Coordination Chemistry

8 Jun 2016

Historical overview of Evans method

Submitted by Adam R. Johnson, Harvey Mudd College
Description: 

This LO grew out of my interest in understanding (deeply) the machinery behind the Evans method calculations. I did these calculations as a grad student to characterize my compounds, and I teach it in both my lecture and lab. Currently I use the metal acac synthesis lab to motivate the problem.

As I crawled back in time, I found a number of helpful references in unusual journals (at least for an organometallic chemist). I hope that my historical presentation is of some interest to faculty, and maybe even for students. However, since I did spend all this time working it up, I am planning to devote a day to the history of the field next spring when I teach again. I already do a brief history…

You can expect a similar (though less in depth) LO on SQUID magnetometry later this summer!

The main points I would want students to get out of this presentation are as follows:

  • In the olden days: spectrometers were so weak that the reference capillary had to be neat TMS, water or other reference compound.
  • The chemical shift of TMS in TMS is NOT the same as TMS at 1% in CDCl3. Thus, there are two competing factors: paramagnetic shift, and diamagnetic shift due to solvent.
  • The shape factor for a spherical cell is -2pi/3, there is no net paramagnetic shift for a spherical cell, only diamagnetic.
  • A complicated NMR tube with both a cylindrical and spherical reference could be constructed to solve for both the paramagnetic and diamagnetic shifts in one experiment.
  • Only one experiment could be done because of instrument drift, and the fact that this was all done on chart recorders with rheostats.
  • Superconducting magnets made it possible to see the TMS peaks in a 1%v/v solution in CDCl3, making the terms related to diamagnetic effects go away since now the reference and sample solutions had the same diamagnetic shift.

 

 

Corequisites: 
Prerequisites: 
Course Level: 
Learning Goals: 

Students will see the path through history of measuring magnetic susceptibility by NMR, including instrument advances.

Students will understand how much NMR has advanced as a tool since the early 1950s

Implementation Notes: 

I have not yet used this in class so I would appreciate any feedback!

Time Required: 
20-30 minutes
Evaluation
Evaluation Methods: 

I would probably not evaluate students on the material presented here; it is of historical interest.

Evaluation Results: 

n/a

31 May 2016

magnetism by Evans method

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 

I usually ask a magnetism question on a homework and then again on my midterm or final exam. I give the students the equations they need. Importantly, for me, magnetic properties are used to help the students predict something about structure. For example, if a Ni(II) 4-coordinate 16-electron complex has unpaired electrons, that suggests that it is tetrahedral rather than square planar.

Evaluation Results: 

This is a fairly straightforward calculation, so the students generally do not have problems with the math (unless they forget to multiply the field strength of the NMR magnet by 1,000,000.

Description: 

After I teach my students about magnetism and magnetic properties in coordination compounds, I spend a day showing how the data is collected and analyzed. I teach them about the Gouy balance, the Evans method of determining magnetism by NMR, and SQUID magnetometry. I also show them real data that I collected as an undergraduate or graduate student, and have them interpret and analyze it.

The only experiment that we can do locally is the Evans method, so I spend more time on this technique. We use the method during the metal acac laboratory.

This learning object includes a short powerpoint presentation outlining the basics of the method, some real data collected by students at Harvey Mudd College, and some links to primary literature in the field to help guide your teaching of the material.

A related learning object goes through the history of the field.

Learning Goals: 

students will understand the basics governing the shift of the NMR signal in a magnetic environment
students, given a data set, will be able to determine the number of unpaired electrons in a coordination complex

Equipment needs: 

none. If you want to collect your own data, then you will need an NMR spectrometer, a paramagnetic compound, and appropriate glassware.

Prerequisites: 
Corequisites: 
Course Level: 
Implementation Notes: 

I do this as a short lecture followed by problems done in small groups in class. If the students don’t finish the problems, they do them as homework.

The powerpoint has some notes to help with the presentation

There are 5 student datasets and a brief explanation

there is a faculty-only file which is an excel spreadsheet which does the calculations. The spreadsheet has the three-term, two-term and one-term versions of the equation, showing that the 2nd and 3rd terms can safely be ignored in most cases; the largest sources of error are the measurment of the mass and volume of the solution!

Time Required: 
one 50 minute class period
15 May 2016

Water reclamation on the ISS: “Houston, we have a problem.”

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 

the exercises were evaluated according to the attached answer keys.

