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Iridium Cyclometalated Complexes with Axial Symmetry. Synthesis and Photophysical Properties of a trans-Biscyclometalated Complex Containing the Terdentate Ligand 2,6-Diphenylpyridine

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posted on 22.03.2004, 00:00 by Matthew Polson, Sandro Fracasso, Valerio Bertolasi, Marcella Ravaglia, Franco Scandola
The first example of an iridium biscyclometalated complex with a C∧N∧C 2,6-diphenylpyridine (dppy)-type ligand, [(4‘-(4-bromophenyl)-2:2‘,6‘:2‘ ‘-terpyridine)Ir(2,6-diphenyl-4-(4-tolyl)pyridine)](NO3) (1), has been synthesized and characterized by various techniques such as X-ray crystallography, mass spectrometry, 1H and 13C NMR, cyclic voltammetry, and both steady-state and time-resolved emission and absorption studies. Preliminary density functional theory calculations have also been conducted. 1 crystallizes in the monoclinic space group P21/n. The crystallographic data are as follows:  C45H31BrN4IrO3·2H2O, a = 17.4308(4) Å, b = 9.0312(2) Å, c = 26.7601(7) Å, β = 104.496(1)°, V = 4078.5(2) Å3, Z = 4. The relatively long Ir−C distances (2.122 and 2.094 Å) reflect the strong mutual trans effect of the cyclometalating carbons. The complex exhibits strong visible absorption and long-lived (1.7 μs) emission (λmax, 690 nm) in room temperature solution. The inherent asymmetry of the coordination environment offers a unique directional character to the emitting excited state, which is predominately ligand-to-ligand charge transfer (dppy → 2,2‘:6‘,2‘ ‘-terpyridine) in nature.

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