Group theory & applications

3 Jun 2017

Fivefold Bonding in a Cr(I) Dimer Updated and Expanded

Submitted by Thomas Brown, SUNY Oswego
Evaluation Methods: 

Students are asked to answer the questions before coming to class and collected. After discussion students can revise their answers.   

Evaluation Results: 

This is a newly revised learning object so no assessment has been collected yet.  

Description: 

This paper describes the synthesis and characterization of a Cr(I) dimer with a very short Cr-Cr distance. Computational studies support fivefold bonding between the chromium atoms. This paper could be used to introduce metal-metal multiple bonds and discuss the molecular orbital interactions of homonuclear diatomics including d-orbitals. More generally, it is a nice example to stimulate the discussion of what constitutes a bond and the various interpretations of bond order. This version of this learning object is a modified and expanded version of Maggie Geselbracht's original LO. It was prepared colleaboratively at the 2017 VIPEr Literature Discussion workshop.

Corequisites: 
Learning Goals: 
Students should be able to:
  • Identify shapes and orientation of d orbitals

  • Create Lewis structures describing ligand binding type from crystal structures.

  • Apply symmetry concepts to assign orbital symmetries and create molecular orbital diagrams

  • Develop and draw the MO diagram of d-orbital interactions and use it to interpret the bonding involved in metal-metal multiple bonds.

  • Evaluate the relationship between bond order and experimental metal-metal bond distance

  • Evaluate effects of ligand design on molecular stability

  • Apply character tables for associated molecular point groups      

  • Rationalize MO interactions of ligands with metal centers in the presence of a metal-metal multiple bond.

 

Implementation Notes: 

Students are asked to read the paper and answer the discussion questions before coming to class. This could be used in an inorganic course after you have talked about MO theory of diatomics but fairly early in our discussion of transition metal chemistry. There is a Perspectives article in Science that goes along with this paper that gives the MOs more explicitly.   

Time Required: 
50 min +
3 Feb 2017

Six-coordinate Carbon In-class Activity

Submitted by Kyle Grice, DePaul University
Evaluation Methods: 

Dr. Grice will evaluate this LO later this year. 

Description: 

This is an in-class exercise developed based on a recent paper in Angewandte Chemie International Edition that reported a crystal structure of "six-coordinate" carbon. We normally think of carbon being four-coordinate at most, but this case has definitive evidence otherwise. However, we can use our inorganic chemistry knowledge to understand the structure and bonding of this molecule and rationalize its stability. Students do a pre-class exercise and then construct the MO of fhe molecule in class together. 

Learning Goals: 

After completion of this Learning Object, students will be able to:

-Assign point groups to organic molecules

-Analyze and discuss chemistry primary literature

-Identify the properties and charges of ligands

-Use Wade's rules to describe clusters

-Construct qualitative MO diagrams using symmetry as a guide

Corequisites: 
Course Level: 
Equipment needs: 

None

Prerequisites: 
Implementation Notes: 

Dr. Grice will be implementing this later this year. 

We have included an instructor guide file under Faculty files. 

Time Required: 
50 min
11 Jan 2017

Group VI metal carbonyl compounds with pincer ligands

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This was developed after the semester in which I teach this material. I look forward to using it next fall and I hope to post some evaluation data at that point.

Description: 

This literature discussion is based on a short paper describing a series of Group VI metal carbonyl compounds that have pincer ligands (Organometallics, 201635, 229). While the paper is relatively straightforward, there are many subtle points that can be brought out by asking the right questions which hopefully this LO does. Some of the questions the students should be able to answer directly from the paper. I feel it is important that they do this. However, these questions nicely set up further questions that require the students to go beyond what is covered in the paper. In addition to the synthesis, there are many questions related to the spectroscopic characterization of these compounds. And of course, it wouldn't be one of my LOs if students weren't being asked to count electrons and do group theory.

Corequisites: 
Prerequisites: 
Learning Goals: 

Upon completing this LO students should be able to

  1. Use the CBC method to count electrons in the tungsten compounds in this paper
  2. Describe the bonding interaction between a metal and a terminal carbonyl ligand
  3. Explain how NMR can be used to characterize these compounds including a discussion of 183W satellites
  4. Relate data from IR spectroscopy to the bonding interaction between a metal and a ligand and describe how the IR data can provide information about the electron donor ability of related ligands
  5. Recognize that some observed trends just do not have good explanations
 
Course Level: 
Implementation Notes: 

This might be a bit on the long side, you could certainly omit some of the questions or have the students work on it outside of class.

