Pairing heterocyclic cations with closo-dodecafluorododecaborate (2−): Synthesis of binary heterocyclium(1+) salts and a Ag4(heterocycle)8 salt of B12F12

Eight binary salts that pair triazolium(1+), imidazolium(1+), pyrimidinium(1+), or purinium(1+) cations with the icosahedral closo-dodecafluorododecaborate(2−) anion (B₁₂F₁₂²⁻) were synthesized using open-air benchtop metathesis reactions in water or acetonitrile. The scale of the reactions varied from just milligrams to nearly one gram of the K₂B₁₂F₁₂ starting material. Other reaction conditions, the scope of the reaction, and the solubilities for the new salts are discussed. Five heterocyclium]₂B₁₂F₁₂] salts, which were obtained in yields ranging from 84% to 99%, displayed significantly higher densities than the corresponding previously reported analogous heterocyclium]₂B₁₂H₁₂] and heterocyclium]CB₁₁H₁₂] salts. A ninth high-density salt consisted of B₁₂F₁₂²⁻ paired with a complex Ag₄(triazole)₈⁴⁺ cation. The structures of eight of the nine new compounds were determined by single-crystal X-ray diffraction analysis. The density of five heterocyclium]₂B₁₂F₁₂] salts was found to increase approximately linearly as the distance between the five-membered-ring heterocyclium(1+) cation centroids decreased. This work demonstrates additional flexibility for the rational design of ionic structures with predictable properties, which will ultimately permit the tailoring of ingredient-response behavior.