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!

The concept of hydrogen bonding is celebrating its 100th birthday. Hydrogen bonds (H-bonds) play a key role in the structure and function of biological molecules, the strength of materials, and molecular binding. Herein, we study H-bonding in mixtures of a hydroxyl-functionalized ionic liquid with the neutral, H-bond-accepting molecular liquid dimethylsulfoxide (DMSO) using neutron diffraction experiments and molecular dynamics simulations. We report the geometry, strength, and distribution of three different types of Hbond OH•••O, formed between the hydroxyl group of the cation and either the oxygen atom of another cation, the counteranion, or the neutral molecule. Such a variety of different strengths and distributions of H-bonds in one single mixture could hold the promise of providing solvents with potential applications in H-bond-related chemistry, for example, to alter the natural selectivity patterns of catalytic reactions or the conformation of catalysts.

The Front Cover shows one of the three types of hydrogen bonding observed in hydroxy‐functionalized halide salts. Here, the halide anion forms a hydrogen bond to the hydroxy group and interacts with the ring system of the cation at the same time. The versatility of structures demonstrates the importance of non‐covalent interactions, in particular the role of hydrogen bonding. More information can be found in the Communication by Ralf Ludwig and co‐workers.