Influence of the ligand shell on the surface orientation of Mn12 single molecule magnets

Here we report the synthesis, investigation as well as surface deposition of a truly axial symmetry Mn12-diphenylphosphinate (Mn12-phn) single molecule magnet. Out of 16 acetate ligands encapsulating the Mn12O12 core, 12 ligands were exchanged by diphenylphosphinate in this compound. Mn12-phn shows well-defined magnetic hysteresis curves indicating a very high crystal quality. A monolayer of Mn12-phn was chemically grafted on a functionalized Au(111) surface via ligand exchange reaction and studied by means of scanning tunneling microscopy and spectroscopy. Via distance voltage spectroscopy we determine the real-space height of the Mn12-phn molecules with high accuracy. A large spread in the measured molecular heights obtained from the distance voltage spectra indicates the absence of preferential orientation of Mn12-phn molecules with respect to the surface which we attribute to the equal anchoring probability of all diphenylphosphinate ligands in Mn12-phn while none of the four acetate ligands are exchanged. These results are compared with the experimental data obtained from a different Mn12 derivative containing 16 thiophenecarboxylate ligands. In general, we show that the substitution of the ligand shell may have a major impact on the surface orientation of the Mn12 clusters deposited on Au, i.e. on the orientation of the easy magnetization axis