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Pseudo‐Octahedral Iron(II) Complexes with Near‐Degenerate Charge Transfer and Ligand Field States at the Franck‐Condon Geometry
Author(s) -
Moll Johannes,
Naumann Robert,
Sorge Lukas,
Förster Christoph,
Gessner Niklas,
Burkhardt Lukas,
Ugur Naz,
Nuernberger Patrick,
Seidel Wolfram,
Ramanan Charusheela,
Bauer Matthias,
Heinze Katja
Publication year - 2022
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202201858
Subject(s) - excited state , ligand (biochemistry) , chemistry , ligand field theory , photochemistry , octahedral molecular geometry , crystallography , spectrochemical series , spectroscopy , non innocent ligand , metal , atomic physics , crystal structure , ion , organic chemistry , physics , biochemistry , receptor , quantum mechanics
Increasing the metal‐to‐ligand charge transfer (MLCT) excited state lifetime of polypyridine iron(II) complexes can be achieved by lowering the ligand's π* orbital energy and by increasing the ligand field splitting. In the homo‐ and heteroleptic complexes [Fe(cpmp) 2 ] 2+ ( 1 2+ ) and [Fe(cpmp)(ddpd)] 2+ ( 2 2+ ) with the tridentate ligands 6,2’’‐carboxypyridyl‐2,2’‐methylamine‐pyridyl‐pyridine (cpmp) and N , N ’‐dimethyl‐ N , N ’‐di‐pyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) two or one dipyridyl ketone moieties provide low energy π* acceptor orbitals. A good metal‐ligand orbital overlap to increase the ligand field splitting is achieved by optimizing the octahedricity through CO and NMe units between the coordinating pyridines which enable the formation of six‐membered chelate rings. The push‐pull ligand cpmp provides intra‐ligand and ligand‐to‐ligand charge transfer (ILCT, LL'CT) excited states in addition to MLCT excited states. Ground and excited state properties of 1 2+ and 2 2+ were accessed by X‐ray diffraction analyses, resonance Raman spectroscopy, (spectro)electrochemistry, EPR spectroscopy, X‐ray emission spectroscopy, static and time‐resolved IR and UV/Vis/NIR absorption spectroscopy as well as quantum chemical calculations.