Synthesis and study of tetranuclear manganese single-molecule magnets

A specific collection of polynuclear metal complexes exhibits unusual intramolecular magnetic properties owing to a large number of unpaired electrons and to an appreciable energy barrier to reorientation (relaxation) of their magnetization vector. These molecules, labeled as single-molecule magnets (SMMs), possess a net magnetization in the absence of an applied field and display magnetization hysteresis; making them attractive nanoscale dimension magnets. Also, SMMs display quantum tunneling of magnetization and quantum phase interference. A significant number of manganese carboxylate clusters with different nuclearities (up to Mn 30 ions) exhibit SMMs behavior.; In this work, the synthesis and characterization of a family of highly-distorted tetranuclear manganese complexes, [Mn₄O₃(O₂CPh-R) ₄(dbm)₃], was explored. Controlled potential electrolysis was applied to achieve the isolation of these complexes in high yields. Also their magnetic properties were also studied, revealing that these complexes possess a well-isolated ground state S = $92$ along with a large and negative zero-field splitting parameter ( D). The hysteresis studies pointed out high rate tunneling processes, confirmed by HFEPR and specific heat capacity measurements. In addition, the specific-site reactivity of these species with functional groups relevant to photosystem II (PSII) (Cl−, Br−, F−, NO₃−, MeO −,…) was achieved, proving the interdisciplinary applications of these clusters.; A second group of [Mn₄O₃Cl₄(O₂ CR)₃(py)₃] species (Mn4, where R = Me, Et) displaying intermolecular anti ferromagnetic coupling between two Mn4 units, [Mn ₄]₂, was studied. Each cluster possesses a well-isolated ground state S = $92$. However, each unit acts as a bias field and the total magnetic behavior is due a contribution of both entities in the dimer, making them the first SMMs with absence of tunneling at zero field and excellent candidates for studying quantum tunneling in a system of truly identical, antiferromagnetically coupled particles with an S = 0 ground state. New clusters with similar properties were synthesized in order to completely understand completely these magnetic properties.