Electronic and magnetic signatures of low-lying spin-flip excitonic states of Mn12O12-acetate

Based upon recent work on the Mn3 monomer and the Mn(taa) there is an expectation that MnIII centers can exist in local spin states with S = 2 (3d up arrow up arrow up arrow up arrow) or S = 1 (3d up arrow up arrow up arrow down arrow). While the high-spin states are usually more stable based on Hunds first rule, the Mn3 monomer, the Mn(taa) and [MnIII6 MnIII]3+ triplesalen provide examples where the presence of S = 1 and S = 0 low-spin states is energetically favorable. In this paper we examine the possibility that such S =1 centers, referred to as Spin-Flip Excitons (SFE) can exist in the Mn12O12(COOR)16[H2O]2 molecule (Mn12-Ac). Our results show that up to eight of these excitons can exist as metastable electronic states. We examine the relative stability per exciton as a function of the number of these excitons and determine spincrossover paths between the Mn12-Ac zero-exciton ground state (S = 10), a four-exciton state (S = 6) and an eight-exciton state (S = 2). The magnetic anisotropy of these states decreases monotonically and significantly with the number of excitons.