Ferric ring systems

Some years ago Grigore Timco synthesized the eight membered ring system [Cr8F8(piv)16] for which the magnetic properties were studied in detail by us. Lately a strong increase in the interest of many other research groups in studying such systems as model compounds for one-dimensional systems could be observed.

Whereas the synthesis of the chromium ring system [Cr8F8(piv)16] is straightforward, the synthesis of analogues ferric wheels requires addition of H-bond donating templates. It turned out that addition of amines to the starting materials is not only necessary to deprotonate the carboxylic acid, but is a prerequisite for the formation of such ring systems.

Certain constraints limit the choice of the amine, which has to have the right basicity and has to be small enough to fit into the cavity of the ring system. Secondary amines like ((CH3)2CH)2NH or (n-Bu)2NH were shown by us to work best.

Structures of [Fe8F8(piv)16(Bu2NH)] and [Fe8F4(OPh)4(piv)12].

Structures of [Fe8F8(piv)16(Bu2NH)] and [Fe8F4(OPh)4(piv)12].

Recently we could show that the iron-wheel [Fe8F8(piv)16(amine)] is a versatile starting material for the preparation of various other metal clusters. Reactions with alcohols lead to especially interesting compounds and are not restricted to aliphatic ones, but phenolates can also be employed in these interconversions. Various ring systems could be isolated in dependence of the steric demand of the used alcoholate. Beside [Fe10(MeO)20(piv)10] or [Fe10F5(EtO)15(piv)10], the phenolate bridged rings [Fe8F4(OPh-X)4(piv)12], with X = H, Cl, Br, I, OMe, tBu could be synthesized, structurally and magnetically characterized.

Structures of [Fe8F4(I-PhO)4(piv)12] and [Fe8(OH)4(I-PhO)4(piv)12].

Structures of [Fe8F4(I-PhO)4(piv)12] and [Fe8(OH)4(I-PhO)4(piv)12].

Magnetic susceptibility and Mössbauer spectra of [Fe8F4(I-PhO)4(piv)12] and [Fe8(OH)4(I-PhO)4(piv)12].

Magnetic susceptibility and Mössbauer spectra of [Fe8F4(I-PhO)4(piv)12] and [Fe8(OH)4(I-PhO)4(piv)12].