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) 3 dme [RE = Y ( 1 ), La ( 2 ), Dy ( 3 ), or Eu ( 4 ); 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 N -oxide (pyterpyNO) to yield RE 2 (tta) 6 (pyterpyNO) n , where n = 2 for RE = Y ( 5 ), Dy ( 6 ), or Eu ( 7 ) and n = 3 for RE = La ( 8 ). The crystal structure of 5 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 ( 9 ), Dy ( 10 ), or Eu ( 11 ), it was possible to isolate the molecular complexes RE 4 (tta) 12 (pyterpyNO) 2 , while using a 5:3 molar ratio, the product La 5 (tta) 12 (pyterpyNO) 3 ( 12 ) can be obtained. 89 Y nuclear magnetic resonance spectroscopy revealed two different yttrium centers at room temperature for 9 . An X-ray diffraction study of 10 showed a symmetrical tetranuclear structure resulting from the coordination of two Dy(tta) 3 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 6 and 10 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 ( 6 ) and Raman ( 10 ) processes in the absence of an applied magnetic field; the rate increased upon application of a 1 kOe field. 7 and 11 showed a bright red emission typical of Eu 3+ . The two complexes have similar emission properties mainly determined by the employed β-diketonato ligands.