Luminescence Color and Intensity Changes of Nitridorhenium(V) Complexes Induced by Protonation/Deprotonation on the Bidentate Azolylpyridine Ligands.

Tricyanidonitridorhenium(V) complexes with azolylpyridines, namely, [ReN(CN) 3 (H-N2py)] - ( 1-H , H-N2py = 2-(3-pyrazolyl)pyridine) and [ReN(CN) 3 (L)] 2- ( 2-a , L = 2-[1,2,3]-triazol-4-yl-pyridine anion (N3py - ), and 3-a , that is, L = 2-(tetrazol-5-yl)-pyridine anion (N4py - )), were newly synthesized and characterized. The structures of the new complexes were determined by single-crystal X-ray analysis. The 1-H complex includes two geometrical isomers in which an isomer is the conformation with the pyridyl (py) and pyrazolyl (pyrz) moieties of H-N2py occupying the trans site to the nitrido (the ax site) and the trans site to the cyanido (the eq site), respectively, in a bidentate fashion; the other isomer is the py and pyrz moieties coordinated to the eq and ax sites. In 2-a and 3-a , the triazolyl (trz) and tetrazoly (tetrz) moieties in N3py - and N4py - occupy the eq site, and the py moieties in N3py - and N4py - coordinate to the ax site. The complex 1-H is deprotonated upon the addition of 1,8-diazabicyclo[5.4.0]undec-7-one or NaOH to produce [ReN(CN) 3 (N2py)] 2- ( 1-a ), and 2-a is protonated upon the addition of p -toluene sulfonic acid (TsOH) to give [ReN(CN) 3 (H-N3py)] - ( 2-H ) in DMSO. The protonation reaction does not occur for 3-a with TsOH in DMSO. All the complexes show one-electron redox waves of the Re(VI)/Re(V) and azolylpyridine ligand-centered processes in 0.1 M ( n -C 4 H 9 ) 4 NPF 6 -DMSO. All the complexes exhibit photoluminescence in DMSO and in the crystalline phase at 296 K. The emissive excited states of the complexes in DMSO were assigned to MLCT with a spin triplet nature. The emission band shifts to shorter and longer wavelengths upon protonation and deprotonation of the coordinated azolylpyridines, respectively. The emission color and intensity changes of 2-H and 2-a in the presence of acidic and basic vapors were investigated.