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 ]·2H 2 O} n ( I ) and [Er(HPydc) 3 ]·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 (GdN 3 O 6 ) and exhibits a tricapped trigonal prismatic geometry having 14 triangular faces. The Pydc ligand adopts chelating and, μ 3 - and μ 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 (ErN 3 O 6 ). 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.