# Halogen-Bonded Supramolecular Parallelograms: From Self-Complementary Iodoalkyne Halogen-Bonded Dimers to 1:1 and 2:2 Iodoalkyne Halogen-Bonded Cocrystals

## TL;DR

This paper describes how iodoalkyne–pyridine halogen bonds form supramolecular parallelograms, including dimers and cocrystals with unique structures.

## Contribution

The study demonstrates the formation of discrete self-complementary iodoalkyne halogen-bonded dimers and cocrystals with parallelogram shapes.

## Key findings

- Iodoalkynyl-substituted compounds form parallelogram-shaped dimers with two self-complementary N–I halogen bonds.
- Discrete supramolecular parallelograms are formed in 1:1 and 2:2 cocrystals using bis-iodoalkyne and dipyridyl components.
- The structures show potential for forming larger halogen-bonded macrocycles through controlled molecular design.

## Abstract

The formation of
supramolecular parallelograms utilizing iodoalkyne–pyridine
halogen bonding is described. The crystal structures of four iodoalkynyl-substituted
(phenylethynyl)pyridines demonstrate the feasibility of discrete self-complementary
dimer formation. These compounds 3-(2-iodoethynyl-phenylethynyl) pyridine
(1), 2-(3-iodoethynyl-phenylethynyl) pyridine (2), 3-(4,5-difluoro-2-iodoethynyl-phenylethynyl) pyridine
(3), and 2-(5-iodoethynyl-2,4-dimethylphenylethynyl)
pyridine (4) all form parallelogram-shaped dimers with
two self-complementary short N–I halogen bonds. The potential
formation of iodoalkynyl halogen-bonded supramolecular macrocycles
is demonstrated by the formation of a discrete halogen-bonded parallelogram-shaped
complex in the 1:1 cocrystal formed from the bis iodoalkyne, 1-iodoethynyl-2-(3-iodoethynyl-phenylethynyl)-4,5-dimethoxybenzene
(6), and the dipyridyl, 5-phenyl-2-(pyridin-3-ylethynyl)pyridine
(7). Furthermore, discrete supramolecular parallelograms
form within the 2:2 cocrystal formed between 1,2-bis(iodoethynyl)-4,5-difluorobenzene and the dipyridyl 4-(3-pyridylethynyl)
pyridine (8).

The formation
of parallelogram-shaped macrocycles facilitated
by iodoalkyne–pyridine halogen bonds is described. These include
self-complementary iodoalkynyl pyridine dimers, a 1:1 dipyridylethyne/bis(iodoalkynyl)tolane cocrystal, and a 2:2 bipyridylalkyne/bis(iodoalkynyl)benzene cocrystal.