Halogen Bonding in Hypervalent Iodine Compounds

Area of Science:

• Inorganic Chemistry
• Crystallography
• Supramolecular Chemistry

Background:

• Halogen bonds are typically defined for monovalent halogen derivatives, involving electrophilic halogens acting as Lewis acids.
• Hypervalent iodine compounds feature complex bonding patterns around the iodine atom.
• Understanding non-covalent interactions in these systems is crucial for predicting crystal structures and reactivity.

Purpose of the Study:

• To demonstrate that geometric features in hypervalent iodine derivatives support classifying certain longer bonds as halogen bonds.
• To propose the use of the term 'halogen bond' for specific interactions in hypervalent iodine compounds.
• To highlight the descriptive advantages of 'halogen bond' over 'secondary bonding' for these interactions.

Main Methods:

• Analysis of geometric features and bonding patterns in ionic and neutral hypervalent iodine derivatives (λ(3)- and λ(5)-iodanes).
• Investigation of electron density distribution and electrostatic potential around iodine atoms.
• Comparison of observed short contacts with established halogen bond definitions and geometrical prerequisites.

Main Results:

• Anisotropic electron density distribution around iodine in hypervalent derivatives creates regions of positive electrostatic potential.
• These positive potentials (caps) influence and potentially dictate crystal packing.
• Short cation-anion contacts and interactions with lone-pair donors in iodane derivatives align with halogen bond characteristics.

Conclusions:

• The directional nature and geometric prerequisites of interactions in hypervalent iodine compounds justify their classification as halogen bonds.
• The term 'halogen bond' offers a more descriptive account of directionality and structure-interaction relationships compared to 'secondary bonding'.
• This broadened definition enhances the understanding of intermolecular forces in hypervalent iodine chemistry and crystal engineering.