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 O_h symmetry (with ⁴T_1g ground state) to D_4h (with ⁴A_2g ground state). This decrease in symmetry is responsible for the quenching of the orbital contribution, as will be discussed in this article.

Keywords:

• Cobalt(II)
• terpyridine derivatives
• magnetic properties
• orbital quenching

Acknowledgements

This research has been performed as part of the Chilean-French International Associated Laboratory for “Multifunctional Molecules and Materials” (LIA M3 CNRS n°1027). Financial supports from the Fondo Nacional de Desarrollo Científico y Tecnológico [FONDECYT (Chile), N°1130433], the CNRS and the Université de Rennes 1 are gratefully acknowledged. FEDER funds are also acknowledged for their participation in to purchase of the D8 VENTURE Bruker AXS diffractometer. D. Toledo thanks CONICYT (Chile) for support of the graduate fellowship N°21120148.