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:


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.

Nov 2017 update – The task group will be organizing a workshop entitled “Interactions Involving Group 14 – 16 Elements as Electrophilic Sites: A World Parallel to Halogen Bond”, 9-10 June 2018, as satellite event of ISXB-3 in Greenville (SC, USA). The workshop is expected to receive the interest of its target scientific community.

“Interactions Involving Group 14-16 Elements as Electrophilic Sites: A World Parallel to Halogen Bond”, 9-10 June 2018; Greenville, SC; USA, IUPAC Workshop @ISXB-3

May 2018 update – The organization of the IUPAC workshop, scheduled as a parallel event of the third International Symposium on Halogen bond (ISXB-3), is proceeding smoothly. Basic information on the workshop is available at
The Workshop will be held at Hyatt Hotel, Greenville, SC, USA, on 9-10 June 2018. Expectedly there will be 17 Invited speakers, 6 Contributed lectures, and 11 poster presentations. Patronage has been secured from the American Chemical Society (from the journal Crystal Growth &Design) and the Royal society of Chemistry (1 from the journals CrystEngComm and 1 from New Journal of Chemistry) to recognize four poster prizes.

July 2018 update – The 31st European Crystallographic Meeting will take place in Oviedo, Spain, 22-27 August 2018. At this meeting on 23 August, Professor Giuseppe Resnati will chair session MS30 titled ‘Halogen and chalcogen bonding in the solid state‘. In session MS32, he will also give an invited talk entitled “Close contacts involving carbon and antimony: Tetrel bonded and pnictogen bonded systems by design”.

January 2019 update – The provisional recommendations titled “Definition of the chalcogen bond” is available for public review till 31 May 2019.

November 2019 update – IUPAC Recommendations published: Aakeroy, C., Bryce, D., Desiraju, G., et al. (2019). Definition of the chalcogen bond (IUPAC Recommendations 2019). Pure and Applied Chemistry, 91(11), pp. 1889-1892.

The mindset of the project, including the “Definition of the chalcogen bond” (published) and the “Definition of the pnictogen bond” and the “Definition of the tetrel bond” (under preparation) have been the topic of invited lectures at the following events:
– 14th International Symposium on Macrocyclic and Supramolecular Chemistry (ISMSC-14, 2-6 June 2019, Lecce, Italy); Lecture: “The Four Seasons, i.e., Halogen Chalcogen, Pnictogem and Tetrel Bonds”, presented by G. Resnati
– 32nd European Crystallographic Meeting (ECM-32, 18-21 August 2019, Wien, Austria); Lecture: “Chalcogen bonding in crystal engineering”, presented by G. Resnati
– 19th European Symposium on Fluorine Chemistry (ESFC-19, 25-29 August 2019, Warsaw, Poland); Lecture: “Fluorine activates tetrel and chalcogen bonds”, presented by G. Resnati. The symposium was also the opportunity to recruit Prof. Ingo Krossing (Univ. Freiburg, Germany) who has accepted to join the activity of the Project for filing the pnictogen bond definition.
– 1st International Conference on Noncovalent Interactions (ICNC-1; 1-5 September 2019, Lisbon, Portugal); Lecture: “Halogen, Chalcogen, Pnictogen, and Tetrel Bonds: Structural Aspects”, presented by G. Resnati. A Project Meeting was also organized during the Conference, including the participation of some Task Group Members (C. Aakeroy, A. Frontera, G. Resnati, K. Rissanen) and other scientist working in the field (K.T. Mahmudov, D. Braga, C. Esterhuisen).

January 2020 update –The discussion among the Project Members aimed at the preparation of a Recommendation to be submitted to Pure and Applied Chemistry and entitled “Definition of Pnictogen Bond” in now quite advanced. Discussion on the general features of a Recommendation entitled “Definition of Tetrel Bond” is still in its infancy, but the an agreement has emerged to plan a Recommendation.
A Workshop tentatively entitled “Chalcogen, Pnictogen, Tetrel Bonds and beyond” is planned as a satellite event of the 2nd International Conference on Noncovalent Interactions (rescheduled 12-22 July 2022, Strasbourg (France)). The aim of this event is to register the consensus on the published definition of chalcogen bond and to tune the details of the definitions of pnictogen bonds and tetrel bonds which are under preparation.

March 2021 update – An IUPAC Recommendation defining the Chalcogen bond has been successfully published (PAC vol. 91, no. 11, 2019, pp. 1889-1892; and a provisional recommendation defining the Pnictogen bond has been recently submitted and is being finalized. The possible IUPAC Recommendation defining the Tetrel bond is the last issue to be tackled within the frame of this Project.
The Task Group Members are now realizing that there might be an interest in extending the mindset used in this Project also to interactions formed by Groups 13 and 18. An option to address this interest is to submit a new Project proposal (tentatively entitle “Categorizing Triel and Noble Gas Bonds, and Other Interactions Involving Groups 13 and18 Elements”).

Page last updated 17 March 2021