Synthesis, Structure, and Spectroscopic Study of Redox-Active Heterometallic Cluster-Based Complexes [Re5MoSe8(CN)6]n

The heterometallic cluster-based compound K₅[Re₅MoSe₈(CN)₆] was obtained by high-temperature reaction from a mixture of ReSe₂ and MoSe₂ in molten potassium cyanide. The redox behavior of the [Re₅MoSe₈(CN)₆]^5- cluster anion was studied by cyclic voltammetry in aqueous and organic media showing two reversible one-electron-redox transitions with E_1/2 of -0.462 and 0.357 V versus Ag/AgCl in CH₃CN. Aqueous media potentials were found to be noticeably shifted to higher values because of solvation. Chemically accessible potentials allowed us to structurally isolate and characterize the [Re₅MoSe₈(CN)₆]ⁿ (n = 3-, 4-, and 5-) cluster complex in several charge states with corresponding cluster skeletal electron (CSE) numbers ranging from 24 to 22. The electronic absorption of the [Re₅MoSe₈(CN)₆]ⁿ cluster complex varies significantly upon a change of the CSE number, especially in the visible and near-IR regions. The local cluster core distortion upon electron removal was confirmed by density functional theory calculation, while the overall geometry of the cluster anion remained practically unaltered.

Synthesis, structures, redox properties, and theoretical calculations of thiohalide capped octahedral hexanuclear technetium(iii) clusters

Thiohalide capped octahedral hexanuclear technetium(iii) clusters were synthesized and characterized.

Technetium complexes with arylselenolato and aryltellurolato ligands

Reactions of (NBu₄)[TcOCl₄] or [TcCl₃(PPh₃)₂(CH₃CN)] with in situ-prepared lithium arylselenolates and -tellurolates give (NBu₄)[Tc^VO(ArE)₄] (E = Se, Te; Ar = phenyl) and [Tc^III(ArE)₃(PPh₃)(CH₃CN)] (E = Se, Te; Ar = phenyl, 2,6-Me₂phenyl, mesityl) complexes, respectively. The products contain square-pyramidal (Tc^V compounds) and trigonal bipyramidal (Tc^III complexes) coordinated technetium atoms. Density functional theory calculations indicate that the Tc-chalcogen bonds in the Tc^III compounds have a greater bond order than those in the Tc^V compounds.

Excited-state characteristics of tetracyanidonitridorhenium(V) and -technetium(V) complexes with N-heteroaromatic ligands

Six-coordinate tetracyanidonitridorhenium(V) and -technetium(V) with axial N-heteroaromatic ligands, (PPh4)2[MN(CN)4L] [M = Re, L = 4-(dimethylamino)pyridine (dmap), 3,5-lutidine (lut), 4-picoline (pic), 4-phenylpyridine (ppy), pyridine (py), 3-benzoylpyridine (3bzpy), 4,4'-bipyridine (bpy), pyrazine (pz), 4-cyanopyridine (cpy), or 4-benzoylpyridine (4bzpy); M = Tc, L = dmap, lut, pic, py, pz, or cpy] were synthesized and characterized. The crystal structures of 11 complexes were determined by single-crystal X-ray analysis. All of the complexes showed photoluminescence in the crystalline phase at room temperature. The emission maximum wavelengths (λ(em)) of the rhenium complexes with dmap, lut, pic, ppy, or py were similar to one another with a quite high emission quantum yield (Φ(em)): λ(em) = 539-545 nm, Φ(em) = 0.39-0.93, and emission lifetime (τ(em)) = 10-45 μs at 296 K. The emission spectra at 77 K exhibited vibronic progressions, and the emissive excited state is characterized as (3)[(d(xy))(1)(dπ*)(1)] (dπ* = d(xz), d(yz)). On the other hand, the emission maximum wavelength of the rhenium complex with 3bzpy, bpy, pz, cpy, or 4bzpy was significantly dependent on the nature of the axial ligand in the crystalline phase: λ(em) = 564-669 nm, Φ(em) ≤ 0.01-0.36, and τ(em) = 0.03-13.3 μs at 296 K. The emission spectra at 77 K in the crystalline phase did not show vibronic progressions. The emissive excited state of the rhenium complex with bpy, pz, cpy, or 4bzpy is assignable to originate from the metal-to-N-heteroaromatic ligand charge-transfer (MLCT)-type emission with a spin-triplet type. The change in the excited-state characteristics of rhenium complexes by the N-heteroaromatic ligand is a result of stabilization of the π* orbital of the N- heteroaromatic ligand to a lower energy level than the dπ* orbitals. The emission spectral shapes of technetium complexes were almost independent of the nature of the N-heteroaromatic ligand with λ(em) = 574-581 nm at room temperature. The different emission characteristics between the pz and cpy coordinate rhenium complexes and the technetium analogues would be due to stabilization of technetium-centered orbitals compared with the rhenium ones in energy.