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

Abstract

Two lanthanide-titanium oxo clusters (LTOCs), formulated as [Eu3Ti3(μ3-O)2(μ3-OH)(CH3O)2(Ac)2(CH3OH)(tbba)12]·CH3OH (1) and [Eu6Ti8(μ3-O)13(μ2-OH)(μ3-OCH3)2(μ2-OCH3)2(H2O)(CH3OH)2(tbba)19]·Htbba·10H2O (2), were synthesized through the solvothermal reaction of 4-tert-butylbenzoate ligand, Eu(Ac)3·3H2O, and Ti(OiPr)4 in methanol. Single-crystal structural analysis reveals that 1 crystallized in the orthorhombic space group Pnn2, and 2 crystallized in the triclinic space group P1. Structurally, the core of 1 can be viewed as a coplanar unit of [Eu3Ti3(μ3-O)2(μ3-OH)]16+ formed through each μ3-O2- and μ3-OH- bridging one Ti4+ and two Eu3+ ions, while that of 2 can be viewed as two units of [Eu3Ti3(μ3-O)3(μ2-O)4(μ2-OCH3)2(CH3OH)]5+ and [Eu3Ti5(μ3-O)6(μ2-OH)(μ3-OCH3)2(H2O)(CH3OH)]14+ connected through four μ2-O units from the [Eu3Ti3(μ3-O)3(μ2-O)4(μ2-OCH3)2(CH3OH)]5+ unit to respectively coordinate two Eu3+ and two Ti4+ ions from the [Eu3Ti5(μ3-O)6(μ2-OH)(μ3-OCH3)2(H2O)(CH3OH)]14+ unit. Measurement of their luminescence properties shows that the luminescence lifetime and quantum yield are 1212 μs and 69.6% for 1 and 857 μs and 56.2% for 2. When F- was introduced into 1 in a molar ratio of F- to 1 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 2; even the molar ratio of F- to 2 is in the range from 2 to 1/4. Investigation on the structures of 1 and 2 reveals that the luminescence lifetime and quantum yield in 1 is significantly larger than that in 2 are attributed to the vibration of the nonradiative O-H vibration groups in 1 being significantly smaller than that in 2.