Can Conventional Bases and Unsaturated Hydrocarbons Be Converted into Gas-Phase Superacids That Are Stronger than Most of the Known Oxyacids? The Role of Beryllium Bonds

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.

Strong Be-N Interaction Induced Complementary Chemical Tuning to Design a Dual-gated Single Molecule Junction

The interaction between pyridines and the π-hole of BeH2 leads to the formation of strong beryllium-bonded complexes. Theoretical investigations demonstrate that the Be-N bonding interaction can effectively regulate the electronic current through a molecular junction. The electronic conductance exhibits distinct switching behavior depending on the substituent groups at the para position of pyridine, highlighting the role of Be-N interaction as a potent chemical gate in the proposed device. The complexes exhibit short intermolecular distances ranging from 1.724 to 1.752 Å, emphasizing their strong binding. Detailed analysis of electronic rearrangements and geometric perturbations upon complex formation provides insights into the underlying reasons for the formation of such strong Be-N bonds, with bond strengths varying from -116.25 to -92.96 kJ/mol. Moreover, the influence of chemical substituents on the local electronic transmission of the beryllium-bonded complex offers valuable insights for the implementation of a secondary chemical gate in single-molecule devices. This study paves the way for the development of chemically gateable, functional single-molecule transistors, advancing the design and fabrication of multifunctional single-molecule devices in the nanoscale regime.

Dismantlement of ammonia upon interaction with Ben (n ≤ 10) clusters

The interaction of ammonia with Be_n (n < 1-10) clusters has been investigated by density functional theory and ab initio calculations. The main conclusion is that, regardless of the size of the Be cluster, neither the structure of ammonia nor that of the Be clusters are preserved due to a systematic dissociation of its NH bonds and a spontaneous H-shift toward the available Be atoms. This H migration not only leads to rather stable BeH bonds, but dramatically enhances the strength of the BeN bonds as well. Accordingly, the maximum stability is found for the interaction with the beryllium trimer, leading to a complex with three NBe and three BeH bonds. Another maximum in stability, although lower than that reached for n = 3, is found for the Be heptamer, since from n = 6, a new NBe bond is formed, so that complexes from n = 6 to n = 10 are characterized by the formation of a NBe₄ moiety, whose stability reaches a maximum at n = 7. The bonding characteristics of the different species formed are analyzed by means of AIM, NBO, ELF and AdNDP approaches.

Disrupting bonding in azoles through beryllium bonds: Unexpected coordination patterns and acidity enhancement

Although triazoles and tetrazole are amphoteric and may behave as weak acids, the latter property can be hugely enhanced by beryllium bonds. To explain this phenomenon, the structure and bonding characteristics of the complexes between triazoles and tetrazoles with one and two molecules of BeF₂ have been investigated through the use of high-level G4 ab initio calculations. The formation of the complexes between the N basic sites of the azoles and the Be center of the BeF₂ molecule and the (BeF₂)₂ dimer leads to a significant bonding perturbation of both interacting subunits. The main consequence of these electron density rearrangements is the above-mentioned increase in the intrinsic acidity of the azole subunit, evolving from a typical nitrogen base to a very strong nitrogenous acid. This effect is particularly dramatic when the interaction involves the (BeF₂)₂ dimer, that is, a Lewis acid much stronger than the monomer. Although the azoles investigated have neighboring N-basic sites, their interaction with the (BeF₂)₂ dimer yields a monodentate complex. However, the deprotonated species becomes extra-stabilized because a second N-Be bond is formed, leading to a new five-membered ring, with the result that the azole-(BeF₂)₂ complexes investigated become stronger nitrogenous acids than oxyacids such as perchloric acid.

Enhancement of tetrel bond involving tetrazole-TtR3 (Tt = C, Si; R = H, F). Promotion of SiR3 transfer by a triel bond

The combination of a CR3 (R = H, F) with a tetrazole can result in a moderate carbon bond, which can be further strengthened by a triel bond. On the other hand, SiR3 group is half transferred between the two N atoms in these conditions.

