Synthesis, structure and optical studies of a family of three-dimensional rare-earth aminoisophthalates [M(μ₂-OH)(C₈H₅NO₄)](M= Y³⁺,La³⁺,Pr³⁺,Nd³⁺,Sm³⁺, Eu³⁺,Gd³⁺,Dy³⁺,and Er³⁺)

Abstract

A hydrothermal reaction of the acetate salts of the rare-earths, 5-aminoisophthalic acid (H₂AIP), and NaOH at 150°C for 3 days gave rise to a new family of three-dimensional rare-earth aminoisophthalates, [M(μ₂-OH)(C₈H₅NO₄)] [M = Y³⁺ (I), La³⁺ (II), Pr³⁺ (III), Nd³⁺ (IV), Sm³⁺ (V), Eu³⁺ (VI), Gd³⁺ (VII), Dy³⁺ (VIII), and Er³⁺ (IX)]. The structures contain M-O(H)-M chains connected by AIP anions. The AIP ions are connected to five metal centers and each metal center is connected with five AIP anions giving rise to a unique (5,5) net. To the best of our knowledge, this is the first observation of a (5,5) net in metal-organic frameworks that involve rare-earth elements. The doping of Eu³⁺/Tb³⁺ ions in place of Y³⁺/La³⁺ in the parent structures gave rise to characteristic metal-centered emission (red = Eu³⁺, green = Tb³⁺). Life-time studies indicated that the excited emission states in the case of Eu³⁺ (4 mol-% doped) are in the range 0.287-0.490 ms and for Tb³⁺ (4 mol-% doped) are in the range of 1.265-1.702 ms. The Nd³⁺-containing compound exhibits up-conversion behavior based on two-photon absorption when excited using λ = 580 nm.