Structure and emission spectrum of the o-phenanthroline adduct of tris(6-methyl-2,4-heptanedionato)europium(III)

The title compound, conveniently abbreviated Eu(MHD)₃·o-phen, has been prepared and characterized by means of its luminescence spectrum and by complete structure determination by X-ray diffraction. The β-diketone ligand is unsymmetrical with a methyl group at one end and an iso-butyl group at the other. Monoclinic crystals having m.p. 186-187°C were isolated from dichloromethane/iso-propanol. The luminescence spectrum is typical for low-symmetry complexes of this type with a single sharp ⁵D₀→⁷F₀ transition at 579.9 nm accompanied by a weak shoulder. The ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions are completely resolved with weak additional transitions that are most likely vibronic in origin. The X-ray structure shows a single eight-coordinate coordination geometry that approximates a square antiprism. The average Eu-O and Eu-N distances are 2.358 and 2.628 Å and are typical. Our initial assumption that the unsymmetrical β-diketone would lead to multiple sites was not substantiated.