Pyrrolidinium-based cations were systematically modified to investigate their influence on ozonide and superoxide anions and to understand the scattering of experimentally determined dimensions of these radical anions. Hence, 1-ethyl-1-methyl-pyrrolidinium, 1-propyl-1-methyl-pyrrolidinium and 1-butyl-1-methyl-pyrrolidinium superoxide, as well as 1-methyl-1-methyl-pyrrolidinium and 1-propyl-1-methyl-pyrrolidinium ozonide have been synthesized via ion exchange in liquid ammonia, and characterized by single-crystal X-ray diffraction. Attempts to crystallize the 1-ethyl-1-methyl-pyrrolidinium and 1-butyl-1-methyl-pyrrolidinium ozonide in the same way failed. Two fundamental causes for the variation in the dimensions of the radical anions were revealed: firstly, the reduced accuracy of the experimental data due to static disorder and increased thermal motion, and secondly, the effects of the environments to which the anions are exposed in the crystal matrix. Quantum-chemical calculations of the isolated or embedded anions were also performed, showing a significant influence of hydrogen bonding and crystal field effects.
