1. Search the Cambridge Structural Database (CSD) and find the structure of FeCl(SANE)₂. Create a data file with the information on that structure.

   Hint:

   • The best way is to perform a Formula search to get all structures in one search.
   • One of the two structures for FeCl(SANE)₂ (1974 paper) you will find in the database is incorrect. The coordinates of some atoms are faulty. However, this doesn't affect the discussions in this problem set.

2. Now, enter the Mercury program and display the unit cell of FeCl(SANE)₂. Try all the four representation styles: wireframe, capped sticks, ball and stick, and spacefill. For each representation, rotate the unit cell and view it from many perspectives.

3. In wireframe representation, measure the intramolecular Fe-Cl and Fe-O distances. As a check, compare these to those reported in the publications. Now, using "Find Contacts" option to find out the two shortest intermolecular Fe/O contacts and measure the Fe-O distances. Compare to those in the "loose dimer". In general what is it about the packing in the C2/c space group which makes the difference?

   Hint:

   • Hide all the hydrogen atoms for clarity.
   • Use the "Find Contacts" feature to examine the intermolecular Fe/O contacts:
     • Read the section 9.4.5 of the Mercury manual and work through the tutorial 1.
     • Click Display on the top-level menu and then Contacts... on the pull-down menu. Then click Add button on the Contacts panel and select Specific... from the pull-down menu.
     • On the resulting Define Specific Contacts panel, set contacts between O and Fe, and select Actual distance. Make sure that intermolecular is checked, and then hit Apply. This should find and display any intermolecular Fe/O contact between 0 ~ 3 Å (default value). If no contact is found, you should change maximum to a larger value (e.g. 4 or 7 Å) and then hit Apply again.
     • Click Build Network tab on the Contacts panel, and hit Expand All to display all the molecules that undergo the Fe/O contacts to the currently displayed molecules. You may remove the hanging (red) contacts by clicking Delete Hanging.

4. Now view, using the full screen area, the unit cell with wireframe representation. Rotate the unit cell to all angles to fully appreciate the view of the packing. Do you see any signs of face-to-face P-stacking of arene rings in the C2/c structure?

   Hint:

   • Displaying a single unit cell is not always a good choice for examining the crystal packing and intermolecular interactions. You may need to include more unit cells in the display in order to check the interactions between molecules in different cells, or to display just a part of unit cell for clarity. To do so, click Display on the top-level menu and then Packing/Slicing... on the pull-down menu, then change the cell dimensions a, b, or c (not have to be integers) on the Packing and Slicing panel.

References

1. J. A. Bertrand, J. L. Breece, P. G. Eller, Inorg. Chem., 13, 125 (1974)
2. C. J. Magurany, C. E. Strouse, Inorg. Chem., 21, 2348 (1982)