Insights of the Structure and Luminescence of Mn2+/Sn2+-Containing Crown-Ether Coordination Compounds.

Crown-ether coordination compounds with Mn2+ and Sn2+ as cations and 12-crown-4, 15-crown-5, and 18-crown-6 as ligands are synthesized. Their luminescence properties and quantum yields are compared and correlated with their structural features. Thus, MnI2(15-crown-5) (1), MnCl2(15-crown-5) (2), [Mn(12-crown-4)2]2[N(Tf)2]2(12-crown-4) (3), Sn3I6(15-crown-5)2 (4), and SnI2(18-crown-6) (5) are obtained by an ionic-liquid-based reaction of MX2 (M: Mn, Sn; X: Cl, I) and the respective crown ether. Whereas 1, 2, and 5 exhibit a centric coordination of Mn2+/Sn2+ by the crown ether, 3 and 4 show a sandwich-like coordination of the cation with two crown-ether molecules. All title compounds show visible emission, whereof 1, 2, and 5 have good luminescence efficiencies with quantum yields of 47, 39, and 21%, respectively. These luminescence properties are compared with recently realized compounds such as Mn3Cl6(18-crown-6)2, MnI2(18-crown-6), Mn3I6(18-crown-6)2, or Mn2I4(18-crown-6), which have significantly higher quantum yields of 98 and 100%. Based on a comparison of altogether nine crown-ether coordination compounds, the structural features can be correlated with the luminescence efficiency, which allows extraction of those conditions encouraging intense emission and high quantum yields.