Structure and Electronic Properties of Large Oligomeric Heterometallic 3d/Ce IV Polyoxometalates.

Merging the rich chemistry of Ce(IV) polyoxometalates (POMs) with that of 3d polyanions remains a challenge due to the strong competition between these highly oxophilic lanthanide cations and 3d metallic ions for coordination to lacunary molecular metal oxides. We report herein the characterization of an unprecedented water stable hexameric Ce IV /Co II POM ( Ce 12 Co 6 ) made of two {(SiW 9 ) 2 Ce 6 } units connected to a {(SiW 10 ) 2 Co 6 (PO 4 ) 2 } core. In addition, the pentameric Ce IV /Ni II compound Ce 6 Ni 8 , where two {PW 9 Ni 3 W} and a {PW 10 Ni 2 } fragments are grafted on a {(PW 9 ) 2 Ce 6 } moiety, has been obtained. Magnetic studies of Ce 6 Ni 8 revealed ferromagnetic interactions between the Ni II centers constituting the {Ni 3 PW 10 } fragments, in agreement with the geometry of such a trinuclear cluster. Related insoluble barium salts of Ce 12 Co 6 and Ce 6 Ni 8 were also prepared, allowing their solid-state electrochemical investigations and showing in particular that in Ce 12 Co 6 , both the cobalt, cerium, and silicotungstate moieties are electroactive. Finally, photophysical studies demonstrate the formation of long-lived reduced POMs photosensitized by [Ru(bpy) 3 ] 2+ , suggesting that Ce 12 Co 6 and Ce 6 Ni 8 could be used as efficient reservoirs of reduction equivalents for photocatalytic reactions.