Tris(bipyridine)iron(II) chloride

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Tris(bipyridine)iron(II) chloride
Fe(bipy)3Cl2.svg
Identifiers
3D model (JSmol)
ChemSpider
PubChem CID
  • InChI=1S/3C10H8N2.2ClH.Fe/c3*1-3-7-11-9(5-1)10-6-2-4-8-12-10;;;/h3*1-8H;2*1H;/q;;;;;+2/p-2
    Key: GBRPARYPGGYWHF-UHFFFAOYSA-L
  • [n+]12ccccc1c1cccc[n+1]1[Fe-4]234([n+]1ccccc1c1cccc[n+1]13)[n+]1ccccc1c1cccc[n+1]14.[Cl-].[Cl-]
Properties
C30H24Cl2FeN6
Molar mass 595.31 g·mol−1
Appearancered solid
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Tris(bipyridine)iron(II) chloride is the chloride salt of the coordination complex tris(bipyridine)iron(II), [Fe(C10H8N2)3]2+ (often shortened to [Fe(bipy3]2+). It is a red, water soluble solid. It is one of the most studied transition metal complexes of 2,2'-bipyridine.

Contents

Structure

Tris(bipyridine)iron(II) center features an octahedral Fe(II) center bound to three bipyridine ligands. As confirmed many times by x-ray crystallography, the dication is octahedral, the Fe(II) center occupying a chiral pocket. The cation has idealized D3 symmetry, and as such both Δ and Λ are observed. The Fe-N distances are near 196 picometers, consistent with low spin complex. [1]

The complex has been isolated as salts with many anions. [2] The chloride salt is readily soluble in aqueous solution, and the hexafluorophosphate salt is soluble in organic solvents such as nitriles. [3]

Synthesis and reactions

The sulfate salt [Fe(bipy)3]SO4 is produced by combining ferrous sulfate with excess bipy in aqueous solution. [4] This result illustrates the preference of Fe(II) for bipyridine vs water. The potentials for |[Fe(bipy)3]2+/3+ and [Fe(phen)3]2+/3+ are very similar. [5]

Addition of cyanide to an aqueous solution of [Fe(bipy)3]SO4 precipitates Fe(bipy)2(CN)2. [6]

[Fe(bipy)3]2+ salts can also be prepared from Iron(II) tetrafluoroborate in the solid state via mechanochemistry. [7]

Electronic absorption spectrum

The electronic absorption spectrum of [Fe(bipy)3]2+ features a metal-to-ligand charge-transfer (MLCT) band at 540 nm (ε = 8,000‑14,000 M−1cm−1), a weak shoulder due to the spin-forbidden 3MLCT transition at 640 nm (ε < 50 M−1cm−1), a higher lying MLCT band at 350 nm (ε = 6,000‑10,500 M−1cm−1), and a bipy π‑π* transition at 290 nm (ε = 40,000‑70,000 M−1cm−1). [8] [9] [10]

Photoinduced Dynamics

In contrast to tris(bipyridine)ruthenium(II), this iron complex is not a useful photosensitizer because its excited states relax too rapidly, a consequence of the primogenic effect.

[Fe(bipy)3]2+ is a model system for photoinduced spin crossover/Light Induced Excited Spin State Trapping (LIESST). Upon photoexcitation of its 1MLCT band, the molecule undergoes intersystem crossing to the high-spin 5d–d state in less than 100 fs. [10] The lifetime of the high-spin state is 650 ps. The large changes in electronic structure, spin state, and Fe–N bond length in the high-spin state lead to strong transient signals in the time-resolved X-ray absorption spectra (XAS) and X-ray emission spectra (XES). Time-resolved Fe K-edge EXAFS has revealed a 0.203 ± 0.008 Å increase in Fe–N bond length in the high-spin state. [11] The large transient signals and ultrafast formation of the high-spin state has led to the application of [Fe(bipy)3]2+ as a reference compound used at many synchrotron beamlines to find temporal overlap of the laser pump and X-ray probe pulses and to measure the instrument response function (IRF). [12] The time resolution of these experiments is typically limited by the ~70 ps duration of the X-ray pulses, so the formation of the high-spin state is effectively instantaneous and the rise of the transient signal is IRF-limited. Since the advent of X-ray free-electron laser (XFEL) and high harmonic generation sources capable of producing sub-picosecond pulses of X-rays, the ultrafast spin-crossover dynamics of [Fe(bipy)3]2+ and related complexes have been a popular target for femtosecond X-ray spectroscopy experiments. The improved time resolution of these experiments enabled detection of the short-lived intermediate 3d–d state, whose lifetime was measured with Fe Kβ XES to be 58 fs in [Fe(bipy)3]2+ [13] and with Fe M2,3-edge XANES to be 39 fs in tris(o-phenanthroline)iron(II). [14]

