Kontakt- und Pseudokontakt-Verschiebungen in den 1H- und 13C-NMR-Spektren des paramagnetischen Komplexes Tricyclopentadienyl-(cyclohexylisonitril)-europium(III) / Contact- and Pseudocontact Shifts in the 1H- and 13C-NMR Spectra of the Paramagnetic, Organometallic Complex Tricyclopentadienyl-(cyclohexylisonitrile)-europium(III)

Abstract

The organometallic NMR shift reagent Eu(C5H5)3 induces large paramagnetic shifts in the 1H-NMR spectrum of cyclohexylisonitrile. The 1:1-adduct (C5H5)3Eu•CNC6H11 has been isolated. The dipolar nature of the paramagnetic shifts of some of the C6H11-protons in this complex is used to fractionate the shifts of the C5H5-nuclei (1H and 13C) into the dipolar and contact contributions. The positive sign of the 13C contact shift is in accord with the usual spin alignment of the free europium ion relative to the external field together with a negative coupling constant. The opposite sign of the 1H contact shift is explained by a polarization mechanism. The anomalous temperature dependence of the 1H contact shift is connected with the strong second order paramagnetism of the europium ion.