Inspired by the transition-metal-oxo
cubical Mn<sub>4</sub>CaO<sub>5</sub> in photosystem II, we herein
report a disc-like heptanuclear mixed-valent cobalt cluster, [Co<sup>II</sup><sub>5</sub>Co<sup>III</sup><sub>2</sub>(mdea)<sub>4</sub>(N<sub>3</sub>)<sub>2</sub>(CH<sub>3</sub>CN)<sub>6</sub>(OH)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>·4ClO<sub>4</sub>]
(<b>1</b>, H<sub>2</sub>mdea = <i>N</i>-methyldiethanolamine),
for photocatalytic oxygen evolution. The topology of the Co<sub>7</sub> core resembles a small piece of cobaltate protected by terminal
H<sub>2</sub>O, N<sub>3</sub><sup>–</sup>, CH<sub>3</sub>CN,
and multidentate <i>N</i>-methyldiethanolamine at the periphery.
Under the optimal photocatalytic conditions, <b>1</b> exhibits
water oxidation activity with a turnover number (TON) of 210 and a
turnover frequency (TOF<sub>initial</sub>) of 0.23 s<sup>–1</sup>. Importantly, electrospray mass spectrometry (ESI-MS) was used to
not only identify the possible main active species in the water oxidation
reaction but also monitor the evolutions of oxidation states of cobalt
during the photocatalytic reactions. These results shed light on the
design concept of new water oxidation catalysts and mechanism-related
issues such as the key active intermediate and oxidation state evolution
in the oxygen evolution process. The magnetic properties of <b>1</b> were also discussed in detail
