A Homochiral {Co^ΙΙ ₁₆Co^ΙΙΙ ₄} Supertetrahedral T₄ Cluster from a Racemic Ligand with Ferromagnetic Behavior and High Photocatalytic Activity

A homochiral mixed-valence cobalt cluster [Co^ΙΙ ₁₆Co^ΙΙΙ ₄(μ₆-O)₄(μ₃-OH)₁₂(S-bme)₁₂(OAc)₆]Cl₆⋅5 CH₃OH⋅18 H₂O (1, Hbme=1H-(benzimidazol-2-yl)ethanol) was synthesized from a racemic ligand and three cobalt salts of CoCl₂⋅6 H₂O, Co(Ac)₂⋅4 H₂O and Co(NO₃)₂⋅6 H₂O in a DMF/MeOH mixed solvent. The enantioselective coordination occurs when a large excess of cobalt ions added in the solution and only the S-configuration of the racemic ligand involved in crystallization. The CD spectra of three crystal samples show identical Cotton signals, indicating the repeatability and the enantiomeric purity of the single crystals. This compound presents a beautiful two-shell Matryoshka-type supertetrahedral T₄ cluster constructed by an inner Co^ΙΙΙ ₄O₄ cubane and four exterior Co^ΙΙ ₄O₄ cubanes bridged by μ₆-O²⁻ and μ₃-OH⁻ ions. This highest nuclear chiral cobalt cluster is the first example of enantiopure cobalt cluster separated from a racemic ligand and is the largest supertetrahedral cobalt cluster up to now. The magnetic studies reveal it behaves as a ferromagnet. Photocatalytic properties of 1 show high catalytic activities for the degradation of the highly toxic triphenyl dye crystal violet (CV) in the presence of H₂O₂ under visible light in aqueous solution. The degradation rate almost reach 100 % at 45 min and can maintain 98.54 % after 8 cycles.