The 2,2′-bipyrimidine (bpm) adducts of the β-diketonate complexes of Eu(III), Sm(III), or Yb(III) with 2,2′,6,6′-tetramethyl-2,4-heptanedione (tmhd) resulted in the formation of dinuclear species. The synthesis and X-ray structure of these three new dinuclear lanthanide complexes are found to be similar. Each lanthanide ion is eight coordinate, bound to six O-atoms from the β-diketonates and 2N atoms from the bridging bpm ligand. They exhibit Ln-Ln distances (Sm(III): 6.935 Å, Eu(III): 6.901 Å, Yb(III): 6.679 Å) and Ln-ligand distances that are consistent with the decrease in radii across the lanthanide series. Absorption spectra of the complexes are dominated by ligand absorptions. Both the solution and solid state emission spectra of the complexes resemble ordinary monomeric lanthanide species, indicating independent ions in the dinuclear species. Cyclic voltammetry of all the complexes appear almost identical with discernable ligand centered redox reactions. The complex with Eu(III) ions, having the lowest possible lanthanide redox potential, was not found to display a signal corresponding to metal reduction.
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The authors are grateful to the Research Corporation (Grant No. CC6396) for financially supporting this research and providing M.H.B with a summer stipend. M.H.B. and S.M.B. would like to thank the Swenson Family Foundation and UMD for a summer stipend and research support. J.D.D. thanks the UMD Department of Chemistry for the Moses Passer Fellowship. R.D.P. is indebted to NSF (CHE-0443345) and the College of William and Mary for the purchase of the X-ray diffraction equipment.