Forbidden hyperfine lines in the EPR spectra of a low-spin cobalt(II) complex

The electron paramagnetic resonance studies on a low-spin cobalt(II) complex in a single crystal reveal the presence of very high intensity forbidden hyperfine lines (ΔI=±1 and ±2). The spacings between the forbidden doublets and their relative intensities have been fitted by the complete diagonalization of the spin Hamiltonian. The quadrupole coupling constant derived here is one of the highest reported for a cobalt compound and this has been interpreted using the molecular orbital approach