New insights in Mn-Ca chemistry from the use of oximate-based ligands: {(Mn22Ca2)-Ca-II/III} and {(Mn2Ca2)-Ca-IV} complexes with relevance to both low- and high-valent states of the oxygen-evolving complex

摘要

The initial use of quinoline-2-aldoxime (qaoH) and 2,6-diacetylpyridine dioxime (dapdoH(2)) in heterometallic Mn-Ca chemistry has afforded a mixed-valence {(Mn22Ca2)-Ca-II/III} cluster containing several {Mn4CaOx} subunits and a 'butterfly'-like ((Mn2Ca2)-Ca-IV) complex, respectively. The one-pot reaction of Mn (O2CPh)(2)center dot 2H(2)O and Ca(O2CPh)2 center dot H2O with qaoH and NEt3 in a 1:1:1:1 molar ratio in a solvent mixture comprising MeCN/MeOH gave complex [Mn22Ca2O14(OH)(4)(OMe)(6)(O2CPh)(22)(qao)(2)(MeCN)(2)(H2O)(4)](OH)(2) (1; 6Mn(II)/16Mn(III)) in 20% yield. A similar reaction with that of 1, albeit with Mn(O2CPh)(2)center dot 2H(2)O and Ca (NO3)(2)center dot 4H(2)O in the presence of dapdoH(2) and NEt3, in a molar ratio of 1:1:2:2 in MeCN/MeOH, led to the smaller nuclearity complex [Mn2Ca2(OMe)(2)(NO3)(2)(dapdo)(4)] (2; 2Mn(IV)) in 40% yield. The reported compounds demonstrate structural and magnetic relevance to both low-and high-valent states of the OEC. (C) 2018 Elsevier Ltd. All rights reserved.