A novel rhenium-aqua structure: the synthesis and structural characterization of (PPh4)4[ReN(H2O)(CN)3-μ-CN-ReN(CN)4] · 5H2O

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-C4H9)4NPF6-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.

Synthesis, Structures, and Photoluminescent Properties of Tricyanidonitridorhenium(V) Complexes with Bipyridine-Type Ligands

Tricyanidonitridorhenium(V) complexes with 2,2'-bipyridine (bpy) derivatives in which the 4 and 4' positions were substituted by X, [ReN(CN)₃(X₂bpy)]^- (X = NMe₂, NH₂, OMe, Me, Cl, and Br), were newly synthesized and characterized. The structures of the new complexes were determined by single-crystal X-ray analysis. UV-vis spectra of the complexes in dimethyl sulfoxide (DMSO) showed that the peak maximum wavelengths of rhenium-to-π* bpy-type-ligand charge transfer were in the range of 474-542 nm. Cyclic voltammograms in n-(C₄H₉)₄NPF₆-DMSO showed one-electron oxidation and reduction waves corresponding to the Re(VI/V) and X₂bpy^0/- processes, respectively. The new complexes and [ReN(CN)₃bpy]^- showed photoluminescence in the crystalline phase at 295 and 80 K and in DMSO at 295 K. The origin of the emission in DMSO was attributed to the triplet nature of the rhenium-to-π* bpy-type-ligand charge-transfer transition. Density functional theory calculations showed that the highest occupied and lowest unoccupied molecular orbitals were primarily localized on the d_xy orbital of the rhenium and π* orbitals of the bpy-type ligand, respectively.

Vapor switching of the luminescence mechanism in a Re(v) complex

A Re(v) mononuclear complex switches the characters of emissive states by methanol vapor via a single-crystal-to-single-crystal ligand exchange reaction.

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, (PPh₄)₂[ReN(CN)₄L] [L = imidazole (Him) (2), 1-methylimidazole (Mim) (3), and pyrazole (pyz) (4)] and (PPh₄)₂[ReN(CN)₄L]·L [L = Him (5) and Mim (6)], were synthesized by the reactions of (PPh₄)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.