Date of Award
Master of Science
Mark R. Pederson
Molecules and materials constructed from Mn atoms offer diverse assortments of geomet- rical and spin structures. The diversity of structures, in comparison with other transition metals, along with nature’s decision to use a Mn-based molecule to catalyze solar-driven water splitting and oxygen evolution, suggests that there is indeed something special about the location of Mn valence electrons, both energetically and geometrically, that endows Mn with its multifaceted behaviors that, in turn, provide such chemical, physical and mag- netic diversity. Based upon recent work on the Mn3 monomer and the Mn(taa) there is an expectation that Mn𝐼 𝐼 𝐼 centers can exist in local spin states with S=2 (3𝑑↑↑↑↑) or S=1 (3𝑑↑↑↑↓). While the high-spin states are usually more stable based on Hund’s first rule, the Mn3 monomer and the 𝑀𝑛(𝑡𝑎𝑎) provide examples where the presence of S=1 states is energetically favorable. In this work we examine the possibility that such S=1 cen- ters, referred to as Spin-Flip Excitons (SFE) can exist in the Mn12O12(COOR)16[H2O]2 molecule (Mn12-Ac). Our results shown 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 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. In other words the creation of excitons provides a means for switching the magnetic strength.
Recieved from ProQuest
Dema, Karma, "Low-Lying Spin-Flip Excitonic States Of 𝑀𝑛12𝑂12 (𝐶𝑂𝑂𝑅)16 [𝐻2𝑂]4 MOLECULE (Mn12 − 𝐴𝑐)" (2022). Open Access Theses & Dissertations. 3485.