Electronic Properties of Oxidized Cyclometalated Diiridium Complexes: Spin Delocalization Controlled by the Mutual Position of the Iridium Centers

Abstract

Four cyclometalated diiridium complexes, with IrCp*Cl (Cp*=η5‐C5Me5−) 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.

A conjugated diosma-octacyclic complex and its mixed-valence singly reduced state

“…S5, ESI †), in combination with the moderate ΔE 1/2 value (Table 1), permits to assign 4 − as a class I rather than class II M-V system, with trapped valences according to the Robin-Day classification; 65 although, most M-V systems have been based on distinct metal oxidation states. [66][67][68][69][70] Recording of the electronic absorption spectrum of 4 − was then attempted to identify a low-lying intervalence charge-transfer (IVCT) absorption, which would otherwise verify the class II M-V assignment.…”

Chiral (Pyridine)-(Imidazoline) NCN′ Pincer Palladium(II) Complexes: Convenient Synthesis via C–H Activation and Characterization

“…Solvents were dried with standard methods and freshly distilled prior to use if needed. 3-(2-Pyridyl)­benzoic acids 1 , 1,3-bis­(2-pyridyl)­benzene 5 , bis­(imidazoline)­benzene 7 , , and the sulfonimines 10 and 12 were prepared according to the literature methods. All other chemicals were used as purchased.…”

Electronic Communication in Binuclear Osmium- and Iridium-Polyhydrides

“…The search for efficient π-linkers (bridging ligands), which promote the cooperative effect between the redox active centers through electronic coupling pathways, is central for success. Unsaturated carbon chains, aromatic polycycles, , aromatic N -heterocycles, bisdioxolenes, bisdithiolenes, dithiolate, cyanide, and cyanamides have been mainly employed so far, as bridging ligands, to provide electronical coupling between metals.…”