Construction and property investigation of inorganic–organic hybrid materials based on metal–salens and Keggin polyoxometalates

Four hybrid materials based on the Keggin polyanions and metal–salens, namely, [Mn(salen)(CH3OH)2]4[SiW12O40] (1), [Mn(salen)(H2O)]2[Mn(salen)(H2O)][PW12O40] (2), [NH(CH2CH3)3]2[Mn(salen)(CH3OH)]2[SiW12O40]·2CH3OH (3), and [(Cu(salen))2Cu(H2O)]2[SiW12O40] (4) (H2salen = N,N′-ethylenebis(salicylideneimine)) have been successfully synthesized. All the compounds are characterized by X-ray single-crystal diffractions, elemental analyses, IR spectra, and thermogravimetric analyses (TGA). Crystal structure analysis reveals that compound 1 exhibits a supramolecular structure containing one Keggin-type [SiW12O40]4− heteropolyanion and four MnIII–salen units. In compound 2, the [PW12O40]3− polyoxoanions and MnIII–salen complex cations are regularly arranged along the c-axis showing an alternating packing arrangement of anionic and cationic layers. While in compound 3, the polyoxoanion [SiW12O40]4− is covalently decorated by two [Mn(salen)(CH3OH)]+ fragments via two terminal oxygen atoms in the opposite sites, giving birth to an unusual Keggin anion supporting transition metal–salen complexes. Compound 4 represents the first example that POM supports trinuclear copper–salen complexes. Photocatalytic experiments of 1–4 indicate that they possess high catalytic activity for photodegradation of RhB under UV irradiation. In addition, the electrochemical behaviors of 1 and 2 are well investigated.