A water-soluble cavitand bearing a benzotriazole upper rim was prepared and characterized. It exists as a dimeric velcraplex in D₂O, but forms host–guest complexes with hydrophobic and amphiphilic guests. Alkanes (C5 to C10), cyclic ketones (C6–C10), cyclic alcohols (C6–C8) and various amphiphilic guests form 1 : 1 cavitand complexes. A cyclic array of hydrogen bonds, bridged by solvent/water (D₂O) molecules, stabilizes the vase conformation of the complexes. With longer alkanes (C12–C15), symmetrical dialkyl amine, urea and phosphate, 2 : 1 host:guest capsules are formed. Computations indicate that additional waters on the upper rim create a self-complementary hydrogen-bonding pattern for capsule formation. 

We describe new container host molecules - deep cavitands with benzimidazole walls and ionic feet - to recognize highly hydrophilic guest molecules in water. The aromatic surfaces of the cavity recognize hydrophobic portions of the guest while bound water molecules mediate hydrogen bonding in the complex. Spectroscopic (NMR) evidence indicates slow in/out exchange on the chemical shift timescale and thermodynamic (ITC) methods show large association constants (Ka up to 6 x 10(4) M-1) for complexation of small, water-soluble molecules such as THF and dioxane. Quantum chemical calculations are employed to optimize the host-guest geometries and elucidate the hydrogen bonding patterns responsible for the binding.

Togni's benziodoxole-based reagents are widely used in trifluoromethylation reactions. It has been established that the kinetically stable hypervalent iodine form (I-CF3) of the reagents is thermodynamically less stable than its acyclic ether isomer (O-CF3). On the other hand, the trifluoromethylthio analogue exists in the thermodynamically stable thioperoxide form (O-SCF3), and the hypervalent form (I-SCF3) has been elusive. Despite the importance of these reagents, very little is known about the reaction mechanisms of their syntheses, which has hampered the development of new reagents of the same family. Herein, we use density functional theory calculations to understand the reasons for the divergent behaviors between the CF3 and SCF3 reagents. We demonstrate that they follow different mechanisms of formation and that the metals involved in the syntheses (potassium in the case of the trifluoromethyl reagent and silver in the trifluoromethylthio analogue) play key roles in the mechanisms and greatly influence the possibility of their rearrangements from the hypervalent (I-CF3, I-SCF3) to the corresponding ether-type form (O-CF3, O-SCF3).

The cooperativity between MX2:XH alkaline-earth bonds and XH:NH3 hydrogen bonds (M=Mg, Ca; X=F, Cl) was investigated at the G4 level of theory. The cooperativity between these two non-covalent linkages is extremely large, to the point that the increase in their bond dissociation enthalpies may be as large as 240%. More importantly, the weaker the interaction, the larger the increase, so in some cases the linkage that stabilizes the most is the alkaline-earth bond, whereas in others is the hydrogen bond. In all cases, the formation of the MX2:XH:NH3 ternary complex is followed by a spontaneous proton transfer, very much as previously found for the Be-containing analogues. Similarly, MX2:FCl:NH3 complexes evolve from a chlorine-shared ternary complex (MX2FClNH3) or from an ion pair (MX2F-NH3Cl+) if M=Ca. Although F is the only halogen without sigma-hole, MgCl2 derivatives induce the appearance of a sigma-hole on it, though less deep than those induced by BeCl2. We have also studied whether Mg and Ca bond-containing complexes MR2:FY (R=H, F, Cl; Y=NH2, OH, F, Cl) may react to form radicals, as it has been found for the Be-containing analogues. These interactions provoke a drastic decrease in the F-Y bond dissociation enthalpy, very much as the one reported for the corresponding Be-analogues, to the point that in some cases the formation of the corresponding MR2F center dot+Y radicals becomes exothermic. Hence, the general conclusion of this study is that Mg or Ca derivatives give place to similar or even larger perturbations on the electron density than those induced by Be, a result not easily predictable.

The thermal decomposition of N-nitrosoamides has experimentally been demonstrated to depend on several factors, such as temperature, solvent and the substituents on the substrate. Consequently, a number of reaction mechanisms have been proposed for this process in the literature. In this work, we present a comprehensive computational investigation in which we examine the detailed reaction mechanisms for two N-nitrosoamides (with aliphatic and aromatic substituents) in two different solvents (mesitylene and methanol). It is shown that the reaction mechanism can change dramatically with the nature of the substrate and the choice of solvent. Importantly, it is found that the polar solvent stabilizes ion-pairs that are unstable in the non-polar solvent, which can play a key role in the mechanism.

