Syntheses, crystal structures and magnetic properties of two mixed-valence Co(iii)Co(ii) compounds derived from Schiff base ligands: field-supported single-ion-magnet behavior with easy-plane anisotropy.

Two μ-phenoxo-μ-azide dinuclear CoCo complexes [Co(N)L(μ-N)Co(N)]·MeOH (1) and [Co(N)L(μ-N)Co(N)]·MeOH (2) (HL and HL are two Schiff base ligands having NO-NO compartments) both possess one hexacoordinate Co(iii) and one pentacoordinate Co(ii) center. DC magnetic susceptibility and magnetization measurements show an appreciable amount of positive magnetic anisotropy (D/hc∼ 40 cm) that is also confirmed by ab initio CASSCF calculations. AC susceptibility measurements of 1 reveal that it exhibits a slow magnetic relaxation with two relaxation channels. The external magnetic field supports the low-frequency (LF) channel that escapes on heating more progressively than the high-frequency (HF) branch. The relaxation time is as slow as τ = 255 ms at T = 1.9 K and B = 0.6 T, where the LF mole fraction is 69%. The complex 2 also displays similar field-supported slow magnetic relaxation with two relaxation channels.