Premium
Electronic Properties of Oxidized Cyclometalated Diiridium Complexes: Spin Delocalization Controlled by the Mutual Position of the Iridium Centers
Author(s) -
Hu Yu Xuan,
Zhang Jing,
Zhang Fangfang,
Wang Xiaoyan,
Yin Jun,
Hartl František,
Liu Sheng Hua
Publication year - 2020
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.201904894
Subject(s) - iridium , delocalized electron , chemistry , ligand (biochemistry) , crystallography , benzene , electron paramagnetic resonance , molecular orbital , photochemistry , molecule , nuclear magnetic resonance , biochemistry , physics , receptor , organic chemistry , catalysis
Abstract Four cyclometalated diiridium complexes, with IrCp*Cl (Cp*=η 5 ‐C 5 Me 5 − ) termini bridged by 1,4‐ and 1,3‐bis( p ‐tolyliminoethyl)benzene ( 1 , 2 ), or 1,4‐ and 1,3‐bis(2‐pyridyl)benzene ( 3 , 4 ), were prepared and characterized by nuclear magnetic resonance (NMR) spectroscopy and single‐crystal X‐ray diffraction (complexes 1 , 2 , and 4 ). The two iridium centers in complexes 1 and 3 are thus bound at the central benzene ring in the para ‐position ( trans ‐Ir2), whereas those in complexes 2 and 4 are in the meta ‐position ( cis ‐Ir2). Cyclic voltammograms of all four complexes show two consecutive one‐electron oxidations. The potential difference between the two anodic steps in 1 and 3 is distinctly larger than that for 2 and 4 . The visible–near‐infrared (NIR)–short‐wave infrared (SWIR) absorption spectra of trans ‐Ir2 monocations 1 + and 3 + are markedly different from those of cis ‐Ir2 monocations 2 + and 4 + . Notably, strong near‐infrared electronic absorption appears only in the spectra of 1 + and 3 + whereas 2 + and 4 + absorb only weakly in the NIR‐SWIR region. Combined DFT and TD‐DFT calculations have revealed that (a) 1 + and 3 + (the diiridium‐benzene trans ‐isomers) display the highest occupied spin‐orbitals (HOSO) and the lowest unoccupied spin‐orbital (LUSO) evenly delocalized over both molecule halves, and (b) their electronic absorptions in the NIR‐SWIR region are attributed to mixed metal‐to‐ligand and ligand‐to‐ligand charge transfers (MLCT and LLCT). In contrast, cis ‐isomers 2 + and 4 + do not feature this stabilizing π‐delocalization but a localized mixed‐valence state showing a weak intervalence charge‐transfer (IVCT) absorption in the SWIR region.