Abstract

This work describes the combined use of synchrotron X-ray diffraction and density functional theory (DFT) calculations to understand the cocrystal formation or phase separation in 2D monolayers capable of halogen bonding. The solid monolayer structure of 1,4-diiodobenzene (DIB) has been determined by X-ray synchrotron diffraction. The mixing behavior of DIB with 4,4′-bipyridyl (BPY) has also been studied and interestingly is found to phase-separate rather than form a cocrystal, as observed in the bulk. DFT calculations are used to establish the underlying origin of this interesting behavior. The DFT calculations are demonstrated to agree well with the recently proposed monolayer structure for the cocrystal of BPY and 1,4-diiodotetrafluorobenzene (DITFB) (the perfluorinated analogue of DIB), where halogen bonding has also been identified by diffraction. Here we have calculated an estimate of the halogen bond strength by DFT calculations for the DITFB/BPY cocrystal monolayer, which is found to be ∼20 kJ/mol. Computationally, we find that the nonfluorinated DIB and BPY are not expected to form a halogen-bonded cocrystal in a 2D layer; for this pair of species, phase separation of the components is calculated to be lower energy, in good agreement with the diffraction results.

Highlights

  • The “halogen bond” is a noncovalent interaction between a halogen atom and a Lewis base. This interaction has been reported for a broad range of cocrystal combinations in the bulk.[1−6] Important parallels are often drawn between halogen bonding and hydrogen bonding, as both are strong, robust, and directional interactions.[7,8]

  • It has been reported that the halogen bond can be just as strong as the hydrogen bond and in certain cases can even dominate over hydrogen bonding in the molecular recognition processes.[9]

  • The difference in the total binding energy per cell obtained by density functional theory (DFT)+D and standard DFT calculations provides us with the intensity of long-range dispersion interaction.[13]

Read more

Summary

Introduction

The “halogen bond” is a noncovalent interaction between a halogen atom (typically Br or I) and a Lewis base (typically N, S, or O atoms). This interaction has been reported for a broad range of cocrystal combinations in the bulk.[1−6] Important parallels are often drawn between halogen bonding and hydrogen bonding, as both are strong, robust, and directional interactions.[7,8] It has been reported that the halogen bond can be just as strong as the hydrogen bond and in certain cases can even dominate over hydrogen bonding in the molecular recognition processes.[9] This makes the halogen bond a powerful tool in crystal engineering and explains its increasing use in materials chemistry. Electron-withdrawing substituents such as fluorine are considered to result in a more positive σ-hole and a greater interaction strength.[16]

Objectives
Methods
Results
Conclusion
Full Text
Paper version not known

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.