Evaluation Results: 

this ended up being a very difficult exercise, possibly more suited for sophomore or junior students. The students required some handholding to get through the exercises, but in the end, they seemed to understand that even seemingly simple aqueous systems are actually quite complicated. For Fall 2016, I intend to reframe and better stage this activity and possibly add in a discussion of EDTA as a complexing agent.

Description: 

Equilibrium reactions are those that are dynamic: the reaction can shift to form more reactants or more products depending on the physical or chemical conditions present. They were discovered and described empirically, but have a thermodynamic basis in the Gibbs Energy of the reaction. A reaction at equilibrium has both reactants and products present, and the rate of formation of products is equal to the rate of formation of reactants. A common application of equilibrium is the chemistry of aqueous acids. Acid strength is measured by the pH scale.

It costs approximately $10,000 per pound to ship supplies to the international space station in orbit around the earth. One way to minimize costs and provide additional life support options for the astronauts is to recycle wastewater back to drinkable water. Russia developed a dehumidifier type device that reclaimed moisture from the air from sweat and breathing, and this was used on the Mir space station in the 1990s. Scientists and Engineers at NASA developed a water reclamation device that improves overall water efficiency on the ISS by reclaiming water from urine. This unit was installed in 2009. However, the device is not working up to specifications and it is your job to figure out what is going wrong and make recommendations to improve it.

This activity was inspired by a conversation I had with Anne Jones from Arizona State at the VIPEr faculty development workshop at Northwestern in 2014.

Learning Goals: 

1.    Read and interpret tabular data
2.    Determine which precipitates might form from a complex mixture of ions
3.    Calculate the maximum solubility of a species in solution
4.    Determine the effect of acid/base chemistry on solubility

 

Equipment needs: 

none

Prerequisites: 
Corequisites: 
Course Level: 
Implementation Notes: 

This was done as a 2 day activity. The first day, students examine the speciation of various polyprotic ions in soluction and predict a precipitate. The second day, students look more closely at the chemical reactions carried out to purify water on the ISS and make a recommendation for an improved procedure.

There was originally going to be additional work involving EDTA complexation and formation constants, but the exercise was too long and this material was cut. However, consideration of the addition of EDTA would allow for a more sophisticated treatment.

This exercise is designed to show the effects of calcium leaching from bones by astronauts. This process is not completely understood, but blood concentrations of calcium are higher for astronauts. This led to a problem with the water purification system developed by NASA.

The keys for this exercise involve the solution of multiple simultaneous equations. This can be done using mathcad, mathmatica, or wolfram alpha. A link to a sample wolfram alpha solution is provided below.

Time Required: 
1 50 minute class period
14 May 2016

Crystal Field Theory and Gems--Guided Inquiry

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 

The 2 worksheets were handed in and graded according to the key. I generally used a +, √, - grading scale for the probelms. I gave a single grade for each group. Answer keys are provided as "faculty only" files.

Evaluation Results: 

The day 1 activities were too long and we didn't get to the square planar CFT derivation. For my next offering, I am adding a day to the unit so the students will see all three geometries. Students struggled a bit at first with the software and visualization but were able to figure it out with some assistance. The students in Fall 2015 had already practiced using Crystalmaker in a prior unit; for 2016, this prior unit has been removed so the visualization will probably take more time. I anticipate using 1.5 days for part 1 and 1.5 days for part 2 in Fall 2016.

Description: 

The colors of transition metal compounds are highly variable. Aqueous solutions of nickel are green, of copper are blue, and of vanadium can range from yellow to blue to green to violet. What is the origin of these colors? A simple geometrical model known as crystal field theory can be used to differentiate the 5 d orbitals in energy. When an electron in a low-lying orbital interacts with visible light, the electron can be promoted to a higher-lying orbital with the absorption of a photon. Our brains perceive this as color. Rubies, dark red, and emeralds, brilliant green, are precious gemstones known since antiquity. What causes the color in these beautiful crystals? Using crystal field theory, we can explain the colors in these gemstones.

Learning Goals: 

1.    Derive the crystal field splitting for d orbitals in an octahedral geometry
2.    Predict the magnitude of d orbital splitting
3.    Relate color, energy, wavelength, and crystal field strength
 

Equipment needs: 

Day 1: none

Day 2: access to laptops (one per group or individual) and crystalmaker software (free download avaialbe)

Prerequisites: 
Corequisites: 
Course Level: 
Implementation Notes: 

This LO was used in a first-year chemistry class at Harvey Mudd College in Fall 2015. I started with a brief lecture (see instructor notes) and then turned the class loose in small groups of about 5 students. I walked through the room to answer questions and guide the groups.

