A new Mn II4Mn III4 cluster from the use of methyl 2-pyridyl ketone oxime in manganese carboxylate chemistry: Synthetic, structural and magnetic studies

Abstract

The use of methyl 2-pyridyl ketone oxime (mpkoH) in manganese benzoate chemistry is reported. The reaction of Mn(O 2CPh) 2 · 2H 2O with two equivalents of mpkoH in CH 2Cl 2 affords the mononuclear complex [Mn II(O 2CPh) 2(mpkoH) 2] ( 2) in high yield. The Mn II atom is coordinated by two monodentate PhCO 2 - groups and two N, N′-bidentate mpkoH chelates in a cis– cis– trans fashion. Reaction mixtures comprising (NBu n 4)[Mn III 4O 2(O 2CPh) 9(H 2O)] and mpkoH in CH 2Cl 2, [Mn IIMn III 2O(O 2CPh) 6(py) 2(H 2O)] and mpkoH in CH 2Cl 2, or Mn(O 2CPh) 2 · 2H 2O, NBu n 4 MnO 4 and mpkoH in MeOH/MeCN/CH 2Cl 2 all lead to the mixed-valent cluster [Mn II 4Mn III 4O 2(OH) 2(O 2CPh) 10(mpko) 4] ( 3) in moderate yields. The cluster molecule has the [Mn 8(μ 4-O) 2(μ 3-OH) 2] 14+ core (another description of the core is [Mn 8(μ 4-O) 2(μ 3-OH) 2(μ-OR′′) 4(μ-ONR‴) 4] 6+). Peripheral ligation is provided by two η 1, four η 1:η 1:μ and four η 1:η 2:μ 3 PhCO 2 - groups, as well as four η 1:η 1:η 1:μ 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 { Mn 2 III O 2 } 2 + subunit.