Organometallic[bond]polyoxometalate hybrid compounds: metallosalen compounds modified by Keggin type polyoxometalates

Hybrid compounds with two functional centers consisting of a metallosalen moiety (Mbond]salen; M = Mn, Co, Ni, and Pd) connected by an alkylene bridging group to a lacunary Keggin type polyoxometalate were synthesized and characterized. In these metallosalen-polyoxometalate compounds (Mbond]salenbond]POM) it was shown by the use of a combination of UVbond]vis, (1)H NMR, EPR, XPS, and cyclic voltammetry measurements that the polyoxometalate exerts a significant intramolecular electronic effect on the metallosalen moiety leading to formation of an oxidized metallosalen moiety. For the Mnbond]salenbond]POM, the metallosalen center is best described as a metalbond]salen cation radical species; that is, a localized "hole" is formed on the salen ligand. For the other Mbond]salenbond]POM compounds, the metallosalen moiety can be described as a hybrid of a metalbond]salen cation radical species and an oxidized metalbond]salen species, that is, a delocalized "hole" is formed at the metallosalen center. It is proposed that these oxidized metallosalen centers are best characterized as stabilized charge transfer (metallosalen donorbond]polyoxometalate acceptor) complexes despite the relatively large distance between the two functional centers.