Dissolving Cellulose in 1,2,3-Triazolium- and Imidazolium-Based Ionic Liquids with Aromatic Anions

We present 1,2,3-triazolium- and imidazolium-based ionic liquids (ILs) with aromatic anions as a new class of cellulose solvents. The two anions in our study, benzoate and salicylate, possess a lower basicity when compared to acetate and therefore should lead to a lower amount of N-heterocyclic carbenes (NHCs) in the ILs. We characterize their physicochemical properties and find that all of them are liquids at room temperature. By applying force field molecular dynamics (MD) simulations, we investigate the structure and dynamics of the liquids and find strong and long-lived hydrogen bonds, as well as significant π–π stacking between the aromatic anion and cation. Our ILs dissolve up to 8.5 wt.-% cellulose. Via NMR spectroscopy of the solution, we rule out chain degradation or derivatization, even after several weeks at elevated temperature. Based on our MD simulations, we estimate the enthalpy of solvation and derive a simple model for semi-quantitative prediction of cellulose solubility in ILs. With the help of Sankey diagrams, we illustrate the hydrogen bond network topology of the solutions, which is characterized by competing hydrogen bond donors and acceptors. The hydrogen bonds between cellulose and the anions possess average lifetimes in the nanosecond range, which is longer than found in common pure ILs.

Abrupt spin crossover in iron(iii) complexes with aromatic anions

Two iron(iii) complexes, [Fe(qsal-X)2]OTs·nH2O, are found to exhibit abrupt spin crossover with the spin transition temperature substituent dependent, and X⋯O halogen bonds linking the spin centres.

Supramolecular heterosynthon assemblies of ortho-phenylenediamine with substituted aromatic carboxylic acids

Co-crystallization experiments conducted between ortho-phenylenediamine (OPDA) and five substituted aromatic acids (phthalic acid, salicylic acid, 4-hydroxybenzoic acid, 4-nitrobenzoic acid and 3,5-dinitrobenzoic acid) reveal the formation of supramolecular networks constructed from acid–base heterosynthons of ortho-phenylenediammonium cations with respective aromatic anions. All of these coformers are generally regarded as safe (GRAS) molecules. The five reported crystal structures are sustained predominantly by intermolecular N+−H...O−, N—H...O− and N—H...O hydrogen-bonding interactions; in addition intramolecular O—H...O and intermolecular O—H...O, O—H...O− and C—H...O interactions contribute to the formation of various networks. Five 1:1 salts [NH2C6H4NH3]+·[COOHC6H4COO]− (1); [NH2C6H4NH3]+·[OHC6H4COO]− (2); [{NH2C6H4NH2}2·{OHC6H4COOH}2·{NH2C6H4NH3}+ 2·{OHC6H4COO}− 2] (OPDPHB) (3); [NH2C6H4NH3]+·[NO2C6H4COO]− (4) and [NH2C6H4NH3]+·[(NO2)2C6H4COO]− (5) were isolated as single crystals by the slow evaporation method and were characterized using spectroscopic and X-ray crystallographic techniques. X-ray diffraction studies confirmed the formation of salts. The pK a difference between the amine and respective acid favours the transfer of a proton from the acid to the amine, which leads to the formation of the anion and the cation. The interactions between these ions resulted in a stable heterosynthon in each case. The asymmetric units of salts (1), (2), (4) and (5) contain one anion and one cation each, but salt (3) consists of two anions, two cations and two neutral species in its asymmetric unit. A polymorph of salt (3) was also isolated from the crystallization of the ground material from liquid-assisted grinding [{NH2C6H4NH2}·{NH2C6H4NH3}+·{OHC6H4COO}−] (OPDPHB 3P). The polymorph crystallized in the monoclinic non-centrosymmetric space group P21. The liquid-assisted grinding experiments using a 1:1 ratio also revealed the formation of the expected salts, except salt (3), where this product matches with polymorph (OPDPHB 3P).

Search for aromatic anions in the P2E3− (E = N, P, As, Sb, Bi) series

Nine aromatic five-membered rings were computationally characterized in the P2E3− (E = N, P, As, Sb, Bi) series of anions.