The physicochemical properties of a 33 isomer grid of mono-chlorobenzamides (Clxx) are reported with comprehensive studies of their crystal structures and interaction environments (Clx = para-/meta-/ortho-chlorobenzoyl and x = para-/meta-/orthoaminopyridine substitutions). The nine compound Clxx series was synthesised from the three p-/m-/o-chlorobenzoyl chlorides and three p-/m-/o-aminopyridine isomers using standard synthetic procedures. Clxx exhibits some similarities to the related Fxx and Brxx congeners e.g. the isomorphous behaviour of Clpp (para-Chloro-N'-(parapyridyl)benzamide) with several close relatives, and there are five isomorphous pairs of Clxx and Brxx crystal structures. Notably Clmp and Clpm both crystallise with Z'=4 in space group P but show important differences. The overall lack of isomers crystallising with solvate molecules is noteworthy, except for Clmm(H 2 O). In all Clxx crystal structures, strong N-H…N hydrogen bonds form, however, Clpo also crystallises as the unexpected Clpo_O polymorph with N-H…O=C intermolecular hydrogen bonding. The Clxo triad (with orthopyridines) exhibits the expected cyclic N-H…N dimer formation with R 2 2 (8) hydrogen bonded rings. The H C atom type, forming weak C-H…Cl hydrogen bonds, is the only favoured interaction partner of chlorine in Clxx. Conformational analyses (gas phase) together with crystal contact enrichment studies place Clxx in context and at the interface of hydrogen and halogen bonding interactions, though strong hydrogen bonding dominates. In Clxx the interaction energies with nearest neighbours are shown to contribute to most of the lattice electrostatic energies. The melting temperatures T m show correlation with both molecular symmetry (Carnelley's rule) and total electrostatic energy of the weak interactions; in addition, these T m values can be well predicted from a linear fit combining both descriptors. In Clxx, N-H…N hydrogen bonds dominate, largely in the absence of solvates, and with five Clxx forming isomorphous pairs with Brxx analogues; Clpp being isomorphous with several close benzamide relatives. Analysis of T m reveals correlations involving both symmetry and electrostatic energies.

A 3 × 3 isomer grid of nine N -(chlorophenyl)pyridinecarboxamides ( NxxCl ) is reported with physicochemical studies and single crystal structures ( Nx = pyridinoyl moiety; xCl = aminochlorobenzene ring; x = para -/ meta -/ ortho -), as synthesized by the reaction of the substituted p -/ m -/ o -pyridinecarbonyl chlorides ( Nx ) with p -/ m -/ o -aminochlorobenzenes ( xCl ). Several of the nine NxxCl crystal structures display structural similarities with their halogenated NxxX and methylated NxxM relatives ( x = p -/ m- / o -substitutions; X = F, Br; M = methyl). Indeed, five of the nine NxxCl crystal structures are isomorphous with their NxxBr analogues as the NpmCl / Br , NpoCl / Br , NmoCl / NmoBr , NopCl / Br , and NooCl / Br pairs. In the NxxCl series, the favored hydrogen bonding mode is aggregation by N–H···N pyridine interactions, though amide···amide intermolecular interactions are noted in NpoCl and NmoCl . For the NoxCl triad, intramolecular N–H···N pyridine interactions influence molecular planarity, whereas NppCl·H 2 O (as a monohydrate) exhibits O–H···O, N–H···O1W, and O1W-H···N interactions as the primary hydrogen bonding. Analysis of chlorine-containing compounds on the CSD is noted for comparisons. The interaction environments are probed using Hirshfeld surface analysis and contact enrichment studies. The melting temperatures ( T m ) depend on both the lattice energy and molecular symmetry (Carnelley’s rule), and the melting points can be well predicted from a linear regression of the two variables. The relationships of the T m values with the total energy, the electrostatic component, and the strongest hydrogen bond components have been analyzed.

The title compounds, C19H12Br2N2O2 and C18H11Br2N3O2, were synthesized in good yields from condensation reactions of 3-bromobenzoyl chloride with 2-aminopyridine or 2-aminopyrimidine using standard condensation reaction conditions and subsequent column chromatography.