Grafting derivatives of Mn-6 single-molecule magnets with high anisotropy energy barrier on Au(111) surface

We study the magnetic proper-ties of two new functionalized single-molecule magnets belonging to the Mn-6 family (general formula [(Mn6O2)-O-III(R-sao)(6)(O2C-th)(2)L-4-(6)], where R = H (1) or Et (2), HO2C-th = 3-thiophene carboxylic acid, L = EtOH, H2O and saoH(2) is salicylaldoxime) and their grafting on the Au(111) surface. Complex 1 exhibits spin ground-state S = 4, as the result of ferromagnetic coupling between the two antiferromagnetic Mn-3(III) triangles, while slight structural changes in complex 2, switch the dominant magnetic exchange interactions from anti- to ferromagnetic, enhancing the spin ground-state to S = 12 and, consequently, the effective energy barrier for the relaxation of magnetization. Direct-current and alternating-current magnetic susceptibility measurements show that the functionalized complexes preserve the main magnetic properties of the cot-responding not-functionalized Mn-6 clusters (i.e., total spin value and magnetic behavior as a function of temperature), though a reduction of the anisotropy barrier is observed in complex 2. For both complexes, the -O2C-th functionalization allows the direct grafting on Au(111) surface by liquid-phase deposition. X-ray photoemission spectroscopy demonstrates that the stoichiometry of the molecular cores is preserved after grafting. Scanning tunneling microscopy (STM) reveals a sub-monolayer distribution of isolated clusters with a slightly higher coverage for complex 1. The cluster stability in the STM images and the S-2p energy positions demonstrate, for both derivatives, the strength of the grafting with the gold surface.