New cobalt(II) coordination polymer based on carboxyphenyl-tpy ligand: Photoluminescence, crystal structures and magnetic properties, without orbital contribution

Abstract

One coordination polymer, [Co(3-ctpy)2(H2O)2]n*2nEtOH (1), was synthesized by a solvothermal method mixing the complex precursor cobalt(II) acetylacetonate (Co(acac)2*2H2O) with 4′-(4-carboxyphenyl)-3,2′:6′,3″-terpyridine (3-Hctpy). This paramagnetic complex has been isolated as a neutral, air and thermal stable solid and has been characterized by elemental analysis, FT-IR and single-crystal X-ray diffraction analysis. The thermal stability and photoluminescence properties were studied in the solid state. The magnetic behavior presents an interesting challenge since the Co(II) ion has a spin 3/2, which leads to multiple possibilities under the influence of an energy crystal field, from the identification of the ground state to possible transitions to excited states. The usual orbital contribution of the magnetic moment has been extinguished, due to an axially distorted octahedral environment for cobalt, changing the Oh symmetry (with 4T1g ground state) to D4h (with 4A2g ground state). This decrease in symmetry is responsible for the quenching of the orbital contribution, as will be discussed in this article.