Iam. Pohl et al., Preparation, structure, and properties of a new giant manganese oxo-alkoxide wheel, [Mn19O12(OC2H4OCH3)(14)(HOC2H4OCH3)(10)]center dot HOC2H4OCH3, CHEM-EUR J, 7(16), 2001, pp. 3438-3445
Alkoxides are of great interest as precursors for sol-gel processing of adv
anced ceramic materials, but there is very little general knowledge about t
he low-valent 3d-element alkoxides. The novel oxo-alkoxide, [Mn19O12(moe)(1
4)- (moeH)(10)] . MOEH (MOE = OC2H2OCH3), was prepared, by metathesis and a
uto-decomposition, from MnCl2 and potassium methoxyethoxide in toluene/MOEH
, and the solid-state structure was determined from single-crystal X-ray di
ffraction data: trigonal cell, space group R3 (no. 148), a = 27.560(3), c =
19.294(2) Angstrom, Z = 3, R1 = 0.0737, wR2 = 0.1609. The individual molec
ules are shaped as flat discs and all Mn atoms are divalent and octahedrall
y coordinated by oxygen atoms in a CdI2-type layer structure. The central M
n atom is coordinated by six mu (3)-oxo atoms, the six middle ring Mn-atoms
by two mu (3)-oxo atoms and four MOB(H) groups, while the peripheral ring
contains twelve Mn atoms coordinated by one mu (3)-oxo atom and five MOE(H)
groups. Differential scanning calorimetry studies showed that the first an
d irreversible changes start at about 100 degreesC. The continuous decrease
of chi T-M with decreasing temperature below 150 K in the magnetic suscept
ibility measurements is probably due to antiferromagnetic interactions. FTI
R and UV/Vis spectroscopy of solid and dissolved samples showed that the so
lid-state structure changes at least to some extent on dissolution in tolue
ne/MOEH.