A new (Mn4Mn4III)-Mn-II cluster from the use of methyl 2-pyridyl ketone oxime in manganese carboxylate chemistry: Synthetic, structural and magnetic studies

摘要

The use of methyl 2-pyridyl ketone oxime (mpkoH) in manganese benzoate chemistry is reported. The reaction of Mn(O2CPh)(2) center dot 2H(2)O with two equivalents of mpkoH in CH2O2 affords the mononuclear complex [Mn-II(O2CPh)(2)(mpkoH)(2)] (2) in high yield. The Mn-II atom is coordinated by two monodentate PhCO2-groups and two N,N'-bidentate mpkoH chelates in a cis-cis-trans fashion. Reaction mixtures comprising (NBU4n)[(Mn4O2)-O-III(O2CPh)(9)(H2O)] and mpkoH in CH2Cl2, [(MnMn2O)-Mn-II-O-III(O2CPh)(6)(py)(2)(H2O)] and mpkoH in CH2Cl2, or Mn(O2CPh)(2) center dot 2H(2)O, NBU4n MnO4 and mpkoH in MeOH/MeCN/CH2Cl2 all lead to the mixedvalent cluster [(Mn4Mn4O2)-Mn-II-O-III(OH)(2)(O2CPh)(10)(mpko)(4)] (3) in moderate yields. The cluster molecule has the [Mn-8(mu(4)-O)(2)(mu(3)-OH)(2)](14+) core (another description of the core is [Mn-8(mu(4)-O)(2)(mu(3)-OH)(2)(mu-OR '')(4)(mu-ONR''')(4)](6+)). Peripheral ligation is provided by two eta(1), four eta(1):eta(1):mu and four eta(1):eta(2):mu(3) PhCO2-groups, as well as four eta(1):eta(1):eta(1):mu mpko(-) ligands. Variable-temperature, solid-state dc and ac magnetic studies were carried out on complex 3 in the 5.0-300 K (dc) and 1.8-10 K (ac) ranges. The data reveal dominant antiferromagnetic interactions and a resulting S = 0 ground state, which is rationalized in terms of the strong antiferromagnetic coupling within the central {(Mn2O2)-O-III}(2+) subunit. (c) 2008 Elsevier Ltd. All rights reserved.