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

Abstract

The reaction of manganese(ii) bromide and the crown ether 18-crown-6 in the ionic liquid [(n-Bu)3MeN][N(Tf)2] under mild conditions (80-130 °C) resulted in the formation of three different coordination compounds: MnBr2(18-crown-6) (), Mn3Br6(18-crown-6)2 () and Mn3Br6(18-crown-6) (). In general, the local coordination and the crystal structure of all compounds are driven by the mismatch between the small radius of the Mn(2+) 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 Mn(2+) 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 Mn(2+) coordinated by six oxygen atoms and Br - and a [MnBr(18-crown-6)MnBr4](-) anion. In this anion, Mn(2+) 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 [Mn2(18-crown-6)(MnBr6)] chain. Herein, 18-crown-6 is exocyclically coordinated by two Mn(2+) 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.

The Bromine‐Rich Bromido Metallates [BMIm]2[SnBr6]·(Br2) and [MnBr(18‐crown‐6)]4[SnBr6]2·(Br2)4.5

“…Compound 2 crystallizes in the space group P 1 (Table ) and consists of [MnBr(18‐crown‐6)] + cations, [SnBr 6 ] 2– anions, and dibromine molecules (Figure ). As already known from Mn 3 Br 6 (18‐crown‐6) 2 , Mn 2+ is coordinated in the equatorial plane and in an additional axial position by a strongly bent molecule of 18‐crown‐6 (Figure a). As a result, all oxygen atoms of the crown ether are able to coordinate the Mn 2+ center with distances of 224.2(2) to 235.2(6) pm.…”

“…Compounds formed in the system ZnBr 2 /Br 2 /(18‐crown‐6):, (a) Coordination compounds (ZnBr 2 ) n (18‐crown‐6) 2 ( n = 4,6,8,10) with multinuclear ZnBr 4 ‐tetraedra chains of increasing lengths; (b). Bromine‐rich bromido zincate Zn 6 Br 12 (18‐crown‐6) 2 · (Br 2 ) 5 and decomposition to Zn 4 Br 8 (18‐crown‐6) 2 · (Br 2 ) 3 or Zn 6 Br 12 (18‐crown‐6) 2 · (Br 2 ) 2 via crystal‐to‐crystal transformation.…”

“…Beside the essential presence of the ionic liquid as the solvent and of SnBr 4 as a Lewis acid, the formation of voluminous cations formed by the coordination of Zn 2+ with 18‐crown‐6 supports the formation of expanded anionic building units as well as the crystallization of the respective compounds. Here, the coordination complexes of Zn 2+ and 18‐crown‐6 show wide adaptability, including i ) a non‐centric coordination of Zn 2+ by only five of six oxygen atoms of the crown ether, ii ) the bending of 18‐crown‐6 to realize six‐fold coordination of Zn 2+ with all six oxygen atoms involved, iii ) the coordination of Zn 2+ to one or two bromine atoms in addition to the crown ether, and iv ) an exocyclic coordination of 18‐crown‐6 by two cations on opposite sides , , . This adaptability is driven by the non‐matching size of Zn 2+ (74 pm) in view of the ring cavity of the crown ether (about 300 pm) .…”

Electrochemical and Fluorescent Properties of Crown Ether Functionalized Graphene Quantum Dots for Potassium and Sodium Ions Detection

“…As shown in Figure S3a,b, a slight increase in fluorescence was observed when increasing concentrations of the two ions were added to the GQDs solutions, regardless of the added salt. For the unbound crown ethers, the observed increase in emission (Figure S3c-f) is particularly evident for the complexation of the ion of interest with the corresponding crown ether (K + for NH 2 -18-crown-6 and Na + for NH 2 -15-crown-5), as also reported in the literature for a similar system [44,45].…”

Green‐Light‐Emitting Diodes based on Tetrabromide Manganese(II) Complex through Solution Process

“…Recent investigations have shown that many manganese(II) complexes display strong photoluminescence with various emitting colors, such as green, yellow, orange, red, etc., [27][28][29][30] originating from d-d transitions. High emissive quantum Adv.…”