Powder samples of 3-Eu at Q-band and low temperature give spectra with intense resonance ranging from ca. 0.5 T (with weaker features at lower field) to the maximum range of the electromagnet (1.7 T). In the wings of the spectrum a regular progression of transitions with separation ca. low-field resonances it was necessary to assume a slight preferential ordering of the system along the molecular z-axis in the magnetic field (as opposed to a true powder average); this is consistent with a negative D (hence easy-axis magnetic anisotropy). The EPR spectra of dimetallic 1-Eu are more complex at low temperatures, and on warming intensity rapidly grows in the middle of the spectrum (see SI Figures ). This is only consistent with an exchange interaction between the two Eu(II) ions. Modelling of low temperature magnetic data shows that this exchange must be very small (|J| < ca. 30 GHz), but this puts it in the same regime as the Eu(II) ZFS, hence very complex spectra result and we have as yet been unable