Trigonal bipyramidal molecular geometry

Hydrogen bond

Crystal structure

Natural bond orbital

Physical chemistry

Embedded system

Chalcogen

Catalysis

Lewis acids and bases

Organic chemistry

Chemistry

Halogen bond

Alkyl

Molecule

Reagent

Computer science

Lone pair

Halogen

Atom (system on chip)

Crystallography

Hypervalent molecule

Chemistry - A European Journal

The additional substituents arising from hypervalency present a number of complicating issues for the formation of noncovalent bonds. The XF 5 molecule (X=Cl, Br, I) was allowed to form a halogen bond with NH 3 as the base. Hypervalent chalcogen bonding is examined by way of YF 4 and YF 6 (Y=S, Se, Te), and ZF 5 (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. YF 4 chalcogen bonding is also strong, and like pnicogen bonding, is enhanced by a heavier central atom. XF 5 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 YF 6 permits only very weak interactions. As the F atoms of SeF 6 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 SeF 3 H 3 ⋅⋅⋅NH 3 , with a binding energy of 7 kcal mol −1 , wherein the base is located in the H 3 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.

Halogen, Chalcogen, and Pnicogen Bonding Involving Hypervalent Atoms