The reaction of [Fe3O(O2CPh)6(H2O)3](O2CPh) with lanthanide/rare earth nitrate salts in the presence of triethanolamine (H3tea) in acetonitrile/methanol solution yields a series of compounds with isostructural tetranuclear core motifs [Fe(III)2Ln(III)2(μ3-OH)2(teaH)2(O2CCPh)6]·3MeCN (Ln = Ce (), Pr (), Nd (), Sm (), Eu (), Gd (), Tb (), Dy (), Ho (), Er (), Tm (), Yb (), Y ()). In all cases the core topology is a defect-dicubane planar or "butterfly" Fe2Ln2 motif. Compounds were investigated using a combination of experimental techniques and theoretical studies. Magnetic susceptibility measurements were carried out on all compounds. The magnetic coupling between the two Fe(III) centres is antiferromagnetic, with JFeFeca. -6.71(4) cm(-1), while the Fe-Ln couplings are much weaker, e.g. JFeGd = 0.18(1) cm(-1). Compounds , , and were selected for Mössbauer studies in order to investigate the influence of isotropic (Gd(III)), highly anisotropic non-Kramers and Kramers (Tb(III) and Dy(III)) and diamagnetic (Y(III)) rare earth ions on the local environment of the Fe(III) centres. Compounds , , and were also studied using X-Band EPR spectroscopy. For , with the diamagnetic Y(III) ion, this made it possible to obtain the D, E, JFeFe and g parameters for the iron centres. It is shown that the low-temperature spectra of compounds , and are determined by magnetic properties of rare-earth ions and the dipole-dipole interactions between the Ln(III) ions. The Fe-Ln interactions were confirmed as very weak and dipolar in nature by the temperature dependence of EPR spectra at T > 20 K.