A chromotropic PtPdCo coordination polymer with dual electrocatalytic activity for water reduction and oxidation.

Here, we present a heterometallic coordination polymer that exhibits heterogeneous electrocatalytic activities for both water reduction and water oxidation. Treatment of the PtII2PdII2 tetranuclear complex [Pd{Pt(NH)(D-pen)}] ([1]; D-Hpen = D-penicillamine) with CoX (X = Cl, Br) provided (PtII2PdII2CoII2) coordination polymers [Co(HO)(1)]X ([2]X), in which the PtII2PdII2 units of [1] are linked by [Co(μ-HO)(HO)] moieties in a 3D network structure. [2]X showed a colour change from orange to dark green upon dehydration, reflecting the geometrical conversion of the Co centres in [Co(μ-HO)(HO)] from an octahedron to a tetrahedron by the removal of aqua ligands. While both [2]Cl and [2]Br electrochemically catalysed water reduction to H in the solid state due to the presence of Pd active centres, water oxidation to O was catalysed only by [2]Br, which is ascribed to the presence of Br ions that mediate the catalytic reactions that occurred at Co active centres.