Redox-active dinuclear oxorhenium(V) pyrazolate complexes

Influence of Di-n-butyl Phosphoric Acid on Cerium Redox and Speciation in Tri-n-butyl Phosphate

The effects of simulated radiolytic degradation of tri-n-butyl phosphate (TBP) on the chemical speciation of cerium were studied by spectrophotometry and electrochemistry of TBP solutions containing increasing amounts of di-n-butyl phosphoric acid (HDBP), a common degradation product of TBP. Tetravalent cerium was found to exchange coordinated nitrate for the dibutyl phosphate anion, forming dinuclear complexes of the formula (CeOCe)(NO3)(6-d)(DBP)d·3TBP (d = 0-3). Compared to Ce(IV), Ce(III) was complexed less strongly by HDBP in TBP, but HDBP displaced both nitrate and TBP to form the series of mononuclear complexes Ce(NO3)(3-d)(HDBP·DBP)d·(3-d)TBP (d = 0-3). Dibutyl phosphate coordination caused large negative shifts in the Ce(IV/III) reduction potential in TBP, indicating a strong stabilization of the tetravalent state. Electrochemical investigation of the reduction of Ce(IV) in TBP revealed it to be a two-electron process in accordance with the dinuclear nature of the organic-phase Ce(IV) complexes. The diffusion coefficients of the d = 0 dinuclear Ce(IV)-nitrate-TBP complex and mononuclear Ce(III)-nitrate-TBP complex in TBP equilibrated with 7 M HNO3 were determined to be (1.16 ± 0.06) × 10-7 cm2/s and (1.9 ± 0.4) × 10-7 cm2/s, respectively, which also is consistent with the larger molecular volume of the dinuclear Ce(IV) complexes.

New O- and N-N-Bridging Complexes of Tc(V), the Role of the Nitrogen Atom Position in Aromatic Rings: Reaction Mechanism, Spectroscopy, DTA, XRD and Hirshfeld Surface Analysis

In this work, O- and N-N-bridging complexes of technetium (V), previously known only for rhenium, were obtained for the first time. Tc(V) complexes with pyridazine (pyd), 1,2,4-triazole (trz), 3,5-dimethylpyrazole (dmpz) and pyrimidine (pyr) were obtained. In three complexes [{TcOCl₂}₂(μ-O)(μ-pyd)₂], [{TcOCl₂}₂(μ-O)(μ-trz)₂]·Htrz·Cl and [{TcO(dmpz)₄}(μ-O)(TcOCl₄)] two technetium atoms are linked by a Tc-O-Tc bond, and in the first two, Tc atoms are additionally linked by a Tc-N-N-Tc bond through the nitrogen atoms of the aromatic rings. We determined the role of nitrogen atom position in the aromatic ring and the presence of substituents on the formation of such complexes. For the first time, a reaction mechanism for the formation of such complexes was proposed. This article details the crystal structures of four new compounds. The work describes in detail the coordination of Tc atoms in the obtained structures and the regularities of the formation of crystal packings. The spectroscopic properties of the obtained compounds and their mother solutions were studied. The decomposition temperatures of the described complexes were determined. An assumption was made about the oligomerization of three-bridged complexes based on the results of mass spectrometry. Through the analysis of non-valent interactions in the structures, π-stacking, halogen-π and CH-π interactions were found. An analysis of the Hirshfeld surface for [{TcOCl₂}₂(μ-O)(μ-pyd)₂], [{TcOCl2}2(μ-O)(μ-trz)₂] and their rhenium analogues showed that the main contribution to the crystalline packing is made by interactions of the type Hal···H/H···Hal (45.4-48.9%), H···H (10.2-15.8%), and O···H/H···O (9.4-16.5%).