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

Two lanthanide-titanium oxo clusters (LTOCs), formulated as [Eu3Ti3(mu(3)-O)(2)(mu(3)-OH)(CH3O)(2)(Ac)(2)(CH3OH)(tbba)(12)]center dot CH3OH (1) and [Eu6Ti8(mu(3)-O)(13)(mu(2)-OH)(mu(3)-OCH3)(2) (mu(2)-OCH3)(2)(H2O)(CH3OH)(2)(tbba)(19)]center dot Htbba center dot 10H(2)O (2), were synthesized through the solvothermal reaction of 4-tert-butylbenzoate ligand, Eu(Ac)(3)center dot 3H(2)O, and Ti((OPr)-Pr-i)(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 P (1) over bar. Structurally, the core of 1 can be viewed as a coplanar unit of [Eu3Ti3(mu(3)-O)(2)(mu(3)-OH)](16+) formed through each mu(3)-O2- and mu(3)-OH- bridging one Ti4+ and two Eu3+ ions, while that of 2 can be viewed as two units of [Eu3Ti3(mu(3)-O)(3)(mu(2)-O)(4)(mu(2)-OCH3)(2)(CH3OH)](5+) and [Eu3Ti5(mu(3)-O)(6)(mu(2)-OH)(mu(3)-OCH3)(2)(H2O)(CH3OH)](14+) connected through four mu(2)-O units from the [Eu3Ti3(mu(3)-O)(3)(mu(2)-O)(4)(mu(2)-OCH3)(2)(CH3OH)](5+) unit to respectively coordinate two Eu3+ and two Ti4+ ions from the [Eu3Ti5(mu(3)-O)(6)(mu(2)-OH)(mu(3)-OCH3)(2)(H2O)(CH3OH)](14+) unit. Measurement of their luminescence properties shows that the luminescence lifetime and quantum yield are 1212 mu s and 69.6% for 1 and 857 mu s 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.