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

Abstract

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 X2bpy0/– 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.

Solvent- and Temperature-Driven Photoluminescence Modulation in Porous Hofmann-Type SrII–ReVMetal–Organic Frameworks

“…The decrease of this distance can be correlated with the increase in the p K a value of a free ligand (5.6 for bpee, 5.4 for bpen, and 4.8 for bpy). Therefore, as noted in earlier works, − the σ-electron-donating character of the N-heteroaromatic ligand influences the Re–N­(ligand) bond distance. As a result, the shortest Re–N­(nitrido) distance of only 1.58(4) Å, very short in comparison to the related compounds (Table S10), is observed in 3·MeOH , showing the longest Re–N­(bpy) bond length of 2.47(3) Å, while the Re–N­(nitrido) distances are much longer in 1·MeOH and 2·MeOH , showing closer Re–N­(pyridine ligand) distances (Table ).…”

“…398, 418, 420, 406, and 480 nm for 1·MeOH , 2·MeOH , 3·MeOH , 3·H 2 O , and 3 , respectively. Their higher energy part (typically below 450 nm) can be mainly ascribed to d–d electronic transitions centered at the Re V sites, that is, the (d xy ) 2 → (d xy ) 1 (d π* ) 1 (d π* = d xz , d yz ), with a d π –p π (nitrido) overlap, electronic transition. − However, the significant parts of the absorption band for 2·MeOH and 3 , as well as the absorption tails of the lowest-energy band in 1·MeOH , 3·MeOH , and 3·H 2 O , are located above 480 nm, which, according to the literature, is a sign of the important contribution from the MLCT (from Re V to organic ligand) electronic transitions. − …”

“…Because the [Re V (CN) 4 (N)­(L)] 2– complexes were recognized to be intrinsically emissive in the solid state, − the detailed photoluminescent studies, including temperature-variable emission and excitation spectra, were performed for the whole family of obtained coordination frameworks, 1·MeOH – 3·MeOH , as well as its postsynthetically modified phases, 3·H 2 O and 3 (Figures , , and S17–S22 and Tables S11–S16). Upon UV irradiation, these materials exhibit visible-light photoluminescence, the color of which is tuned from green through yellow to orange, depending on the applied organic ligand (Figure a–c), as well as the solvent content (Figure d–f).…”

“…We focused on a specific class of CPs, called Hofmann-type frameworks, typically composed of inorganic cyanido-bridged {M-[M′(CN) 4 ]} or {M-[M″(CN) 2 ] 2 } layers (M = divalent 3d metal ions; M′ = Ni II , Pd II , Pt II ; M″ = Ag I , Au I ) bonded by pyrazine or bipyridyl organic spacers. − This specific type of coordination compounds combines the advantages of the MOF materials, such as rich and tunable porosity and high stability under treatment by chemical and physical stimuli, with a great functional potential of heterometallic cyanido-bridged frameworks, broadly utilized in the generation of diverse magnetic and optical properties, − including tunable vis-to-near-IR (NIR) photoluminescence. , The conjunction of cyanido and organic bridges provides attractive porosity governing their magnetic − and sorption properties. − Although the Hofmann-type CPs can be emissive because of the insertion of luminescent guest molecules, this combination leads to the loss of porosity. , Thus, to ensure the presence of interstitial solvent together with the emission properties in Hofmann-type CPs, photoluminescence has to be induced directly by the coordination skeleton. This is a difficult task because the 3d metal ions are often emission quenchers and the commonly used [M′(CN) 4 ] 2– ions are spatially separated, which hampers their emission originating from metallophilic interactions. , However, similar but rarely explored cyanidonitrido [Re V (CN) 4 (N)­(L)] 2– (N 3– = nitrido and L = organic ligand) complexes are intrinsically emissive because of their d–d or metal-to-ligand charge-transfer (MLCT) transitions. − At the same time, they are good candidates for the construction of Hofmann-type CPs thanks to the nearly square-planar alignment of cyanido ligands. , Therefore, we present a synthetic route toward a novel class of luminescent MOFs employing these promising Re V building blocks. For additional organic spacers inducing the MOF structure, we selected 1,2-bis­(4-pyridyl)­ethane (bpen), 1,2-bis­(4-pyridyl)­ethylene (bpee), and 4,4′-bipyridine (bpy) ligands, while for the second metal centers, we used optically silent but flexible Sr 2+ ions .…”

Guest-Tunable Excited States in a Cyanide-Bridged Luminescent Coordination Polymer

“…This was supported by the emission spectra of CdRe, CdRe’, CdRe’_MeOH, and CdRe’_EtOH at 77 K (Figure S4). The resulting vibrational progression of the spectra is a characteristic of emission from the 3 [(d xy ) 1 (d π *) 1 ] (d π * = d xz , d yz ) state. ,− …”