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

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) Angstrom, b = 5.4040(10) Angstrom, c = 30.761(4) Angstrom, beta = 94.810(10)degrees, V = 2632.3(7) Angstrom(3), 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-(HO)-O-... short intramolecular hydrogen bonds with a non-centered hydrogen atom, and bridged by maleic acid with hydrogen bond of (OHO)-O-... to form whole crystal. The hydrogen maleate anion is linked to the individual pyridinium cation by intermolecular hydrogen bond of N(sp(2))-(HO)-O-... and N(sp(3))-(HO)-O-.... The heterocycle is fully protonated, which arouses amino-in-lino 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. (C) 2002 Elsevier Science B.V. All rights reserved.