Synthesis, crystal molecular structure, and magnetic characteristics of coordination polymers formed by Co(ii) diketonates with pentaheterocyclic triphenodioxazines

Abstract

Stable crystalline complexes of Co(II) acetylacetonate [Co(II)(acac)₂], trifluoacetylacetonate [Co(II)(tfac)₂] and hexafluoroacetylacetonate [Co(II)(hfac)₂] with triphenodioxazines (TPDOs) were synthesized and their structures studied using X-ray crystallography. In the crystal, complexes [Co(II)(tfac)₂]TPDO and [Co(II)(hfac)₂]TPDO form infinite ⋯N⋯Co⋯N⋯ chains featuring 1D coordination polymeric structures, whereas in the [Co(II)(acac)₂]TPDO complex, the Co(acac)₂ units fill only half of the possible crystallographic positions. The electron accepting trifluoro substituents in the diketonate moieties significantly enhance the thermal stability of the complexes with TPDO. Of all the complexes, only [Co(II)(hfac)₂]TPDO does not dissociate into the components in solution. In all studied complexes, the Co(II) atom is in a high-spin state and has distorted octahedral surroundings. Distortion of the octahedral polyhedrons appears as axial stretching of the octahedrons along the Co–N bonds; it is due to the specific features of the crystalline structure of the metal polymeric chain in the compounds.