The reaction of S,S′‐bis(2‐pyridylmethyl)‐1,2‐thiobenzene and CoCl2 affords a water‐soluble cobalt(II) complex, [(bptb)CoCl2], which has been characterized using various methods. Under blue light, together with CdS nanorods as a photosensitizer and ascorbic acid as a sacrificial electron donor, [(bptb)CoCl2] can catalyze hydrogen generation from water and can work for 90 h. Under optimal conditions, this photocatalytic system achieves a turnover number (TON) of 22 900 moles of H2 per mole of catalyst during 60 h of irradiation, and the highest apparent quantum yield is ca 26.63% at 469 nm. Moreover, [(bptb)CoCl2] exhibits much higher activity than [(bpte)CoCl2] (bpte = S,S′‐bis(2‐pyridylmethyl)‐1,2‐thioethane; TON = 6740 moles of H2 per mole of catalyst during 60 h of irradiation), indicating that bptb can constitute a better catalyst for hydrogen production than bpte. This result can be attributed to the electronic properties of the ligands (bptb and bpte). The introduction of phenyl makes the electron distribution more uniform in the cobalt complex, allowing easier formation of the Co(III)–H species, further promoting the formation of hydrogen.

A dinuclear copper(II) complex, [CuII2(L)2] is afforded by the reaction of CuCl2·2H2O with a triazenido ligand, 1‐[(2‐carboxymethyl) benzene]‐3‐[2‐carboxybenzene] triazene (H2L). Structural investigation shows that the copper‐copper distance [2.3985(7) Å] is significantly shorter than the sum of the van der Waals radii of Cu (1.40 Å), suggesting that there are metal‐metal bonds in [CuII2(L)2]. In solid, there is a strong antiferromagnetic interaction between copper(II) ions (J = –135.6 cm–1). In homogeneous environment, [CuII2(L)2] shows electrocatalytic activities for hydrogen generation both from acetic acid with a turnover frequency (TOF) of 32 mol of hydrogen per mole of catalyst per hour [mol(H2)·mol–1(catalyst)·h–1] at an overpotential (OP) of 941.6 mV, and neutral buffer with a TOF of 512 mol(H2)·mol–1(catalyst)·h–1 at an OP of 836.7 mV.

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