ESR and Magnetic Susceptibility Studies on High-Spin Tetrahedral Cobalt(II)–Thiolate Complexes: An Approach to Rubredoxin-Type Active Sites

Abstract

Abstract 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≈−100 cm−1, E≈0, gx≈gy<gz. This parameter set shows that Co(SPh)42− 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.