Inner-sphere vs. outer-sphere reduction of uranyl supported by a redox-active, donor-expanded dipyrrin

Abstract

The uranyl(vi) complex UO2Cl(L) of the redox-active diimino-dipyrrin anion, L– is reported and its reactions with inner- and outer-sphere reductants studied.

Triggering Redox Activity in a Thiophene Compound: Radical Stabilization and Coordination Chemistry

“…Upon deprotonation of HL to form KL,a ni ntense band at 654 nm appeared in the UV/vis spectrum ( Figure 5), and is similar, although red-shifted, to the HOMO-LUMO transition in related dipyrromethene compounds; [6] the band seen at 295 nm is indicative of reprotonation of KL and highlights its sensitivity to water. Oxidation of KL to the radical LC resulted in ac onsiderable hypsochromic shift of the lowenergy absorption band from 654 to 456 nm, which is explained by an increase in the SOMO(a)-LUMO(a)g ap, according to TD-DFT calculations,f rom 4.41 keV in KL to 5.41 keV in LC.I ncorporation of the dinuclear core in Cu 2 I 2 -(LC)leads to the appearance of additional absorption bands,in particular ab road absorption at 826 nm (765 nm in the calculated spectrum), mainly involving the SOMO(b)-LUMO(b)t ransition.…”

“…Accordingly,w eh ave shown that aN -donor-expanded dipyrrin ligand [5] is redox active and able to mediate sequential electron transfer to au ranyl(VI) center ( Figure 1). [6] Ligand-centered oxidation was also seen in Ni complexes of asimilar bis(phenolate)dipyrrin ligand, with the one-electron oxidation product characterized as aligand-centered radical. [6] Ligand-centered oxidation was also seen in Ni complexes of asimilar bis(phenolate)dipyrrin ligand, with the one-electron oxidation product characterized as aligand-centered radical.…”

Triggering Redox Activity in a Thiophene Compound: Radical Stabilization and Coordination Chemistry

“…[5] Electron Localization Function (ELF) calculations were carried out using the TopMod suite. [6] Molecular orbital surfaces and electron densities from ELF calculations were exported as cubefiles, visualized in UCSF-Chimera [7] and rendered with the Pov-Ray raytracer program.…”

“…This calculated structure is different to that seen in the X-ray crystal structure of L •2+ which is planar, presumably due to the presence of the BF4 − counter-ion which interacts with both imine nitrogen atoms. Upon deprotonation of HL to form KL, an intense band at 654 nm appears ( Figure 5), and is similar, although red-shifted, to the HOMO-LUMO transition in related dipyrromethene compounds; [6] the band seen at 295 nm is indicative of re-protonation of KL and highlights its sensitivity to water. Oxidation of KL to the radical L • results in a considerable hypsochromic shift of the low-energy absorption band, from 654 to 456 nm, which is explained by an increase in the SOMO ( While the cyclic voltammogram (CV) of HL displays a single irreversible reduction at Ep c -1.46 V versus ferrocene ( Figure S11), the CV of KL consists of two reversible events, with an oxidation at -0.12 V and a reduction at -1.33 V (Figure 6).…”

“…The initial reduction occurs at the ligand, forming a U(VI) ligand-centered radical prior to reduction of the uranium center, ultimately to U(IV). [6] Ligandcentered oxidation was also seen in Ni complexes of a similar bis(phenolate)dipyrrin ligand, with the one-electron oxidation product characterized as a ligand-centered radical. [7] In contrast to the nitrogen-containing heterocycles found in dipyrrins, porphyrinoids and sub-porphyrins, [8] studies on the redox activity of sulfur-containing heterocycles such as thiophene are more limited, despite their use in tuning the electronic properties of molecular compounds [9] and polymeric materials.…”