Einkernige und oxoverbrückte zweikernige Fe(III)-Komplexe von N-Alkyl-N,N-bis(2-pyridylmethyl)aminen / Mononuclear and Oxo-Bridged Binuclear Fe(III) Complexes of N-Alkyl-N,N-bis(2-pyridylmethyl)amines

Abstract

Abstract Tridentate amines of the type N-alkyl-N,N -bis(2-pyridylmethyl)amine with alkyl = methyl L1, benzyl L2 and adamantyl L3 form mononuclear Fe(III) complexes LFeCl3. In the presence of various carboxylates binuclear μ-oxo-bis(μ-carboxylato) Fe(III) complexes [L2Fe2O(RCO2)2]2+ are formed. These compounds can be synthesized from mono-, bi-, tri- and tetranuclear iron complexes as starting materials. The crystal structures of three mononuclear and four binuclear complexes show that the tridentate ligand is always facially coordinated to Fe. While in binuclear complexes of L1 and L2 the Namin-atom is trans to the oxo-bridge, in a complex of L3 a coordination with one Npyridin atom trans to that bridge is found. In all complexes the Fe-Namine distances increase with increasing space requirement of the alkyl substituent. The effects of different ligands trans to Namine and Npyridin are discussed. 57Fe Mößbauer spectra show that the electric field gradient at Fe vanishes in L1FeCl3 and L2FeCl3 despite non-cubic ligand spheres. For both mono- and binuclear complexes a correlation between isomer shift δ and Fe-N distances exists. The strong increase of Lamb-Mößbauer factors on cooling to 4,2 K and the Goldanski-Karyagin effect observed for some complexes can be explained by the displacement parameters of the Fe-atoms obtained by X -ray structure analysis.