 2007, 36, 280−295. (24) Cook, T. R.; Vajpayee, V.; Lee, M. H.; Stang, P. J.; Chi, K.-W. Biomedical and biochemical applications of self-assembled metallacycles and metallacages. Acc. Chem. Res. 2013, 46, 2464−2474. (25) Wiley, C. A.; Holloway, L. R.; Miller, T. F.; Lyon, Y.; Julian, R. R.; Hooley, R. J. Electronic effects on narcissistic self-sorting in multicomponent self-assembly of Fe-iminopyridine meso-helicates. Inorg. Chem. 2016, 55, 9805−9815. (26) Kershaw Cook, L. J.; Kulmaczewski, R.; Mohammed, R.; Dudley, S.; Barrett, S. A.; Little, M. A.; Deeth, R. J.; Halcrow, M. A. A unified treatment of the relationship between ligand substituents and spin state in a family of iron(II) complexes. Angew. Chem., Int. Ed. 2016, 55, 4327−4331. (27) Edder, C.; Piguet, C.; Bernadellini, G.; Mareda, J.; Bochet, C. G.; Bünzli, J.-C.; Hopfgartner, G. Unusual electronic effects of electronwithdrawing sulfonamide groups in optically and magnetically active self-assembled noncovalent heterodimetallic d-f podates. Inorg. Chem. 2000, 39, 5059−5073. (28) Bohn, A.; Sénéchall-David, K.; Vanoutryve, J.; Guillot, R.; Rivière, E.; Banse, F. Synthesis and characterization of iron(II) complexes with a BPMEN-type liagnd bearing π-accepting nitro groups. Eur. J. Inorg. Chem. 2017, 24, 3057−3063. (29) Lewis, J. E. M.; Beer, P. D.; Loeb, S. J.; Goldup, S. M. Metal ions in the synthesis of interlocked molecules and materials. Chem. Soc. Rev. 2017, 46, 2577−3591. (30) Nitschke, J. R. Construction, substitution, and sorting of metallo-organic structures via subcomponent self-assembly. Acc. Chem. Res. 2007, 40, 103−112. (31) Castilla, A. W.; Ramsey, W. J.; Nitschke, J. R. Stereochemistry in subcomponent self-assembly. Acc. Chem. Res. 2014, 47, 2063−2073. (32) Young, M. C.; Holloway, L. R.; Hooley, R. J. A supramolecular sorting hat: Stereocontrol in metal-ligand self-assembly by complementary hydrogen bonding. Angew. Chem., Int. Ed. 2014, 53, 9832− 9836. (33) Frischmann, P. D.; Kunz, V.; Stepanenko, V.; Würthner, F. Subcomponent self-assembly of a 4 nm M4L6 tetrahedron with ZnII vertices and perylene bisimide dye edges. Chem. - Eur. J. 2015, 21, 2766−2769. (34) Beves, J. E.; Campbell, C. J.; Leigh, D. A.; Pritchard, R. G. A Solomon link through an interwoven molecular grid. Angew. Chem., Int. Ed. 2013, 52, 6464−6467. (35) Grommet, A. B.; Nitschke, J. R. Direct phase transfer of an FeII4L4 cage and encapsulated cargo. J. Am. Chem. Soc. 2017, 139, 2176−2179. (36) Fulmer, G. R.; Miller, A. J. M.; Sherden, N. H.; Gottlieb, H. E.; Nudelman, A.; Stoltz, B. M.; Bercaw, J. E.; Goldberg, K. I. NMRchemical shifts of trace impurities: Common laboratory solvents, organics, and gases in deuterated solvents relevant to the organometallic chemist. Organometallics 2010, 29, 2176−2179. (37) Please note, due to the partially occupied paramagnetic highspin states it was exceedingly difficult to obtain 13C NMR spectra, especially of the mononuclear complexes. Thus, not all carbon atoms appear in the spectra, although we accumulated 5k scans at 176.1 MHz (Bruker Avance III HD Ascend 700) when trying to record the spectra. No 13C NMR could be recorded for 1[NO2](BF4)2. (38) Mealli, C.; Lingafelter, E. C. The X-ray crystal structure of a lowspin pseudo-octahedral complex of iron(II). J. Chem. Soc. D 1970, 885. (39) Sarma, R. J.; Otto, S.; Nitschke, J. R. Disulfides, imines, and metal coordination within a single system: Interplay between three dynamic equilibria. Chem. - Eur. J. 2007, 13, 9542−9546. (40) Peters, W.; Fuchs, M.; Sicius, H.; Kuchen, W. The first application of 2D-NMR to the spectral analysis of a paramagnetic complex. Example: Bis[R-(+)-P,P-diethylthiophosphinic acid-N-αmethylbenylamido]nickel(II). Angew. Chem., Int. Ed. Engl. 1985, 24, 231−233.

