ESR AND MAGNETIC-SUSCEPTIBILITY STUDIES ON HIGH-SPIN TETRAHEDRAL COBALT(II)-THIOLATE COMPLEXES - AN APPROACH TO RUBREDOXIN-TYPE ACTIVE-SITES

Magnetic susceptibility and ESR studies on high-spin (S = 3/2) tetrahedral cobalt(II)-thiolate complexes were performed for A2[Co(SPh)4]; A = Me4N (1a), Et4N (1b), Ph4P (1c) and (Et4N)2[Co(SR)4]; R = C6H4-p-Me (2), C6H4-p-Cl (3), C6F5 (4). It was found that the magnitude of zero-field splitting and the anisotropy of g-factor are exceptionally large for 1c as D almost-equal-to -100 cm-1, E almost-equal-to 0, g(x) almost-equal-to g(y) < g(z). This parameter set shows that Co(SPh)4(2-) in 1c is strongly affected by an axial distortion. On the contrary, a rhombic distortion with moderate magnitude was found for 1a (D* = 6.5 cm-1, E/D = -0.21) and 1b (D* = 5.0 cm-1, E/D = 0.19). The results for the other compounds are D* = 7.0 cm-1, E/D = 0.14 for 2, D* = 12 cm-1, E/D = 0.10 for 3, and D* = 2.0 cm-1, E/D = 0.02 for 4. Attempts were made to correlate the magnetic properties and the coordination geometry for 1a-c by use of available X-ray data. As a result, the importance of the orientation of the thiolate ligands was confirmed.