General Chemistry

10 May 2018

3D Sym Op

Submitted by Caroline Saouma, University of Utah
Evaluation Methods: 

None

Description: 

This is a great app that helps students see the symmetry in molecules. It allows you to choose a molecule (by name, structure, or point group) and display a 3D rendition of it. You can then have it display the symmetry elements, and/or apply all the symmetry operations. 

It is available for both android and apple phones: (probably easier to just search for it)

apple: https://itunes.apple.com/us/app/3d-sym-op/id1067556681?mt=8

android: https://play.google.com/store/apps/details?id=com.nus.symmo&hl=en_US

Topics Covered: 
Prerequisites: 
Learning Goals: 

A student should be able to find symmetry elements in molecules. 

Corequisites: 
Implementation Notes: 

In class I project my phone screen so they can see it, and I encourage the students to work along with their phones. I prefer this to models, as it is hard to remember what things looked like before you did the transformation, and moreover, my students have a hard time finding the symmetry elements. 

 

I encourage the students to play with it anytime they have a few spare moments- waiting for the bus, in line for food, etc. 

17 Jan 2018

Metal Tropocoronand Complexes

Submitted by Anthony L. Fernandez, Merrimack College
Evaluation Methods: 

I assess the student learning by the quality of the discussion generated by this exercise.

Evaluation Results: 

I have used this exercise several times, but I am reporting the results from the Fall 2017 semester.

Students accessed the structures, measured the bond angles using Mercury, and calculated the tau4' values without any difficulties (questions 1 and 2).

When they got to the third question, they could describe what they observed, but struggled with the language. They were very concerned about how to name the observed structures. They were not satisfied with using the terms "distorted square planar" and "distorted tetrahedral" to describe the structures. (This then led into the discussion of the tau4' values and why focusing on the names of the strucutres was limiting.)

All of my students were also able to calculate the LFSE values for the Ni(II) center in the four geometries. They asked about the spin state, but I prodded them to talk it through themselves and think back to previous discussions. They quickly realized that for some of the geometries there is no difference between the HS and LS configurations. They decided to calculate the LFSE for both configuations when they were different. Once their calculations were complete, the students determined that square planar should be the preferred geometry based upon the LFSE.

The last question is the one that threw a monkey wrench into what they thought they knew. They were surprised that a d8 metal center would adopt a tetrahedral geometry since this was contrary to what they had originally learned. I then asked about what other influences would impact the observed geometry. About half of my students said that the steric repulsion of the four donor atoms (and other atoms in the tropocoronand ligand) in a square planar arrangement was greater than that in a tetrahedral arrangement. These students were then able to make the connection to the fact that this must outweigh the LFSE value and favor the geometric transition of  the nickel center.

Description: 

This exercise looks at the metal complexes of tropocoronand ligands, which were first studied by Nakanishi, Lippard, and coworkers in the 1980s. The size of the metal binding cavity in these macrocyclic ligands can be varied by changing the number of atoms in the linker chains between the aminotroponeimine rings, similar to crown ethers. These tetradentate ligands bind a number of +2 metal centers (Cd, Co, Cu, Ni, and Zn) and the geometry of the donor atoms around the metal center changes with the number of atoms in the linker chains. This exercise focuses on the tropocoronand complexes of Ni(II) and students are asked to quantitatively describe the geometry around the metal using the tau4' geometric parameter. This then leads to a discussion of the factors that influence the geometric arrangement of ligands adopted by a metal center. This exercise is used to introduce the concept of flexible metal coordination geometries in preparation of the discussion of metal binding to biological macromolecules and the entatic effect.

Learning Goals: 

After completing this exercise, a student should be able to:

  • access structures from the CCDC using their online form,
  • measure bond angles in a crystal structure using appropriate tools,
  • calculate the tau4' value for a four-coordinate metal center,
  • calculate the ligand field stabilization energy for a complex in a number of different geometries,
  • identify the factors that influence the geometry arrangment of ligands around a metal center, and 
  • explain how the interplay of these factors favor the observed geometry. 
Equipment needs: 

Students will need to have access to the CIF files containing the structural data. These files are part of the Cambridge Structural Database and can be accessed through that if an institutional subscription has been purchased. 

