High-frequency and -field electron paramagnetic resonance of high-spin cobalt(II) and nickel(II) scorpionate complexes

by Krzystek, J.; Ozarowski, Andrew; Desrochers, Patrick J.; Vicic, David A.; Trofimenko, S.; Telser, Joshua

Trispyrazolylborates, or "scorpionates" have long been known as effective and versatile chelating ligands for many transition metal ions. We re-visit here complexes of general formula: [TpR,R'ML], where Tp = trispyrazolylborate ligand; R = 3-substituent on the pyrazole ring, R' = 5-substituent; M = Ni(II) or Co(II), L = Cl-, Br-, I-, NCO-, NCS-, or N3-. The 4-coordinate, pseudo-tetrahedral geometry results in the "high-spin" ground state: S = 3/2 for Co(II) and S = 1 for Ni(II). X-ray crystallog. and electronic absorption spectroscopic studies will be reported; however, the emphasis is on high-frequency and -field EPR (HFEPR, frequencies 95 - 700 GHz, magnetic fields 0 - 25 T). HFEPR allows accurate detn. of spin Hamiltonian parameters for high-spin transition metal ions not possible from conventional EPR nor other techniques. The resulting parameters will be used to provide a picture of the electronic structure of the M(II) ion.