Magnetic anisotropies and slow magnetic relaxation of three tetrahedral tetrakis(pseudohalido)-cobalt() complexes

Three mononuclear tetrakis(pseudohalido)-cobalt( ii ) complexes (Ph 4 P) 2 [Co(E) 4 ] (E = N 3 − , 1 ; NCO − , 2 ; NCS − , 3 ) have been synthesized and structurally characterized. Each compound contains a distorted tetrahedral Co 2+ ion coordinated by four pseudohalide ligands. The magnetic properties of 1-3 have been studied using direct-current magnetic measurements and high-frequency and -field EPR spectroscopy (HFEPR), suggesting easy-axis magnetic anisotropy for 1 and 2 and easy-plane anisotropy for 3 . Analysis of the HFEPR spectra yielded D values of −5.23 and +3.63 cm −1 for 2 and 3 , respectively. The absence of the EPR signal in 1 is consistent with a large, negative value of the zero-field splitting (ZFS) parameter D in 1 . The nature of magnetic anisotropies of 1-3 has also been confirmed by ab initio calculations. The calculated D values are consistent with those determined using magnetometry and HFEPR studies. Alternating current (AC) magnetic susceptibilities reveal slow magnetic relaxation under an applied magnetic field, thus indicating that 1-3 are field-induced single-ion magnets (SIMs). Magnetic anisotropies and slow magnetic relaxation of three homoleptic cobalt( ii ) complexes with different pseudohalide ligands were studied via magnetometry, HFEPR and theoretical calculations.