Can we quantitatively evaluate the mutual impacts of intramolecular metal-ligand bonds the same as intermolecular noncovalent bonds?

In this paper, we have reviewed several equations for calculating the cooperative energy of two chemical bonds between three fragments/species, regardless of whether they are atoms, ions or molecules, and whether the bonds between them are intra- or intermolecular. It is emphasized that two chemical bonds upon cooperation in a new compound change the bond dissociation energy of each other exactly by the same quantitative value, their cooperative energy, regardless of the nature of the bonds or whether one bond is very weak and another one is very strong. However, the final benefit/drawback of weak bonds from this cooperation can be considerably larger than that of strong bonds. The above statements are supported by a computational study on the various types of inter- and intramolecular chemical bonds.

Ye Olde supramolecular chemistry, its modern rebranding and overarching trends in chemistry

We can describe current contingency of supramolecular chemistry as "post-halogen bonding", with clear reference to the success of the σ-hole model and the halogen bond concepts. This phase is characterized by a strong push towards a new nomenclature for non-covalent interactions, a group-by-group one focusing on the electrophile. As such nomenclature increasingly meets IUPAC endorsement, its proposers report resistances to such ideas, especially in the inorganic and coordination chemistry communities. The whole issue has been generating considerable debate in the last decade. Herein we fully embrace such discussion in the hope of involving a larger share of the relevant communities. Alternative descriptions are here reevaluated, novel views reconnected with older ones, and it is ultimately questioned whether the introduction of such a nomenclature and its subtending ideas would be beneficial. The themes of appreciation of general trends in chemistry, of counterintuitive interactions, of positioning of novel nomenclature with respect to existing ones, and of the extension of group-by-group naming from main block to d-block elements - as key and currently unresolved issues - are discussed. Equivalent, alternative and arguably more comprehensive descriptions are tentatively given, in the hope to overcome controversies together in the pursuit of higher rewards: a comprehensive shared view of supramolecular forces and a common language to express it.

Revisiting conventional noncovalent interactions towards a complete understanding: from tetrel to pnicogen, chalcogen, and halogen bond

Typical noncovalent interactions, including tetrel (TtB), pnicogen (PniB), chalcogen (ChalB), and halogen bonds (HalB), were systematically re-investigated by modeling the N⋯Z interactions (Z = Si, P, S, Cl) between NH3 - as a nucleophilic, and SiF4, PF3, SF2, and ClF - as electrophilic components, employing highly reliable ab initio methods. The characteristics of N⋯Z interactions when Z goes from Si to Cl, were examined through their changes in stability, vibrational spectroscopy, electron density, and natural orbital analyses. The binding energies of these complexes at CCSD(T)/CBS indicate that NH3 tends to hold tightly most with ClF (-34.7 kJ mol-1) and SiF4 (-23.7 kJ mol-1) to form N⋯Cl HalB and N⋯Si TtB, respectively. Remarkably, the interaction energies obtained from various approaches imply that the strength of these noncovalent interactions follows the order: N⋯Si TtB > N⋯Cl HalB > N⋯S ChalB > N⋯P PniB, that differs the order of their corresponding complex stability. The conventional N⋯Z noncovalent interactions are characterized by the local vibrational frequencies of 351, 126, 167, and 261 cm-1 for TtB, PniB, ChalB, and HalB, respectively. The SAPT2+(3)dMP2 calculations demonstrate that the primary force controlling their strength retains the electrostatic term. Accompanied by the stronger strength of N⋯Si TtB and N⋯Cl HalB, the AIM and NBO results state that they are partly covalent in nature with amounts of 18.57% and 27.53%, respectively. Among various analysis approaches, the force constant of the local N⋯Z stretching vibration is shown to be most accurate in describing the noncovalent interactions.

Malonaldehyde-like Systems: BeF2 Clusters—A Subtle Balance between Hydrogen Bonds, Beryllium Bonds, and Resonance

The stability of malonaldehyde is governed by intramolecular hydrogen bonds (IMHBs) as well as in malonaldehyde-like systems where oxygen is replaced by N or S at any of the basic sites. As beryllium bonds have been shown to strongly cooperate with hydrogen bonds, this work explores at the high level ab initio G4 level of theory the effect of including this non-covalent interaction in the system through its association with BeF2. Although malonaldehyde follows the expected trends, where the formation of a pseudocyclic form is favored also when IMHB and Be bonds are present, the subtle balance between both non-covalent interactions leads to some surprising results when other heteroatoms are involved, to the point that interaction energies can be much larger than expected or even cyclization is not favored. A complete analysis using different computational tools gives an answer to those cases escaping the predictable trends.