The first day’s activities were taken from a J. Chem. Educ. article (J. Chem. Educ., 2015, 92, 1369-1372). This article has a lot of detail that could be adapted for local use. The related activity "metal and Ionic Lattices Guided Inquiry Worksheet" may be appropriate as review/background material, depending on the placement of this activity in your syllabus.

The second day’s activities rely on the use of crystalmaker, a structure visualization program. There is a free demo version available (http://crystalmaker.com/software/index.html)

Fairly detailed instructor notes are included as a "faculty only" file.

The references for the structures I used are here:

Gibbs G V, Breck D W, Meagher E P (1968)  Structural refinement of hydrous and anhydrous synthetic beryl, Al2(Be3Si6)O18 and emerald, Al1.9Cr0.1(Be3Si6)O18 Note: hydrous emerald. Lithos 1:275-285

Wang X, Hubbard C, Alexander K, Becher P (1994)  Neutron diffraction measurements of the residual stresses in Al2O3 - ZrO2 (CeO2) ceramic composites _cod_database_code 1000059. Journal of the American Ceramic Society 77:1569-1575

I relied on a book called "The science of Color" and a website on color theory (linked below) to develop the 2nd days activities.

The Science of Color,” volume 2, edited by Alex Byrne and David R. Hilbert, MIT Press, Cambridge MA, 1997, pp. 10-17.

Time Required: 
2 50 minute class periods
22 Apr 2016
Evaluation Methods: 

I evaluate the students informally by moving among the groups working on the activity and allowing them to present answers to the different questions, then giving other groups opportunities to affirm or challenge the answers.

I also evaluate the success of this LO by gauging student success on ligand-field questions on a subsequent exam.

Evaluation Results: 

In this context (we have already seen a lot of symmetry and group theory), the students are pretty good at seeing how the symmetry labels for d orbitals change going from Oh to C4v, so I like the way the activity guides them to think about that.

Students are more mixed in their ability to see how orbitals move around as ligands move or change.  I expect this, but I am typically surprised that they still have trouble seeing the connection to crystal field theory and recognizing that the orbitals in this case are all antibonding, so greater overlap means more destabilization.

Finally, the part about triple bonding to the oxo really throws most of them for a loop. Even when they label the orbitals as π*, they tend to forget that there must be a corresponding π-bonding MO.

Since I introduced this activity, it seems that student performance on LF questions on exams has improved slightly, but I only have a few years of data points so it's hard to say for sure.

Description: 

Students work in groups to derive the ligand-field diagram for a square-pyramidal vanadium(III) oxo complex using octahedral V(III) as a starting point. The activity helps students to correlate changes in orbital energies as a function of changing ligands and geometry as well as rationalizing why certain geometries can be particularly good (or bad) for particular complexes. The activity also helps students see why oxo complexes of early metals are frequently best described as triple bonds.

Learning Goals: 
  • Students shoud be able to apply symmetry and group theory to understand frontier molecular orbital splittings and degeneracies
  • Students will be able to use correlation to predict the ordering of frontier molecular orbitals for an unknown complex from a known starting point
  • Students will be able to distinguish among σ and π effects and predict their importance in determining frontier MO structure for metal complexes
  • Students will be able to rationalize the preference of metal complexes for particular geometries based on number and type of bonding ligand as well as d-electron count
Corequisites: 
Course Level: 
Implementation Notes: 

I use this activity in a class where we first discuss the effect of changing geometry or ligands on the ligand field splittings for metal complexes using octahedral as a starting point.  Thus, the students have already seen tetrahedral, square-planar, and trigonal bipyramidal ligand field diagrams.

Then I break up the students into groups of 3-4 to work on the activity.  After about 30 minutes of work as I move among the groups to answer questions or correct misconceptions, we circle up to go over the answers, which I write out on the document camera (this part usually spills over into the next class).

Time Required: 
~45 minutes
21 Feb 2016

Ligands that Favor/Force Tetrahedral Geometry

Submitted by Marion E. Cass, Carleton College
Topics Covered: 
Prerequisites: 
Course Level: 
Corequisites: 
Learning Goals: 

Learning Goals:

Learning Objectives:  Going into this exercise:

  1. Students should be able to determine the oxidation state and d electron count for a given set of metal complexes.
  2. Based on the d electron configuration of a metal ion, students should be able to propose whether that metal ion should prefer a tetrahedral or a square planar geometry for a 4 coordinate complex.
  3. Students should have been introduced to the Jahn-Teller distortion.

