4th International Symposium on Halogen Bonding

The International Symposium on Halogen Bonding (ISXB-4) was held online from 2 to 5 November 2020 after being postponed from an event scheduled from 22 to 27 March 2020 in Stellenbosch, South Africa, owing to travel restrictions brought about by the COVID-19 pandemic. The ISXB-4 was the latest in the series of ISXB conferences initiated in 2014 by Giuseppe Resnati and Pierangelo Metrangolo. It focused primarily on halogen bonding, but incorporated all forms of σ- and π-hole type bonding, including hydrogen bonding. The symposium aimed to cover both experimental and theoretical aspects of a broad range of fields such as medicinal chemistry, chemical biology, materials science, catalysis, crystal engineering and industrial applications.

When the change to the online format for the conference was announced in July 2020 the response was overwhelmingly positive: where 88 delegates were due to attend the original on-site conference, 220 delegates from 29 different countries joined the online conference with great enthusiasm. This excellent turnout was aided by IUCr funding, thanks to which we were able to support the attendance of 30 young scientists, 13 (43%) of whom were female. The supported scientists represented 14 countries spread over 4 continents. As a result of their generous support, the IUCr was one of the sponsors with a virtual sponsor booth; these booths allowed delegates to get further information about the exhibitor and make contact with a company representative.

The many delegates were not disappointed: the scientific presentations were of an extremely high quality. A total of 25 invited speakers and 45 oral presenters gave live or pre-recorded talks in six sessions: the 'Nature of X-bonding' and 'Supramolecular chemistry and crystal engineering' on 3 November, 'Solid state properties' and 'Understanding X-bonding behaviour' on 4 November, and 'Applications in synthesis, catalysis and industry' and 'Applications in solution chemistry and biology' on 5 November. Within each session, all the oral presenters contributed to a live discussion on the theme, moderated by well-known members of the halogen-bond community. These discussions elicited enthusiastic participation from the audience through a question-and-answer chat function and resulted in some lively debates.

There were also 90 poster presenters divided between two poster sessions on 3 and 4 November. The standard was extremely high, but in the end, Vinu Panikkattu of Kansas State University, USA, was awarded the IUCr journals poster prize for his poster 'Exploring the strength and competition between chalcogen and halogen bonds through experiment and theory'.

Vinu Panikkattu presenting his prize-winning poster.

In addition to the scientific content, the social aspect of the conference was not forgotten: the welcome function included a session of "speed greeting" where delegates were randomly dealt into small groups so that they could greet old friends or get to know new members of the community. Delegates also had the opportunity to meet on an individual basis through the meeting hub, while every day ended with break-away "rooms" to give delegates the opportunity to get together and chat.

These social interactions combined with the live discussions meant that although delegates were sitting in front of computer screens spread over 17 time zones, they still felt a sense of community. ISXB-4 Virtual was, as a result, a resounding success. The organisers would like to thank the sponsors, particularly the IUCr, and all of the delegates for their role in achieving this.