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

Ten new 3D lanthanide-based compounds, {[Ln4(CPOA)6(H2O)4]·H2O}n (Ln = Eu (1), Gd (2), Tb (3), Dy (4), Ho (5))
and [Ln­(CPOA)­(C2O4)0.5(H2O)]n (Ln = Eu (1a), Gd (2a), Tb (3a), Dy (4a), Ho (5a)) (CPOA2– = 4-carbomethoxybenzoate),
have been synthesized by a hydrothermal method under different temperatures.
The compounds 1–5 were obtained at
140 °C. When the temperature went up to 180 °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 P1̅, whereas
compounds 1a–5a belong to the monoclinic
system with space group P21/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 (χM″)
of 4 exhibit a strong frequency dependence, suggesting
the existence of slow magnetic relaxation behavior in 4.