The Effect on the Luminescent Properties in Lanthanide-Titanium OXO Clusters.

Two lanthanide-titanium oxo clusters (LTOCs), formulated as [EuTi(μ-O)(μ-OH)(CHO)(Ac)(CHOH)(tbba)]·CHOH () and [EuTi(μ-O)(μ-OH)(μ-OCH)(μ-OCH)(HO)(CHOH)(tbba)]·Htbba·10HO (), were synthesized through the solvothermal reaction of 4--butylbenzoate ligand, Eu(Ac)·3HO, and Ti(OPr) in methanol. Single-crystal structural analysis reveals that crystallized in the orthorhombic space group 2, and crystallized in the triclinic space group 1. Structurally, the core of can be viewed as a coplanar unit of [EuTi(μ-O)(μ-OH)] formed through each μ-O and μ-OH bridging one Ti and two Eu ions, while that of can be viewed as two units of [EuTi(μ-O)(μ-O)(μ-OCH)(CHOH)] and [EuTi(μ-O)(μ-OH)(μ-OCH)(HO)(CHOH)] connected through four μ-O units from the [EuTi(μ-O)(μ-O)(μ-OCH)(CHOH)] unit to respectively coordinate two Eu and two Ti ions from the [EuTi(μ-O)(μ-OH)(μ-OCH)(HO)(CHOH)] unit. Measurement of their luminescence properties shows that the luminescence lifetime and quantum yield are 1212 μs and 69.6% for and 857 μs and 56.2% for . When F was introduced into in a molar ratio of F to of 1:3, its quantum yield was increased 1.3 times, and the lifetime increased from 1.2 to 1.4 ms. However, no obvious enhancement in the emission intensity was observed in ; even the molar ratio of F to is in the range from 2 to 1/4. Investigation on the structures of and reveals that the luminescence lifetime and quantum yield in is significantly larger than that in are attributed to the vibration of the nonradiative O-H vibration groups in being significantly smaller than that in .