Syntheses and catalytic properties of two new multi-manganese-substituted silicotungstates

Transition-metal-substituted polyoxometalates have attracted attention due to their remarkable physicochemical properties and applications in many research areas. Two new multi-manganese-substituted silicotungstates, tetramer [{Mn3Cl(OH)3(SiO4)}4(SiW9O34)4]36- (1) and banana-shaped [((MnOH2)0.5Mn2SiW9O34)2(SiW6O26)]22- (2), were prepared under hydrothermal conditions and characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, etc. Compound 1 comprises four {SiW9O34} fragments, one {Mn3Cl(OH)3}4 cluster and four {SiO4} groups; it can form a 1 D-chain by connecting [{Mn3Cl(OH)3(SiO4)}4(SiW9O34)4]36− cluster units with Na+ cations. Banana-shaped 2 consists of two {(MnIIOH2)0.5MnIII2SiW9O34} fragments connected by a hexavacant {SiW6O26} motif, and it displays an interesting 3-D architecture by bridging banana-shaped [((MnIIOH2)0.5MnIII2SiW9O34)2(SiW6O26)]18- polyanion with four-member Na-cluster. 3-D packing of 2 along the c-axis creates two types of elliptical channels with sizes of 7.86 Å × 13.35 Å and 16.03 Å × 25.28 Å, respectively. Also, while coupling with [Ir(ppy)2(dtbbpy)]+ as photosensitizer and triethanolamine (TEOA) as sacrificial electron donor, both compounds show decent catalytic activity towards hydrogen production under visible LED light irradiation.