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

Two new complexes of gadolinium(III) and erbium(III) with pyridine-2,6-dicarboxylic acid (H(2)Pydc),{Na-3[Gd(Pydc)(3)]center dot 2H(2)O}(n) (I) and [Er(HPydc)(3)]center dot 10H(2)O (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, mu(3)- and mu(5)-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.