Hydrogen Bonding in Pyridinium Picrates: From Discrete Ion Pairs to 3D Networks

A series of 20 picrates of pyridine derivatives were synthesized and their crystal structures studied by X-ray diffraction. The characteristic pyridinium-picrate synthon I was found to be present in 15 structures. The geometry of the pyridinium-picrate ion pair was found to be governed by additional C-H center dot center dot center dot O and N-H center dot center dot center dot O hydrogen bonds with the o-nitro groups of the picrate. If additional hydrogen donors are present on the pyridine cation, hydrogen bonds between these donors and nitro groups of picrate anions of neighboring ion pairs connect the ion pairs into 1D, 2D, or 3D supramolecular architectures. Synthon I was absent in five structures, in two cases as a result of protonation of an amino substituent on the pyridine ring, and in two cases as a result of insertion of a water molecule between the pyridinium cation and the picrate anion.