Synthesis of two new copper-sandwiched polyoxotungstates and the influence of nuclear number on catalytic hydrogen evolution activity

To focus on renewable energy, we have been devoted to developping energy-efficient, robust and low cost water reduction catalysts (WRCs). Two hybrid inorganic-organic hexa/octa-CuII-sandwiched POM: [Cu(dap)2]2[{Cu8(dap)4(H2O)2} (SiW9O34)2]·7H2O (1) and [Cu(dap)2(H2O)]2[Cu(dap)2]2[{Cu6(dap)2}(SiW9O34)2]·8H2O (2) (dap = 1,2-diaminopropane, 1,4-H2NDC = 1,4-naphthalenedicarboxylic acid) were synthesized under hydrothermal conditions. The new copper complexes were applied as water reduction catalysts (WRCs) in the presence of [Ir(ppy)2(dtbbpy)][PF6] as a photosensitizer and triethanolamine (TEOA) as a sacrificial electron donor. Meanwhile, the number of nuclear substituted polyoxotungstates was the critical factor influencing photocatalysis. The experimental results matched well with the conclusions obtained via density functional theory (DFT). It is noteworthy that our research not only enriches the field of CuII-sandwiched POM chemistry but also provides an investigation of the relationship between photocatalytic activity and the nuclear number of Cu-substituted POMs. These results may guide us to synthesize different nuclear copper-substituted polyoxotungstates and develop their applications toward energy and environmental uses.