In situ oxidation of 2,9-dimethyl-1,10-phenanthroline for synthesis of nickel(II) complexes containing highly preorganized acidic ligand

Preorganized ligands have proven to be important in inorganic chemistry, biomedical,environmental, and industrial fields.1 Ligand preorganization means that the freeligand has the same conformation as is required to complex the target metal ion. These ligands have a rigid phen backbone, with only limited movement possible for the donor groups at the 2 and 9 positions of the phen, leads to high levels of preorganization. 1,10-Phenanthroline-2,9-dicarboxylic acid (H2PDA) with flat and rigid skeleton is one of the most prominent preorganized ligands which is used to prepare coordination compounds with selectivity metal ion, luminescence and magnetic properties.2 As continuation of our efforts to develop systems containing dicarboxylic acids,3 we employed H2PDA to synthesis Ni(II) coordination complexes formulated as [Ni(PDA)(H2O)2 ] (1) and [Ni(PDA)(phen)].5H2O (2) (Fig. 1). These compounds have been characterized by melting point, elemental analysis, infrared spectroscopy (IR), and thermogravimetric (TGA) analysis.