Novel Functionalized Rare Earth Metal Clusters and Polymers. Neuartige Funktionalisierte Seltenerdmetallcluster und Polymere

Novel functionalized rare earth metal clusters and polymers have been prepared, characterized and investigated with respect to various potential applications.
The literature known tetra- and pentanuclear rare earth metal hydroxy clusters [Ln4(?3-OH)2(Ph2acac)10] (Ln = Pr, Nd, Sm) and [Ln5(?4-OH)(?3-OH)4(Ph2acac)10] (Ln = Y, Eu) were embedded into different polymer matrices applying the miniemulsion polymerization technique to give cluster-polymer hybrid nanocompounds with narrow size distributions. The polymer matrices involved were composed of polystyrene (PS), poly(methyl methacrylate) (PMMA), poly(lauryl methacrylate) (PLMA) and poly(butyl acrylate-co-methyl methacrylate) (PBA-co-MMA). As a consequence of encapsulation, aqueous dispersions containing the hydrophobic clusters with more than 1000 mg.L-1 could be prepared. Subsequent optical investigations revealed the retention of the encapsulated clusters' photophysical properties in aqueous dispersions. Additionally, a very efficient energy transfer from the ligand and polymeric unit to the Eu3+-ions was observed.
Envisioning a functionalization of these pure Ph2acac clusters, the pentanuclear mixed ligated rare earth metal hydroxy clusters [Ln5(?4-OH)(?3-OH)4(??AA)4(Ph2acac)6] (1-6) (Ln = Y: ??AA = D-PhGly (1), L-Pro (2), L-Val (3), L-Trp (4), Ph2Gly (5); Ln = Dy: ??AA = D-PhGly (6)) were reproducibly prepared in gram scale and the corresponding solid state structures were established via single crystal X-ray analysis. Clusters 1-6 display a square pyramidal {Ln5(?4-OH)(?3-OH)4}10+ scaffold, which is coordinatively and electronically saturated by six chelating Ph2acac ligands and four amino acid ligands acting as bridging chelates. The hydrodynamic radius rH of valine cluster 3 was determined via NMR-based PGSE diffusion experiments, revealing the retention of the cluster's scaffold upon dissolution. Furthermore, 2D NMR experiments with 3 showed a heteronuclear cross coupling between 89Y and 1H nuclei.