Coordination Complexes of a Neutral 1,2,4-Benzotriazinyl Radical Ligand: Synthesis, Molecular and Electronic Structures, and Magnetic Properties

A series of d-block metal complexes of the recently reported coordinating neutral radical ligand 1-phenyl-3-(pyrid-2-yl)-1,4-dihydro-1,2,4-benzotriazin-4-yl (1) was synthesized. The investigated systems contain the benzotriazinyl radical 1 coordinated to a divalent metal cation, Mn(II) , Fe(II) , Co(II) , or Ni(II) , with 1,1,1,5,5,5-hexafluoroacetylacetonato (hfac) as the auxiliary ligand of choice. The synthesized complexes were fully characterized by single-crystal X-ray diffraction, magnetic susceptibility measurements, and electronic structure calculations. The complexes [Mn(1)(hfac)2 ] and [Fe(1)(hfac)2 ] displayed antiferromagnetic coupling between the unpaired electrons of the ligand and the metal cation, whereas the interaction was found to be ferromagnetic in the analogous Ni(II) complex [Ni(1)(hfac)2 ]. The magnetic properties of the complex [Co(1)(hfac)2 ] were difficult to interpret owing to significant spin-orbit coupling inherent to octahedral high-spin Co(II) metal ion. As a whole, the reported data clearly demonstrated the favorable coordinating properties of the radical 1, which, together with its stability and structural tunability, make it an excellent new building block for establishing more complex metal-radical architectures with interesting magnetic properties.