Hydrogen bonding in proton-transfer compounds of 5-sulfosalicylic acid with ortho-substituted monocyclic heteroaromatic Lewis bases

The crystal structures of the 1:1 proton-transfer compounds of 5-sulfosalicylic acid with the ortho-substituted monocyclic heteroaromatic Lewis bases, 2-aminopyridine, 2-hydroxypyridine and 2-aminopyrimidine, viz. 2-aminopyridinium 5-sulfosalicylate (1), 2-hydroxypyridinium 5-sulfosalicylate monohydrate (2) and 2-aminopyrimidinium 5-sulfosalicylate monohydrate (3) have been determined and their hydrogen-bonding patterns described. All compounds are monoclinic, space group P21/c, with Z=4 in cells with dimensions a=7.898(5), b=11.159(11), c=14.912(7) Å, β=96.849(11)° (1);=7.260(2), b=15.292(3), c=12.615(2) Å, β=102.45(5)° (2) and a=7.0430(7), b=12.1871(16), c=16.2825(12) Å, β=101.364(7)° (3). All three compounds show some molecular disorder, in 1 within the cation species and with both 2 and 3, a similar rotational disorder in the anion sulfonate group. Hydrogen bonding in all three compounds together with significant cation-anion or cation-cation inter-ring π–π interactions generate three-dimensional layered polymer structures.