Deuterium-Enhanced Photoluminescence and Magnetic Properties in Octanuclear Terbium(III) Complexes Containing a Hexadentate N2O4-Type Ligand

Abstract

Two new octanuclear lanthanide coordination complexes [Tb8(dpim)4(mu-OH)8(NO3)8] (1) and [Tb8(dpim)4(mu-OD)8(NO3)8] (2) were prepared using terbium(III) nitrate salt in ethanol and deuterium oxide (for only 2) and a hexadentate ligand [(2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(6-methoxyphenol)] (H2dpim). The molecular structures of 1 and 2 comprise octanuclear compounds featuring eight Tb(III) ions, four dpim2- ligands, eight OH-/OD- bridges, and eight nitrato ligands. One Tb(III) ion is located in the inner N2O2 compartment of dpim2- and bonded to two nitrate anions. Two Tb(III) ions are located in the distorted outer O2O2 ' compartment of the dpim2- ligand and coordinated by a hydroxyl bridge. Three Tb(III) ions are connected through a hydroxyl group, while one Tb(III) ion is connected to an adjacent [Tb2(dpim)]4+ derivative unit. Consequently, the structure consists of an octanuclear complex with four corner-sharing incomplete cuboidal {Tb3O4} cores, decorated with eight terminal nitrato, methoxy, and phenolato ligands. The structure of 2 is isomorphic to that of 1, except that it contains OD-. Photoluminescence spectroscopy revealed that the octanuclear complexes exhibited strong luminescence in the 488-620 nm range. Complex 2, with OD- bridging ligands, exhibited considerably higher emission than 1 because of the deuteration effect. The quantum yields of 1 and 2 were 19 and 75%, respectively. Magnetic measurements revealed that the magnetic behavior of 2 exhibited a slightly stronger contribution from the depopulation of Stark levels and antiferromagnetic couplings compared to 1.