Some interesting features of the rich chemistry around electron-deficient systems

In this short review, different phenomena that are triggered by the interaction of different compounds or clusters of compounds with electron-deficient systems, in particular beryllium and boron compounds, have been discussed in some detail. Particular attention was devoted to the huge acidity enhancements that can be induced through the interaction of conventional bases with B or Be containing compounds, which change these conventional bases in extremely strong proton donors. We have paid also attention to the cooperativity between Be bonds with other weak interactions, which results in a substantial increase of their strength, that can lead in some specific cases to the spontaneous formation of ion-pairs in the gas phase. Finally, the behavior of different Be derivatives as electron and anion sponges is discussed as well as the conditions needed to have clusters exhibiting rather strong Be–Be bonds, even though the Be–Be interaction in Be2 dimer is extremely weak. Finally, some attention was paid to systems with extremely short Be–Be distances but without a bond.

Beryllium bonding: insights from the σ- and π-hole analysis

Beryllium bonding is actually a subclass of secondary bonding. Similar to the case of halogen bonding, the σ- and π-holes on the Be atom of the monomers give in zeroth approximation the direction of electrophilic attack favorable to the formation of beryllium bonds. The nature of beryllium bonding is purely electrostatic so that the symmetry-adapted perturbation theory energy decomposition perfectly explains the relevance of the polarization and dispersion contribution on the formation of the beryllium bond.

Not Only Hydrogen Bonds: Other Noncovalent Interactions

In this review, we provide a consistent description of noncovalent interactions, covering most groups of the Periodic Table. Different types of bonds are discussed using their trivial names. Moreover, the new name “Spodium bonds” is proposed for group 12 since noncovalent interactions involving this group of elements as electron acceptors have not yet been named. Excluding hydrogen bonds, the following noncovalent interactions will be discussed: alkali, alkaline earth, regium, spodium, triel, tetrel, pnictogen, chalcogen, halogen, and aerogen, which almost covers the Periodic Table entirely. Other interactions, such as orthogonal interactions and π-π stacking, will also be considered. Research and applications of σ-hole and π-hole interactions involving the p-block element is growing exponentially. The important applications include supramolecular chemistry, crystal engineering, catalysis, enzymatic chemistry molecular machines, membrane ion transport, etc. Despite the fact that this review is not intended to be comprehensive, a number of representative works for each type of interaction is provided. The possibility of modeling the dissociation energies of the complexes using different models (HSAB, ECW, Alkorta-Legon) was analyzed. Finally, the extension of Cahn-Ingold-Prelog priority rules to noncovalent is proposed.

Modulating the intrinsic reactivity of molecules through non-covalent interactions

Non-covalent interactions as tools for modifying molecular properties.

Coordination of Be and Mg Centres by HCN Ligands - Be…N and Mg…N Interactions

ωB97XD/aug-cc-pVTZ calculations were performed for clusters of Z2+ cations (Z=Be and Mg) and HCN molecules (up to six molecules). The clusters of Be(CH3 )2 and Mg(CH3 )2 with HCN species were also calculated to analyse the influence of the Be/Mg-C formally covalent bonds on interactions of Be or Mg centre with ligands. The beryllium and magnesium centres possess different areas of a positive electrostatic potential that depend on a number of HCN ligands in the cluster considered. Numerous correlations between geometrical, energetic and topological parameters of the clusters considered are discussed since various theoretical approaches are applied; Quantum Theory of 'Atoms in Molecules', Natural Bond Orbital method and decomposition of the energy of interaction. The Be/Mg…N interactions classified as beryllium and magnesium bonds possess numerous characteristics which are known for the hydrogen bonds. Different types of coordination of Be and Mg centres analysed here exist also in crystal structures.

Alkaline-earth (Be, Mg and Ca) bonds at the origin of huge acidity enhancements

The interaction between alkaline-earth derivatives with the general formula X₂M (X = H, F and Cl; M = Be, Mg and Ca) and a set of Lewis bases, including first and second-row hydrides, namely YH_n (Y = O, N, F, S, P and Cl) hydrides, as well as other typical cyclic organic bases, such as aniline, 1H-1,2,3-triazole, 1H-tetrazole and phenylphosphine, was investigated using the G4 ab initio composite method. Contrary to what was expected, it was found that the interactions involving Mg and Ca derivatives were not necessarily weaker than those between beryllium bonds. The origin is two-fold: larger deformation of the interacting systems when Be-derivatives are involved and appearance of secondary non-covalent interactions in the formation of some of the Mg- and Ca-containing complexes. Hence, the dissociation of the latter complexes may require higher enthalpies than that of the Be complexes. These deformations are triggered by a significant redistribution of electron density of the two interacting moieties, which also result in dramatic changes in the reactivity of the interacting compounds and in particular in the intrinsic basicity of the Lewis bases investigated, to the point that conventional bases, such as ammonia or aniline, upon complexation with MCl₂ (M = Be, Mg and Ca), become stronger Brønsted acids than phosphoric acid, whereas other bases, such as 1H-tetrazole, become stronger acids than perchloric acid.