Students can also access these CIF files by requesting the structures from the Cambridge Crystallographic Data Centre (CCDC). The identifiers provided in the faculty-only files can be submitted using the "Access Structures" page (https://www.ccdc.cam.ac.uk/structures/) and the associated CIF files can be viewed or downloaded. Students can then measure the bond angles in the JSmol viewer or in Mercury (which is freely available from the CCDC) after downloading the files.

The CIF files for the copper complexes were not available in the CSD, so I created those CIF files from data found in the linked article.

Prerequisites: 
Corequisites: 
Subdiscipline: 
Implementation Notes: 

I have used this activity in a two different ways.

  • In the past, I have assigned this as a homework assignment and have had students complete questions 1-4 outside of our class meeting time. They requested the structures from the CCDC or used our copy of the CSD on their own time. I then facilitated a dicussion of their answers before discussing the last question as a group in class. This approach worked well.
  • This year, I decided to use this exercise as an in-class group activity. I began class with a discussion of geometric indices using the presentation that is also available on the VIPEr site and is included in the "Related activities" section. I then broke my class up into groups of three students and had each group work through the activity. After the students completed the exercise, I then shared the calculations that I did for the zinc complexes so that they could remove the complication of the LFSE values from the discussion. I was much happier with this approach because I was able to focus the discussion a bit more and use the zinc data to reinforce the overall point of the exercise.

Note that in the original articles, the dihedral angle "between the two sets of planes defined by the nickel and two nitrogen atoms of the troponeiminate 5-membered chelate rings" was reported. I have decided to use the more current tau4' parameter in this exercise.

Time Required: 
45-60 minutes
10 Jan 2018

What happened to my green solution?

Submitted by Anthony L. Fernandez, Merrimack College
Evaluation Methods: 

I do not do any formal assessment of student learning for this activity, but instead I judge understanding by the quality of the in-class dicussion.

I have also used similar questions on exams in the past to see if the students can apply these ideas to different reactions.

Evaluation Results: 

I have experienced mixed results with this exercise over the three years I have used it. I find that my students have no trouble identifying that a reaction has occurred and they readily recognize that the color change is a consqeuence of the reaction.

My students tend to struggle with the composition of the complex ions in solution. For the CrCl3 solution, students provide many possible compositions of the coordination complex including the neutral complex, [CrCl3(OH2)3], and the hexaaqua complex, [Cr(OH2)6]3+.  More than 2/3 of the students suggest one of the two predominant complex ions that are present in solution. For the Cr(NO3)3 solution, students often want to use the nitrate as a ligand on the chromium center.

All of my students are usually able to write the balanced reactions and explain the changes in the UV-visible spectra once they identify the composition of the complex cations.

Description: 

Students in inorganic chemistry courses are often interested in the colors of transition metal complexes. This in-class activity serves an introduction to reactions of coordination complexes and pushes students to think about the relationship between the color of a complex cation and its structure. Students are provided with pictures of aqueous solutions of two chromium(III) salts [CrCl3*6 H2O and Cr(NO3)3*9 H2O] at two different times and are then asked to explain the changes observed in the solutions. This activity was inspired by a laboratory experiment which was done as part of the inorganic laboratory course for many years ("Determination of Delta_oct in Cr(III) Complexes" from Szafran, Z., Pike, R.M., and Singh, M.M "Microscale Inorganic Chemistry: A Comprehensive Laboratory Experience" Wiley, New York, (c)1991) .

Learning Goals: 

After completing this exercise, students should be able to:

  • describe how the color of a solution is related to the composition of the coordination complex present in solution,
  • explain how the change in color of a solution indicates that a reaction has occured, and
  • determine the identities of the products and reactants of a reaction that has taken place in solution.

If the UV-visible data are also provided, students should also be able to relate the shifts in the peaks observed in the UV-visible spectra to the position of the ligands in the spectrochemical series.

Equipment needs: 

No equipment is needed for this in-class activity. 

Corequisites: 
Subdiscipline: 
Course Level: 
Implementation Notes: 

I usually use this activity to introduce reactions of coordination complexes in lecture, which falls just after a section in my text on the colors of coordination complexes. While my students have seen many transformations in lab, I use this to connect the two portions of the course. For added empahsis you could make the aqueous solutions and bring them to class.

