30 Jul 2012

Exploration of Nitrosyl Complexes

In-Class Activity

Submitted by Bradley Kraft, St. John Fisher College
Categories
Description: 

This in-class activity and the related problem set allows students to discover the linear and bent bonding modes of NO to metals based on VSEPR theory through guided inquiry.  Two examples follow which illustrate how the electrons are counted in NO complexes depending on the coordination mode/formal charge of NO. Students must have had prior practice in counting electrons of complexes to complete the problems.   

Six problems, half of them from the more recent chemical literature, are given.  These include simple electron counting, determination of the oxidation state of the metal in a nitrosyl complex, prediction of the bonding mode of NO, and determination of the identity of an unknown metal in a nitrosyl complex given the NO bonding mode.  The last two questions involve examples that deviate from the expected.  The unusual Cp*3U(NO) complex is introduced to the students by asking them to discuss if the observations and coordination mode observed in the x-ray structure is expected or unexpected.  The last electron count problem poses some additional challenges.

Learning Goals: 

Students should be able to critique a given nitrosyl complex and deduce:

  • The formal electron count of nitrosyl complexes.
  • Whether a nitrosyl ligand is formally NO+ or NO- in a given coordination complex and if a linear or bent M-N-O geometry is expected.
Equipment needs: 

None

Implementation Notes: 

I plan to use this in the spring semester as an in-class activity with students working in groups of 2 or 3, but haven’t tried it yet.  If you do decide to try it, let me know how it goes!

Time Required: 
30 minutes
Evaluation
Evaluation Methods: 

I would assess the effectiveness of this exercise by posing a related question on an exam or quiz.

Creative Commons License: 
Creative Commons Licence

Comments

I used a slightly modified version of this LO in my junior/senior organometallics class today. we did the first page, and then examples 1, 2, and 5 (the organometallic ones). We all struggled with electron counting as I use the CBC/neutral ligand method; however once I decided that NO is an XL ligand and donates 3 (or 4) electrons, I was able to get the answers. We used this activity to also discuss redox acitve ligands (such as Alan Heyduk's work at UC Irvine).

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