where S is the electron spin quantum number, 𝜇 𝐵 is the Bohr magneton, B is the applied magnetic field, g is the electronic g-value (treated as isotropic), and D and E are the axial and rhombic components, respectively, of the ZFS interaction matrix. Higher-order ZFS terms, possible for S = 7/2, were neglected. Good simulations were found with |D| = 4.8 GHz and |E/D| = 0.25 (Figure ). The high degree of rhombicity (the rhombic limit is given by |E/D| = 1/3) is consistent with the high distortion of the structure of 1-Eu from trigonal bipyramidal. This rhombicity parameter is larger than we found for the related 6-and 8-coordinate respectively. The magnitude of D for 1-Eu is intermediate between those two complexes and there does not appear to be an obvious correlation with Eu-P distances or P-Eu-P angles.