Luminescent Lanthanide(III) Carboxylate−Phosphonates with Helical Tunnels

Abstract

Hydrothermal reactions of lanthanide(III) salts with H4PMIDA (N-(phosphonomethyl)iminodiacetic acid) led to seven new isostructural lanthanide(III) carboxylate phosphonates, namely, Ln(HPMIDA)(H2O)2·H2O (Ln = Gd, 1; Tb, 2; Dy, 3; Y, 4; Er, 5; Yb, 6; Lu, 7). Their structures feature a novel 3D framework. The lanthanide(III) ion is eight-coordinated by a chelating HPMIDA in a tetradentate fashion (1 N and 3 O), one carboxylate oxygen and one phosphonate oxygen from two other HPMIDA anions, and two aqua ligands. The HPMIDA anion is hexadentate. It chelates with a Ln(III) ion tetradentatedly and also bridges with two other Ln(III) ions. The phosphonate group is singly protonated. One of the carboxylic groups is unidentate, whereas the other is bidentate bridging. Compound 2 exhibits very strong characteristic emission bands for the terbium(III) ion in the visible region under 380 nm excitation, with the Tb (5D0) lifetime for λex,em = 380 and 488 nm being about 1 ms. Compounds 1 and 5 display very broad ligand-centered emission bands in the blue light region.