Effect of the Mn Oxidation State on Single-Molecule-Magnet Properties: Mn^III vs Mn^IV in Biologically Inspired DyMn₃O₄ Cubanes

Abstract

Inspired by the ferromagnetic coupling in the cubane model CaMnIV3O4 of the oxygen-evolving complex of photosystem II, 3d–4f mixed-metal DyMn3O4 clusters were prepared for investigation of the magnetic properties. For comparison, YMnIV3O4 and YMnIV2MnIIIO4 clusters were investigated as well and showed ferromagnetic interactions, like the calcium analogue. DyMnIV3O4 displays single-molecule-magnet properties, while the one-electron-reduced species (DyMnIV2MnIIIO4) does not, despite the presence of a MnIII center with higher spin and single-ion anisotropy.

Tetranuclear [MnIIIMn3IVO4] Complexes as Spectroscopic Models of the S2 State of the Oxygen Evolving Complex in Photosystem II

“…In-situ oxidation of a close OEC structural model complex, CaMn 4 O 4 (OPiv) 8 , gives rise to two EPR signals at g = 4.9 and g = 2, attributed to different spin states of the cluster corresponding to a [CaMn 4 O 4 (OPiv) 8 ] + species, although further structural, spectroscopic, and magnetic data have not been provided . Follow-up computational studies disagree on the assignment of the two signals, one of them suggesting that the two signals must be due to structurally very different clusters. , In general, systematic studies that probe the effect of small structural changes on the spectroscopic and magnetic properties of S 2 model clusters are very rare, likely due to the synthetic challenges of accessing a series of isolable clusters that are suitable for comparisons. , Indeed, despite significant efforts to prepare tetra- and penta-nuclear clusters that are relevant to the S-state intermediates in terms of structure, redox state, or spectroscopy, accurate models for benchmarking against the biological system are rare. ,,− …”

CaMn3IVO4 Cubane Models of the Oxygen‐Evolving Complex: Spin Ground States S<9/2 and the Effect of Oxo Protonation

“…Treatment of 1‐Ca with Y(OTf) 3 leads to the analogous complex 1‐Y [50] . Magnetic studies show that 1‐Y has a similar S G =9/2 [66] . Desymmetrization of the pseudo ‐ C 3 symmetric complexes 1‐Ca and 1‐Y was achieved via substitution of two acetate moieties with a chelating bis‐oxime proligand (H 2 N 4 O 2 ).…”

“…[50] Magnetic studies show that 1-Y has as imilar S G = 9/2. [66] Desymmetrization of the pseudo-C 3 symmetric complexes 1-Ca and 1-Y was achieved via substitution of two acetate moieties with ac helating bis-oxime proligand (H 2 N 4 O 2 ). Treatment of 1-Ca with H 2 N 4 O 2 results in the formation of 2-Ca via ap rotonolysis reaction.…”

Mechanistically Driven Control over Cubane Oxo Cluster Catalysts

“…Transition metal and heterometallic 47-51 cubanes are attractive and sought-after targets for new design approaches in coordination chemistry. They are quite versatile catalytic model systems -both for nature's cuboidal and heterometallic {CaMn4O5} oxygen evolving complex (OEC) of photosystem II [52][53][54][55] and for crucial surface motifs of oxide-based water oxidation catalysts (WOCs). [56][57][58] While much emphasis has been placed on elucidating the oxygen evolution pathways of synthetic cubane clusters, considerably less is known about their own formation processes.…”

“…Transition metal and heterometallic − cubanes are attractive and sought-after targets for new design approaches in coordination chemistry. They are quite versatile catalytic model systemsboth for nature’s cuboidal and heterometallic {CaMn 4 O 5 } oxygen evolving complex (OEC) of photosystem II − and for crucial surface motifs of oxide-based water oxidation catalysts (WOCs). − While much emphasis has been placed on elucidating the oxygen evolution pathways of synthetic cubane clusters, considerably less is known about their own formation processes. − Heterometallic cubanes provide particularly excellent opportunities to study synergistic effects in oxide-related as well as in bioinspired molecular catalysts, but their targeted construction remains demanding . To the best of our knowledge, the influence of inorganic anions on the assembly pathways of oxo clusters in solution remains rather unexplored.…”