Vapochromic Ionic Liquids from Metal–Chelate Complexes Exhibiting Reversible Changes in Color, Thermal, and Magnetic Properties

Abstract

Vapor- and gas-responsive ionic liquids (ILs) comprised of cationic metal-chelate complexes and bis(trifluoromethanesulfonyl)imide (Tf(2)N) have been prepared, namely, [Cu(acac)(BuMe(3)en)][Tf(2)N] (1 a), [Cu(Bu-acac)(BuMe(3)en)][Tf(2)N] (1 b), [Cu(C(12)-acac)(Me(4)en)][Tf(2)N] (1 c), [Cu(acac)(Me(4)en)][Tf(2)N] (1 d), and [Ni(acac)(BuMe(3)en)][Tf(2)N] (2 a) (acac = acetylacetonate, Bu-acac = 3-butyl-2,4-pentanedionate, C(12)-acac = 3-dodecyl-2,4-pentanedionate, BuMe(3)en = N-butyl-N,N',N'-tetramethylethylenediamine, and Me(4)en = N,N,N',N'-trimethylethylenediamine). These ILs exhibited reversible changes in color, thermal properties, and magnetic properties in response to organic vapors and gases. The Cu(II)-containing ILs are purple and turn blue-purple to green when exposed to organic vapors, such as acetonitrile, methanol, and DMSO, or ammonia gas. The color change is based on the coordination of the vapor molecules to the cation, and the resultant colors depend on the coordination strength (donor number, DN) of the vapor molecules. The vapor absorption caused changes in the melting points and viscosities, leading to alteration in the phase behaviors. The IL with a long alkyl chain (1 d) transitioned from a purple solid to a brown liquid at its melting point. The Ni(II)-containing IL (2 a) is a dark red diamagnetic liquid, which turned into a green paramagnetic liquid by absorbing vapors with high DN. Based on the equilibrium shift from four- to six-coordinated species, the liquid exhibited thermochromism and temperature-dependent magnetic susceptibility after absorbing methanol.

Solvatochromic CuII‐Containing Ionic Liquids with Ether Side Chains: Control of Solvent Response through Intramolecular Coordination

“…The DSC data are listed in Table 1, and the DSC traces are -85 -30.3 [b] 6.2 [a,b] 25.7 [a,b] -124 [b] [ ). [7] The value of T g /T m is in good agreement with the empirical rule (T g /T m = 2:3). [10] It seems that [1][Tf 2 N] has a rather low melting point despite having a five-coordinate structure with no flexibility in the substituent, as supported by X-ray crystallography (see below).…”

“…The DSC traces are presented in Figure ). [7] This is, because the butyl substituent in this salt is free before and after coordination of DMSO, similar to [2][Tf 2 N] (Figure 3b). When an excess of DMSO (4 equiv.)…”

“…This group of liquids contains the mixed-ligand solvatochromic complexes [Cu(acac)(Me 2 NCH 2 CH 2 NMeR)][Tf 2 N] {acac = acetylacetonato, R = alkyl, Tf 2 N = (F 3 CSO 2 ) 2 N -}. [7] The introduction of the substituent (R) and the use of the Tf 2 N anion produced ionic liquids from the solvatochromic complexes. The color change is based on the absorption of vapor molecules, which coordinate to the metal center.…”

Redox Active Glyme-Li Salt Solvate Ionic Liquids Based on Tetrabromoferrate(III)

“…[1][2][3] This new subset of ILs, referred to as solvate ILs, has become especially important for preparing metal ion-based ILs, which can be used as a thermally stable electrolyte for energy storage devices. Unlike aprotic ILs and metal salt binary mixtures employed as typical IL-based battery electrolytes, solvate ILs can provide a high concentration of metal ions required for fast electrode reactions in batteries.…”

Spin-Crossover Behavior of Hofmann-Type-Like Complex Fe(4,4’-bipyridine)Ni(CN)4·nH2O Depending on Guest Species

“…1 showed vapochromic behavior [35][36][37][38][39][40][41]. The orange powder of 1 displayed a color change on exposure to certain organic compounds, such as ethanol, acetone, 2-propanol, etc., in the gas phase.…”