A heteroleptic push-pull substituted iron(II) bis(tridentate) complex with low-energy charge-transfer states

Andreas K.C. Mengel, Christoph Förster, Aaron Breivogel, Katharina Mack, Julian R. Ochsmann, Frederic Laquai, Vadim Ksenofontov, Katja Heinze

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49 Scopus citations

Abstract

A heteroleptic iron(II) complex [Fe(dcpp)(ddpd)]2+ with a strongly electron-withdrawing ligand (dcpp, 2,6-bis(2-carboxypyridyl)pyridine) and a strongly electron-donating tridentate tripyridine ligand (ddpd, N,N'-dimethyl-N,N'-dipyri-dine-2-yl-pyridine-2,6-diamine) is reported. Both ligands form six-membered chelate rings with the iron center, inducing a strong ligand field. This results in a high-energy, highspin state (5T2, (t2g)4(eg×)2) and a low-spin ground state (1A1, (t2g)6(eg×)0). The intermediate triplet spin state (3T1, (t2g)5(eg×)1) is suggested to be between these states on the basis of the rapid dynamics after photoexcitation. The low-energy π×orbitals of dcpp allow low-energy MLCT absorption plus additional low-energy LL 'CT absorptions from ddpd to dcpp. The directional charge-transfer character is probed by electrochemical and optical analyses, Möβbauer spectroscopy, and EPR spectroscopy of the adjacent redox states [Fe(dcpp)(ddpd)]3+ and [Fe(dcpp)(ddpd)]+ , augmented by density functional calculations. The combined effect of push-pull substitution and the strong ligand field paves the way for long-lived charge-transfer states in iron(II) complexes.

Original languageEnglish (US)
Pages (from-to)704-714
Number of pages11
JournalChemistry - A European Journal
Volume21
Issue number2
DOIs
StatePublished - Jan 7 2015

Keywords

  • Charge transfer
  • Excited states
  • Iron
  • Ligand field splitting
  • Tridentate ligands

ASJC Scopus subject areas

  • Chemistry(all)

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