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Synthesis, Structural Characterization, and Phosphorescence Properties of Trigonal Zn(II) Carbene Complexes.

Stefan KoopOndřej MrózekLars JaniakAndrey BelyaevMarkus PutscherChristel M MarianAndreas Steffen
Published in: Inorganic chemistry (2023)
The sterically demanding N -heterocyclic carbene ITr ( N , N '-bis(triphenylmethyl)imidazolylidene) was employed for the preparation of novel trigonal zinc(II) complexes of the type [ZnX 2 (ITr)] [X = Cl ( 1 ), Br ( 2 ), and I ( 3 )], for which the low coordination mode was confirmed in both solution and solid state. Because of the atypical coordination geometry, the reactivity of 1-3 was studied in detail using partial or exhaustive halide exchange and halide abstraction reactions to access [ZnLCl(ITr)] [L = carbazolate ( 4 ), 3,6-di- tert -butyl-carbazolate ( 5 ), phenoxazine ( 6 ), and phenothiazine ( 7 )], [Zn(bdt)(ITr)] (bdt = benzene-1,2-dithiolate) ( 8 ), and cationic [Zn(μ 2 -X)(ITr)] 2 [B(C 6 F 5 ) 4 ] 2 [X = Cl ( 9 ), Br ( 10 ), and I ( 11 )], all of which were isolated and structurally characterized. Importantly, for all complexes 4-11 , the trigonal coordination environment of the Zn II ion is maintained, demonstrating a highly stabilizing effect due to the steric demand of the ITr ligand, which protects the metal center from further ligand association. In addition, complexes 1-3 and 8-11 show long-lived luminescence from triplet excited states in the solid state at room temperature, according to our photophysical studies. Our quantum chemical density functional theory/multireference configuration interaction (DFT/MRCI) calculations reveal that the phosphorescence of 8 originates from a locally excited triplet state on the bdt ligand. They further suggest that the phenyl substituents of ITr are photochemically not innocent but can coordinate to the electron-deficient metal center of this trigonal complex in the excited state.
Keyphrases
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