Hydrogen-Bonding in the Structures of the Hydrated Proton-Transfer Compounds of Isonipecotamide with the Isomeric Indole-2- and Indole-3-Carboxylic Acids

Abstract

The structures of two hydrated proton-transfer compounds of 4-piperidinecarboxamide (isonipecotamide) with the isomeric heteroaromatic carboxylic acids indole-2-carboxylic acid and indole-3-carboxylic acid, namely 4-carbamoylpiperidinium indole-2-carboxylate dihydrate (1) and 4-carbamoylpiperidinium indole-3-carboxylate hemihydrate (2) have been determined at 200 K. Crystals of both 1 and 2 are monoclinic, space groups P21/c and P2/c, respectively with Z = 4 in cells having dimensions a = 10.6811(4), b = 12.2017(4), c = 12.5456(5) A, β = 96.000(4)° (1) and a = 15.5140(4), b = 10.2908(3), c = 9.7047(3) A, β = 97.060(3)° (2). Hydrogen-bonding in 1 involves a primary cyclic interaction involving complementary cation amide N–H···O(carboxyl) anion and anion hetero N–H···O(amide) cation hydrogen bonds [graph set R 2 2 (9)]. Secondary associations involving also the water molecules of solvation give a two-dimensional network structure which includes weak water O–H···π interactions. In the three-dimensional hydrogen-bonded structure of 2, there are classic centrosymmetric cyclic head-to-head hydrogen-bonded amide–amide interactions [graph set R 2 2 (8)] as well as lateral cyclic amide-O linked amide–amide extensions [graph set R 4 2 (8)]. The anions and the water molecule, which lies on a twofold rotation axis, are involved in secondary extensions. The structure determinations of the hydrated proton-transfer compounds of piperidine-4-carboxamide (isonipecotamide) with indole-2-carboxylic acid and indole-3-carboxylic acid has allowed a description of the inherent hydrogen-bonding features of the respective two- and three-dimensional structures.