A Mononuclear Co(II) Coordination Complex Locked in a Confined Space and Acting as an Electrochemical Water-Oxidation Catalyst: A "Ship-in-a-Bottle" Approach.

Preparing efficient and robust water oxidation catalyst (WOC) with inexpensive materials remains a crucial challenge in artificial photosynthesis and for renewable energy. Existing heterogeneous WOCs are mostly metal oxides/hydroxides immobilized on solid supports. Herein we report a newly synthesized and structurally characterized metalorganic hybrid compound [{Co3(m3-OH)(BTB) 2(dpe) 2} {Co( H2O) 4(DMF) 2} 0.5] n . nH2O (Co-WOC-1) as an effective and stable water-oxidation electrocatalyst in an alkaline medium. In the crystal structure of Co-WOC-1, a mononuclear CoII complex {Co(H2O) 4(DMF) 2} 2+ is encapsulated in the void space of a 3D framework structure and this translationally rigid complex cation is responsible for a remarkable electrocatalytic WO activity, with a catalytic turnover frequency (TOF) of 0.05 s 1 at an overpotential of 390 mV (vs. NHE) in 0.1m KOH along with prolonged stability. This host-guest system can be described as a ship-in-a-bottle, and is a new class of heterogeneous WOC.