At the Interface of Isomorphous Behavior in a 3 × 3 Isomer Grid of Monochlorobenzamides: Analyses of the Interaction Landscapes via Contact Enrichment Studies

International audience ; 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-/ortho-aminopyridine 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'-(para-pyridyl)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 ortho-pyridines) 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 ...