期刊
CHEMPHYSCHEM
卷 22, 期 18, 页码 1850-1856出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cphc.202100424
关键词
halide salts; ionic liquids; hydrogen bonding; X-ray crystallography; IR spectroscopy
资金
- Deutsche Forschungsgemeinschaft (DFG, German Science Foundation) [LU-506/12-2, 269854963, LU-506/14-2, 286149019]
- Projekt DEAL
The structural versatility of halide salts can be controlled by the nature of hydrogen bonding interactions. Two types of hydrogen bonding, 'intra-ionic' and 'inter-ionic', are observed in the X-ray structures of these salts. Additionally, a third type of hydrogen bonding is found in some molten halide salts.
The paradigm of supramolecular chemistry relies on the delicate balance of noncovalent forces. Here we present a systematic approach for controlling the structural versatility of halide salts by the nature of hydrogen bonding interactions. We synthesized halide salts with hydroxy-functionalized pyridinium cations [HOCnPy](+) (n=2, 3, 4) and chloride, bromide and iodide anions, which are typically used as precursor material for synthesizing ionic liquids by anion metathesis reaction. The X-ray structures of these omnium halides show two types of hydrogen bonding: 'intra-ionic' H-bonds, wherein the anion interacts with the hydroxy group and the positively charged ring at the same cation, and 'inter-ionic' H-bonds, wherein the anion also interacts with the hydroxy group and the ring system but of different cations. We show that hydrogen bonding is controllable by the length of the hydroxyalkyl chain and the interaction strength of the anion. Some molten halide salts exhibit a third type of hydrogen bonding. IR spectra reveal elusive H-bonds between the OH groups of cations, showing interaction between ions of like charge. They are formed despite the repulsive interaction between the like-charged ions and compete with the favored cation-anion H-bonds. All types of H-bonding are analyzed by quantum chemical methods and the natural bond orbital approach, emphasizing the importance of charge transfer in these interactions. For simple omnium salts, we evidenced three distinct types of hydrogen bonds: Three in one!
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