Koordination des Anions von 2,4-Dicyanoglutaconsäurediethylester an tripodEisen(II)-Einheiten. Die Entstehung helikaler Strukturen Coordination of the Anion of 2,4-Dicyano Glutaconic Acid Diethyl Ester to ?r/po</Iron(II)-Fragments. Formation of Helical Structures

Z. Naturforsch. 56 b, 735-746 (2001); eingegangen am 16. Februar 2001 2,4-Dicyano Glutaconic Acid Diethyl Ester Anion, Cyano Bridges, Helix The anion of 2,4-dicyano glutaconic acid diethyl ester, [NCC(COOEt)CHC(COOEt)CN]_ ( I ), as an a,u;-dinitrile with a three atom spacer is a highly variable ligand capable of binding in a monodentate 77'-fashion, in a bidentate chelate fashion, and as a p 2-bridging entity. TripodFe(l)2, 2, [tripod = CH3C(CH2PPh2)3] contains one chelating ligand I and one terminally coordinated ligand I . Variable temperature NMR spectroscopy shows, that, while the structure is static at 193 K, dynamic exchange of the donor functions of chelating and terminally bonded ligands occurs at higher temperature. TripodFe(l)2, 2, is obtained from a 1:1:2 mixture of tripod, Fe(II)aq (BF4)2, and Nal-2H20 . With a stoichiometry 1:1:1 of these ingredients and an additional naif equivalent of sodium cyanide, the dinuclear compound [tripodFe{p-NCC(COOEi)CHC(COOEi)CN}2{n-CN}Fetripod]BF4, 3 BF4, is obtained. The structure of 3+ shows a helical arrangement of the ligands 1~ around the Fe Fe axis which is a consequence of the incomensurability of the bridging ligands l~and ^-CN. The two iron centers in 3 BF4 differ by their coordination to the carbon or to the nitrogen terminus of the bridging cyano group. This difference is reflected by the NMR spectra, Mössbauer spectra and cyclovoltammograms.