I usually project the pictures on a screen at the front of the class and I therefore need a device to project it from and a projector.

I break up my class into groups and let them work on this activity collaboratively. I usually let them discuss the problem for about 5-10 minutes and I check in with each group individually. If they are having trouble determining the composition of the coordination complexes, I remind them that they need to write out the formulas in the current way that we represent coordiantion complexes. This usually gets them thinking about primary vs. secondary coordination spheres and waters of hydration. I then let them work for another 10 minutes so that they can write the reactions. I then bring the class together to discuss the results. If time allows, I share the UV-visible data with the entire class and as them to explain the observed changes.

Time Required: 
20-30 minutes
14 Aug 2017

Chapter 21--Stanley Organometallics

Submitted by George G. Stanley, Louisiana State University
Description: 

Chapter 21 from George Stanley's organometallics course, Polymerization

 

this chapter covers the history of polymerization reactions.

Unlike the vast majority of the chapters in this series, there are no powerpoint slides for this chapter.

Everyone is more than welcome to edit the materials to suit their own uses, and I would appreciate being notified of any mistakes that are found.


Subdiscipline: 
Corequisites: 
Course Level: 
14 Aug 2017

Chapter 20--Stanley Organometallics

Submitted by George G. Stanley, Louisiana State University
Description: 

Chapter 20 from George Stanley's organometallics course, Metathesis

 

this chapter covers the history of metathesis reactions.

Unlike the vast majority of the chapters in this series, there are no powerpoint slides for this chapter.

Everyone is more than welcome to edit the materials to suit their own uses, and I would appreciate being notified of any mistakes that are found.


Subdiscipline: 
Corequisites: 
Course Level: 
14 Aug 2017

Chapter 19--Stanley Organometaliics

Submitted by George G. Stanley, Louisiana State University
Description: 

Chapter 19 from George Stanley's organometallics course, Polymerization and Metathesis

 

this chapter covers polymerization catalysis and olefin metathesis.

The powerpoint slides contain answers to some of the in-class exercises, so those are behind the "faculty only" wall. I share these with students after the class, but not before.

Everyone is more than welcome to edit the materials to suit their own uses, and I would appreciate being notified of any mistakes that are found.


Subdiscipline: 
Corequisites: 
Course Level: 
14 Aug 2017

Chapter 18--Stanley Organometallics

Submitted by George G. Stanley, Louisiana State University
Description: 

Chapter 18 from George Stanley's organometallics course, Cross-coupling

 

this chapter covers a variety of different named cross-coupling reactions.

The powerpoint slides contain answers to some of the in-class exercises, so those are behind the "faculty only" wall. I share these with students after the class, but not before.

Everyone is more than welcome to edit the materials to suit their own uses, and I would appreciate being notified of any mistakes that are found.


Subdiscipline: 
Corequisites: 
Course Level: 
14 Aug 2017

Chapter 17--Stanley Organometallics

Submitted by George G. Stanley, Louisiana State University
Description: 

Chapter 17 from George Stanley's organometallics course, Acetic Acid

 

this chapter covers the various catalytic methods for the production of acetic acid.

The powerpoint slides contain answers to some of the in-class exercises, so those are behind the "faculty only" wall. I share these with students after the class, but not before.

Everyone is more than welcome to edit the materials to suit their own uses, and I would appreciate being notified of any mistakes that are found.


Subdiscipline: 
Corequisites: 
Course Level: 
14 Aug 2017

Chapter 16--Stanley Organometallics

Submitted by George G. Stanley, Louisiana State University
Description: 

Chapter 16 from George Stanley's organometallics course, Hydroformylation

 

this chapter covers hydroformylation catalysis and includes a historical perspective.

The powerpoint slides contain answers to some of the in-class exercises, so those are behind the "faculty only" wall. I share these with students after the class, but not before.

Everyone is more than welcome to edit the materials to suit their own uses, and I would appreciate being notified of any mistakes that are found.


Subdiscipline: 
Corequisites: 
Course Level: 

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