Spontaneous H2Loss through the Interaction of Squaric Acid Derivatives and BeH2

Discovering trends in the Lewis acidity of beryllium and magnesium hydrides and fluorides with increasing clusters size

We have reported in the last years the strong effect that Be- and Mg-containing Lewis acids have on the intrinsic properties of typical bases, which become acids upon complexation. In an effort to investigate these changes when the Be and Mg derivatives form clusters of increasing size, we have examined the behavior of the (MX2)n (M = Be, Mg; X = H, F; n = 1, 2, 3) clusters when they interact with ammonia, methanimine, hydrogen cyanide and pyridine, and with their corresponding deprotonated forms. The complexes obtained at the M06-2X/aug-cc-pVTZ level were analyzed using the MBIE energy decomposition formalism, in parallel with QTAIM, ELF, NCIPLOT and AdNDP analyses of their electron density. For n = 1 the interaction enthalpy for the different families of monomers, Be (Mg) hydrides and Be (Mg) fluorides, follows the same trend as the intrinsic basicity of the base that interacts with them. This interaction is greatly reinforced after the deprotonation of the base, resulting in a significant enhancement of the intrinsic acidity of the corresponding MX2-Base complex. For (MX2)2 clusters a further reinforcement of the interaction with the base is observed, this reinforcement being again larger for the deprotonated complexes. However, the concomitant increase of their intrinsic acidity is one order of magnitude larger for hydrides than for fluorides. Unexpectedly, the cyclic conformers (MX2)3, which are more unstable than the linear ones, become the global minima after association with the base and the same is true for the deprotonated complex. Accordingly, a further increase of the intrinsic acidity of the (MX2)3-Base complexes with respect to the (MX2)2-Base ones is observed. This effect is maximum for (MgF2)3 clusters, to the point that the (MgF2)3-Base complexes become more acidic than nitric acid, the extreme case being the cluster (MgF2)3-NCH, whose acidity is higher than that of perchloric acid.

Enhancement of Thermodynamic Gas-Phase Acidity and Basicity of Water by Means of Secondary Interactions

A series of A⋅water, B⋅water complexes (A=acid, B=base) are studied at the G4 level of theory to show that water acidity or basicity can be modulated by non-covalent interactions. Protic and non-protic acids interacting with water form hydrogen bonds or other kinds of non-covalent interactions, respectively, that may dramatically change the acidity of water up to almost 360 kJ ⋅ mol^-1 in terms of enthalpy. Similarly, hydrogen bonds responsible for the interaction between typical small nitrogen-containing Lewis bases and water can enhance the proton affinity of water by almost 300 kJ ⋅ mol^-1 . Our results reveal that these large enhancements are linearly related with the binding energy of the charged complexes, and are determined by the Lewis acid-base properties of the molecule involved in the interaction, allowing a quite precise modulation of the corresponding acid-base properties of water.

Fostering the Basic Instinct of Boron in Boron-Beryllium Interactions

A set of complexes L₂HB···BeX₂ (L = CNH, CO, CS, N₂, NH₃, NCCH₃, PH₃, PF₃, PMe₃, OH₂; X = H, F) containing a boron-beryllium bond is described at the M06-2X/6-311+G(3df,2pd)//M062-2X/6-31+G(d) level of theory. In this quite unusual bond, boron acts as a Lewis base and beryllium as a Lewis acid, reaching binding energies up to -283.3 kJ/mol ((H₂O)₂HB···BeF₂). The stabilization of these complexes is possible thanks to the σ-donor role of the L ligands in the L₂HB···BeX₂ structures and the powerful acceptor nature of beryllium. According to the topology of the density, these B-Be interactions present positive laplacian values and negative energy densities, covering different degrees of electron sharing. ELF calculations allowed measuring the population in the interboundary B-Be region, which varies between 0.20 and 2.05 electrons upon switching from the weakest ((CS)₂HB···BeH₂) to the strongest complex ((H₂O)₂HB···BeF₂). These B-Be interactions can be considered as beryllium bonds in most cases.

Large Proton-Affinity Enhancements Triggered by Noncovalent Interactions

High affinity: The proton affinity (PA) of the OH group of YH_x OH compounds is always increased by noncovalent interaction (NCI) with a Lewis base (LB; see figure). This PA enhancement depends on the type of NCI. Weak NCIs can give rise to PA enhancements equal to or even larger than strong NCIs. The binding energies of protonated species play a major role in the case of sigma-hole interactions.

Complexes between neutral oxyacid beryllium salts and dihydrogen: a possible way for hydrogen storage?

Very stable 1 : 1 and 1 : 2 complexes between oxyacid beryllium salts and H₂ are found.

