A self-assembled monolayer (SAM) of a single molecule magnet (SMM) bearing a tetrairon(III) core and sulfur-containing terminal groups was exposed to aqueous solution. The effect of the chemical environment on the monolayer was investigated using cyclic voltammetry, X-ray photoelectron spectroscopy, and atomic force microscopy. The physisorbed SMM molecules desorbed and the sulfur atoms in the remaining SMM were oxidized during immersion in H 2 O, while the Fe(III) ions remained intact. We found that the SMM molecules concomitantly formed aggregates on the surface. These transformations caused significant changes to the redox properties of the SMM. The present research highlights the fragile nature of the SMM SAM against particular chemical environments and provides important insights into the exploitation of surface-tethered SMMs for a variety of applications.Single molecule magnets (SMMs) are a unique class of functional molecules. They possess versatile magnetic properties and show rich quantum behavior such as magnetic hysteresis of a molecular origin 1 and quantum tunneling of magnetization. 2 Since the first discovery of molecular magnetism in [Mn 12 (OAc) 16 (H 2 O) 4 O 12 ] (Mn 12 acetate), 3 SMMs have attracted considerable interest because of their potential for information storage device applications. In addition, SMMs offer a peculiar opportunity to explore magnetism at the nanoscale. Because it is desirable to immobilize SMM molecules on a solid surface to utilize and probe their magnetism, many studies have been devoted to create two-dimensional assemblies of SMMs. Several different approaches have been reported to deposit Mn 12 acetate, which is the archetypal SMM, on substrates including stamp-assisted deposition on a Si substrate, 4 immobilization by ligand-exchange on the surfaces of self-assembled monolayers (SAMs), 5-9 and grafting via electrostatic interactions. 10 Moreover, direct deposition onto metal surfaces can be achieved using organosulfur derivatives of Mn 12 acetate. 11-14 It is important to retain the useful magnetic properties for these surfacetethered SMMs. However, it is known that the Mn 12 acetate loses the useful magnetic property on a solid surface due to the structural instability of its inorganic core in the highly strained surface environment. [15][16][17][18] To avoid this, a different class of SMMs featuring tetrairon(III) cores (Fe 4 ) has been developed. It has recently proven that Fe 4 SMMs are sufficiently chemically robust to maintain magnetic hysteresis after direct deposition. 19,20 Besides developing methodology for surface immobilization, the practical application of SMMs requires an understanding of the chemical stability of their surface assembly against various chemical environments. Although the characterization of such stability is very important given the intrinsically fragile nature of SMMs, the available knowledge on this subject is quite limited. Currently the peculiar properties of SMMs emerge only at low temperatures, and this fact hampers their utili...