Tetrel bonds between PySiX3 and some nitrogenated bases: Hybridization, substitution, and cooperativity

Competition of hydrogen, tetrel, and halogen bonds in COCl2-HOX (X=F, Cl, Br, I) complexes

The present study investigates the competition between hydrogen, halogen, and tetrel bonds from the interaction of COCl₂ with HOX using quantum chemistry simulations at the MP2/aug-cc-pVTZ computational level, in which five configurations were optimized, including adducts I -V. Two hydrogen bonds, two halogen bonds, and two tetrel bonds were obtained for five forms of adducts. The compounds were investigated using spectroscopic, geometry, and energy properties. Adduct I complexes are more stable than others, and adduct V halogen bonded complexes are more stable than adduct II complexes. These results are in agreement with their NBO and AIM results. The stabilization energy of the XB complexes depends on the nature of both the Lewis acid and base. The stretching frequency of the O-H bond in adducts I, II, III, and IV displayed a redshift, and a blue shift was observed in adduct V. The results for the O-X bond showed a blue shift in adducts I and III and a red shift in adducts II, IV, and V. The nature and characteristics of three types of interactions are investigated via NBO analysis and atoms in molecules (AIM).

Strongly Bound π-Hole Tetrel Bonded Complexes between H2SiO and Substituted Pyridines. Influence of Substituents

Ab initio calculation at the MP2/aug-cc-pVTZ level has been performed on the π-hole based N … Si tetrel bonded complexes between substituted pyridines and H 2 SiO. The primary aim of the study is to find out the effect of substitution on the strength and nature of this tetrel bond, and its similarity/difference with the N … C tetrel bond. Correlation between the strength of the N … Si bond and several molecular properties of the Lewis acid (H 2 SiO) and base (pyridines) are explored. The properties of the tetrel bond are analyzed using AIM, NBO, and symmetry-adapted perturbation theory calculations. The complexes are characterized with short N … Si intermolecular distances and high binding energies ranging between -142.72 and -115.37 kJ/mol. The high value of deformation energy indicates significant geometrical distortion of the monomer units. The AIM and NBO analysis reveal significant coordinate covalent  bond character of the N … Si π-hole bond.  Sharp differences are also noticed in the orbital interactions present in the N … Si and N … C tetrel bonds.

Tetrel Bonds between Phenyltrifluorosilane and Dimethyl Sulfoxide: Influence of Basis Sets, Substitution and Competition

Ab initio calculations have been performed for the complexes of DMSO and phenyltrifluorosilane (PTS) and its derivatives with a substituent of NH₃, OCH₃, CH₃, OH, F, CHO, CN, NO₂, and SO₃H. It is necessary to use sufficiently flexible basis sets, such as aug’-cc-pVTZ, to get reliable results for the Si···O tetrel bonds. The tetrel bond in these complexes has been characterized in views of geometries, interaction energies, orbital interactions and topological parameters. The electron-donating group in PTS weakens this interaction and the electron-withdrawing group prominently strengthens it to the point where it exceeds that of the majority of hydrogen bonds. The largest interaction energy occurs in the p-HO₃S-PhSiF₃···DMSO complex, amounting to −122 kJ/mol. The strong Si···O tetrel bond depends to a large extent on the charge transfer from the O lone pair into the empty p orbital of Si, although it has a dominant electrostatic character. For the PTS derivatives of NH₂, OH, CHO and NO₂, the hydrogen bonded complex is favorable to the tetrel bonded complex for the NH₂ and OH derivatives, while the σ-hole interaction prefers the π-hole interaction for the CHO and NO₂ derivatives.

Enhancement of the Tetrel Bond by the Effects of Substituents, Cooperativity, and Electric Field: Transition from Noncovalent to Covalent Bond

The T⋅⋅⋅N tetrel bond (TB) formed between TX₃ OH (T=C, Si, Ge; X=H, F) and the Lewis base N≡CM (M=H, Li, Na) is studied by ab initio calculations at the MP2/aug-cc-pVTZ level. Complexes involving TH₃ OH contain a conventional TB with interaction energy less than 10 kcal/mol. This bond is substantially strengthened, approaching 35 kcal/mol and covalent character, when fluorosubstituted TF₃ OH is combined with NCLi or NCNa. Along with this enhanced binding comes a near equalization of the TB T⋅⋅⋅N and the internal T-O bond lengths, and the associated structure acquires a trigonal bipyramidal shape, despite a high internal deformation energy. This structural transformation becomes more complete, and the TB is further strengthened upon adding an electron acceptor BeCl₂ to the Lewis acid and a base to the NCM unit. This same TB strengthening can be accomplished also by imposition of an external electric field.

Comparison for Electron Donor Capability of Carbon-Bound Halogens in Tetrel Bonds

The tetrel bond formed by HC≡CX, H2C=CHX, and H3CCH2X (X=F, Cl, Br, I) as an electron donor and TH3F (T=C, Si, Ge) was explored by ab initio calculations. The tetrel bond formed by H3CCH2X is the strongest, as high as -3.45 kcal/mol for the H3CCH2F···GeH3F dimer, followed by H2C=CHX, and the weakest bond is from HC≡CX, where the tetrel bond can be as small as -0.8 kcal/mol. The strength of the tetrel bond increases in the order of C < Si < Ge. For the H3CCH2X and HC≡CX complexes, the tetrel bond strength shows a similar increasing tendency with the decrease of the electronegativity of the halogen atom. Electrostatic interaction plays the largest role in the stronger tetrel bonds, while dispersion interaction makes an important contribution to the H2C=CHX complexes.

