Chloride–hydrogen interactions of picolinic, nicotinic and isonicotinic acid chloride hydrochlorides in the crystalline state

Abstract

The crystal structures of the three isomers of the chemically labile pyridinecarboxylic acid chloride hydrochlorides were analyzed in order to study the weak interactions of the chloride anion with hydrogens. The chloride anions in the crystal structure of 1a have a slightly distorted square-planar interaction sphere with four hydrogens in the equatorial plane (plane of the molecule) with Cl⁻⋯H distances varying from 2.041(1) Å [NH⁺⋯Cl⁻] to 2.933(1) Å [CH⋯Cl⁻]. Nicotinic and isonicotinic acid chloride hydrochloride 1b and 1c show that chloride anion has a crucial role in the formation of bridged dimeric structures. The crystal lattices of 1b and 1c manifest similar herring-bone packing patterns. The chloride anions of 1b and 1c have slightly deformed planar interaction geometries to five and six hydrogens, respectively, with Cl⁻⋯H distances varying from 2.334(1) and 2.385(4) Å [NH⁺⋯Cl⁻] to 2.781(3) and 2.833(6) Å [CH⋯Cl⁻] in 1b and 1c, respectively. The difference in the packing of the isomers was attributed to Cl⁻⋯C contacts in 1a and on the other hand to end-to-end intermolecular interactions of the dimers of 1b and 1c, which could not exist with herring-bone packing of 1a. The moisture sensitive crystals of 1a, 1b, and 1c were obtained by sublimation of the compounds by heating in vacuo.