Cataloguing the Energetic Contributions to the Supramolecular Assembly of para-Substituted N,N′-Diphenylureas and Their Organometallic Derivatives in the Solid State: A Density Functional Theory Approach

Abstract

Crystal engineering relies on the predictability of the elaborate interplay of cohesive and conformational energies driven by both intra- and intermolecular interactions of the constituent molecules. In an effort to better understand these influences on the crystal packing of para-substituted N,N′-diphenylureas (pDPUs) and organometallic derivatives, we present a detailed computational investigation of pDPU species utilizing solid-state density functional theory (DFT) and demonstrate the applicability of predictive supramolecular synthons applied toward the growth of related organometallic complexes. Dominant noncovalent interactions of pDPUs can be tuned by altering the electron-withdrawing character of the para substituents. The strength of this electron-withdrawing nature governs the inclination of the molecules to form either dominant electrostatic or π-stacking intermolecular interactions in the crystal structure due to potential molecular conformational stabilization through intramolecular C–H···O electrostatic interactions between ortho phenyl hydrogens and the urea oxygen atoms. This propensity is also influenced by the symmetry of para substitutions in mono- and disubstituted DPUs. The results of the holistic DFT investigation show a relationship between gas-phase and solid-state conformations and also present evidence of mechanisms leading to deviations in predicted crystallization behaviors on the basis of the balance of intra- and intermolecular interactions. The foundational computational study was expanded to build on previous experimental and theoretical work involving zerovalent transition-metal complexes in which p-isocyanophenyl DPUs were appended with group IV metal carbonyl fragments. In this study, we synthesized an asymmetric analogue of the latter in which N-(p-isocyanophenyl)-N′-phenylurea (pCNHDPU) was appended to a Mo(CO)5 metal carbonyl fragment, allowing us to associate the crystallization behaviors and interactions of organometallic DPU derivatives with those of simpler pDPUs. It was observed that the supramolecular assembly of the organometallic complexes display similar predictive patterns as well as additional complexities to molecular packing arising from the bulkier metal carbonyl substituents. An inclusive computational categorization of DPU-based systems in complement to experimental data will aid in the advancement of design rules for the patterned crystal growth of DPU and related systems for the development of innovative materials having unique solid-state properties.