Origin of isotropic shifts in lanthanide complexes: a study of the temperature dependence of the 1H n.m.r. spectra of the tetrakis-N,N-diethyldithiocarbamatolanthanate(III) anions

Abstract

The ¹H n.m.r. spectra of the tetraethylammonium tetrakis-N,N-diethyldithiocarbamatolanthanate(III), Et₄N⁺ Ln(dtc)^–₄, ion pairs in acetonitrile solution, where Ln = Pr, Nd, Tb, Dy, Ho, Er, Tm and Yb, have been measured at various temperatures. The temperature dependences of the paramagnetic shifts of the Ln(dtc)^–₄ anion are interpreted in terms of both a T^–1 and a T^–2 contribution. It is shown that a treatment due to Bleaney satisfactorily accounts for the T^–2 contribution. It is suggested that there is a significant contact contribution which is reflected in the T^–1 term.