In the present work an in depth deep electronic study of multicenter XBs (FX)n/NH3 (X = Cl, Br and n = 1–5) is conducted. The ways in which X∙∙∙X lateral contacts affect the electrostatic or covalent nature of the X∙∙∙N interactions are explored at the CCSD(T)/aug-cc-pVTZ level and in the framework of the quantum theory of atoms in molecules (QTAIM). Calculations show that relatively strong XBs have been found with interaction energies lying between −41 and −90 kJ mol−1 for chlorine complexes, and between −56 and −113 kJ mol−1 for bromine complexes. QTAIM parameters reveal that in these complexes: (i) local (kinetics and potential) energy densities measure the ability that the system has to concentrate electron charge density at the intermolecular X∙∙∙N region; (ii) the delocalization indices [δ(A,B)] and the exchange contribution [VEX(X,N)] of the interacting quantum atoms (IQA) scheme, could constitute a quantitative measure of the covalence of these molecular interactions; (iii) both classical electrostatic and quantum exchange show high values, indicating that strong ionic and covalent contributions are not mutually exclusive.

In supramolecular chemistry, the rational design of self‐assembled systems remains a challenge. Herein, hydrogen‐bonded rosettes of melamine and ammeline have been theoretically examined by using dispersion‐corrected density functional theory (DFT‐D). Our bonding analyses, based on quantitative Kohn–Sham molecular orbital theory and corresponding energy decomposition analyses (EDA), show that ammeline is a much better building block than melamine for the fabrication of cyclic complexes based on hydrogen bonds. This superior capacity is explained by both stronger hydrogen bonding and the occurrence of a strong synergy.

Ion recognition is still an emerging topic in supramolecular chemistry and has aroused great attention in the last few years. In this work, we have examined the assemblies of selected hexameric rosettes of melamine and ammeline and their capacities to host halide and alkali ions in the gas phase and in water. Using relativistic dispersion-corrected density functional theory (DFT-D), we first studied the stability and the effect of introducing monovalent anions (Cl − , Br − , and I − ) and cations (Na + , K + , and Rb + ) in the center of the rosette's cavity. Finally, we explored the interactions in two stacked rosettes with an interlayer ion. Our computations reveal that aminesubstituted triazines are promising candidates for anion and cation recognition either in self-assembled monolayers or pillar array structures. The anion recognition process is governed by both the electrostatic and charge-transfer (donor−acceptor) interactions, while the cation recognition is governed by electrostatic and polarization. In addition, melamine and ammeline could constitute a potent mixture for dual-ion recognition strategies.

charge density descriptors were used to evaluate the aromaticity of M in each complex. Results show that the hydrogen and halogen (XBs) bond interactions, which direct the self-assembly process in these complexes, are anti-cooperative. Binding energies decrease in the following order: M/ (CA) n > M/(TCA) n > M/(CABr) n > M/(CACl) n (for all values of n). Brominated CA arises as a potential compound to self-assembly with M via XBs. Keywords Cyanuric acid • Supramolecular • Molecular building blocks • Hydrogen bond • Halogen bondPublished as part of the special collection of articles "CHITEL 2015 -Torino -Italy".

Hydrogen‐bonded supramolecular systems are known to obtain extra stabilization from the complexation with ions, like guanine quadruplex (GQ). They experience strong hydrogen bonds due to cooperative effects. To gain deeper understanding of the interplay between ions and hydrogen‐bonding cooperativity, relativistic dispersion‐corrected density functional theory (DFT‐D) computations were performed on triple‐layer hydrogen‐bonded rosettes of ammeline interacting with alkali metal cations and halides. Our results show that when ions are placed between the stacks, the hydrogen bonds are weakened but, at the same time, the cooperativity is strengthened. This phenomenon can be traced back to the shrinkage of the cavity as the ions pull the monomers closer together and therefore the distance between the monomers becomes smaller. On one hand this results in a larger steric repulsion, but on the other hand, the donor‐acceptor interactions are enhanced due to the larger overlap between the donating and accepting orbitals leading to more charge donation and therefore an enhanced electrostatic attraction.

Cyanuric acid is shown to be the best supramolecular building block to obtain cage-like clusters. Its triazine ring is also superior to the melamine one for capturing anions as well as cations.

Invited for this month's cover picture are Professor Célia Fonseca Guerra from Vrije Universiteit Amsterdam and Leiden University (The Netherlands) and André Nicolai Petelski from UTN‐FRRe University of Argentine (Argentina). The cover picture shows a colored pallet of melamine and ammeline tautomers that form hydrogen‐bonded hexameric rosettes. When it comes to self‐assembling capabilities, one of the ammeline structures (red) is shown to be distinctly superior to melamine, both in the gas phase and in water. Quantum chemical computations explain that this is due to the presence of stronger pair interactions and the manifestation of a large cooperativity effect. Read the full text of their Full Paper at 10.1002/open.201800210.

The melamine (M)/cyanuric acid (CA) supramolecular system is perhaps one of the most exploited in the field of self-assembly because of the high complementarity of the components. However, it is necessary to investigate further the factors involved in the assembly process. In this study, we analyzed a set of 13 M n /CA m clusters (with n , m = 1, 2, 3), taken from crystallographic data, to characterize the nature of the hydrogen bonds involved in the self-assembly of these components as well as to provide greater understanding of the phenomenon. The calculations were performed at the B3LYP/6-311++G(d,p) and ω-B97XD (single point) levels of theory, and the interactions were analyzed within the framework of the quantum theory of atoms in molecules and by means of molecular electrostatic potential maps. Our results show that the stablest structure is the rosette-type motif and the aggregation mechanism is governed by a combination of cooperative and anticooperative effects. Our topological results explain the polymorphism in the self-assembly of coadsorbed monolayers of M and CA. Graphical abstract The aggregation steps of the melamine-cyanuric co-crystal is driven by a hydrogen-bonded network which is governed by a complex combination of cooperative and anticooperative effects.