Products of reactions between ReX3 (X=Cl, I) and N-heterocyclic compounds – Structural and spectroscopic studies

Paramagnetic Rhenium Iodide Cluster with N-Heterocyclic Carbene

triangulo-Trirhenium nonaiodide Re₃I₉ reacts with 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes) to produce the novel 13-electron paramagnetic cluster Re₃I₈(IMes)₂, which was characterized by means of X-ray diffraction analysis, ESR spectroscopy, magnetometry, and quantum chemistry.

Stabilization of Re37+/Re38+ Metalloclusters by Cyanide Ligands in New Trinuclear Rhenium Cluster Complexes [{Re3X3}(CN)9]4-/[{Re3X3}(CN)9]5- (X = Br or I)

The interaction of rhenium(III) halides Re₃Br₉ and Re₃I₉ with aqueous solution of sodium cyanide resulted in the formation of the first trinuclear halide-cyanide rhenium cluster complexes [{Re₃X₃}(CN)₉]^5-/[{Re₃X₃}(CN)₉]^4- (X = Br or I) crystallized as salts of the compositions Cs₄Na[{Re₃Br₃}(CN)₉]·5.25H₂O (1), Cs₄Na[{Re₃I₃}(CN)₉]·6H₂O (2), Cs₄[{Re₃Br₃}(CN)₉]·2H₂O·0.5CsCl (3), and Cs₄[{Re₃I₃}(CN)₉]·(4). All of the compounds are stable in air in the solid state and in aqueous solution. The substitution of apical halide ligands in the parent compounds Re₃X₉ by cyanides led to reduction of the original metallocluster Re₃⁹⁺ (12 cluster valence electrons (CVEs)) to Re₃⁷⁺ (14 CVEs), forming the compounds 1 and 2. The apical CN^- ligands affect the electronic structure of the Re₃ metallocluster stabilizing reduced form. Complexes 1 and 2 represent the first examples of triangular rhenium clusters with the Re₃⁷⁺ metallocluster. The reaction of 1 and 2 with H₂O₂ resulted in formation of compounds 3 and 4 with the formal charge of the Re₃ metallocluster equal to 8+, and no further oxidation to Re₃⁹⁺ occurred. The compounds were characterized by the X-ray diffraction analysis, NMR and UV-vis spectroscopies, mass spectrometry, cyclic voltammetry, and magnetic susceptibility measurements.

The {Re4} Tetrahedral Cyanometalate Cluster Anion [{Re4(μ3-CCN)4}(CN)12]8- with Inner (μ3-CCN)3- Ligands and Its Features in Coordination of Cu2+ Cations

A reaction between ReI₃ and KCN at elevated temperature led to the formation of the new cyanometalate cluster anion [{Re₄(μ₃-CCN)₄}(CN)₁₂]^8- (1). The anion contains μ₃-CCN^3- ligands, which are stabilized by the coordination to the triangular faces of the tetrahedral {Re₄} metallocluster in a μ₃ mode. The compound crystallized as a potassium salt, and its crystal structure was determined by single-crystal X-ray diffraction analysis. It was shown that μ₃-CCN^3- ligands are ambidentate and can interact with transition-metal cations similarly to terminal CN groups, resulting in the polymer framework formation.

A long symmetric N⋯H⋯N hydrogen bond in bis-(4-amino-pyridinium)(1+) azide(1-): redetermination from the original data

The structure of the title mol-ecular salt, C₁₀H₁₃N₄⁺·N₃^-, has been redetermined from the data published by Qian & Huang [Acta Cryst. (2010), E66, o3086; refcode WACMIY (Groom et al., 2016)]. The improvement of the present redetermination consists in a correction of the site-occupancy parameter of the bridging H atom between the pyridine rings, as well as of its position. The present study has shown that the bridging H atom (site symmetry 2) is involved in a symmetric N⋯H⋯N hydrogen bond, which is one of the longest ever observed [N⋯N = 2.678 (3) Å]. In addition, there are also present weaker N_am-H⋯N_az hydrogen bonds (am = amine and az = azide) of moderate strength and π-electron pyridine⋯π-electron inter-actions in the structure. All the azide N atoms also lie on a twofold axis.

Synthesis of Oxorhenium(V) and Oxotechnetium(V) Complexes That Bind to Amyloid-β Plaques

Alzheimer's disease is characterized by the presence of amyloid plaques in the brain. The primary constituents of the plaques are aggregated forms of the amyloid-β (Aβ) peptide. With the goal of preparing technetium-99(m) complexes that bind to Aβ plaques with the potential to be diagnostic imaging agents for Alzheimer's disease, new tetradentate ligands capable of forming neutral and lipophilic complexes with oxotechentium(V) and oxorhenium(V) were prepared. Nonradioactive isotopes of technetium are not available so rhenium was used as a surrogate for exploratory chemistry. Two planar tetradentate N3O ligands were prepared that form charge-neutral complexes with oxorhenium(v) as well as a ligand featuring a styrylpyridyl functional group designed to bind to Aβ plaques. All three ligands formed complexes with oxorhenium(V), and each complex was characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. The oxorhenium(V) complex with a styrylpyridyl functional group binds to Aβ plaques present in post-mortem human brain tissue. The chemistry was extrapolated to technetium-99(m) at the tracer level for two of the ligands. The resulting oxotechnetium(V) complexes were sufficiently lipophilic and charge-neutral to suggest that they have the potential to cross the blood-brain barrier but exhibited modest stability with respect to exchange with histidine. The chemistry presented here identifies a strategy to integrate styrylpyridyl functional groups into tetradentate ligands capable of forming complexes with [M═O](3+) cores (M = Re or Tc).