Surface-supported arrays of Fe-4-type Single-Molecule Magnets retain a memory effect and are of current interest in the frame of molecule-based information storage and spintronics. To reveal the spin structure of [Fe-4(L)(2)(dpm)(6)] (1) on Au an isomorphous compound [Fe3Cr(L)(2)(dpm)(6)] was synthesized and structurally and magnetically characterized (H3L is tripodal ligand 11-(acetylthio)-2,2-bis-(hydroxymethyl)undecan-1-ol and Hdpm is dipivaloylmethane). The new complex contains a central Cr3+ ion and has a S = 6 ground state as opposed to S = 5 in 1. Low-temperature X-ray Magnetic Circular Dichroism studies at Fe-and Cr-L-2,L-3 edges revealed that the antiparallel alignment between Fe and Cr spins is preserved on surfaces. Moreover the different Fe-L-2,L-3 spectral features found in the homo-and heterometallic species disclose the opposing contribution of the central Fe3+ ion in the former compound proving that its ferrimagnetic spin structure is retained on surfaces.