Noncovalent bond between tetrel π-hole and hydride

The π-hole above the plane of the X2T'Y molecule (T' = Si, Ge, Sn; X = F, Cl, H; Y = O, S) was allowed to interact with the TH hydride of TH(CH3)3 (T = Si, Ge, Sn). The resulting THT' tetrel bond is quite strong, with interaction energies exceeding 30 kcal mol-1. F2T'O engages in the strongest such bonds, as compared to F2T'S, Cl2T'O, or Cl2T'S. The bond weakens as T' grows larger as in Si > Ge > Sn, despite the opposite trend in the depth of the π-hole. The reverse pattern of stronger tetrel bond with larger T is observed for the Lewis base TH(CH3)3, even though the minimum in the electrostatic potential around the H is nearly independent of T. The THT' arrangement is nonlinear which can be understood on the basis of the positions of the extrema in the molecular electrostatic potentials of the monomers. The tetrel bond is weakened when H2O forms an OT' tetrel bond with the second π-hole of F2T'O, and strengthened if H2O participates in an OHO H-bond.

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.

Influence of N-Base and O-Base Hybridization on Triel Bonds

The complexes of TrR₃ (Tr = B and Al; R = H, F, Cl, and Br) with three N-bases (NH₃, CH₂NH, and HCN) and three O-bases (CH₃OH, H₂CO, and CO) are utilized to explore the hybridization effect of N and O atoms on the strength, properties, and nature of the triel bond. The sp-hybridized O and N atoms form the weakest triel bond, followed by the sp²-hybridized O atom or the sp³-hybridized N atom, and the sp³-hybridized O atom or the sp²-hybridized N atom engages in the strongest triel bond. The hybridization effect is also related to the substituent of TrR₃. Most complexes are dominated by electrostatic, with increasing polarization contribution from sp to sp² to sp³. Although the CO oxygen engages in a weaker triel bond, its carbon atom is a better electron donor and the interaction energy even amounts to -37 kcal/mol in the BH₃ complex.

Influence of alkali substituents on the strength, properties, and nature of tetrel bond between TH3F and pyridine

Ab initio calculations have been performed for the complexes of TH₃F (T=C, Si, and Ge) with pyridine and its alkali derivatives to study the influence of an alkali substituent on the strength, properties, and nature of tetrel bond. The introduction of an alkali atom into the electron donor has a prominent enhancing effect on the strength of tetrel bond, which depends on the T atom as well as the alkali atom and its substitution position. The enhancing effect becomes larger in the C < Ge < Si, Li < Na < K, and para- < meta- < ortho- patterns. The interaction energy varies in a wide range from 2 to 40 kcal/mol. Both electrostatic and polarization including charge transfer are responsible for the enhancing effect of an alkali atom. The formation of a tetrel bond results in an elongation of F-T bond and a red shift of F-T stretch vibration, which is big enough to be detected with infrared spectroscopy. Electrostatic interaction is dominant in all complexes, while polarization is smaller or larger than dispersion in the complexes of CH₃F or TH₃F(T=Si and Ge).

A Million Crystal Structures: The Whole Is Greater than the Sum of Its Parts

The founding in 1965 of what is now called the Cambridge Structural Database (CSD) has reaped dividends in numerous and diverse areas of chemical research. Each of the million or so crystal structures in the database was solved for its own particular reason, but collected together, the structures can be reused to address a multitude of new problems. In this Review, which is focused mainly on the last 10 years, we chronicle the contribution of the CSD to research into molecular geometries, molecular interactions, and molecular assemblies and demonstrate its value in the design of biologically active molecules and the solid forms in which they are delivered. Its potential in other commercially relevant areas is described, including gas storage and delivery, thin films, and (opto)electronics. The CSD also aids the solution of new crystal structures. Because no scientific instrument is without shortcomings, the limitations of CSD research are assessed. We emphasize the importance of maintaining database quality: notwithstanding the arrival of big data and machine learning, it remains perilous to ignore the principle of garbage in, garbage out. Finally, we explain why the CSD must evolve with the world around it to ensure it remains fit for purpose in the years ahead.

