The crystal structure of an anomalous and tautomeric salt: 2:1 complex of (E)-2(1H)-6-methyl-pyridiniminium hydrogen maleate with maleic acid

Abstract

An anomalous salt in the 2:3 ratio of the original partners of 2-amino-3-methylpyridine and maleic acid, named tautomerically and structurally as the 2:1 complex of (E)-2(1H)-6-methyl-pyridiniminium hydrogen maleate with maleic acid, has been prepared and characterized by X-ray crystallography. The salt crystallizes in the monoclinic space group C2/c with a=15.891(2)Å,b=5.4040(10)Å,c=30.761(4)Å,β=94.810(10)°, V=2632.3(7)Å3,Z=4. The maleic acid partner adopts two forms of configuration, the hydrogen maleate anion and the original maleic acid. The hydrogen maleate anion is tied by O–H⋯O short intramolecular hydrogen bonds with a non-centered hydrogen atom, and bridged by maleic acid with hydrogen bond of OH⋯O to form whole crystal. The hydrogen maleate anion is linked to the individual pyridinium cation by intermolecular hydrogen bond of N(sp2)–H⋯O and N(sp3)–H⋯O. The heterocycle is fully protonated, which arouses amino–imino tautomerization. The geometrical arrangement in the crystal structure is characterized by the formation of laminar dimers of centrosymmetric pyridiniminium hydrogen maleate that is arranged in a manner of layer upon layer.