Structures, Luminescence, and Magnetic Properties of Several Three-Dimensional Lanthanide-Organic Frameworks Comprising 4-Carboxyphenoxy Acetic Acid

Ten new 3D lanthanide-based compounds, {[Ln(4)(CPOA)(6)(H2O)(4)]center dot H2O} (Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5)) and [Ln(CPOA)(C2O4)(0.5)(H2O)] (Ln = Eu (1a), Gd (2a), Tb (3a), Dy (4a), Ho (5a)) (CPOA(2-) = 4-carbomethoxybenzoate), have been synthesized by a hydrothermal method under different temperatures. The compounds 1-5 were obtained at 140 degrees C. When the temperature went up to 180 degrees C, the ligands partly decomposed to C2O42-, then came into being compounds 1a-5a. The two series of compounds displayed the differences not only in structure but also in thermal stability and luminescent and magnetic properties. Compounds 1-5 crystallize in the triclinic system, space group P (1) over bar, whereas compounds 1a-5a belong to the monoclinic system with space group P2(1)/c. Thermal analyses were carried out on 1-5 and 1a-3a. Solid luminescence studies of compounds 1 and 1a, 3 and 3a, and 4 and 4a show the characteristic bands of Eu3+, Tb3+, and Dy3+, respectively. Magnetic properties were investigated on 2-4 and 2a-4a. The out-of-phase signals (chi(M)'') of 4 exhibit a strong frequency dependence, suggesting the existence of slow magnetic relaxation behavior in 4.