Synthesis, characterization and X-ray crystal structure of a chromium(III) complex obtained from a proton-transfer compound containing 1,10-phenanthroline-2,9-dicarboxylic acid and 2,6-pyridinediamine

The novel 1,10-phenanthroline-2,9-dicarboxylate containing Chromium(III) complex, (pydaH)[Cr(phendc)(2)] - 5H(2)O, was synthesized using proton-transfer compound LH2, (pydaH(2))(2+)(phendc)(2-), (pyda: 2,6-pyridinediamine; phendcH(2): 1,10-phenaiithroline-2,9-dicarboxylic acid) and thoroughly characterized by elemental analysis, IR spectroscopy, X-ray crystallography and cyclic voltammetry. The complex crystallizes in the monoclinic space group P2(1)/(n) with four formula units in the unit cell. The unit cell dimensions are: a = 13.962(3) angstrom, 6 = 14.529(3) angstrom, c = 16.381(3) angstrom and beta =106.691(4)degrees. In this complex, 1,10-phenanthroline-2,9-dicarboxylate acts as a tridentate ligand and the lattice is composed of anionic hexacoordinated complex, [Cr(phendc)2]-, 2,6-pyridiniumdiamine counter ion, (pydaH)(+), and five lattice water molecules. Crystallographic characterization revealed that the resulting supramolecular structure is strongly stabilized by complicated network of hydrogen bonds between the crystallization water molecules, counter ion and both coordinated and uncoordinated carboxylate groups. There is no relevant pi-pi interaction for this anionic complex between pyda or phende moieties. The electrochemical studies indicated over potential for both the cathodic and anodic peaks of the complex with respect to the free Cr3+ ion, as a consequence of the energy requirement for rearrangement of the ligand at electrode surface.