## Geometry Indices

Submitted by Anthony L. Fernandez, Merrimack CollegeIn the primary literature, goemetry indices are being used quite often to describe four- and five-coordinate structures adopted by transition metal complexes. This slide deck, which is longer than the intended 5 slides, describes the three common geometry indices (tau4, tau4', and tau5) and provides example calculations for structures that are freely available in the Teaching Subset of the Cambridge Structural Database. (Students can access these structures in Mercury, which is freely available from the CCDC, or via a web request form for which the link is provided below.)

After viewing this presentation, students should be able to:

- recall the common geometries adopted by transition metal centers in four- and five-coordinate structures,
- describe the limiting geometries for each CN,
- recall the formulas for the three geometry indices (tau4, tau4', and tau5),
- calculate the value of the appropriate geometry index for a given structure, and
- identify the geometry exhibited by a TM center.

I have found that this presentation can be used effectively in one of several ways:

- the presentation is given in class and then students complete an exercise in which they calculate the geometry indices for a number of transition metal complexes before the leave class,
- the presentation is given in class and then students complete an exercise in which they calculate the geometry indices for a number of transition metal complexes outside of class (as homework), or
- the presentation is provided to them as a PDF file as part of the pre-class assignment and then students complete an exercise in which they calculate the geometry indices for a number of transition metal complexes when they are in class.