Synthesis, crystal structures and characterization of iron(III) and cobalt(III) complexes bearing 2,2′-bipyridylcarboxylate ligands

The Fe(III) complex [FeIII(bpdc)(Hbpdc)] (1) (bpdc = 2,2′-bipyridyl-6,6′-dicarboxylate and Hbpdc = 2,2′-bipyridyl-6′-carboxyl-6-carboxylate) and the Co(III) complex [CoIII(bpc)2]PF6 (2) (bpc = 2,2′-bipyridyl-6-carboxylate) have been synthesized by the reactions of 2,2′-bipyridyl-6,6′-dicarboxylic acid (H2bpdc) with the corresponding metal salts under hydrothermal conditions. The X-ray crystal structures of complexes 1 and 2 were determined. Both of them are mononuclear compounds. In complex 1, the iron center is eight-coordinated by one bpdc ligand and one Hbpdc ligand resulting in a distorted dodecahedron geometry. On the other hand, decarboxylation of H2bpdc occurred in the preparation of compound 2, which is six-coordinated by two bpc ligands with a distorted octahedral geometry. The complexes were further investigated by spectroscopic methods, thermal gravimetric analyses or cyclic voltammetry.