Strong Tetrel Bonds: Theoretical Aspects and Experimental Evidence

Abstract

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.

Hexacoordinated Tetrel‐Bonded Complexes between TF4 (T=Si, Ge, Sn, Pb) and NCH: Competition between σ‐ and π‐Holes

“…Despite any barriers to their formation, these tetrel bonds occur widely and are of great import in a number of chemical and biological processes. [35][36][37][38][39][40][41][42] The scale and effects of the geometric deformation of the TR 4 molecule required to accommodate a Lewis base have been assessed quantitatively. [9,10] Scores of tetrel bonds have been identified within protein structures, [11][12][13][14][15] and are implicated in the catalytic process of several enzymes.…”

“…[31][32][33][34] This strengthening is amplified when either molecule acquires an electric charge. [35][36][37][38][39][40][41][42] The scale and effects of the geometric deformation of the TR 4 molecule required to accommodate a Lewis base have been assessed quantitatively. [43][44][45][46] There has also been some consideration of the rather unusual bases carbenes [47,48] or π-systems [33] as tetrel bond acceptors.…”

Influence of monomer deformation on the competition between two types of σ-holes in tetrel bonds

“…The concept of the σ-hole [19][20][21][22][23] , introduced with a view toward clarifying halogen bonding phenomenon [23][24][25][26][27][28][29][30][31] has been extended to a large family of noncovalent interactions where an electronegative atom is able to interact with a nucleophile. Although at first glance implausible, the attractive force is based on a local depletion of electron density around the halogen 32,33 , chalcogen 34,35 , pnicogen 36,37 , tetrel [38][39][40] or noble gas atoms [41][42][43][44] , usually directly opposite a σ-bond, hence its common appellation as a σ-hole. 45 Study over the years [46][47][48][49] has established that the strength of each σ-hole is enhanced by reduced electronegativity and enhanced polarizability of the central atom, coupled with electron-withdrawing power of its substituent.…”

“…Charge transfer makes a major contribution as well, augmented by dispersion forces. 37,39,[59][60][61][62][63][64] There are also other factors that mitigate against a strict correlation between interaction energy and σ-hole intensity. [65][66][67][68][69] There are geometric deformations that accompany complexation 65 that influence both the σ-hole depth and the overall energetics.…”

On the capability of metal–halogen groups to participate in halogen bonds

“…The resulting area of positive electrostatic potential has gained the sobriquet of a σ-hole, which can attract an anion or any other nucleophile. The XB is not dependent solely on this electrostatic attraction, but also benefits from polarization/charge transfer and dispersion contributions 15-18 . This sort of phenomenon is not limited to halogen atoms; replacement of X by atoms from the chalcogen [19][20][21][22][23][24][25][26][27] , pnicogen [28][29][30][31][32][33][34][35][36][37][38][39] , and tetrel [40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55] families of elements can lead to very similar noncovalent bonds, which are generally named after the particular type of atom, e.g. tetrel bonds.…”