The complexes (N 4444)3[Ln(dcnm)6] (Ln=La–Nd, Sm; N4444= tetrabutylammonium) display a decrease in the melting point upon fast cooling from a melt, which is shown by in situ synchrotron based X-ray powder diffraction to be due to the formation of a second, less thermodynamically stable, polymorph.
Chesman, A. S. R., Yang, M., Mallick, B., Ross, T., Gass, I. A., Deacon, G. B., Batten, S. R., & Mudring, A-V. (2011). Melting point suppression in new lanthanoid(III) ionic liquids by trapping of kinetic polymorphs: an in situ synchrotron powder diffraction study. Chemical Communications, 48(1), 124-126. https://doi.org/10.1039/c1cc14744g