Synthesis and crystal structures of mono-helical complexes of zinc(II) and europium(III) with 1,2-bis{[3-(2-pyridyl)pyrazol-1-yl]ethoxy}ethane

A new multidentate ligand L, 1,2-bis{[3-(2-pyridyl)pyrazol-1- yl]ethoxy}ethane, has been synthesized by linking two 3-(pyridin-2- yl)pyrazoles with a 1,2-bis(ethoxy)ethyl spacer. Coordination of L with zinc(II) and europium(III) centres has led to mononuclear complexes of [Zn(L)](ClO₄)₂ (1) and [Eu(L)Cl₂](ClO₄) (2). X-ray crystal structures of both complexes have shown that L adopted a helical coordination geometry around both metal centres. The spectroscopic properties of both complexes have also been determined. In 1, photoluminescence was dominated by ligand centred ¹(π-π*) fluorescence. In 2, ligand-to-metal energy transfer leading to ⁵D₀ → ⁷Fn luminescence at the europium(III) centre was observed.