Density functional theory calculations are employed to investigate the mechanism and energies of the decomposition of N-nitrosoamides in the presence of a resorcinarene-based self-assembled nanocapsule. From experiments, it is known that confinement in the capsule inhibits the thermal decomposition of these compounds. N-Nitrosoamides with both aromatic and aliphatic substituents are considered here and the calculations show that, for both kinds, binding to the capsule leads to a significant increase in the energy barrier of the rate-determining step, the 1,3 N -> O acyl transfer reaction. A distortion-interaction analysis is conducted to probe the reasons behind the inhibition of the reaction. In addition, we characterized hypothetical intermediates that might be involved in the formation of the decomposition products inside the capsule. Interestingly, it is found that the capsule stabilizes ion-pair species that are unstable in mesitylene solution. Finally, a possible explanation is proposed for the observed encapsulation of the decomposition product of only one of the substrates.

Non-covalent interactions unavoidably involve a certain disturbance of the electronic density of the interacting systems. Such perturbations are particularly strong when dealing with electron deficient systems such as boron, beryllium, magnesium (pre-p elements) or calcium (a pre-d element) derivatives. Indeed, these compounds have been shown to modify the intrinsic reactivity of the systems interacting with them. In the first part of this paper, we present an overview on (i) how electron deficient systems, acting as Lewis acids, modulate the intrinsic acidity of Lewis bases, explaining for instance why a typical base, such as aniline, can be converted by association with borane into an acid as strong as phosphoric acid; (ii) how other weak non-covalent interactions, such as halogen bonds, permit one to modulate the intrinsic basicity of typical oxyacids changing them into strong BrOnsted bases; (iii) how cooperativity between different non-covalent interactions may lead to the spontaneous formation of ion-pairs in the gas phase; (iv) how non-covalent interactions generate sigma-holes in systems where this feature is not present; and (v) how these interactions can induce exergonic and spontaneous formation of neutral radicals. In the second part of the paper, we show, by using G4 high-level ab initio calculations, that the acidity enhancement phenomenon is a general mechanism whenever a given base interacts with non-protic and protic acids. In the non-protic acid case, the underlying mechanism behind the enhancement is similar to the one reported for electron-deficient compounds, whereas the protic acid case appears in complexes stabilized through conventional hydrogen bonds. We also show that the former could be classified as an a priori mechanism, whereas the latter would be an a posteriori mechanism. This same a posteriori mechanism is behind the significant basicity enhancement of water and ammonia when interacting with conventional N-bases. Finally, we present a detailed analysis of the role that deformation can play in the intensity and nature of these enhancements.

The structures and stabilities of 2,2'-diBeX-1,1'-biphenyl (X = H, F, Cl, CN) derivatives and their affinities for F-, Cl-, and CN- were theoretically investigated using a B3LYP/6-311 + G(3df, 2p)//B3LYP/6-31 + G(d,p) model. The results obtained show that the 2,2'-diBeX-1,1'-biphenyl derivatives (X = H, F, Cl, CN) exhibit very high F-, Cl-, and CN- affinities, albeit lower than those reported before for their 1,8-diBeX-naphthalene analogs, in spite of the fact that the biphenyl derivatives are more flexible than their naphthalene counterparts. Nevertheless, some of the biphenyl derivatives investigated are predicted to have anion affinities larger than those measured for SbF5, which is considered one of the strongest anion capturers. Therefore, although weaker than their naphthalene analogs, the 2,2'-diBeX-1,1'-biphenyl derivatives can still be considered powerful anion sponges. This study supports the idea that compounds containing -BeX groups in chelating positions behave as anion sponges due to the electron-deficient nature and consequently high intrinsic Lewis acidity of these groups.

Hydrogen has been proposed as a long-term non-fossil fuel to be used in a future ideal carbon-neutral energetic economy. However, its low volumetric energy density hinders its storage and transportation. Metal-organic frameworks (MOFs) represent very promising materials for this purpose due to their very extended surface areas. Azolates, in particular tetrazolates, are - together with carboxylate functionalities - very common organic linkers connecting metallic secondary building units in MOFs. This study addresses, from a theoretical perspective, the H-2 adsorptive properties of tetrazolate linkers at the molecular level, following a size-progressive approach. Specifically, we have investigated how the physisorption energies and geometries are affected when changing the environment of the linker by considering the azolates in the gas phase, immersed in a finite cluster, or being part of an infinite extended crystal material. Furthermore, we also study the H-2 adsorptive capacity of these linkers within the cluster model.