Preparation, structure, and properties of a new giant manganese oxo-alkoxide wheel, [Mn19O12(OC2H4OCH3)14(HOC2H4OCH3)10]. HOC2H4OCH3.
Alkoxides are of great interest as precursors for sol-gel processing of advanced ceramic materials, but there is very little general knowledge about the low-valent 3d-element alkoxides. The novel oxo-alkoxide, [Mn19O12(moe)14-(moeH)10].MOEH (MOE = OC2H2-OCH3), was prepared, by metathesis and auto-decomposition, from MnCl2 and potassium methoxyethoxide in toluene/MOEH, and the solid-state structure was determined from single-crystal X-ray diffraction data: trigonal cell, space group R3 (no. 148), a = 27.560(3), c = 19.294(2) A, Z = 3, R1 = 0.0737, wR2 = 0.1609. The individual molecules are shaped as flat discs and all Mn atoms are divalent and octahedrally coordinated by oxygen atoms in a CdI2-type layer structure. The central Mn atom is coordinated by six mu3-oxo atoms, the six middle ring Mn-atoms by two mu3-oxo atoms and four MOE(H) groups, while the peripheral ring contains twelve Mn atoms coordinated by one mu3-oxo atom and five MOE(H) groups. Differential scanning calorimetry studies showed that the first and irreversible changes start at about 100 degrees C. The continuous decrease of (chiM)T with decreasing temperature below 150 K in the magnetic susceptibility measurements is probably due to antiferromagnetic interactions. FTIR and UV/Vis spectroscopy of solid and dissolved samples showed that the solid-state structure changes at least to some extent on dissolution in toluene/MOEH.
Pohl
I A
IA
Department of Inorganic Chemistry, Uppsala University, Sweden.
Westin
L G
LG
Kritikos
M
M