References

  1. ↑ Chàvez, Jennifer E.; Crotti, Corrado; Zangrando, Ennio; Farnetti, Erica (2016). "Iron complexes with nitrogen bidentate ligands as green catalysts for alcohol oxidation". Journal of Molecular Catalysis A: Chemical. 421: 189–195. doi:10.1016/j.molcata.2016.05.023.
  2. ↑ Batten, Stuart R.; Murray, Keith S.; Sinclair, Nathan J. (2000). "Tris(2,2′-bipyridyl- N , N ′)iron(II) diperchlorate". Acta Crystallographica Section C Crystal Structure Communications. 56 (8): e320. Bibcode:2000AcCrC..56E.320B. doi:10.1107/S0108270100009185.
  3. ↑ Maurer, A. B.; Meyer, G. J. (2020). "Stark spectroscopic evidence that a spin change accompanies light absorption in transition metal polypyridyl complexes". Journal of the American Chemical Society. 142 (15): 6847–6851. doi:10.1021/jacs.9b13602. PMID   32216315.
  4. ↑ Avdeeva, Varvara V.; Vologzhanina, Anna V.; Goeva, Lyudmila V.; Malinina, Elena A.; Kuznetsov, Nikolay T. (2014). "Boron Cluster Anions [BnHn]2– ( n = 10, 12) in Reactions of Iron(II) and Iron(III) Complexation with 2,2′-Bipyridyl and 1,10-Phenanthroline". Zeitschrift für Anorganische und Allgemeine Chemie. 640 (11): 2149–2160. doi:10.1002/zaac.201400137.
  5. ↑ Wong, C. L.; Kochi, J. K. (1979). "Electron Transfer with Organometals. Steric Effects as Probes for Outer-Sphere and Inner-Sphere Oxidations of Homoleptic Alkylmetals with Iron(III) and Iridate(IV) Complexes". Journal of the American Chemical Society. 101 (19): 5593–5603. Bibcode:1979JAChS.101.5593W. doi:10.1021/ja00513a024.
  6. ↑ Schilt, Alfred A. (1970). "Dicyanobis(1,10-phenanthroline)Iron(II) and Dicyanobis(2,2′-bipyridine)iron(II)". Inorganic Syntheses. Vol. 12. pp. 247–251. doi:10.1002/9780470132432.ch43. ISBN   978-0-470-13171-8.
  7. ↑ T. Munir, E. Aneggi, W. Baratta, L. Genesin, F. Trigatti, D. Zuccaccia. Rapid and Efficient Solid‐state Mechanosynthesis of Bipyridine Metal Complexes. Chemistry–A European Journal, 2025, e202501214. doi.org/10.1002/chem.202501214
  8. ↑ Maurer, A. B.; Meyer, G. J. (2020). "Stark spectroscopic evidence that a spin change accompanies light absorption in transition metal polypyridyl complexes". Journal of the American Chemical Society. 142 (15): 6847–6851. doi:10.1021/jacs.9b13602. PMID   32216315.
  9. ↑ Schmid, L.; Chábera, P.; Rüter, I.; et al. (2022). "Borylation in the second coordination sphere of FeII cyanido complexes and its impact on their electronic structures and excited-state dynamics". Inorganic Chemistry. 61 (40): 15853–15863. doi:10.1021/acs.inorgchem.2c01667. PMC   9554916 . PMID   36167335.
  10. 1 2 Auböck, G.; Chergui, M. (2015). "Sub-50-fs photoinduced spin crossover in [Fe(bpy)3]2+". Nature Chemistry. 7 (8): 629–633. doi:10.1038/nchem.2305.
  11. ↑ Gawelda, W.; Pham, V.-T.; van der Veen, R. M.; et al. (2009). "Structural analysis of ultrafast extended X-ray absorption fine structure with subpicometer spatial resolution: Application to spin crossover complexes". The Journal of Chemical Physics. 130 (12): 124520. doi:10.1063/1.3081884. hdl:10261/65191. PMID   19334864.
  12. ↑ Fondell, M.; Eckert, S.; Jay, R. M.; et al. (2017). "Time-resolved soft X-ray absorption spectroscopy in transmission mode on liquids at MHz repetition rates". Structural Dynamics. 4 (5): 054902. doi:10.1063/1.4993755. PMC   5555770 . PMID   28852689.
  13. ↑ Kjær, K. S.; Van der Driel, T. B.; Harlang, T. C. B.; et al. (2019). "Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy". Chemical Science. 10 (22): 5749–5760. doi:10.1039/C8SC04023K. PMID   31293761.
  14. ↑ Zhang, K.; Ash, R.; Girolami, G. S.; Vura-Weis, J. (2019). "Tracking the metal-centered triplet in photoinduced spin crossover of Fe(Phen)32+ with tabletop femtosecond M-edge X-ray absorption near-edge structure spectroscopy". Journal of the American Chemical Society. 141 (43): 17180–17188. doi:10.1021/jacs.9b07332. PMID   31587557.
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