Spectroscopic and Structural Characterization of the Nine-Coordinate Adduct of Tris(dipivaloylmethanato)europium(III) with 2,2':6',2"-terpyridine
Tris(dipivaloylmethanato)(2,2':6',2"-terpyridine)europium(III), [Eu(DPM)3terpy], was synthesized from [EU(DPM)3] and 2,2':6',2"-terpyridine in carbon tetrachloride. The complex was characterized by infrared and luminescence spectroscopy. The infrared spectrum indicated all three nitrogen atoms of the terpyridine ligand were bound to the metal ion. The luminescence spectrum was recorded at 77 K and revealed a broad (15 cm-1) unresolvable single transition in the 5D0 -> 7F0 region. The 5D0 -> 7F1 region contained six bands and the 5D0 -> 7F2 region contained nine bands, indicating two distinct emitting metal centers. The luminescence spectrum suggested that the site symmetry of both metal centers is C1. The structure of [Eu(DPM)3terpy] was solved by single-crystal X-ray diffraction methods. The complex was found to crystallize in the monoclinic space group P21/a with a = 18.487 (6) Å, b = 28.175 (7) Å, c = 19.434 (10) Å, ß = 91.57 (3)°, and V = 10118.8, Å3. Two isomers were found to exist in the unit cell with the ligating atoms forming a nine-coordinate distorted tricapped trigonal prism with each metal center. The two isomers differ by only small variations in bond angles and distances due to steric effects. The average Eu-O and Eu-N bond distances are 2.380 and 2.645 Å for the first Eu (III) ion and 2.385 and 2.663 Å for the second Eu(III) ion. The site symmetry of both metal centers is C1, which is consisten with the luminescence spectrum.