Koordination Des Anions Von 2,4-Dicyanoglutaconsäurediethylester An Tripodeisen(Ii)-Einheiten. Die Entstehung Helikaler Strukturen

Abstract

The anion of 2,4-dicyano glutaconic acid diethyl ester, [NCC(COOEt)CHC(COOEt)CN]- (1- ), as an α,μ;-dinitrile with a three atom spacer is a highly variable ligand capable of binding in a monodentate η1-fashion, in a bidentate chelate fashion, and as a μ2-bridging entity. TripodFe(1)2, 2, [tripod = CH3C(CH2PPh2)3] contains one chelating ligand 1- and one terminally coordinated ligand 1-- . 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(1)2, 2, is obtained from a 1:1:2 mixture of tripod, Fe(II)aq (BF4)2, and Na1-2H2O . With a stoichiometry 1:1:1 of these ingredients and an additional naif equivalent of sodium cyanide, the dinuclear compound [tripodFe{μ-NCC(COOEt)CHC(COOEt)CN}2{μ-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 1- and μ-CN. The two iron centers in 3BF4 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