A solid-state study of eight-coordinate lanthanide(III) complexes (Ln = Eu, Gd, Tb, Dy) with 1-hydroxy-2-pyridinone

merFour lanthanide complexes of 1-hydroxy-2-pyridinone (HOPO) have been synthesised from aqueous solution at pH 7 and their structures and luminescent properties have been established. This ligand coordinates to lanthanide(III) ions as an anionic bidentate chelate (1-oxy-2pyridinonate, OPO–) and crystallographic analyses show the formation of two structural types with different stoichiometries. In the first part of this series (Eu, Gd) the structural type consists of dimer units Na2[Ln2(OPO)8]·9H2O, crystallising in the orthorhombic system, space group P212121. The immediate coordination sphere around Ln is occupied by the eight oxygen atoms of four bidentate OPO– ligands. These complexes display the Na+ ions associated with the complex anion via interactions with bridging CO and NO groups of the ligands, inducing a polymeric structure. In the second part of the series (Tb, Dy) the structures obtained are [Ln(OPO)3(H2O)2]·H2O, crystallising in triclinic system, space group P. The Tb(III) and Dy(III) ions are also eight-coordinated but two water molecules occupy the coordination sphere instead of one ligand OPO–. The Dy(III), Eu(III) and Tb(III) complexes display in the solid state and at room temperature a photoluminescence that is achieved by an indirect excitation process (antenna effect). The terbium(III) complex exhibits intense sensitized green emission, which is temperature independent.