Synthesis, Crystal Structures of Gadolinium(III) and Erbium(III) Complexes Derived from Pyridine-2,6-Dicarboxylic Acid and Fluorescent Sensing of Picric Acid

Abstract

Two new complexes of gadolinium(III) and erbium(III) with pyridine-2,6-dicarboxylic acid (H2Pydc),{Na3[Gd(Pydc)3]·2H2O}n (I) and [Er(HPydc)3]·10H2O (II), were prepared and their crystal structures were determined by X-ray crystallography (CIF files CCDC nos. 940633 (I) and 872068 (II)). The gadolinium atom in I is nine-coordinate (GdN3O6) and exhibits a tricapped trigonal prismatic geometry having 14 triangular faces. The Pydc ligand adopts chelating and, μ3- and μ5-bridging coordination modes. The 1D chains are further joined by Na atoms to generate a 3D coordination polymer. The structure is additionally stabilized by H-bonding. The Erbium polyhedron in II is also a tricapped trigonal prism (ErN3O6). The HPydc anions in II behave as tridentate chelating ligands. The complex molecules are connected to each other through hydrogen bonding interactions to form a three-dimensional network. Fluorescence titration experiments for complex II displayed highly sensitive fluorescence quenching efficiency of 98.3% against picric acid.