Shifts in Valence States in Bimetallic MXenes Revealed by Electron Energy-Loss Spectroscopy (EELS)

MXenes are an emergent class of two-dimensional materials with a very wide spectrum of promising applications. The synthesis of multiple MXenes, specifically solid-solution MXenes, allows fine tuning of their properties, expands their range of applications, and leads to enhanced performance. The functionality of solid-solution MXenes is closely related to the valence state of their constituents: transition metals, oxygen, carbon, and nitrogen. However, the impact of changes in the oxidation state of elements in MXenes is not well understood. In this work, three interrelated solid-solution MXene systems (Ti2-yNbyCTx, Nb2-yVyCTx, and Ti2-yVyCTx) were investigated with scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS) to determine the localized valence states of metals at the nanoscale. The analysis demonstrates changes in the electronic configuration of V upon modification of the overall composition and within individual MXene flakes. These shifts of oxidation state can explain the nonlinear optical and electronic features of solid-solution MXenes. Vanadium appears to be particularly sensitive to modification of the valence state, while titanium maintains the same oxidation state in Ti-Nb and Ti-V MXenes, regardless of stoichiometry. The study also explains Nb's influential role in the previously observed electronic properties in the Nb-V and Nb-Ti systems.

Base-stabilized formally zero-valent mono and diatomic molecular main group compounds

Various compounds are known for transition metals in their formal zero oxidation state, while similar compounds of main-group elements are recently realized and limited to only a few examples. Lewis...

Interaction of Th(IV), Pu(IV) and Fe(III) with ferritin protein: how similar?

Ferritin is the main protein of Fe storage in eukaryote and prokaryote cells. It is a large multifunctional, multi-subunit protein consisting of heavy H and light L subunits. In the field of nuclear toxicology, it has been suggested that some actinide elements, such as thorium and plutonium at oxidation state +IV, have a comparable `biochemistry' to iron at oxidation state +III owing to their very high tendency for hydrolysis and somewhat comparable ionic radii. Therefore, the possible mechanisms of interaction of such actinide elements with the Fe storage protein is a fundamental question of bio-actinidic chemistry. We recently described the complexation of Pu(IV) and Th(IV) with horse spleen ferritin (composed mainly of L subunits). In this article, we bring another viewpoint to this question by further combining modeling with our previous EXAFS data for Pu(IV) and Th(IV). As a result, the interaction between the L subunits and both actinides appears to be non-specific but driven only by the density of the presence of Asp and Glu residues on the protein shell. The formation of an oxyhydroxide Th or Pu core has not been observed under the experimental conditions here, nor the interaction of Th or Pu with the ferric oxyhydroxide core.

5 Sulfur Fluoride Exchange (SuFEx)

Sulfur Fluoride Exchange (SuFEx) click chemistry is a new generation technology for creating stable molecular connections with absolute reliability under metal-free conditions. SuFEx builds upon the fundamental principles of click chemistry by exploiting a unique blend of stability and latent reactivity of high oxidation state sulfur fluoride [e.g., S(VI)] functionalities to forge stable covalent linkages at connective SuFEx hubs. In this review, we focus mainly on the SuFEx hubs, sulfuryl fluoride (SO2F2), thionyl tetrafluoride (SOF4), ethenesulfonyl fluoride (ESF), 1-bromoethene-1-sulfonyl fluoride (BESF) and, 2-substituted alkyne-1-sulfonyl fluorides (SASFs). We describe each connector’s unique reactivity and their application to SuFEx click chemistry.

Structure, Reactivity and Luminescence Studies of Triphenylsiloxide Complexes of Tetravalent Lanthanides

Among the 14 lanthanide elements (Ce-Lu), until recently, the tetravalent oxidation state was readily accessible in solution only for cerium while Pr(IV), Nd(IV), Dy(IV) and Tb(IV) had only been detected...