A new series of tetrahedral Co(ii) complexes [CoLX] (X = NCS, Cl, Br, I) manifesting single-ion magnet features.

A series of tetrahedral Co complexes [CoLX] (X = NCS (1), Cl (2), Br (3) and I (4); L = 9,9-dimethyl-4,5-bis(diphenylphosphino) xanthene) based on a P-donor ligand has been prepared to investigate the influence of terminal ligand field strength on the anisotropy of Co single-ion magnets. It has been observed that heavier and softer terminal ligands are able to decrease the anisotropy of the tetrahedral Co centers. Thorough analyses of experimental and theoretical studies show that all complexes have an easy-axis type magnetic anisotropy and slow relaxation behaviors of tetrahedral Co centers. Detailed ab initio theory studies disclose that the changes in the ligand field strength imposed by the terminal ligands result in modifying the single ion anisotropy (D) of polyhedra 1-4. Furthermore, the isostructural Zn analogue (5) has been prepared to examine the influence of dipolar interactions between adjacent Co centres and magnetic dilution experiments were performed.