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In the title compound, 2C17H19N2+·2H2PO4−·3H3PO4·CH3OH, Tröger base, phospho­ric acid and methanol are included in the crystal structure, the asymmetric unit of which contains three protonated acid units. The structure includes hydro­philic layers of dihydrogen phosphate anions, phospho­ric acid and methanol which are inter­connected by O—H⋯O hydrogen bonds. These layers alternate with the more hydro­phobic Tröger base. Each Tröger base acts as a proton donor in an N—H⋯O hydrogen bond.

Alkanes and most of their -and , -substituted derivatives show a remarkable alternation in their melting points with increasing chain length [1,2]. The same phenomenon also occurs within series of substances with a constant number of C-atoms. One of these isomeric series are the octenes where the melting points of the 2-and 4-octenes are relatively higher than those of 1-and 3-octenes. This holds for the series of cis-as well as for the series of trans-isomers.Single crystals of all trans-octenes have been grown in situ using a miniature zone melting procedure [3], and their X-ray analyses have been carried out. Crystal structures of cis-octenes have been determined by X-ray powder diffraction using lattice energies minimisations [4]. The structural similarities and differences between the trans-and cis-isomers of each serie could be analyzed based on the packing arrangements of hydrocarbon chains and the end groups. The melting point alternation in both isomeric series can be explained based on the calculations of lattice energies.