Competition of intermolecular interactions in the self-assembly of co-crystals of trifluoro-meta-arylenediamines (benzene, nitrobenzene, pyridine) with 12-, 15-, and 18-membered crown ethers

Abstract

Two sets of co-formers, polyfluorinated arylenediamines with variable structural elements and macrocyclic ethers of different sizes, were used to study the patterns of self-assembly of co-crystals and to rank the intermolecular interactions. The co-crystallization stoichiometry was found to increase from 1 : 1 to 2 : 1 in the series trifluoro-1,3-phenylenediamine, 2,4-diaminotrifluoropyridine, and 2,4-diaminotrifluoronitrobenzene and with decreasing crown ether size due to restructuring of guest–host interactions and forming guest–guest interactions. 18-Crown-6 and 15-crown-5 ethers form the typical N–H⋯O_cr H-bonds connecting two O_cr atoms with one bifunctional proton donor NH₂; when going to 12-crown-4, two O_cr atoms become connected with the H_amino atoms of two arylenediamine molecules. Modes of guest–guest bonding and supramolecular motifs in 2 : 1 co-crystals are determined by HB acceptors and p + π systems in arylenediamine: o-N–H⋯N_het and p-N–H⋯F interactions form face-to-face dimers united in a chain; p-N–H⋯O_nitro and o-N–H⋯O_nitro contacts generate head-to-tail and head-to-side chains; π⋯π and X⋯π (X = F, O, N) electron interactions form off-set stacks. Quantum chemical calculations reveal an increase of the packing enthalpies and bonding energies with increasing arylenediamine electron affinity and crown ether size. According to MEP, BCP and NCI analyses, these effects are caused either by strengthening of the interactions due to a greater electrostatic contribution, or by multiplying bonding contacts. Quantifying the interactions allowed us to identify the key supramolecular synthons and related elements of the co-former structure, which can serve as tools in the molecular crystal design.