Influence of Substituents in the Benzene Ring on the Halogen Bond of Iodobenzene with Ammonia

The effects on the CI··N halogen bond between iodobenzene and NH3 of placing various substituents on the phenyl ring are monitored by quantum calculations. Substituents R = N(CH3)2, NH2, CH3, OCH3, COCH3, Cl, F, COH, CN, and NO2 were each placed ortho, meta, and para to the I. The depth of the σ-hole on I is deepened as R became more electron-withdrawing which is reflected in a strengthening of the halogen bond, which varied between 3.3 and 5.5 kcal/mol. In most cases, the ortho placement yields the largest perturbation, followed by meta and then para, but this trend is not universal. Parallel to these substituent effects is a progressive lengthening of the covalent C-I bond. Formation of the halogen bond reduces the NMR chemical shielding of all three nuclei directly involved in the C-I··N interaction. The deshielding of the electron donor N is most closely correlated with the strength of the bond, as is the coupling constant between I and N, so both have potential use as spectroscopic measures of halogen bond strength.

Search for an exothermic halogen bond between anions

A halogen-bonded complex containing a pair of anions can be made more stable than the isolated anions if the Lewis acid is a long carbon chain, fully substituted by CN groups, with an I atom on one end and a COO− group on the other, with Cl− as base.

Porous materials formed by four self-construction processes

Multiple self-construction behavior of cyclic oligoesters is described.

Chalcogen Bond Involving Zinc(II)/Cadmium(II) Carbonate and Its Enhancement by Spodium Bond

Carbonate MCO3 (M = Zn, Cd) can act as both Lewis acid and base to engage in a spodium bond with nitrogen-containing bases (HCN, NHCH2, and NH3) and a chalcogen bond with SeHX (X = F, Cl, OH, OCH3, NH2, and NHCH3), respectively. There is also a weak hydrogen bond in the chalcogen-bonded dyads. Both chalcogen and hydrogen bonds become stronger in the order of F > Cl > OH > OCH3 > NH2 > NHCH3. The chalcogen-bonded dyads are stabilized by a combination of electrostatic and charge transfer interactions. The interaction energy of chalcogen-bonded dyad is less than -10 kcal/mol at most cases. Furthermore, the chalcogen bond can be strengthened through coexistence with a spodium bond in N-base-MCO3-SeHX. The enhancement of chalcogen bond is primarily attributed to the charge transfer interaction. Additionally, the spodium bond is also enhanced by the chalcogen bond although the corresponding enhancing effect is small.

Proximity Effects of Substituents on Halogen Bond Strength

It is well known that the presence of an electron-withdrawing substituent (EWS) placed near the halogen (X) atom on a Lewis acid molecule amplifies the ability of this unit to engage in a halogen bond with a base. Quantum calculations are applied to examine how quickly these effects fade as the EWS is moved further and further from the X atom. Conjugated alkene and alkyne chains of varying lengths with a terminal C-I first facilitate analysis as to how the number of these multiple bonds affects the strength of CI··N XB to NH₃. Then, electron-withdrawing F and C≡N substituents are placed on the opposite end of the chain, and their effects on the XB properties are monitored as a function of their distance from I. These same EWSs are added to the ortho, meta, and para positions of aromatic iodobenzene. It is found that the XB grows in strength as more triple bonds are added to the alkyne, but there is little change caused by elongating an alkene. The cyano group has a much stronger effect than does F. While F strengthens the XB, its effects are quickly attenuated as it is moved further from I. The consequences of C≡N substitution are stronger and extend over a longer distance. Placement of an EWS on the phenyl ring diminishes with distance: o > m > p, and the effects of disubstitution are nearly additive. These trends apply not only to energetics but also to geometries, properties of the wave function, σ-hole depth, and NMR shielding.

Relative Strengths of a Pnicogen and a Tetrel Bond and Their Mutual Effects upon One Another

The ability of the T and Z atoms of TR₃ZR₂ to engage in a noncovalent interaction with NH₃ is assessed by DFT calculations, where the T atom refers to C, Si, and Ge; Z = As, Sb, and P; and substituents R = H and F. In most instances, the tetrel bond (TB) is both stronger and shorter than the pnicogen bond (ZB). These two bond strengths can be equalized, or preference shifted to the ZB, if F substituents are placed on the Z and H on the T atoms. Employing C as the T atom results in a very weak TB, with the ZB clearly favored energetically. The simultaneous formation of both TB and ZB weakens both, particularly the latter, but both bonds survive intact. Geometric and spectroscopic perturbations of the subunits reflect the two types of noncovalent bonds.

Significant bonding rearrangements triggered by Mg4 clusters

The structure, stability, and bonding of the complexes formed by the interaction of Mg₄ clusters and first row Lewis bases, namely, ammonia, water, and hydrogen fluoride, have been investigated through the use of high-level G4 single-reference and CASPT2 multireference formalisms. The adducts formed reflect the high electrophilicity of the Mg₄ cluster through electron density holes in the neighborhood of each metallic center. After the adduct formation, the metallic bonding of the Mg₄ moiety is not significantly altered so that the hydrogen shifts from the Lewis base toward the Mg atoms lead to new local minima with enhanced stability. For the particular case of ammonia and water, the global minima obtained when all the hydrogens of the Lewis base are shifted to the Mg₄ moiety have in common a very stable scaffold with a N or an O center covalently tetracoordinated to the four Mg atoms, so the initial bonding arrangements of both reactants have completely disappeared. The reactivity features exhibited by these Mg₄ clusters suggest that nanostructures of this metal might have an interesting catalytic behavior.

