MONONUCLEAR AND OXO-BRIDGED BINUCLEAR FE( III) COMPLEXES OF N-ALKYL-N,N-BIS(2-PYRIDYL-METHYL)AMINES

Tridentate amines of the type N-alkyl-N,N-bis(2-pyridylmethyl)amine wi th alkyl = methyl L1, benzyl L2 and adamantyl L3 Form mononuclear Fe(I II) complexes LFeCl3. In the presence of various carboxylates binuclea r mu-oxo-bis(mu-carboxylato) Fe(VI) complexes [L2Fe2O(RCO2)(2)](2+) ar e formed. These compounds can be synthesized from mono-, bi-, tri- and tetranuclear iron complexes as starting materials. The crystal struct ures of three mononuclear and four binuclear complexes show that the t ridentate ligand is always facially coordinated to Fe. While in binucl ear complexes of L1 and L2 the N-amin-atorn is trans to the oxo-bridge , in a complex of L3 a coordination with one N-pyridin atom trans to t hat bridge is found. In all complexes the Fe-N-amine distances increas e with increasing space requirement of the alkyl substituent. The effe cts of different ligands trans to N-amine and N-pyridin are discussed. Fe-57 Mobbauer spectra show that the electric field gradient ar Fe va nishes in L1FeCl(3) and L2FeCl(3) despite non-cubic Ligand spheres, Fo r both mono- and binuclear complexes a correlation between isomer shif t delta and Fe-N distances exists. The strong increase of Lamb-Mobbaue r factors on cooling to 4,2 K and the Goldanski-Karyagin effect observ ed for some complexes can be explained by the displacement parameters of the Fe-atoms obtained by X-ray structure analysis.