Synthesis and magnetic properties of (C5H5)3Ce·HMPA

Abstract

The 1:1 adduct (C5H5)3Ce·OP(NMe2)3 of cerium(III)-triscyclopentadienide with hexamethylphosphoric triamide (HMPA) was synthesized, isolated, purified and characterized by elemental analysis, IR- and 1H-NMR spectroscopy. The 1H-NMR spectrum obtained in solution in CDCl3 at room temperature exhibits a single signal for the Cp-proton at 5.6 ppm and a signal for the CH3-proton of the base HMPA at 0.49 ppm. The paramagnetic shift due to the Ce(III) ion could be evaluated by comparison to the corresponding signals of the homologous diamagnetic compound Cp3La·HMPA. The temperature-dependent paramagnetic susceptibility of the compound was measured within the temperature range from 4.2 up to 300 K. From the 1/χmol vs. T-plot the empirical constant C=0.78 m3 K mol−1 was evaluated with a Curie-Weiss constant θ of −71 K. The temperature dependence of the magnetic moment (μeff) is consistent with a Ce(III) ion. The ground state of the Ce ion is only partially populated. The magnetic moment at room temperature is 2.25 μB, an indication of covalency, as it has been observed for several Ce(III)-organometallics.