Following the Presentation/Discussion:

  1. Students should be introduced to the concept that there are ligands that will force (or less successfully distort while trying to force) tetrahedral geometry on metals ions with d electron configurations that prefer to have a different geometry.
  1. Students should be introduced to the concept that by favoring one geometry over another, one oxidation state of a metal can be preferred over another for a given metal.
  1. Students will be introduced to one application of how ligands of this type can be used to facilitate experiments that probe the chemistry of certain metalloproteins.
Time Required: 
15 minutes
25 Jan 2016

Otterbein Symmetry In-Class Activity/Take home activity

Submitted by Kyle Grice, DePaul University
Evaluation Methods: 

I gave students participation credit for doing this activity, and asked students to comment on the activity during my teaching evaluations. 

Evaluation Results: 

Students commented in the teaching evaluations that they really liked this activity and it helped them understand symmetry a lot better than just reading the text and going to the lectures. 

Description: 

<p>This is an in-class activity I made for my students in a Junior/Senior-level one-quarter inorganic course.&nbsp;</p><p>Unfortunately it was waaay too long for the 1.5 h class (i gave them about 45 min). I recommend taking this and adapting it to a take-home exercise or homework set, which is probably what I will do this coming year.&nbsp;</p><p>Students used Otterbein to look at various structures, starting with low symmetry, working up to very high symmetry structures. I had them go through the &quot;challenge&quot; so they couldn&#39;t see the keys at first, but then go back to check their answers.&nbsp;</p><p>Before class, I had students watch a TED-talk video on symmetry (see web resources) and lectured for about 45 minutes on point groups and symmetry elements. They were also expected to read the chapter on symmetry from MFT.&nbsp;</p>

Learning Goals: 

-          Students will be able to visualize chemical species as 3-dimensional objects

-          Students will practice identifying symmetry elements of chemical species

-          Students will practice determining point groups of chemical species

-          Students will practice recognizing molecules of low and high symmetry

Corequisites: 
Equipment needs: 

I ran this activity in a computer lab. You need internet connection and computers with the proper specs to use Otterbein. Students could bring their own laptops to do the exercise. 

Prerequisites: 
Course Level: 
Implementation Notes: 

Give your students plenty of time, or make this a take-home assignmnet/homework assignment. Stuedents did enjoy this and found it very useful compared to just work on a flat surace. 

Time Required: 
45+ minutes
11 Jan 2016
Evaluation Methods: 

When implemented during the 2016-2017 school year a formal lab report will be required. However, other suitable methods would include, but are not limited to an oral presentation or a lab memo.

Evaluation Results: 

The experiment described herein will be piloted during the 2016-2017 school year. However, all complexes have been prepared by undergraduate students/researchers at all levels during the completion of the original project. 

Description: 

In this experiment, students will synthesize and characterize a series of Ru(II) p-cymene piano-stool complexes. Each complex will contain p-cymene as the "seat" and two chloride donors in addition to a phosphine or phosphite with varying amounts of fluorine, which together serve as the "stands". There are a total of four phosphine ligands and three phosphites, which include triphenylphosphine and trimethylphosphite that do not contain any fluorine. This experiment combines complex synthesis, characterization, data analysis and data sharing.

Course Level: 
Learning Goals: 

A student should be able to:

  1. Prepare a series of Ru(II) phosphine and phosphite complexes
  2. Characterize the complexes by multi-nuclear NMR spectroscopy
  3. Characterize the complexes by UV-vis spectroscopy
  4. Analyze structural data in Mercury
  5. Use physical characterization data to formulate trends
  6. Use data tables when appropriate
  7. Express conclusions
  8. Write a full ACS journal style lab report 
Corequisites: 
Equipment needs: 

Standard laboratory equipment/glassware

Rotary evaporator

FT-NMR with multinuclear capablity 

UV-vis spectrophotometer

Implementation Notes: 

This experiment will be piloted during the 2016-2017 school year. If others in the VIPEr community try this experiment please post your comments and/or consider filling out the feedback file attached and sending to john-lee@utc.edu

Students will synthesize and characterize one compound each, and should share spectral and other characterization data in order to perform a complete study for their report. All complexes are air-stable and can be prepared without the need for anaerobic techniques. Students should form a hypothesis on the donor ability of the ligand and then use their characterization data along with the structure of the phosphine or phosphite to support and/or refine their original predictions.

