Neutral stibinyl and bismuthinyl radicals are typically short-lived, reactive species. Here we show the synthesis and solid-state structures of two stable stibinyl [L(Cl)Ga]₂Sb· 1 and bismuthinyl radicals [L(I)Ga]₂Bi· 4, which are stabilized by electropositive metal centers. Their description as predominantly metal-centered radicals is consistent with the results of NMR, EPR, SQUID, and DFT studies. The Lewis-acidic character of the Ga ligands allow for significant electron delocalization of the Sb- and Bi- unpaired radical onto the ligand. Single-electron reduction of [L(Cl)Ga]₂Sb· gave LGaSbGa(Cl)L 5, the first compound containing a Ga=Sb double bond. The π-bonding contribution is estimated to 9.56 kcal mol⁻¹ by NMR spectroscopy. The bonding situation and electronic structure is analyzed by quantum mechanical computations, revealing significant π backdonation from the Sb to the Ga atom. The formation of 5 illustrates the high-synthetic potential of 1 for the formation of new compounds with unusual electronic structures.

The discovery of decamethyldizincocene [Zn₂(η⁵-Cp*)₂] (Cp* = C₅Me₅), the first complex containing a covalent zinc–zinc bond, by Carmona in 2004 initiated the search for this remarkable class of compounds. Low-valent organozinc complexes can either be formed by ligand substitution reactions of [Zn₂(η⁵-Cp*)₂] or by reductive coupling reactions of Zn(II) compounds. To the best of our knowledge, until now 25 low-valent Zn–Zn bonded molecular compounds stabilized by a variety of sterically demanding, very often chelating, organic ligands have been synthesized and characterized. There are two major reaction pathways of [Zn₂(η⁵-Cp*)₂]: it can either react with cleavage of the Zn–Zn bond or by ligand substitution. In addition, upon reaction with late transition metal complexes, [Zn₂(η⁵-Cp*)₂] was found to form novel intermetallic complexes with Cp*Zn and Cp*Zn₂ acting as unusual one-electron donor ligands. Very recently, the potential capability of [Zn₂(η⁵-Cp*)₂] to serve as a suitable catalyst in hydroamination reactions was demonstrated. Finally, the recent work on Cd–Cd bonded coordination compounds is reviewed.

Bimetallic transition-metal oxides, such as spinel-like Co_xFe_3-xO₄ materials, are known as attractive catalysts for the oxygen evolution reaction (OER) in alkaline electrolytes. Nonetheless, unveiling the real active species and active states in these catalysts remains a challenge. The coexistence of metal ions in different chemical states and in different chemical environments, including disordered X-ray amorphous phases that all evolve under reaction conditions, hinders the application of common operando techniques. Here, we address this issue by relying on operando quick X-ray absorption fine structure spectroscopy, coupled with unsupervised and supervised machine learning methods. We use principal component analysis to understand the subtle changes in the X-ray absorption near-edge structure spectra and develop an artificial neural network to decipher the extended X-ray absorption fine structure spectra. This allows us to separately track the evolution of tetrahedrally and octahedrally coordinated species and to disentangle the chemical changes and several phase transitions taking place in Co_xFe_3-xO₄ catalysts and on their active surface, related to the conversion of disordered oxides into spinel-like structures, transformation of spinels into active oxyhydroxides, and changes in the degree of spinel inversion in the course of the activation treatment and under OER conditions. By correlating the revealed structural changes with the distinct catalytic activity for a series of Co_xFe_3-xO₄ samples, we elucidate the active species and OER mechanism.