Synthesis and crystal structure of ebastinium hydrogen fumarate

The structure of ebastinium hydrogen fumarate {systematic name: 1-[4-(4-tert-butylphenyl)-4-oxobutyl]-4-(diphenylmethoxy)piperidin-1-ium (E)-3-carboxy-1-hydroxyprop-2-en-1-olate}, C₃₂H₄₀NO₂ ⁺·C₄H₃O₄ ⁻, a 1:1 salt formed in the reaction between ebastine and fumaric acid is presented. All examined crystals were found to be twinned by pseudo-merohedry. The structure is extensively disordered, with over half (20 out of 35) its non-hydrogen atoms modelled as lying over two sets of sites. In the crystal, cation–anion pairs are linked by a strong N—H...O hydrogen bond [N...O = 2.697 (11) Å]. These units interact via weaker C—H...O and C—H...π contacts to form layers lying parallel to the bc plane. The hydrogen fumarate anions are linked by a very short O—H...O hydrogen bond [O...O = 2.5402 (17) Å], augmented by weak C—H...O contacts into pairs of R ² ₂(6) ring motifs to form chains that extend parallel to the b-axis direction. Comparisons to similar crystal structures are presented.