(41) Luchinat, C.; Steuernagel, S.; Turano, P. Applications of 2D NMR techniques to paramagnetic systems. Inorg. Chem. 1990, 29, 4351−4353. (42) Rigaku Oxford Diffraction, 2015, CrysAlisPro Software system, version 1.171.38.41, Rigaku Corporation, Oxford, UK. (43) Sheldrick, G. M. SHELXT − Integrated space-group and crystalstructure determination. Acta Crystallogr., Sect. A: Found. Adv. 2015, A71, 3−8. (44) Sheldrick, G. M. Crystal structure refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, C71, 3−8. (45) Dolomanov, O. V.; Bourhis, L. J.; Gildea, R. J.; Howard, J. A. K.; Puschmann, H. OLEX2: A complete structure solution, refinement and analysis program. J. Appl. Crystallogr. 2009, 42, 339−341. (46) Farrugia, L. J. WinGX and Ortep for Windows: An update. J. Appl. Crystallogr. 2012, 45, 849−854. (47) Nitschke, J. R. Dynamic covalent and supramolecular direction of the synthesis and reassembly of copper(I) complexes. Angew. Chem., Int. Ed. 2004, 43, 3073−3075. (48) Hoselton, A.; Wilson, L. J.; Drago, R. S. Substituent effects on the spin equilibrium observed with hexadentate ligands of iron(II). J. Am. Chem. Soc. 1975, 97, 1722−1729. (49) Vellas, S. K.; Lewis, J. E.; Shankar, M.; Sagatova, A.; Tyndall, J. D. A.; Monk, B. C.; Fitchett, C. M.; Hanton, L. R.; Crowley, J. D. [Fe2L3]4+ cylinders derived from bis(bidentate) 2-pyridyl-1,2,3-triazole “click” ligands: Synthesis, structures and exploration of biological activity. Molecules 2013, 18, 6383−6407. (50) The first example of this class of molecules was presented here: Hannon, M. J.; Painting, C. L.; Jackson, A.; Hamblin, J.; Errington, W. An inexpensive approach to supramolecular architecture. Chem. Commun. 1997, 1807−1808. (51) Lazar, H. A.; Forestier, T.; Barrett, S. A.; Kilner, C. A.; Létard, J. F.; Halcrow, M. A. Thermal and light-induced spin-crossover in salts of the heptadentate complex [tris(4-{pyrazol-3-yl}-3-aza-3-butenyl)amine]iron(II). Dalton Trans. 2007, 4276−4285. (52) Struch, N.; Wagner, N.; Schnakenburg, G.; Weisbarth, R.; Klos, S.; Beck, J.; Lützen, A. Thiazolylimines as novel ligand systems for spin-crossover centred near room temperature. Dalton Trans. 2016, 45, 14023−14029. (53) Schottel, B. L.; Chifotides, H. T.; Dunbar, K. R. Anion-π interactions. Chem. Soc. Rev. 2008, 37, 68−83. (54) Wang, D.-X.; Wang, M.-X. Anion-π interactions: Generality, binding strengths, and structure. J. Am. Chem. Soc. 2013, 135, 892− 897. (55) Robertazzi, A.; Krull, F.; Knapp, E.-W.; Gamez, P. Recent advances in anion-π interactions. CrystEngComm 2011, 13, 3293− 3300. (56) Giese, M.; Albrecht, M.; Rissanen, K. Experimental investigations of anion-π interactions − applications and biochemical relevance. Chem. Commun. 2016, 52, 1778−1795. (57) Chifotides, H. T.; Dunbar, K. R. Anion-π interactions in supramolecular architectures. Acc. Chem. Res. 2013, 46, 894−906. (58) Gamez, P.; Mooibroek, T. J.; Teat, S. J.; Reedijk. Anion binding involving π-acidic heteroaromatic rings. Acc. Chem. Res. 2007, 40, 435−444. (59) Interestingly, we also found other derivatives of this specific ligand system to crystallize easily, for example the tetranuclear derivative: Struch, N.; Topić, F.; Rissanen, K.; Lützen, A. Electron deficient trifluoromethyl-substituted sub-components affect the properties of M4L4 tetrahedral cages. Dalton Trans. 2017, 46, 10809−10813. (60) Tuna, F.; Lees, M. R.; Clarcson, G. J.; Hannon, M. J. Readily prepared metallo-supramolecular triple helicates designed to exhibit spin-crossover behaviour. Chem. - Eur. J. 2004, 10, 5737−5750. (61) Gütlich, P.; Hauser, A.; Spiering, H. Thermal and optical switching of iron(II) complexes. Angew. Chem., Int. Ed. Engl. 1994, 33, 2024−2054. (62) Struch, N.; Brandenburg, J. G.; Schnakenburg, G.; Wagner, N.; Beck, J.; Grimme, S.; Lützen, A. A case study on mechanical strain in I


