The first heterometallic Mn–Ca cluster containing exclusively Mn(III) centers

Synthetic model of the asymmetric [Mn 3 CaO 4 ] cubane core of the oxygen-evolving complex of photosystem II

“…Although these individual transitions are unlikely to be resolved, they will manifest as an m S -dependent broadening of each ENDOR line (27). To model this behavior in our simulations, NQI parameters P jj and η were respectively set to 2.5 MHz and 0.2, intermediate of values found for Mn IV centers in other exchange-coupled clusters (14,28). To further simplify the analysis of the ENDOR spectrum, the isosceles triangle model (above) was applied.…”

“…Although biochemical studies had previously shown Ca to be essential for OEC activity, and X-ray spectroscopy had established the presence of an oxo-bridged Mn 4 Ca heteronuclear cluster, these crystallographic data reenergized efforts to achieve the synthesis of the OEC in the laboratory. Several Mn∕Ca compounds are now known (12)(13)(14)(15), but there is only one complex that has approached the cubane moiety of the OEC structure (16). We here report the development of methodology for synthesizing in the absence of a protein milieu the [Mn 3 CaO 4 ] cubane with an external metal attached to it.…”

Calcium and heterometallic manganese–calcium complexes supported by tripodal pyridine-carboxylate ligands: structural, EPR and theoretical investigations

“…Remarkably, the MnCa complex represents a rare example of a complex containing a µ 1,1 -carboxylate bridge between Mn and Ca ions 39 and of a low nuclearity binuclear Mn-Ca complex. 32 In this work, we have also succeeded structurally characterizing the corresponding homometallic calcium(II) complexes, Ca 1 and Ca 2 , As expected, by comparing these species and the heterometallic Mn-Ca species, it is evident that the Mn 2+ ion, when present in solution, easily replaces calcium in the first coordination sphere of the supporting ligand.…”

“…[11][12][13][14] Many oxo/acetato-bridged polynuclear manganese complexes have been synthesized [15][16][17][18][19][20][21] in order to improve the understanding of the structural and spectroscopic properties, and function of the OEC. By contrast, the synthesis and investigation of hetero-nuclear manganese-calcium complexes are still largely unexplored with less than twenty examples of synthetic clusters [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] or polymers [37][38][39][40] isolated to date, incorporating Mn in the (II-IV) oxidation states. Amongst these compounds, if the two oxo-bridged cubane clusters, [Mn IV 3 CaO 4 ] 6+ and [Mn IV 3 Ca 2 O 4 ] 8+ isolated in 2011 by the groups of Agapie [33][34][35] and Christou, 24 have emerged as the best structural models of the OEC cubanoid unit, the first structural mimic of the full site of the OEC, a cubane Mn IV 3 Mn III-CaO 4 linked to a dangling Mn III via one oxo bridge of the cubane, has just been reported by Zhang et al 41 Even if the OEC contains Mn ions in high oxidation states (like Agapie's, Christou's and Zhang's models), it is interesting to note that the OEC is assembled via the so-called "photoactivation" process, initiated by Mn 2+ in the presence of cofactordepleted PSII, Ca 2+ , chlorides, water and light.…”

A family of hexanuclear Mn(III) single-molecule magnets

“…The ease of synthesis of [Mn 3 ] and [Mn 6 ] and their relative solution stability have enabled them to be utilized as starting materials -building blocks for construction of a host of discrete and infinite supramolecular architectures [14,21,31,37,41,[44][45][46][47][48][49][50][51][52][53][54][55][56][57]. The employment of auxiliary pyridyl-type ligands into the reaction mixtures of [Mn 3/6 ] or in solutions of preformed [Mn 3/6 ] has yielded several discrete (i.e.…”