Halogen, Chalcogen, and Pnicogen Bonding Involving Hypervalent Atoms

• Published in: Chemistry : a European journal Vol. 24; no. 32; pp. 8167 - 8177
• Main Authors: Scheiner, Steve, Lu, Jia
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 07.06.2018
• Subjects: AIM; Ammonia; Antimony; Atomic properties; Bonding strength; Chalcogen bonds; Chemical bonds; Chemistry; Deformation; hypervalency; Lewis acid; lone pairs; Molecular chains; NBO; sigma hole; Staphylococcal enterotoxin H; Tellurium; lone pairs; sigma hole; NBO; AIM; hypervalency
• DOI: 10.1002/chem.201800511
• ISSN: 0947-6539; 1521-3765

The additional substituents arising from hypervalency present a number of complicating issues for the formation of noncovalent bonds. The XF5 molecule (X=Cl, Br, I) was allowed to form a halogen bond with NH3 as the base. Hypervalent chalcogen bonding is examined by way of YF4 and YF6 (Y=S, Se, Te), and ZF5 (Z=P, As, Sb) is used to model pnicogen bonding. Pnicogen bonds are particularly strong, with interaction energies approaching 50 kcal mol−1, and also involve wholesale rearrangement from trigonal bipyramidal in the monomer to square pyramidal in the complex, subject to a large deformation energy. YF4 chalcogen bonding is also strong, and like pnicogen bonding, is enhanced by a heavier central atom. XF5 halogen bond energies are roughly 9 kcal mol−1, and display a unique sensitivity to the identity of the X atom. The crowded octahedral structure of YF6 permits only very weak interactions. As the F atoms of SeF6 are replaced progressively by H, a chalcogen bond appears in combination with SeH⋅⋅⋅N and NH⋅⋅⋅F H‐bonds. The strongest such chalcogen bond appears in SeF3H3⋅⋅⋅NH3, with a binding energy of 7 kcal mol−1, wherein the base is located in the H3 face of the Lewis acid. Results are discussed in the context of the way in which the positions and intensities of σ‐holes are influenced by the locations of substituents and lone electron pairs. Bonding theory: Hypervalent chalcogen bonding is examined by way of YF4 and YF6 (Y=S, Se, Te), and ZF5 (Z=P, As, Sb) and XF5 (X=Cl, Br, I) are used to model pnicogen and halogen bonding, respectively. is used to model pnicogen bonding. Pnicogen bonds are particularly strong and involve wholesale rearrangement from trigonal bipyramidal in the monomer to square pyramidal in the complex (see figure).