Close contacts involving germanium and tin in crystal structures: experimental evidence of tetrel bonds

Abstract

Modeling indicates the presence of a region of low electronic density (a Bσ-hole^) on group 14 elements, and this offers an explanation for the ability of these elements to act as electrophilic sites and to form attractive interactions with nucleophiles. While many papers have described theoretical investigations of interactions involving carbon and silicon, such investigations of the heavier group 14 elements are relatively scarce. The purpose of this review is to rectify, to some extent, the current lack of experimental data on interactions formed by germanium and tin with nucleophiles. A survey of crystal structures in the Cambridge Structural Database is reported. This survey reveals that close contacts between Ge or Sn and lone-pair-possessing atoms are quite common, they can be either intra-or intermolecular contacts, and they are usually oriented along the extension of the covalent bond formed by the tetrel with the most electron-withdrawing substituent. Several examples are discussed in which germanium and tin atoms bear four carbon residues or in which halogen, oxygen, sulfur, or nitrogen substituents replace one, two, or three of those carbon residues. These close contacts are assumed to be the result of attractive interactions between the involved atoms and afford experimental evidence of the ability of germanium and tin to act as electrophilic sites, namely tetrel bond (TB) donors. This ability can govern the conformations and the packing of organic derivatives in the solid state. TBs can therefore be considered a promising and robust tool for crystal engineering.

Not Only Hydrogen Bonds: Other Noncovalent Interactions

“…Furthermore, hypervalent species of silicon and germanium are very common [121][122][123][124][125][126][127][128][129][130][131]. Nevertheless, the heavier tetrel atoms (Ge-Pb) participate in noncovalent tetrel bonding interactions when they are in a chemical context avoiding hypervalency, see for instance the SiO 12 (OH) 8 cage in Figure 9 [132,133]. In fact, since the atomic polarizability increases in a given group of the periodic table on going from lighter to heavier elements, the stronger interactions in this group are expected for tin and lead [134][135][136].…”

Theoretical and Crystallographic Study of Lead(IV) Tetrel Bonding Interactions

“…Moreover, hypervalent species with Ge and Si (also considered metalloids) are also known . Nevertheless, heavier tetrel atoms can engage in noncovalent σ‐hole interactions if placed in a chemical environment that prevents hypervalency …”

“…[26] Nevertheless, heavier tetrel atomsc an engage in noncovalent s-hole interactions if placed in ac hemicale nvironment that prevents hypervalency. [27] There are several examplesi nt he literature in which tetrel bondingi nteractions involving Pb II have been used in crystal engineering and supramolecular chemistry;however, s-hole interactions involving Pb IV have been scarcely reported. [28] In these previous reports,t heoretical studiesa re devoted to tin(IV) with little attention to lead(IV), or focusedo nh ypervalency.I na ddition, in previous works, the Cambridge Crystallographic Database (CSD) has either not been analyzed or the focus has been on penta-and hexavalentd erivatives.…”

Interactions in Model Ionic Dyads and Triads Containing Tetrel Atoms

“…Interest in tetrel bonding has been steadily growing over the last few years, especially since the tetrahedral configuration of the sp 3 hybridized carbon atom is central to a significant portion of organic chemistry. Insights gained from studies of tetrel bonding may find potentially useful applications in fields such as organic synthesis and supramolecular chemistry; for example, tetrel bonding appears to be relevant for the well-known S N 2 organic reaction [ 18 ], hydrophobic interactions [ 22 ], and in protein folding and ligand-acceptor interactions [ 19 , 23 , 24 ].…”