Molecular multinuclear praseodymium manganese crown-ether coordination compounds.

Crown-ether-coordination compounds of praseodymium(III), manganese(II) and the crown ether 18-crown-6 ((C2H4O)6, 18c6) are prepared in [Bu3MeN][NTf2] ([Bu3MeN]+/[(C4H9)3(CH3)N]+: tributylmethylammonium; [NTf2]-/[(CF3SO2)2N]-: bis(trifluoromethylsulfonyl)amide) as an ionic liquid. Specifically, the reaction of PrCl3, PrI3, MnCl2 or MnI2 with 18c6 at 80-100 °C results in the novel compounds [PrCl3(18c6)] (1), [MnCl2(18c6)] (2), [Bu3MeN][PrI2(18c6)][MnI4] (3), [Bu3MeN]2[MnI4] (4), [Bu3MeN]2[(Pr(I0.82Cl0.18)Cl(18c6))2][MnI4]2 (5) and [(PrCl2(18c6)MnI3)2] (6). They contain mononuclear arrangements of Pr3+ (1) and Mn2+ (2) with 18c6. 3 and 5 contain both Pr3+ and Mn2+ in a single compound but in different molecular building units ([PrI2(18c6)]+, [(Pr(I0.82Cl0.18)Cl(18c6))2]+, and [MnI4]2-) with a great distance between them (Pr-Mn > 700 pm). Finally, 6 represents the first crown-ether coordination compound with Pr3+ and Mn2+ in a single tetranuclear molecule. All 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 Pr3+ (3 and 5), show typical luminescence of Mn2+, whereas 1 and 6 show Pr3+-type transitions, with 6 showing particularly intense emission. Pr3+ → Mn2+ 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).