A series of complexes [EtN][Ln(NCS)(HO)] (Ln = Pr, Tb, Dy, Ho, Yb) have been structurally characterized, all showing the same structure, namely a distorted square antiprismatic coordination geometry, and the Ln-O and Ln-N bond lengths following the expected lanthanide contraction. When the counterion is Cs, a different structural motif is observed and the eight-coordinate complex Cs[Nd(NCS)] isolated. The thorium compounds [MeN][Th(NCS)(NO)] and [MeN][Th(NCS)(NO)] have been characterized, and high coordination numbers are also observed. Finally, attempts to synthesize a U(III) thiocyanate compound has been unsuccessful; from the reaction mixture, a heterocycle formed by condensation of five MeCN solvent molecules, possibly promoted by U(III), was isolated and structurally characterized. To rationalize the inability to isolate U(III) thiocyanate compounds, thin-layer cyclic voltammetry and IR spectroelectrochemistry have been utilized to explore the cathodic behavior of [EtN][U(NCS)] and [EtN][U(NCS)(bipy)] along with a related uranyl compound [EtN][UO(NCS)]. In all examples, the reduction triggers a rapid dissociation of [NCS] ions and decomposition. Interestingly, the oxidation chemistry of [EtN][UO(NCS)] in the presence of bipy gives the U(IV) compound [EtN][U(NCS)], an unusual example of a ligand-based oxidation triggering a metal-based reduction. The experimental results have been augmented by a computational investigation, concluding that the U(III)-NCS bond is more ionic than the U(IV)-NCS bond.

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