added an update
1,3,5-Trimethylpyridinium iodide was synthesized, and the structure was investigated by X-ray crystallography. The compound crystallizes in the Orthorhombic crystal system in the space group Cmcm with cell parameters a = 8.9850(9), b = 15.767(2), c = 6.9940(6)Å, Z = 4, R1 = 0.0215. The 1,3,5-trimethylpyridinium cation is on a crystallographic mirror plane, and another perpendicular mirror plane bisects the molecule. The pyridinium cation has C2v symmetry and a quarter of the molecule is independent.