Compounds 1-RE were synthesised from the combination of three equivalents of Et3NH + Br4catH -with equimolar RE 3+ and tpa (Scheme S1). Variation of the order of addition and stirring versus no stirring affords either single crystals suitable for structure determination or bulk microcrystalline samples in good yield for RE = Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The single crystal X-ray structural analyses indicate that the large crystals, which were obtained from the solution without stirring, comprised 1-RE without the inclusion of solvent, while elemental and thermogravimetric analyses (Figures and) are consistent with the presence of MeCN giving the formula 1-RE•0.5MeCN for all RE. Powder X-ray diffractograms for 1-RE•0.5MeCN (Figure ) are similar with the patterns calculated using the single crystal X-ray diffraction data for 1-RE, suggesting bulk samples are representative of single crystal. The compounds were insoluble in all standard solvents and all measurements were performed in the solid state.