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.

Hydrogen bonds, and σ-hole and π-hole bonds – mechanisms protecting doublet and octet electron structures

For various interactions electron charge shifts try to protect the former doublet or octet electronic structure of the Lewis acid centre.

Quantification of Lewis acid induced Brønsted acidity of protogenic Lewis bases

Coordination of a Lewis acid to a protogenic Lewis base increases the Brønsted acidity between 20–50 pK_a units.

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.

Off the Beaten Track-A Hitchhiker's Guide to Beryllium Chemistry

This Minireview aims to give an introduction to beryllium chemistry for all less-experienced scientists in this field of research. Up to date information on the toxicity of beryllium and its compounds are reviewed and several basic and necessary guidelines for a safe and proper handling in modern chemical research laboratories are presented. Interesting phenomenological observations are described that are related directly to the uniqueness of this element, which are also put into historical context. Herein we combine the contributions and experiences of many scientist that work passionately in this field. We want to encourage fellow scientists to reconcile the long-standing reservations about beryllium and its compounds and motivate intense research on this spurned element. Who on earth should be able to deal with beryllium and its compounds if not chemists?

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.

Fullerene and corannulene derivatives acting as insulators of Cl−and BeH2

Corannulene and its benzo-derivatives C_xH₁₀(x= 20–60) as prototypes of non-planar π-aromatic systems have been studied as insulators of BeH₂and Cl⁻.

Interplay between Beryllium Bonds and Anion-π Interactions in BeR2:C6X6:Y- Complexes (R = H, F and Cl, X = H and F, and Y = Cl and Br)

A theoretical study of the beryllium bonds in BeR₂:C₆X₆ (R = H, F, Cl and X = H and F) has been carried out by means of MP2/aug′-cc-pVDZ computational methods. In addition, the ternary complexes BeR₂:C₆X₆:Y⁻ (Y = Cl and Br) have been analyzed. Geometric, energetic and electronic aspects of the complexes have been taken into account. All the parameters analyzed provide a clear indication of favorable cooperativity in both interactions observed, beryllium bond and aromatic ring:anion interaction.

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.

Acidity enhancement of unsaturated bases of group 15 by association with borane and beryllium dihydride. Unexpected boron and beryllium Brønsted acids

BeH₂and BH₃association with unsaturated bases of group 15 increases their acidity and changes the trend. Ethynyl : BeH₂complexes unexpectedly behave as Be acids.

Neutral alkaline-metal and alkaline-earth-metal derivatives of imidazole and benzimidazole

A theoretical study of the minima and connecting transition states of the neutral complexes formed by alkaline-metal and alkaline-earth-metal derivatives of imidazolate and benzimidazolate anions has been carried out using B3LYP/6-31+G(d,p), B3LYP/6-311+G(3df,2p), and G3B3 methods. Two and three nondegenerated minima and two and four TS structures have been identified for imidazole and benzimidazole derivatives, respectively. The most stable minima of the alkaline-metal derivatives of both systems correspond to the metal interacting with the imidazole ring, whereas in the alkaline-earth-metal derivatives, the preferred minima depend on the substituent. A remarkable feature of some minima is the fact that some of the metal-aromatic interactions follow the classical π-cation pattern, even though the global structure corresponds to a neutral salt, constituting a class of noncovalent interaction of great interest in the chemistry of aromatic and heterocyclic complexes. A CSD search has confirmed that the two bonding modes, N-σ and π, are present in the solid phase. The π mode has been analyzed by comparison with other azoles.

Cooperativity in beryllium bonds

Positive cooperativity is found in beryllium bonded complexes similar to that described for hydrogen bonded systems.