Melting point suppression in new lanthanoid(iii) ionic liquids by trapping of kinetic polymorphs: an in situsynchrotron powder diffraction study

Abstract

The complexes (N(4444))(3)[Ln(dcnm)(6)] (Ln = La-Nd, Sm; N(4444) = 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.

Lanthanoid‐Based Ionic Liquids Incorporating the Dicyanonitrosomethanide Anion

“…While unusual, this behaviour has also been observed in the related series of complexes (N 4444 ) 3 [Ln(dcnm) 6 ]. In situ synchrotron‐based X‐ray powder diffraction analysis revealed recrystallisation of the complexes as a second polymorph upon cooling 27…”

“…This result may have been due to hydrogen‐bonding interactions between the choline countercations, as observed in the crystal structure of 5 Ce , and highlights the necessity of using countercations with minimal interactions in the synthesis of ILs. The thermal properties of complexes 4 Ln and 5 Ce show that smaller ammonium countercations are not suitable for forming ILs with the [Ln(dcnm) 6 ] 3− trianion, whereas complexes (N 4444 ) 3 [Ln(dcnm) 6 ] (Ln=La–Nd) could all be classified as ILs 27…”

“…The trianions [Ln(dcnm) 6 ] 3− may be synthesised in high yield, and the previously reported low melting points of their tetraethylammonium salts suggested that an IL may be synthesised when such an anion is coupled with a judiciously selected countercation. Recently, we reported the synthesis of the first series of lanthanoid‐based ILs to contain the dicyanonitrosomethanide ligand, (N 4444 ) 3 [Ln(dcnm) 6 ] (Ln=La, Ce, Pr, Nd), which displayed polymorph‐dependent melting points, as proven by a novel in situ synchrotron‐based X‐ray powder diffraction technique 27. Herein, we report an extension of the family of ionic liquids with the [Ln(dcnm) 6 ] 3− anion and a variety of cations, and examine the crystal structures of the complexes and their thermal behaviour.…”

Long-lived luminescent soft materials of hexanitratosamarate(iii) complexes with orange visible emission

“…The molecular structure of 1 is shown in Fig. 11,13,16 The unique Sm (1) and Sm (2) ions are both located in a special position. Selected bond lengths and angles are summarized in Tables 2 and 3.…”

“…The luminescence lifetimes of complexes 1-5 vary from 114.4 to 130.3 μs in acetonitrile, which is longer than those of most Sm(III) complexes. 10,11 Experimental Materials All chemical reagents and solvents of analytical grade were purchased from standard commercial sources. 21 Furthermore, the lifetime for [MC 1 mim] 3 [Sm-(NO 3 ) 6 ] in acetonitrile (114.4 μs) is longer than in its solid state (98.5 μs).…”