Preparation, structure, and properties of a new giant manganese oxo-alkoxide wheel, [Mn19O12(OC2H4OCH3)(14)(HOC2H4OCH3)(10)]center dot HOC2H4OCH3

摘要

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 = OC2H2OCH3), 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) Angstrom, 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 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 and irreversible changes start at about 100 degreesC. The continuous decrease of chi T-M 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. [References: 45]