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(μ-OH)₈(NO₃)₈] (1) and [Tb₈(dpim)₄(μ-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 dpim^2– ligands, eight OH^–/OD^– bridges, and eight nitrato ligands. One Tb(III) ion is located in the inner N₂O₂ compartment of dpim^2– and bonded to two nitrate anions. Two Tb(III) ions are located in the distorted outer O₂O₂′ compartment of the dpim^2– 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.