Fluorescence and energy transfer properties of heterometallic lanthanide-titanium oxo clusters coordinated with anthracenecarboxylate ligands

Two 9-anthracenecarboxylate (9-AC) coordinated heterometallic TOC compounds, [Ln(2)Ti(10)O(14)-(ClO4)(2)((OPr)-Pr-i)(14)(9-AC)(2)(CH3CN)(2)]center dot 2H(2)O, Ln = Nd (1) and Eu (2), along with two benzoate (bza) analogues, [Ln(2)Ti(10)O(14)(ClO4)(2)((OPr)-Pr-i)(14)(bza)(2)((HOPr)-Pr-i)(2)], Ln = Nd (3) and Eu (4), were prepared by one step in situ solvothermal synthesis, and characterized by single crystal analysis. To date, only about ten lanthanum-titanium oxo clusters have been reported. Except for two Ti28 clusters, the compounds are all small clusters (Ti <= 4). The cluster structures of 1-4 adopt a Ti10Ln2 core structure with pseudo-C-i symmetry, which is similar to the fundamental structure of Ti12 clusters. Furthermore, except for their structures, the properties of lanthanum-titanium oxo clusters have never been studied. Herein, the fluorescence properties of these compounds are studied in detail. The metal centered emission of Eu(III) is completely quenched by 9-AC due to the lower triplet energy of the coordinated ligand. Enhanced ligand centered fluorescence is found for 2 in comparison with that of 1.