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

Abstract Based upon recent work on the Mn 3 monomer and the Mn(taa) there is an expectation that Mn III centers can exist in local spin states with S = 2 (3 d ↑ ↑ ↑ ↑ ) or S = 1 (3 d ↑ ↑ ↑ ↓ ). While the high-spin states are usually more stable based on Hunds first rule, the Mn 3 monomer, the Mn(taa) and [ Mn 6 III Mn III ] 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 Mn 12 O 12 ( COOR ) 16 [ H 2 O ] 2 molecule ( Mn 12 -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 spin-crossover paths between the Mn 12 -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.