pH-Dependent Syntheses, Luminescent, and Magnetic Properties of Two-Dimensional Framework Lanthanide Carboxyarylphosphonate Complexes

A series
of novel organic–inorganic complexes based on trivalent
lanthanide and HOOC–C6H4–CH2PO­(OH)­(OC2H5) (H2L′)
formulated as Ln­(HL)­(H2L)­(H2O) (H3L = HOOC–C6H4–CH2PO­(OH)2, Ln
= La, 1; Ce, 2; Pr, 3; Nd, 4; Sm, 5; Eu, 6; Gd, 7; and Tb, 8) have been obtained as single phases by
regulating the pH values under hydrothermal conditions. They are isomorphous
and feature a network in which the LnO7 polyhedra are interconnected
by bridging CPO3 tetrahedra into inorganic layers. These
layers are further cross-linked by hydrogen bonds of the carboxyl
acid groups of ligands into a S-shape pillared framework architecture.
Luminescent measurements indicate that complexes 1–5 and 7 exhibit ligand-centered blue light emission
bands. Complexes 6 and 8 display Ln-centered
strong red and green luminescence, respectively. To elucidate the
energy transfer process between ligands and metal ions, the energy
levels of the relevant electronic states have been estimated. Simultaneously
Eu3+ and Tb3+ were observed to accept energy
with their several different 5Dj, resonance levels depending on the lowest triplet state energy level
of the ligand. Magnetic properties of 7 and 8 have also been studied.