Multimetallic compounds containing cyclometalated Ir(III) units: Synthesis, structure, electrochemistry and photophysical properties

The reaction of the cyclometalated IrIII dimer [{(ppy)2Ir}2(μ-Cl)2] (ppyH = 2-phenylpyridine) with silver triflate followed by a multidentate ligand [1,4-bis[3-(2-pyridyl)pyrazolylmethyl]benzene (bppb), 1,3,5-tri[3-(2-pyridyl)pyrazolylmethyl]-2,4,6-trimethylbenzene (tppb), 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz), 2-chloro-4,6-bis(dipyridin-2-ylamino)-1,3,5-triazine (cddt) or 2,4,6-tris(dipyridin-2-ylamino)-1,3,5-triazine (tdat)] afforded di- or trinuclear compounds: [{Ir(ppy)2}2(μ-bppb)](OTf)2 (1), [{Ir(ppy)2}3(μ-tppb)](OTf)3 (2), [{Ir(ppy)2}2(μ-tptz-OH)](OTf) (3), [{Ir(ppy)2}2(μ-cddt)](OTf)2 (4) and [{Ir(ppy)2}2(μ-tdat)](OTf)2 (5). All of these compounds contain cationic metal cores with corresponding triflate counter anions. The molecular structures of 1–4 reveal that the structural feature of the Ir(ppy)2 center of the starting precursor is conserved in the products. Also, because of the nature of the ligands, there is virtually no electronic communication between the IrIII centers except in 3 where a ring hydroxylation at the triazine carbon atom is effected upon metalation. Compounds 1–5 are robust in solution where they retain their structural integrity. The UV–Vis and emission spectra of 1–5 compounds are very similar to each other with the exception of 3 which seems to possess a different electronic structure. All the compounds are luminescent at room temperature. The emission bands indicate significant contribution from 3LC. Increase in the number of ‘Ir(ppy)2’ units does not have any effect on emission color.

Use of multidentate ligands has afforded a number of multinuclear cyclometalated Ir(III) compounds including a dinuclear compound in which the central triazine ring of the bridging ligand is hydroxylated.Figure optionsDownload as PowerPoint slideResearch highlights
► Synthesis of multinuclear cyclometalated Ir(III) compounds.
► Nitrogen donor bridging ligands promotes multi-nuclear metal assembly.
► Solution and solid-state structural characterization of multinuclear cyclometalated Ir(III) compounds.
► Photoluminescence behavior of multinuclear cyclometalated Ir(III) compounds.