Stoichiometrically Controlled Assembly of Lanthanide Molecular Complexes of the Heteroditopic Divergent Ligand 4'-(4-Pyridyl)-2,2':6',2″-terpyridine N -Oxide in Hypodentate or Bridging Coordination Modes. Structural, Magnetic, and Photoluminescence Studies

Mononuclear rare-earth tris-β-diketonato complexes RE(tta) dme [RE = Y ( ), La ( ), Dy ( ), or Eu ( ); Htta = 2-thenoylacetone; dme = 1,2-dimethoxyethane] react cleanly at room temperature in a 1:1 molar ratio with the heteroditopic divergent ligand 4'-(4-pyridyl)-2,2':6',2″-terpyridine -oxide (pyterpyNO) to yield RE (tta) (pyterpyNO) , where = 2 for RE = Y ( ), Dy ( ), or Eu ( ) and = 3 for RE = La ( ). The crystal structure of revealed a dinuclear compound with two pyterpyNO's bridging through the oxygen atom in a hypodentate mode leaving the terpyridine moieties uncoordinated. Using a metal:pyterpyNO molar ratio of 2 for RE = Y ( ), Dy ( ), or Eu ( ), it was possible to isolate the molecular complexes RE (tta) (pyterpyNO) , while using a 5:3 molar ratio, the product La (tta) (pyterpyNO) ( ) can be obtained. Y nuclear magnetic resonance spectroscopy revealed two different yttrium centers at room temperature for . An X-ray diffraction study of showed a symmetrical tetranuclear structure resulting from the coordination of two Dy(tta) fragments to the two hypodentate terpyridines of the dinuclear unit and presenting two different coordination sites for metals with coordination numbers of 8 and 9. Magnetic studies of and revealed the presence of an antiferromagnetic interaction between the two Dy(III) atoms bound by the NO bridges. These compounds displayed a slow relaxing magnetization through Orbach ( ) and Raman ( ) processes in the absence of an applied magnetic field; the rate increased upon application of a 1 kOe field. and showed a bright red emission typical of Eu . The two complexes have similar emission properties mainly determined by the employed β-diketonato ligands.