Ni12 tetracubane cores with slow relaxation of magnetization and efficient charge utilization for photocatalytic hydrogen evolution

Abstract

We report two Ni₁₂ multicubane topologies enclosed in the polyanions [Ni₁₂(OH)₉(WO₄)₃(PO₄)(B-α-PW₉O₃₄)₃]²¹⁻{Ni₁₂W₃₀} and [Ni₁₂(OH)₉(HPO₄)₃(PO₄)(B-α-PW₉O₃₄)(A-α-PW₉O₃₄)₂]²¹⁻{Ni₁₂W₂₇} that magnetically behave as Ni₁₂ units clearly distinguishing them from typical Ni₄ cubanes as shown by magnetic studies together with high field and frequency electron paramagnetic resonance (HFEPR). Beyond the unprecedented static properties, {Ni₁₂W₃₀} shows the unusual coexistence of slow relaxation of the magnetization and a diamagnetic ground state (S = 0), providing the unique opportunity of studying the essentially elusive magnetic relaxation behavior in excited states. The cubane-topology dependent activity of {Ni₁₂W₃₀} and {Ni₁₂W₂₇} as homogeneous HER photocatalysts unveils the structural key features significant for the design of photocatalysts with efficient charge utilization exemplified by high quantum yields (QY) of 10.42% and 8.36% for {Ni₁₂W₃₀} and {Ni₁₂W₂₇}, respectively.