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

Abstract

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 (Φem) being 0.65–0.75 in the solid state at 296 K. In contrast, the Φem and τem 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.

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. − …”

“…The crude yellow solid of K 2 [Re V (CN) 4 (N)]·H 2 O was recrystallized using a water/methanol mixture to obtain pink microcrystals . Finally, the organic (PPh 4 + ) salt (PPh 4 ) 2 [Re V (CN) 4 (N)] was precipitated from a water solution using a slight excess of PPh 4 Cl. − …”

“…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. ,− …”