A hexa-Cu cluster sandwiched silicotungstate with reactive oxygen species catalytic ability and anti-tumor activity in PC12 cells

• To our knowledge, SCW displays a novel structure, with the Cu ions existing in different coordination configurations in the solid state, a phenomenon not commonly seen in polyoxometalates. • The synthetic method of SCW will serve as a good example for subsequent synthesis and formation of such highnuclear transition metal cluster substituted silicotungstate. • SCW can catalyze the production of reactive oxygen species (ROS) in water phase efficiently. • SCW exhibits ability in anti ROS-sensitive tumor cells. A sandwich-type polyoxometalate (POM) based on a hexa-nuclear copper cluster and trivacant B- α -Keggin-type silicotungstate [Cu(en) 2 ][Cu(en) 2 H 2 O] 2 {[Cu(en) 2 ][Cu 6 (en) 2 (H 2 O) 2 (SiW 9 O 34 ) 2 ]}·8H 2 O (SCW) (ethylenediamine = en) has been synthesized and structurally featured by X-ray photoelectron spectrum (XPS), IR and UV spectra, and single-crystal X-ray diffraction (SXRD). According to the structural analysis, the principal element of the SCW is a 1- D linear polyoxoanion that is alternately joined by {[Cu 6 (en) 2 (H 2 O) 2 (SiW 9 O 34 ) 2 ]} 8– fragments and [Cu(en) 2 ] 2+ complexes. The cations of SCW are present in two forms: [Cu(en) 2 H 2 O] 2+ and [Cu(en) 2 ] 2+ . Notably, the Cu ions have been shown to coexist in the SCW with quad-coordination, penta-coordination, and hexa-coordination, which is rare in polyoxometalates. It is also demonstrated that SCW can efficiently catalyze the production of reactive oxygen species (ROS) by the synergistic action between copper complexes and POM fragments. Furthermore, SCW exhibits ability in anti ROS-sensitive tumor cells, such as PC12 cells.