MnBr2/18-crown-6 coordination complexes showing high room temperature luminescence and quantum yield

The reaction of manganese(II) bromide and the crown ether 18-crown-6 in the ionic liquid [(n-Bu)(3)MeN] [N(Tf)(2)] under mild conditions (80-130 degrees C) resulted in the formation of three different coordination compounds: MnBr2(18-crown-6) (1), Mn3Br6(18-crown-6)(2) (2) and Mn3Br6(18-crown-6) (3). In general, the local coordination and the crystal structure of all compounds are driven by the mismatch between the small radius of the Mn2+ cation (83 pm) and the ring opening of 18-crown-6 as a chelating ligand (about 300 pm). This improper situation leads to different types of coordination and bonding. MnBr2(18-crown-6) represents a molecular compound with Mn2+ coordinated by two bromine atoms and only five oxygen atoms of 18-crown-6. Mn3Br6(18-crown-6)(2) falls into a [MnBr(18-crown-6)](+) cation - with Mn2+ coordinated by six oxygen atoms and Br -and a [MnBr(18-crown-6) MnBr4](-) anion. In this anion, Mn2+ is coordinated by five oxygen atoms of the crown ether as well as by two bromine atoms, one of them bridging to an isolated (MnBr4) tetrahedron. Mn3Br6(18-crown-6), finally, forms an infinite, non-charged (1)(infinity)[Mn-2(18-crown-6)(MnBr6)] chain. Herein, 18-crown-6 is exocyclically coordinated by two Mn2+ cations. All compounds show intense luminescence in the yellow to red spectral range and exhibit remarkable quantum yields of 70% (Mn3Br6(18-crown-6)) and 98% (Mn3Br6(18-crown-6)(2)). The excellent quantum yield of Mn3Br6(18-crown-6)(2) and its differentiation from MnBr2(18-crown-6) and Mn3Br6(18-crown-6) can be directly correlated to the local coordination.