Influence of F-position and solvent on coordination geometry and single ion magnet behavior of Co(ii) complexes

Three mononuclear Co(ii) complexes with the compositions of [Co(L₁)₂] (1), [Co(L₂)₂(CH₃CN)] (2) and [Co(L₃)₂] (3) (HL₁= 2-((E)-(2-fluorobenzylimino)methyl)-4,6-dibromophenol, HL₂= 2-((E)-(3-fluorobenzylimino)methyl)-4,6-dibromophenol and HL₃= 2-((E)-(4-fluorobenzylimino)methyl)-4,6-dibromophenol) were prepared and structurally determined. The changes in the F-positions in the ligands and solvents led to the formation of these products with various coordination geometries. Both complexes1and3are four-coordinated and their coordination geometries can be described as tetrahedron and seesaw, whereas complex2is five coordinated with a coordination configuration in between trigonal bipyramid and square pyramid. Static magnetic studies reveal that all these complexes exhibit considerable easy-axis magnetic anisotropy. The easy-axis magnetic anisotropy of1and3mainly derives from the first quartet excited state, whereas that of2primarily originates from the first, third and fourth quartet excited states established by theoretical calculations. All the resulting complexes display field-induced slow magnetic relaxation. Complex3represents the first Co(ii) single ion magnet with a seesaw coordination geometry.Ab initiocalculations predict that the magnetic anisotropy will enhance when the seesaw coordination geometry varies from distortion to regulation.