Activation of Dinitrogen as A Dipolarophile in 1,3-Dipolar Cycloadditions: A Theoretical Study Using Nitrile Imines as "Octet" 1,3-Dipoles

Theoretical calculations at the G4MP2 level of theory demonstrate that it is possible to activate dinitrogen to make it react in dipolar cycloadditions using neutral beryllium derivatives and other neutral metallic compounds. For the particular case of beryllium, the barrier decreases more than 40 kJ·mol^–1 with respect to the non-catalysed reaction. The activation achieved is lower than using diazonium salts (models of protonated N₂), but still in a range that can be experimentally attainable.

Beryllium subphthalocyanines self-assembling properties

Beryllium subphthalocyanines have been recently shown to be suitable candidates for photochemical devices if combined with appropriate donor systems. The ability of beryllium subphthalocyanines to self-assemble is explored for the first time by means of density functional theory calculations. Free dimers of beryllium subphtalocyanine and their corresponding complexes with water and pyridine are computed at the wB97X-D/6-311+G(d,p) level of theory. In contrast with the behavior reported for beryllium phthalocyanines, for beryllium subphtalocyanines, beryllium–aza–nitrogen intermolecular interactions are observed, suggesting that these species are likely to self-assemble. Aggregates of related structures such as beryllium subporphyrazines with axial groups confirm the importance of hydrogen bonds in the stacking.

Modulating the strength of tetrel bonding through beryllium bonding

Quantum chemical calculations were performed to investigate the stability of the ternary complexes BeH2···XMH3···NH3 (X = F, Cl, and Br; M = C, Si, and Ge) and the corresponding binary complexes at the atomic level. Our results reveal that the stability of the XMH3···BeH2 complexes is mainly due to both a strong beryllium bond and a weak tetrel-hydride interaction, while the XMH3···NH3 complexes are stabilized by a tetrel bond. The beryllium bond with a halogen atom as the electron donor has many features in common with a beryllium bond with an O or N atom as the electron donor, although they do exhibit some different characteristics. The stability of the XMH3···NH3 complex is dominated by the electrostatic interaction, while the orbital interaction also makes an important contribution. Interestingly, as the identities of the X and M atoms are varied, the strength of the tetrel bond fluctuates in an irregular manner, which can explained by changes in electrostatic potentials and orbital interactions. In the ternary systems, both the beryllium bond and the tetrel bond are enhanced, which is mainly ascribed to increased electrostatic potentials on the corresponding atoms and charge transfer. In particular, when compared to the strengths of the tetrel and beryllium bonds in the binary systems, in the ternary systems the tetrel bond is enhanced to a greater degree than the beryllium bond. Graphical Abstract A tetrel bond can be strengthened greatly by a beryllium bond.

Hydrogen and Dihydrogen Bonds in the Reactions of Metal Hydrides

The dihydrogen bond-an interaction between a transition-metal or main-group hydride (M-H) and a protic hydrogen moiety (H-X)-is arguably the most intriguing type of hydrogen bond. It was discovered in the mid-1990s and has been intensively explored since then. Herein, we collate up-to-date experimental and computational studies of the structural, energetic, and spectroscopic parameters and natures of dihydrogen-bonded complexes of the form M-H···H-X, as such species are now known for a wide variety of hydrido compounds. Being a weak interaction, dihydrogen bonding entails the lengthening of the participating bonds as well as their polarization (repolarization) as a result of electron density redistribution. Thus, the formation of a dihydrogen bond allows for the activation of both the MH and XH bonds in one step, facilitating proton transfer and preparing these bonds for further transformations. The implications of dihydrogen bonding in different stoichiometric and catalytic reactions, such as hydrogen exchange, alcoholysis and aminolysis, hydrogen evolution, hydrogenation, and dehydrogenation, are discussed.

On the existence and characteristics of π-beryllium bonds

The existence of π-beryllium bonds explains the stability of the complexes between ethylene and acetylene and BeX2 (X = H, F, and Cl) derivatives. These linkers involve a significant charge transfer from the π(CC) bonding orbitals into the empty p orbitals of Be and to a much smaller degree into the σ(BeH)* antibonding orbitals. The significant deformation of the BeX2 moiety and the slight deformation of the unsaturated hydrocarbon result in distortion energies as high as the dissociation energy of the complex. The π-beryllium bonds are about four times stronger than conventional π-hydrogen bonds and even stronger than the strongest π-hydrogen bond reported to date in the literature. The topology of their electron density is characterized as being very flat in the bonding region between the π-system and Be, which leads to topologically unstable structures close to catastrophe points. Among the functionals considered in our study M06 is the one that leads to values in better agreement with CCSD(T)/aug-cc-pVTZ calculations used as a reference. B3LYP underestimates some interactions, whereas M06-2X overestimates all of them. MP2 also yields good agreement with the CCSD(T) method.