Time Required: 
50 minutes or so
4 Jan 2017
Description: 

This is a great new textbook by George Luther III from the University of Delaware.  The textbook represents the results of a course he has taught for graduate students in chemical oceanography, geochemistry and related disciplines.  It is clear that the point of the book is to provide students with the core material from inorganic chemistry that they will  need to explain inorganic processes in the environment.  However the material is presented in such a clear, logical fashion and builds so directly on fundamental principles of physical inorganic chemistry that the book is actually applicable to a much broader audience.  It provides a very welcome presentation of frontier orbital theory as a guide to predicting and explaining much inorganic chemical reactivity.  There are numerous very  helpful charts and tables and diagrams.  I found myself using the book for a table of effective nuclear charges when I was teaching general chemistry last semester.  The examples are much more interesting that the typical textbook examples and would be easy to embellish and structure a course around.  There is also a helpful companion website that provides powerpoint slides, student exercises and answers.  The book covers some topics not typically seen in inorganic textbooks like the acidity of solids but the presentation of this information makes sense in light of the coherent framework of the text.  We so often tell our students "structure dictates function".  This text really make good on that promise.  My only complaint is that I wish the title were something more generic so that I could use it for a second semester of introductory-esque material that we teach after students have taken a single semester of intro chem and two semesters of organic chemistry.  So much of what is covered in this textbook is precisely what a second semester sophomore chemistry major should know before proceeding on in the major.  But the title makes the book hard to sell to chemistry majors and that is regrettable. 

Prerequisites: 
Course Level: 
29 Dec 2016

The Monsanto acetic acid process

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This was developed after the semester in which I teach this material. I look forward to using it next fall and I hope to post some evaluation data at that point.

Description: 

This literature discussion is based on one of early papers detailing the mechanism for the Monsanto acetic acid process (J. Am. Chem. Soc., 1976, 98, 846). In this communicaiton the identification of key intermediates in this process is carried out using infrared spectroscopy. While the paper is an easy read, there are lots of subtle points that can be brought out by asking the right questions which hopefully this LO does. Although we have plenty of excellent LOs asking students to identify the individual steps in the catalytic mechanism, this LO takes a slightly different approach and marches students through the mechanism.

Course Level: 
Prerequisites: 
Corequisites: 
Subdiscipline: 
Learning Goals: 

Upon completing this LO students should be able to

  1. Use the CBC method to count electrons in the rhodium compounds in this paper
  2. Describe the bonding interaction between a metal and a terminal carbonyl ligand
  3. Identify the various reactions taking place in the Monsanto acetic acid process
  4. Relate data from IR spectroscopy to the bonding interaction between a metal and a ligand and to the identification of intermediates in this process
Time Required: 
50 minutes or so
28 Dec 2016

Isotope Effects in Arene C-H Bond Activation by Cp*Rh(PMe3)

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

This LO was used in class to help a student guide a discussion of the paper. We did not cover all of the LO in a 75 minute class period, as we let the discussion take us where it wanted to. 


A better way to ensure student preparation would be to collect the questions at the beginning (or end, if they wanted to use their notes in class) of class to ensure that they had really studied the paper.

Evaluation Results: 

I used this LO as a guided reading handout and did not collect the answers so I do not have any assessment data at this time.

Although my students found this paper to be relatively dense and hard to follow at times. The paper separates out the Results and Discussion sections, so at times it seems repetitive. However, once they had worked their way through the paper, the students found the results interesting and the methods informative. We were able to discuss it at a high level in class.

Description: 

This literature discussion is based on a paper by Bill Jones and Frank Feher (J. Am. Chem. Soc., 1986, 108, 4814-4819). In this paper, they study the activation of aromatic C-H bonds by a rhodium complex. Through careful experimental design, they were able to examine isotope effects on the selectivity of the reaction. Analysis of the rate data allowed them to prepare a reaction coordinate free energy diagram. This paper also introduces the effects of C-H bond breaking in early or late transition states on the vibrational energy spacing at both ground and excited states. The paper is a good way to bring kinetic isotope effects into the classroom. The paper also introduces the concept of deuterium labeling experiments and what that information can tell you.

