To determine the magnitude of D, high-field EPR (HFEPR) measurements were carried out on pelletized samples at 4.5 K (Figure for [Co(2)](ClO4)2, Figure for [Co(1)](ClO4)2 and [Co(3)](ClO4)2). The absence of additional EPR lines in the HFEPR spectra shows that no inter-doublet transitions occur up to 375 GHz, setting |D| ≥ 15 cm -1 as a lower limit but preventing an accurate determination of D. The large (negative) D value is also responsible for the absence of Ms = ± 1/2 intra-doublet signals. The assignment of the geff = 7.9 signal to an intra-Kramer transition is confirmed by the linear trend of the peak positions in the entire experimental frequency range (Figure ).