Experimental and Theoretical Studies of Dimers Stabilized by Two Chalcogen Bonds in the Presence of a N···N Pnicogen Bond

The structure of the 5,6-dichloro-2,1,3-benzoselenadiazole homodimer, obtained by adding the ligand, 4,5-dichloro-o-phenylenediamine, to the methanolic solution of SeCl₄, was determined by X-ray crystallography, augmented by Fourier transform infrared, Raman, and NMR spectroscopy. The binding motif involves a pair of Se···N chalcogen bonds, with a supplementary N···N pnicogen bond. Quantum calculations provide assessments of the strengths of the individual interactions as well as their contributing factors. All together, these three bonds compose a total interaction energy between 5.4 and 16.8 kcal/mol, with the larger chalcogen atom associated with the strongest interactions. Replacement of the Se atoms by S and Te analogues allows analysis of the dependence of these forces on the nature of the chalcogen atom. Calculations also measure the importance to the binding of the presence of a second N atom on each diazole unit as well as the substituted phenyl ring to which it is fused.

The Importance of Strain (Preorganization) in Beryllium Bonds

In order to explore the angular strain role on the ability of Be to form strong beryllium bonds, a theoretical study of the complexes of four beryllium derivatives of orthocloso-carboranes with eight molecules (CO, N₂, NCH, CNH, OH₂, SH₂, NH₃, and PH₃) acting as Lewis bases has been carried out at the G4 computational level. The results for these complexes, which contain besides Be other electron-deficient elements, such as B, have been compared with the analogous ones formed by three beryllium salts (BeCl₂, CO₃Be and SO₄Be) with the same set of Lewis bases. The results show the presence of large and positive values of the electrostatic potential associated to the beryllium atoms in the isolated four beryllium derivatives of ortho-carboranes, evidencing an intrinsically strong acidic nature. In addition, the LUMO orbital in these systems is also associated to the beryllium atom. These features led to short intermolecular distances and large dissociation energies in the complexes of the beryllium derivatives of ortho-carboranes with the Lewis bases. Notably, as a consequence of the special framework provided by the ortho-carboranes, some of these dissociation energies are larger than the corresponding beryllium bonds in the already strongly bound SO₄Be complexes, in particular for N₂ and CO bases. The localized molecular orbital energy decomposition analysis (LMOEDA) shows that among the attractive terms associated with the dissociation energy, the electrostatic term is the most important one, except for the complexes with the two previously mentioned weakest bases (N₂ and CO), where the polarization term dominates. Hence, these results contribute to further confirm the importance of bending on the beryllium environment leading to strong interactions through the formation of beryllium bonds.

σ-Hole and Lone-Pair Hole Interactions in Chalcogen-Containing Complexes: A Comparative Study

The potentiality of sp3-hybridized chalcogen-containing molecules to participate in lone-pair (lp) hole interactions was reported for the first time. lp hole interactions were characterized and compared to σ-hole ones for OF2 and SF2 molecules as a case study. Various quantum mechanical calculations, including molecular electrostatic potential (MEP), maximum positive electrostatic potential (V s,max), point of charge (PoC), symmetry-adapted perturbation theory (SAPT), quantum theory of atoms in molecule (QTAIM), and reduced density gradient-noncovalent interaction (RDG-NCI) calculations, were carried out. The more significant findings to emerge from this study are the following: (i) the V s,max calculation was proved to be an unreliable method to determine the precise σ-hole and lp hole locations. (ii) The maximum positive electrostatic potential of the σ hole and lp hole was found to be at the F-Chal···PoC angle (θ) of 180° and at the centroid of XYlp plane, respectively. (iii) Lewis basicity has a significant effect on the strength of σ-hole and lp hole interactions. (iv) The studied molecules more favorably interact with Lewis bases via the σ hole compared to the lp hole, and (v) stabilization of the σ-hole and lp hole interactions stems from the electrostatic and dispersion forces, respectively.

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.

Microhydration of a Carbonyl Group: How does the Molecular Electrostatic Potential (MESP) Impact the Formation of (H2O)n:(R2C═O)Complexes?

The presence of a carbonyl group in a molecule usually leads to the identification of a π-hole on the molecular electrostatic potential (MESP) of the species. How does this electrophilic site influence the formation of microhydrated complexes? To address this point, a panel of R₂CO solutes with various MESPs was selected, and we identified the structures and properties of several complexes containing one, two, three and six water molecules. The following solutes were considered in the present study: H₂CO, F₂CO, Cl₂CO,(NC)₂CO and H₂C═CO. Geometry optimizations and frequency calculations were carried out at the LC-ωPBE/6-311++G(d,p) level, with the GD3BJ empirical correction for dispersion. For a number of n water molecules around the R₂CO solute, the structure and the features of the most stable (H₂O)_n:(R₂CO) complexes are highly dependent on the MESP of the isolated R₂CO solute. The formation of pi-hole bondings appears to play a decisive role in the initiation of a three-dimensional organization of water molecules around the solute.