Heat capacity measurements on the Ln = Gd case of the butterfly molecule series [Fe₃Ln(µ₃–O)₂ (CCl₃COO)₈(H₂O)(THF)₃], in brief {Fe₃LnO₂}, is presented. In the previously studied {Fe₃YO₂} butterfly, where the magnetic properties stem only from the Fe³⁺ ions, magnetic chains of spin-5/2 Fe₃Y clusters had been identified and described. The substitution of the nonmagnetic Y³⁺ ion by the magnetic Gd³⁺ adds magnetic interactions to the clusters, but not magnetic anisotropy. The heat capacity measurement shows an excess over the contribution of the antiferromagnetically coupled Fe₃Gd magnetic clusters at very low temperature, which can be described as magnetic spin-1 chains using a Blume–Capel model. The intercluster interaction constant ℐ _ch = −55(5) mK is very similar to that of {Fe₃YO₂}, which shows that the interaction is mainly controlled by the magnitude of the cluster’s magnetic moment.