IRON DODECACARBONYL

Chemical properties

stabilized with 5%–10% methanol; black crystal(s); sensitive to air [STR93]

Chemical properties

Tri-iron dodecacarbonyl forms deep green, diamagnetic crystals which decompose at 140°C, but which can be sublimed slowly in vacuo. It dissolves in organic solvents and in pentacarbonyl iron in which its molecular weight corresponds to Fe3(CO)12.

Preparation

Tri-iron Dodecacarbonyl was first obtained by thermal decomposition of non aqueous solutions of the enneacarbonyl at 100°C : 6Fe2(CO)9 -> 2Fe3(CO)12+6Fe(CO)5 but is now usually prepared from solutions of carbonylferrate anions. One method uses the oxidation of these ions with manganese(IV) oxide followed by acidification and extraction of the carbonyl into petroleum ether. In another method,iron pentacarbonyl is treated with aqueous triethylamine to form the dark red [Et3NH][Fe3(CO)11H] which is then acidified and the carbonyl extracted into petroleum ether.

Structure and conformation

The structure of Fe3(CO)12 (Fig.9) is related to that of Fe2(CO)9 in that it can be described as a triangular metal cluster in which one bridging group of the Fe2(CO)9 system is replaced by an Fe(CO)4 group. This X-ray data is in agreement with the M?ssbauer spectrum which shows the presence of two types of iron atom ; two of the iron atoms show substantial quadrupole splitting and have isomer shifts similar to those of the iron atoms in Fe2(CO)9, while the other iron atom shows little splitting as might be expected for an octahedral environment. A similar structure is possessed by the [Fe3(CO)11H] anion in which one of the bridging carbonyl groups is replaced by a bridging hydrogen atom.