Multifaceted Bicubane Co4 Clusters: Magnetism, Photocatalytic Oxygen Evolution, and Electrical Conductivity

Abstract

The use of 1‐(hydroxymethyl)‐3,5‐dimethylpyrazole (HL), a functionalized pyrazole ligand, to assemble with CoX2 (X = Cl or Br) in the presence of triethylamine under low‐temperature solvothermal conditions gave rise to two tetranuclear cobalt(II) clusters, [Co4L6X2] [X = Cl (1), Br (2)]. Both CoII4 clusters are isostructural and protected by four µ2‐N1:O2 and two µ3‐N1:O3L– as well as terminal X anions to form a face‐shared open bicubane structural motif. Magnetic susceptibility measurements indicated that there is an intramolecular antiferromagnetic interaction between four CoII atoms in 1 and 2. Although the core motif of 1 and 2 is not classic Co4O4 monocubane, both are active catalysts for water oxidation, and their relative O2‐evolution rates are dependent on the halogen terminal ligands, which is also supported by spin‐polarized density functional theory (DFT) calculations. Both clusters exhibit semiconductor behavior with σ values on the 10–9 S cm–1 scale at room temperature; however, mechanical iodine doping results in up to an astonishing 105‐fold maximum enhancement of solid‐state conductivity relative to the undoped samples. This work therefore presents a new core type of cobalt cluster that possesses photocatalytic oxygen‐evolution capabilities, provides new insight into the catalysis‐related mechanism based on the relative oxygen‐evolution efficiency, and applies the iodine‐doping strategy to boost the conductivity of cluster compounds.