Paramagnetic 1 H NMR monitoring of the reaction revealed the formation [Tm(Cp ttt )2I], identified by comparison with the 1 H NMR spectrum of an authentic sample, along with a new set of signals (see Figure ). After evaporation of the solvent, the crude product was washed several times with pentane to remove [Tm(Cp ttt )2I]. Recrystallization of the remaining solid from hot toluene afforded crystals of 6 suitable for XRD studies. Its molecular structure (Figure ) features a trinuclear Tm(III) complex in which each thulium center is coordinated by a chelating carboxylate group and two h 5 -coordinated Cp ttt ligands.