Time Required: 
Two to Three 3-hour lab periods
15 Oct 2015

Point Group Battles Activity

Submitted by Darren Achey, Kutztown University
Evaluation Methods: 

Whoever identifies the point group correctly first gets 2 points for their team.

If the team answers correctly after both competitors answer, the team receives 1 point.

The team with the most points wins (I usually give 2 points extra credit on the next exam)

Evaluation Results: 

Students really seemed to enjoy the fun competitiveness this activity had.  There was very good participation amongst all students in the class.  Some students really gained a lot of confidence in their ability to assign point groups through this activity, particularly since it occurred roughly two weeks after point groups were first introduced and they had some time to practice visualizing the symmetry elements prior to this activity.  I think it would not be a good idea to use this as an introductory activity for point group assignment, as students would have a tough time assigning these molecules and objects right away.

Description: 

In this activity, a pair of students are show an object or molecule and are asked to determine the point group before their competitor.

This activity is meant to be a fun way to develop the students ability to rapidly assign point groups to molecules and objects.  I wait until a week or two after the symmetry concepts are first shown to students so that they have developed some comfort with identifying symmetry elements and point groups prior to this activity.  Students really seem to enjoy the competitive nature of this activity and really get into determining the point groups (even if they are not the person up front at the time).  The ground rules that I use for this activity are in the instructor answer key, but they can easily be adapted for groups of different sizes (my Inorganic class usually is between 10-15 students).

Learning Goals: 


1. Students will accurately obtain the point groups of a variety of molecules and objects

2.  Students will develop the ability to identify point groups quickly

Equipment needs: 

A printout of the answer key and the objects/molecules that are already cut into individual pieces.

Slips of paper with each students name on it

Point Group flow charts for students (if you choose to give these, the flow chart I use is from the Shriver/Atkins Inorganic Chemistry book)

Prerequisites: 
Corequisites: 
Implementation Notes: 

I assign teams randomly by using the slips of paper to pick teams.

I assign the competitors randomly also from within the team and do not allow anyone to go twice before everyone has gone once.

I choose the molecule or object randomly as well

Other ground rules I use are in the faculty answer key

 

Time Required: 
45 minutes
16 Sep 2015

Iron Cross-Coupling Catalysis

Submitted by Laurel Goj Habgood, Rollins College
Evaluation Methods: 

Our proposed evaluation method is a written report in the style of an Inorganic Chemistry communication.  Instructors may choose an alternative method, such as an oral presentation, that is more appropriate for their class.

Evaluation Results: 

This experiment will be piloted during the 2015-2016 school year.  Evaluation results are forthcoming.

Description: 

In this experiment, students will synthesize and characterize an iron complex followed by completion of two series of catalytic cross-coupling reactions mimicking the methodology utilized by organometallic chemists to balance catalyst efficacy and substrate scope.  Initially the complex Fe(acac)3 [acac =  acetylacetone] is prepared.  Two sets of catalytic reactions are completed: one comparing different iron catalysts (Fe(acac)3, FeCl2, FeCl3) while the other compares substrates (4-chlorotoluene, 4-chlorobenzonitrile, 4-chlorotrifluorotoluene). This experiment was designed during the June 2015 “Improving Inorganic Chemistry Pedagogy” workshop funded by the Associated Colleges of the South.

Corequisites: 
Learning Goals: 

●      Prepare Fe(acac)3 and perform appropriate characterization.

●      Develop skills in manipulating chemicals in an air-free environment.

●      Determine efficacy of catalytic reactions (% product) using appropriate analytical technique

●      Provide explanations for differences in product yields grounded by inorganic theory

Equipment needs: 

FT-IR spectrometer

GC, GC/MS, or NMR spectrometer

Air-Free equipment to maintain nitrogen-environment 

Implementation Notes: 

This experiment will be piloted during the 2015-2016 school year.  As we collect data we will post additional information regarding experimental details and evaluation methods.  We welcome others in the VIPEr community to help us test this!  If you do try this, consider filling out the evaluation file attached and sending to lhabgood@rollins.edu.

Students will synthesize and characterize the iron complex individually.  Each student should complete an appropriate subset of the catalytic reactions such that the pooled class data has each catalytic reaction replicated in triplicate.  The Fe(acac)3 complex is commercially available so it is possible to complete the lab in two sessions if students are provided with all three catalysts initially.

Time Required: 
Three 3-hour lab sessions: (1) Synthesize iron complex, demonstrate air-free techniques, (2) Perform catalytic reactions with appropriate analysis for product yield, (3) Complete catalytic reactions with appropriate analysis for product

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