A polyoxometalate-based complex with visible-light photochromism as the electrocatalyst for generating hydrogen from water.

Two polyoxometalate (POM)-based complexes formulated as (HL1)2(Mo8O26)·2HL1·11H2O (L1 = 3-(5-(1H-pyrazol-4-yl)-1H-1,2,4-triazol-3-yl)pyridine) (1) and Co2(L2)4[P2Mo(VI)5O23Mo(II)(H2O)2]·3H2O (L2 = 4-(5-(2H-1,2,4-triazol-3-yl)-2H-1,2,4-triazol-3-yl)pyridine) (2) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Complex 1 shows a bi-capped POM with the two Mo centers from the [Mo8O26](4-) moiety coordinated by two HL1 ligands via two Mo-N bonds. Complex 2 consists of a mononuclear unsaturated coordinated Co(ii) unit and a [P2Mo(VI)5O23Mo(II)(H2O)2](4-) moiety, in which [P2Mo(VI)5O23Mo(II)(H2O)2](4-) shows a chain-like structure constructed from edge-sharing or vertex-sharing {MoO6} and {PO4} polyhedra. The two complexes are both soluble in neutral aqueous solution and they can electrocatalyze the H2 evolution reaction (HER) from water with lowered overpotentials and enhanced currents, and complex 1 shows better electrocatalytic activity for the HER than complex 2. Complex 1 shows visible-light photochromism. In the presence of complex 1, the HER current is enhanced with visible-light irradiation in comparison with the current without light irradiation.

Octamolybdate-based metal-organic framework with unsaturated coordinated metal center as electrocatalyst for generating hydrogen from water.

Two octamolybdate-based MOFs with unsaturated coordinated metal centers formulated as Cu(3)(Mo(8)O(26))(H(2)O)(2)(OH)(2)(L1)(4) (L1 = 4H-4-amino-1,2,4-triazole) (1) and Ag(4)(Mo(8)O(26))(L2)(2.5)(H(2)O) (L2 = 3,5-dimethyl-4-amino-4H-1,2,4-triazole) (2) were synthesized and structurally characterized by single-crystal X-ray diffractions. Complex 1 exhibits a 1D chain-like structure. In complex 2, 1D Ag-octamolybdate chains in the ac plane are covalently embedded into the 2D Ag-L2 layer, and the Ag-octamolybdate chains in the bc plane covalently link the 2D layers into 3D architecture. The two complexes both exhibit electrocatalytic activities toward generating H(2) from water with lowered overpotentials and enhanced currents, and the Cu complex exhibits better electrocatalytic activity toward generating H(2) from water than the Ag complex.