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) (H₃<i>L</i> = HOOC–C₆H₄–CH₂PO­(OH)₂, Ln = La, <b>1</b>; Ce, <b>2</b>; Pr, <b>3</b>; Nd, <b>4</b>; Sm, <b>5</b>; Eu, <b>6</b>; Gd, <b>7</b>; and Tb, <b>8</b>) 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 <b>1</b>–<b>5</b> and <b>7</b> exhibit ligand-centered blue light emission bands. Complexes <b>6</b> and <b>8</b> 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 ⁵D_<i>j</i>, resonance levels depending on the lowest triplet state energy level of the ligand. Magnetic properties of <b>7</b> and <b>8</b> have also been studied