An important aspect of this paper, and what makes it so interesting, is that they are able to get two kinetic isotope effects, one for each step of the reaction. From these two KIEs alone they are able to determine the unexpected rate-determining step of the reaction. It is a triumph of mechanistic investigation into intermediates that are undetectable.

This LO presents a series of guided reading questions that help a student approach and understand the material presented in the paper in a more thorough way. Part one is a guided inquiry that allows the students to derive and understand differing zero point energies for proteated and deuterated compounds. Part two guides students  through the results presented in the paper to help them better understand how experimental data can be used to understand the mechanism of a chemical reaction. There is more to the paper than kinetic isotope effects, but that is the focus I chose while developing it. The LO is suitable for junior or senior undergraduates in an organometallics course or unit within an inorganic course.

I would like to acknowledge Ryan Pakula and Joanne Redford from my Chem 165 course in 2008 who wrote early versions of some of the questions about vibrational states, and a careful critical read by Nancy Williams, who understands this stuff at a much deeper level than I do.

Course Level: 
Learning Goals: 

upon completing this LO students should be able to
:
1. calculate and interrelate reduced mass, vibrational frequency, force constant, and zero point energies for vibrational states of bonds
2. define kinetic isotope effects (normal, and inverse)
3. calculate/predict/estimate a normal and inverse KIE for a chemical reaction from IR data.
4. interpret and describe a reaction coordinate diagram for a chemical reaction
5. count and classify metal complexes using CBC method

Subdiscipline: 
Implementation Notes: 

I used this LO as a guided reading handout for a senior-level organometallics class. The questions and the paper were provided to the students a week in advance and the in-class activity was a student-led discussion of the paper.

Time Required: 
1 50-75 minute class period for discussion
28 Dec 2016

Virtual Issue of Organometallics

Submitted by Chip Nataro, Lafayette College

You can find the virtual issue with our editorial and all of the papers here.

Subdiscipline: 
Prerequisites: 
Corequisites: 
Course Level: 
27 Dec 2016

Binding dinitrogen to titanium sandwich compounds

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This LO was developed after the course I would use it in had ended. I am looking forward to using it next year and I hope to post some evaluation results at that point.

Description: 

The literature discussion is based on one of the early papers from the Chirik group (J. Am. Chem. Soc., 2004, 126, 14688). In this communication, the coordination of N2 to a series of (C5H4R)2Ti fragments is examined. Being a communication, it is very short and that helps make it less intimidating for undergraduates. But don't be fooled, it is very rich in the fundamental concepts of orgnaometallic chemistry. The nitrogen fixation reaction has real world significance and is therefore an interesting big picture idea to talk about in relation to this paper. The bonding of Cp ligands is discussed in the context of this paper. In addition, this paper also presents paramagnetic and dimagnetic Ti(II) compounds and thus provides an opportunity to discuss the characterization of paramagnetic compounds. The use of X-ray crystallography and IR spectroscopy in relation to the strength of a bonding interaction between ligands and a metal center is also discussed. Finally, there is an opportunity to apply group theory to determine the number of IR active bands in the IR spectrum of a carbonyl compound. The supporting info for this paper is such a key part of this LO that links to both the paper and the supporting info are included below. In addition, there is a link to a Hoffman paper detailing the MO diagram for Cp2M compounds which might prove useful in discussing the paramagentic and diamagnetic Ti(II) compounds.

Prerequisites: 
Course Level: 
Corequisites: 
Learning Goals: 

Upon completing this LO students should be able to

  1. Describe why nitrogen fixation is a significant chemical reaction worthy of study
  2. Use the CBC method to count electrons in the titanium compounds in this paper
  3. Describe the bonding in compounds with Cp ligands
  4. Describe how a paramagnetic substance can be recognized when using standard characterization techniques and suggest other means of characterizing paramagnetic compounds
  5. Relate data from IR spectroscopy and X-ray crystallography to the bonding interaction between a metal and a ligand
Time Required: 
50 minutes

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