The thermal and light-induced magnetic properties of a family of metal-diluted spin-crossover complexes, [FexM1–x(phen)2(NCS)2] (phen = 1,10-phenantholine and M = NiII, CdII), are reported and compared to previous results obtained for the same series but with ZnII ions used to substitute FeII ions; the ultimate goal was to validate the influence of the size and nature of the inert metal ion on the light-induced properties of spin-crossover compounds. For all of the materials, we measured the thermally induced spin-crossover temperature (T1/2) and T(LIESST) (LIESST = light-induced excited spin-state trapping) values systematically. We observed clearly that the dilution has a strong effect on the magnetic and photomagnetic properties. The magnitude of these effects depends strongly on the nature of the diluting metal. This comparison gives insights into the effect of the size of the diluting ion on T(LIESST) and T1/2 and completes the previous studies on the effect of internal pressure on the lifetime of the photoinduced state.