Molecular multinuclear praseodymium manganese crown-ether coordination compounds

Crown-ether-coordination compounds of praseodymium(iii), manganese(ii) and the crown ether 18-crown-6 ((C$_2$H$_4$O)$_6$, 18c6) are prepared in [Bu$_3$MeN][NTf$_2$] ([Bu$_3$MeN]$^+$/[(C$_4$H$_9$)$_3$(CH$_3$)N]$^+$: tributylmethylammonium; [NTf$_2$]$^−$/[(CF$_3$SO$_2$)$_2$N]$^−$: bis(trifluoromethylsulfonyl)amide) as an ionic liquid. Specifically, the reaction of PrCl$_3$, PrI$_3$, MnCl$_2$ or MnI$_2$ with 18c6 at 80–100 °C results in the novel compounds [PrCl$_3$(18c6)] (1), [MnCl$_2$(18c6)] (2), [Bu$_3$MeN][PrI$_2$(18c6)][MnI$_4$] (3), [Bu$_3$MeN]$_2$[MnI$_4$] (4), [Bu$_3$MeN]$_2$[(Pr(I$_{0.82}$Cl$_{0.18}$)Cl(18c6))$_2$][MnI$_4$]$_2$ (5) and [(PrCl$_2$(18c6)MnI$_3$)$_2$] (6). They contain mononuclear arrangements of Pr$^{3+}$ (1) and Mn$^{2+}$ (2) with 18c6. 3 and 5 contain both Pr$^{3+}$ and Mn$^{2+}$ in a single compound but in different molecular building units ([PrI$_2$(18c6)]$^+$, [(Pr(I$_{0.82}$Cl$_{0.18}$)Cl(18c6))$_2$]$^+$, and [MnI$_4$]$^{2−}$) with a great distance between them (Pr–Mn > 700 pm). Finally, 6 represents the first crown-ether coordination compound with Pr$^{3+}$ and Mn$^{2+}$ in a single tetranuclear molecule. ... mehrAll title compounds are characterized by X-ray diffraction (single crystals, powder diffraction with Rietveld analysis), infrared spectroscopy, thermal analysis, and photoluminescence spectroscopy. 2–5, even when containing Pr$^{3+}$ (3 and 5), show typical luminescence of Mn$^{2+}$, whereas 1 and 6 show Pr$^{3+}$-type transitions, with 6 showing particularly intense emission. Pr$^{3+}$ → Mn$^{2+}$ energy transfer is not observed, which can be ascribed to the specific distances between the luminescent centers (3 and 5) or the symmetry of the molecule (6).