A particularly challenging task is the design of anion receptors, because anions are larger than cations and are pH‐ and solvent‐sensitive. The first host for anionic guests is a dendritic octadentate N ligand, which upon reaction with CuCl2, encapsulates chloride ions (Cl6, see picture) as guests by means of anion–π interactions in an electron‐deficient cavity formed by four pyridine rings.

Different acid-base conjugates were made by combining a range of bases and superbases with acetic and propionic acid. Only the combinations that contained superbases were capable of dissolving cellulose. Proton affinities were calculated for the bases. A range, within which cellulose dissolution occurred, when combined with acetic or propionic acid, was defined for further use. This was above a proton affinity value of about 240 kcal mol(-1) at the MP2/6-311+G(d,p)//MP2/ 6-311+G(d,p) ab initio level. Understanding dissolution allowed us to determine that cation acidity contributed considerably to the ability of ionic liquids to dissolve cellulose and not just the basicity of the anion. By XRD analyses of suitable crystals, hydrogen bonding interactions between anion and cation were found to be the dominant interactions in the crystalline state. From determination of viscosities of these conjugates over a temperature range, certain structures were found to have as low a viscosity as 1-ethyl-3-methylimidazolium acetate, which was reflected in their high rate of cellulose dissolution but not necessarily the quantitative solubility of cellulose in those ionic liquids. 1,5-Diazabicyclo[4.3.0]non-5-enium propionate, which is one of the best structures for cellulose dissolution, was then distilled using laboratory equipment to demonstrate its recyclability.

Future biorefinery concepts are seriously entertaining the use of ionic liquids (ILs) as a platform media for the processing of woody material as a second-generation biomass feedstock.The main motivation is the demonstrated efficiency of some molten salts in the dissolution of cellulose, a major structural and solvolytically resistant component of lignocellulosic materials.The first report of the use of molten salts for the modification of cellulose came in the form of a patent by Graenacher, [1] where alkyl pyridinium chlorides were used to dissolve cellulose, thus allowing for efficient chemical modification from those media. The melting points of most alkyl pyridinium chloride salts are above 100 8C and, as such, these species do not fall under the common definition of ionic liquids. Nevertheless, the molten compounds solvated cellulose to such a state as to allow for acylation to a high degree. The next generational advance was the discovery by Rogers and co-workers [2] that dialkyl imidazolium based ionic liquids, with melting points below 100 8C, can dissolve cellulose. The most successful of these was 1-butyl-3-methylimidazolium chloride ([bmim]Cl]). This advance was further refined by Ohno et al.[ Despite the high efficiency for the solvation of cellulose, lignin, [5] and even wood [6] in an increasing range of dialkyl imidazolium based ionic liquids, sustainability of prospective processes will depend on the chemical stability of solutes and ionic liquids under process and recycling conditions. There are already some indications that ionic liquids such as [emim][OAc] react chemically with lignocellulosic solutes. [7] This reactivity may lower the recovery of the media upon recycling, although, in the case of the reaction of C2 imidazolium positions with C1 reducing end groups of cellulose, [7a,b] it is possible that this reaction is reversible under aqueous conditions, owing to the lability of the conjugate linkage.A bigger concern is the method of recycling to yield a pure ionic liquid. For most processes, high-purity ionic liquid will be required to maintain efficiency of dissolution and overall sustainability of the process. Decomposition of dialkyl imidazolium based ILs containing basic anions in the presence or absence of solutes proceeds according to three main pathways. From knowledge of the chemical stability of these cations, the pathways are most easily illustrated using a 1,3-diethylimidazolium cation ([eeim] + ) as countercation (Scheme 1).In relation to lignocellulose chemistry, pathway a, which involves formation of dialkyl imidazol-2-ylidene intermediates, has been demonstrated in the conjugation of cellulosic reducing end groups at C2 on the imidazolium ring. The publication by Liebert and Heinze, [7a] whereby the more basic [emim][OAc] reacts with oligocellulose reducing end groups to a much greater extent than [bmim]Cl or [emim]Cl, suggests that this reaction is likely dependent on the basicity of the anion. The initial step of this reaction is most likely deprotonation at C2, and t...

A ratiometric thermometer based on a mixed-metal Ln(III) metal-organic framework is reported that has good sensitivity in a wide temperature range from 4 to 290 K and a quantum yield of 22% at room temperature. The sensing mechanism in the europium-doped compound Tb0.95Eu0.05HL (H4L = 5-hydroxy-1,2,4-benzenetricarboxylic acid) is based not only on phonon-assisted energy transfer from Tb(III) to Eu(III) centers, but also on phonon-assisted energy migration between neighboring Tb(III) ions. It shows good performance in a wide temperature range, especially in the range 4-50 K, reaching a sensitivity up to 31% K(-1) at 4 K.

Future biorefinery concepts are seriously entertaining the use of ionic liquids (ILs) as a platform media for the processing of woody material as a second-generation biomass feedstock. The main motivation is the demonstrated efficiency of some molten salts in the dissolution of cellulose, a major structural and solvolytically resistant component of lignocellulosic materials.The first report of the use of molten salts for the modification of cellulose came in the form of a patent by Graenacher, [1] where alkyl pyridinium chlorides were used to dissolve cellulose, thus allowing for efficient chemical modification from those media. The melting points of most alkyl pyridinium chloride salts are above 100 8C and, as such, these species do not fall under the common definition of ionic liquids. Nevertheless, the molten compounds solvated cellulose to such a state as to allow for acylation to a high degree. The next generational advance was the discovery by Rogers and co-workers [2] that dialkyl imidazolium based ionic liquids, with melting points below 100 8C, can dissolve cellulose. The most successful of these was 1-butyl-3-methylimidazolium chloride ([bmim]Cl]). This advance was further refined by Ohno et al. [3] into room-temperature ionic liquids capable of dissolving cellulose, such as 1-ethyl-3-methylimidazolium formate ([emim][CO 2 H]) [3a] or 1-ethyl-3-methylimidazolium dimethylphosphate ([emim][Me 2 PO 4 ]). [3b] From the structures listed in the claims of the Rogers patent, [2b] BASF have also refined this list down to room-temperature ionic liquids, such as 1-ethyl-3-methylimidazolium acetate ([emim]- [OAc]). It has been reported by BASF, by oral dissemination and unofficial reports, that [emim][OAc] has higher dissolving efficiency for cellulose and has lower toxicity than structures such as [bmim]Cl. However, no detailed studies comparing chlorides with carboxylates or other such structures have been published, although certainly their undeniable high efficiency for dissolution and chemoselectivity has been demonstrated for a number of cellulose modification applications. [4] Despite the high efficiency for the solvation of cellulose, lignin, [5] and even wood [6] in an increasing range of dialkyl imidazolium based ionic liquids, sustainability of prospective