Novel carbon-centered heteroscorpionate ligands: Cu(I) complexes and luminescence properties

Abstract Herein, we describe the synthesis of N,N′,S donor ligands 2-(1-(3,5-diisopropyl-1 H -pyrazol-1-yl)-3-(methythio)propyl)-4-methoxy-3,5-dimethylpyridine (L1) and 2-(1-(3,5-diisopropyl-1 H -pyrazol-1-yl)-2-(methythio)ethyl)-4-methoxy-3,5-dimethylpyridine (L2). Cu(I) complexes were prepared by reacting L1 or L2 with [Cu(CH 3 CN) 4 ]BF 4 or CuCl. The coordination behavior of the thioether arm of the ligands was found to determine the nuclearity of the resulting complexes, in which [Cu(L1)PPh 3 ]BF 4 ( 1 ) is polynuclear, [Cu(L2)PPh 3 ]BF 4 ( 2 ) is mononuclear, while [Cu(L1)] 2 (BF 4 ) 2 ( 3 ), [Cu(L2)CH 3 CN] 2 (BF 4 ) 2 ( 4 ), and [Cu(L1)Cl] 2 ( 5 ) are dinuclear. In the dimeric complex [Cu(L2)Cl] 2 ( 6 ), the sulfur atoms are not metal-bound. Rather, the two bridging chloride ions link the two copper centers. Compounds 4 – 6 are luminescent in the solid state, and exhibit emission bands centered at 490 nm ( 4 ), 544 nm ( 5 ), and 562 nm ( 6 ), respectively. Their excitation spectra display bands at 280 nm and 380 nm. According to DFT calculations, the HOMO is distributed partially over the metal centers and partially over the chloride anions ( 5 and 6 ) or the sulfur atoms ( 4 ) of the ligands, while the LUMO is a π∗ antibonding pyridine orbital. This suggests that the emission properties are derived from metal-to-ligand charge-transfer (MLCT), halide-to-ligand charge-transfer (XLCT), and ligand-to-ligand charge-transfer (LLCT) excited states.