Co(II)-promoted transformation of diethyl(quinolin-2-ylmethyl)phosphonate to quinoline-2-carboxylate (2-qca): Synthetic, structural and magnetic studies of [Co(2-qca)2(EtOH)2]

The interaction of the diethyl(quinolin-2-ylmethyl)phosphonate (2-qmpe) ligand with CoCl2 · 2H2O unexpectedly leads to the formation of a compound with the formula [Co(2-qca)2(EtOH)2] (2-qca = quinoline-2-carboxylate). This compound is a product of the oxidative cleavage of the C–P bond in 2-qmpe and the formation of the 2-qca ligand. The title compound was characterized by infrared, ligand field, EPR spectroscopy and low temperature magnetic (1.8–300 K) studies. Particularly, the crystal and molecular structures were determined by the X-ray diffraction. The CoN2O4 chromophore shows an elongated octahedron geometry, resulting from the two didentate N,O-bonded chelate ligands and two ethanol molecules – quinolil nitrogen atoms are located in axial positions and oxygen atoms are positioned in the basal plane. The crystal packing is due to hydrogen bonds and π–π stacking interactions, which give rise to a three-dimensional (3D) polymeric network. The magnetic properties reflect the molecular character of the compound, with a very weak magnetic exchange interaction. The moments are enhanced due to an important orbital contribution via spin–orbit coupling.

The synthesis and single-crystal X-ray structural characterization of a novel compound of the formula [Co(2-qca)2(EtOH)2] (2-qca = quinoline-2-carboxylate) is reported. This compound has been synthesized by the oxidative decomposition of the diethyl(quinolin-2-ylmethyl)phosphonate ligand. In this reaction the cobalt(II) ion promotes C–P bond cleavage. Detailed characterization of Co(2-qca)2(EtOH)2 includes structural, spectroscopic and magnetic studies.Figure optionsDownload as PowerPoint slide