Introduction to symmetry operations and symmetry elements: glide reflections

This video introduces you to a crystallographic symmetry operation called the glide reflection.

Many of the symmetry elements of a crystal are the same as those of discrete molecules: mirror planes, rotation axes, inversion centres and improper rotation axes, which we introduced in our video "Introduction to Symmetry Operations and Point Groups". However, crystal structures have another class of symmetry operations that involve a translational element: screw rotations and glide reflections. Screw rotations were described in the previous video in this series; in this video we will look at the fundamentals of glide reflections. We will first define glide reflections and glide planes, before looking at two types of crystallographic glide reflections: axial glides and diagonal glides.

Resources:
- Explore symmetry operations, and in particular glide reflections, in 3D by manipulating crystal structures from the Cambridge Structural Database (CSD) using the CCDC's visualization software Mercury. A free version of CCDC's Mercury is available to download: https://www.ccdc.cam.ac.uk/Community/...
- Structures in the CSD are identified with refcodes. The refcodes used in this video are BAFWOX and MALIAC13. These can be download from Access Structures: https://www.ccdc.cam.ac.uk/structures/

In this video:
-00:18 Learning outcomes
-00:50 Definition of glide reflections and glide planes
-01:34 Relationship between glide reflections and chirality
-02:24 Describing glide reflections: location of the glide plane and direction of translation
-03:00 Naming glide reflections: conventions for axial and diagonal glides
-03:30 Notes on the translational component of a glide reflection
-04:00 Example: the c-glide in CSD entry MALIAC13 (malic acid)
-04:50 Exercise: work out the type of glide reflection in CSD entry BAFWOX
-05:40 Solution: the n-glide reflection in CSD entry BAFWOX
-06:56 The periodicity of glide planes in CSD entry BAFWOX
-07:06 Summary
-07:34 Try it yourself: tips for exploring symmetry in free Mercury

The images and animation frames of these molecules are prepared using Mercury, the CCDC visualization software. A free version is available to download. More advanced functionality from the CCDC enables you explore molecules and structures in more detail. To find out how to access more advanced functionality with a CSD-Core license see https://www.ccdc.cam.ac.uk/solutions/...

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