Tetrel Interactions from an Interacting Quantum Atoms Perspective

Tetrel bonds, the purportedly non-covalent interaction between a molecule that contains an atom of group 14 and an anion or (more generally) an atom or molecule with lone electron pairs, are under intense scrutiny. In this work, we perform an interacting quantum atoms (IQA) analysis of several simple complexes formed between an electrophilic fragment (A) (CH₃F, CH₄, CO₂, CS₂, SiO₂, SiH₃F, SiH₄, GeH₃F, GeO₂, and GeH₄) and an electron-pair-rich system (B) (NCH, NCO-, OCN-, F-, Br-, CN-, CO, CS, Kr, NC-, NH₃, OC, OH₂, SH-, and N₃-) at the aug-cc-pvtz coupled cluster singles and doubles (CCSD) level of calculation. The binding energy ( E bind AB ) is separated into intrafragment and inter-fragment components, and the latter in turn split into classical and covalent contributions. It is shown that the three terms are important in determining E bind AB , with absolute values that increase in passing from electrophilic fragments containing C, Ge, and Si. The degree of covalency between A and B is measured through the real space bond order known as the delocalization index ( δ AB ). Finally, a good linear correlation is found between δ AB and E xc AB , the exchange correlation (xc) or covalent contribution to E bind AB .

Quantitative Assessment of Tetrel Bonding Utilizing Vibrational Spectroscopy

A set of 35 representative neutral and charged tetrel complexes was investigated with the objective of finding the factors that influence the strength of tetrel bonding involving single bonded C, Si, and Ge donors and double bonded C or Si donors. For the first time, we introduced an intrinsic bond strength measure for tetrel bonding, derived from calculated vibrational spectroscopy data obtained at the CCSD(T)/aug-cc-pVTZ level of theory and used this measure to rationalize and order the tetrel bonds. Our study revealed that the strength of tetrel bonds is affected by several factors, such as the magnitude of the σ-hole in the tetrel atom, the negative electrostatic potential at the lone pair of the tetrel-acceptor, the positive charge at the peripheral hydrogen of the tetrel-donor, the exchange-repulsion between the lone pair orbitals of the peripheral atoms of the tetrel-donor and the heteroatom of the tetrel-acceptor, and the stabilization brought about by electron delocalization. Thus, focusing on just one or two of these factors, in particular, the σ-hole description can only lead to an incomplete picture. Tetrel bonding covers a range of -1.4 to -26 kcal/mol, which can be strengthened by substituting the peripheral ligands with electron-withdrawing substituents and by positively charged tetrel-donors or negatively charged tetrel-acceptors.

Strong Tetrel Bonds: Theoretical Aspects and Experimental Evidence

In recent years, noncovalent interactions involving group-14 elements of the periodic table acting as a Lewis acid center (or tetrel-bonding interactions) have attracted considerable attention due to their potential applications in supramolecular chemistry, material science and so on. The aim of the present study is to characterize the geometry, strength and bonding properties of strong tetrel-bond interactions in some charge-assisted tetrel-bonded complexes. Ab initio calculations are performed, and the results are supported by the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) approaches. The interaction energies of the anionic tetrel-bonded complexes formed between XF₃M molecule (X=F, CN; M=Si, Ge and Sn) and A- anions (A-=F-, Cl-, Br-, CN-, NC- and N₃-) vary between -16.35 and -96.30 kcal/mol. The M atom in these complexes is generally characterized by pentavalency, i.e., is hypervalent. Moreover, the QTAIM analysis confirms that the anionic tetrel-bonding interaction in these systems could be classified as a strong interaction with some covalent character. On the other hand, it is found that the tetrel-bond interactions in cationic tetrel-bonded [p-NH₃(C₆H₄)MH₃]⁺···Z and [p-NH₃(C₆F₄)MH₃]⁺···Z complexes (M=Si, Ge, Sn and Z=NH₃, NH₂CH₃, NH₂OH and NH₂NH₂) are characterized by a strong orbital interaction between the filled lone-pair orbital of the Lewis base and empty BD*M-C orbital of the Lewis base. The substitution of the F atoms in the benzene ring provides a strong orbital interaction, and hence improved tetrel-bond interaction. For all charge-assisted tetrel-bonded complexes, it is seen that the formation of tetrel-bond interaction is accompanied bysignificant electron density redistribution over the interacting subunits. Finally, we provide some experimental evidence for the existence of such charge-assisted tetrel-bond interactions in crystalline phase.

Implications of monomer deformation for tetrel and pnicogen bonds

Monomer rearrangement raises the interaction energy by up to 20 kcal mol⁻¹and intensifies its σ-hole by a factor of 1.5–2.9.

The effect of anions on noncovalent interactions in model clusters of chalcogen-containing (CH3)2X (X = O, S, Se) molecules

A computational study of F⁻⋯(CH₃)₂O⋯CH₃F with F⁻ bound to the protons of the two methyl groups, found significant enhancement of the O⋯C interaction relative to the neutral (CH₃)₂O⋯CH₃F dyad.

Regulation of coin metal substituents and cooperativity on the strength and nature of tetrel bonds

Ab initio calculations have been performed for the tetrel-bonded dyad MCN⋯TF₄ (M = Cu, Ag, and Au; T = C, Si, Ge, and Sn) and C₂H₄…MCN…TF₄ and C₂(CN)₄…MCN…TF₄.

Comparison of tetrel bonds in neutral and protonated complexes of pyridineTF3and furanTF3(T = C, Si, and Ge) with NH3

Protonation not only changes the primary interaction mode between α/β-furanCF₃/p-PyCF₃and NH₃but also prominently enhances the strength of the Si/Ge⋯N tetrel bond.

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.