Project Details Categorizing Chalcogen, Pnictogen, and Tetrel Bonds, and Other Interactions Involving Groups 14-16 Elements

Project No.:
Start Date:
01 July 2016
End Date:
Division Name:
Organic and Biomolecular Chemistry Division
Division No.:


This project extends criterions inspiring IUPAC Recommendations on halogen and hydrogen bonds (project 2009-032-1-100 and 2004-026-2-100) to the categorizing of interactions involving Groups 14-16 elements.

Definition(s) will be proposed:

– enabling a consistent and unambiguous terminology for most interactions given by Groups 14-16 elements;

– registering the emerging consensus on proposals suggesting to use terms chalcogen bond, pnictogen bond, and tetrel bond exclusively for interactions wherein Groups 14-16 elements are the electrophile.

Proposed definitions(s) will balance wide applicability (i.e., generality) and robust descriptive power (i.e., specificity), and convey specific information on the interactions, e.g., polar characters, geometries.


The proposed terminology will typically apply to interactions of organic derivatives and to phenomena involving compounds of biopharmaceutical interest. The project is best supported by the Organic and Biomolecular Chemistry Division (Division III) that is best entitled to involve the necessary set of stakeholders and interest groups which consists in all those having a strong experimental interest in drug design, molecular materials assembly, and related topics.

Experimental results and theoretical calculations consistently show that the electron density distribution in Group 14-16 elements presents regions of lower electron density on the extension(s) of the covalent bond(s) the elements are involved in, and regions of higher density orthogonal to the covalent bond(s). The surface electrostatic potential is typically negative in the latter regions and positive, or less negative, in the former ones. Elements of these Groups can thus form attractive interactions with both electron rich and electron poor sites (i.e., nucleophiles and electrophiles, respectively) and these interactions are more stabilizing when involving the regions of lower, and higher, electron density, respectively.

A recent IUPAC Recommendations (Pure Appl. Chem. 2013, 85, 1711-1713; proposed to use the term halogen bond exclusively for interactions wherein the electrophilic site is the Group 17 element. Recently, the terms chalcogen bond, pnictogen bond, and tetrel bond have been given analogous definitions and are used preferentially for interactions wherein the Groups 14-16 elements are the electrophilic site. Unfortunately, the terms are also used for interactions wherein the Group 14-16 are the nucleophile, for instance when binding partially positive hydrogen atoms. This use is probably an inheritance of practices developed before the anisotropic distribution of the electron density around covalently bound atoms was recognized.

This Project will classify the structural characteristics at the chalcogen, pnictogen, and tetrel sites favouring the formation of stabilizing interactions with nucleophiles. It will categorize theoretical and experimental fingerprints of interactions wherein Group 14-16 elements are the electrophile. These structural, theoretical, and experimental features will enable for proposing (possibly in Recommendation(s) in Pure Appl. Chem.) definition(s) that suggest the terms chalcogen bond, pnictogen bond, and tetrel bond are used exclusively for interactions wherein the corresponding elements are the electrophile, in keeping with the definitions of halogen bond and hydrogen bond.


A kick-off meeting of the project will be organized in Milan (Italy) early 2017 and a symposium tentatively entitled “Chalcogen, Pnictogen, and Tetrel Bonds: Fundamentals and Applications” is being organized within the Parallel Program at the 24th Congress and General Assembly of the International Union of Crystallography (21–28 August 2017, Hyderabad, India).

Dec 2016 – Project announcement published in Chem. Int. Nov 2016, p. 22;

April 2017 – In place of a report of the kick-off event, an editorial titled ‘Bonding matters‘ has been published in Crystal Growth & Design ( published online 5 Apr 2017)

July 2017 update – A symposium on the topics addressed by the project is planned in the summer 2018. It is expected as a satellite event of a Major Symposium on related topics and the task group is now identifying the Major Symposium this IUPAC event is going to be linked with. The symposium initially planned within the Parallel Program at the 24th Congress and General Assembly of the International Union of Crystallography will not take place and instead Prof Giuseppe Resnati will present a keynote titled “The halogen bond in crystal chemistry and beyond”, on 27 August 2017 at 0900 – 1000 hrs (see detailed IUCR 2017 program).

In September, the task group chair will give a lecture presenting the topics of the Project at “HBOND 2017” ( Held in Jyväskylä, Finland, this symposium is focused on hydrogen bond, the parent interactions of chalcogen, pnictogen and tetrel bonds which are addressed in this IUPAC Project 2016-001-2-300.
Task group members meeting at HBOND 2017, and including Prof. Kari Rissanen from Jyväskylä, will also review and discuss the first draft of the chalcogen bond definition.

Page last updated 26 July 2017