Article

Inorganic Chemistry supramolecular complexes to manipulate the spin state of iron(II) centres. Eur. J. Inorg. Chem. 2015, 2015, 5503−5510. (63) Isley, W. C., III; Zarra, S.; Carlson, R. K.; Bilbesi, R. A.; Ronson, T. K.; Nitschke, J. R.; Gagliardi, L.; Cramer, C. J. Predicting paramagnetic 1H-NMR chemical shifts and state-energy separations in spin-crossover host-guest systems. Phys. Chem. Chem. Phys. 2014, 16, 10620−10628. (64) Danjanovic, M.; Samuel, P. P.; Roesky, H. W.; Enders, M. NMR-analysis of an Fe(I)-carbene complex with strong magnetic aniosotropy. Dalton Trans. 2017, 46, 5159−5169. (65) A rough correlation with Hammett parameters is observed. This was also observed in ref 7a. Nonetheless quite some scattering was observed here. (66) This trend can also be observed in a small number of systems with temperature-dependent data presented in the literature. Negative cooperativity through mechanical coupling was proposed as the underlying mechanism. (67) Telfer, S. G.; Bocquet, B.; Williams, A. F. Thermal spincrossover in binuclear iron(II) helicates: Negative cooperativity and a mixed spin state in solution. Inorg. Chem. 2001, 40, 4818−4820. (68) Charbonniére, L. J.; Williams, A. F.; Piguet, C.; Bernadinelli, G.; Rivara-Minten, E. Structural, magnetic, and electrochemical properties of dinuclear triple helices: Comparison with their monodentate analogues. Chem. - Eur. J. 1998, 4, 485−493. (69) Piguet, C.; Rivara-Minten, E.; Bernadelli, G.; Bünzli, J.-C.; Hopfgartner, G. Non-covalent lanthanide podates with predetermined physicochemical properties: Iron(II) spin-state equilibria in selfassembled heterodinuclear d-f supramolecular complexes. J. Chem. Soc., Dalton Trans. 1997, 3, 421−434. (70) Gütz, C.; Hovorka, R.; Struch, N.; Bunzen, J.; Meyer-Eppler, G.; Qu, Z.-W.; Grimme, S.; Topić, F.; Rissanen, K.; Cetina, M.; Engeser, M.; Lü tzen, A. Enantiomerically pure trinuclear helicates via diastereoselective self-assembly anc characterization of their redox chemistry. J. Am. Chem. Soc. 2014, 136, 11830−11838. (71) Gennarini, F.; David, R.; López, I.; Le Mest, Y.; Régelier, M.; Belle, C.; Thibon-Pourret, A.; Jamet, H.; Le Poul, N. Influence of asymmetry on the redox properties of phenoxo- and hydroxo-bridged dicopper complexes: Spectroelectrochemical and theoretical studies. Inorg. Chem. 2017, 56, 7707−7719. (72) Wood, C. S.; Ronson, T. K.; Belenguer, A. M.; Holstein, J. J.; Nitschke, J. R. Two-stage directed self-assembly of a cyclic [3]catenane. Nat. Chem. 2015, 7, 354−358.

J


Electron-Deficient Pyridylimines: Versatile Building Blocks for

Recommend Documents