Synthesis and Photoluminescence of Tetracyanidonitridorhenium(V) Complexes with Five-Membered N-Heteroaromatic Ligands and Photoluminescence-Intensity Change

Novel tetracyanidonitridorhenium(V) complexes with five-membered N-heteroaromatic ligands, (PPh 4 ) 2 [ReN(CN) 4 L] [L = imidazole (Him) ( 2 ), 1-methylimidazole (Mim) ( 3 ), and pyrazole (pyz) ( 4 )] and (PPh 4 ) 2 [ReN(CN) 4 L]·L [L = Him ( 5 ) and Mim ( 6 )], were synthesized by the reactions of (PPh 4 ) 2 [ReN(CN) 4 ] ( 1 ) with Him, Mim, and pyz, and their structures were determined by single-crystal X-ray analysis. The complexes 2 , 3 , 4 , and 6 showed intense photoluminescence, with the emission quantum yields (Φ em ) being 0.65-0.75 in the solid state at 296 K. In contrast, the Φ em and τ em values of 5 are significantly smaller and shorter, respectively, than the relevant values of 2 . The interconversion reactions among 1 , 2 , and 5 accompanied by large photoluminescence-intensity changes were accomplished by solvent-free reactions and exposure of water. The mechanochemical reaction of 2 with 1 mol equiv of Him in the solid state gave 5 . Complex 5 was also obtained by the mechanochemical reaction of 1 with 2 mol equivalents of Him in the solid state. By placing solid of 5 in water, the solid showed intense photoluminescence to give 2 . Complex 1 was produced under vacuum at 185 °C from 2 or 5 .