posted on 2023-04-04, 20:05authored byAshlyn
R. Hale, Khalil A. Abboud, George Christou
New members of the Mn70 and Mn84 torus-like
cluster family have been prepared from a hybrid comproportionation–alcoholysis
reaction of [Mn12O12(O2CR)16(H2O)4] in alcohol in the presence of R′CO2H with NnBuMnO4 or
MnII salts as initiators. Reactions using MeCO2H in nPrOH or nBuOH gave [Mn70O60(O2CMe)70(OnPr)20(nPrOH)18.5(H2O)21.5] (3) and [Mn70O60(O2CMe)70(OH)3(OnBu)17(nBuOH)7.5(H2O)32.5] (4), respectively, whereas EtCO2H in nPrOH gave [Mn84O72(O2CEt)84(OnPr)24(nPrOH)16(H2O)32] (5). They consist of
alternating near-linear [Mn3(μ3-O)4]+ and distorted-cubane [Mn4(μ3-O)2(μ3-OR)2]6+ units bridged by syn,syn-μ-RCO2– and μ3-O2– groups and overall
are [Mn14]5 and [Mn14]6 oligomers, the repeating unit containing two Mn3 and
two Mn4 units. 3/4/5 possess external diameters (including organic ligands) of 4.0/4.1/4.6
nm, respectively, and crystallize as supramolecular nanotubes but
with different packing arrangements. Considering all Mn70/Mn84 tori now available, we conclude that the Mn70 vs Mn84 nuclearity is determined by the relative
bulk of the carboxylates vs the alkoxides, their increasing bulk favoring
Mn84 and Mn70, respectively, with carboxylates
larger than acetate giving Mn84. Alternating current (ac)
magnetic susceptibility studies revealed frequency-dependent χ″M signals below ∼2.4
K, indicating 3–5 to be new members of the giant
[Mn14]n torus family of giant
single-molecule magnets (SMMs), in which Mn84 and Mn70 are the largest homometallic Mn/O clusters and SMMs to date.