This learning object focuses on concepts of metal-metal bonding. In the late 1990’s, Greg Robinson published two research articles focused on the first gallyne, containing a Ga-Ga triple bond, and the first ferrogallyne, which contained an Fe-Ga triple bond. I use an article published in Chemical and Engineering News (Dagani, R. “Gallium ‘Triple Bonds’ Under Fire” Chem. Eng. News, 1998, 76(11), p31-35) to introduce students to the controversy about the ferrogallyne and gallyne compounds and several “rebuttals” provided by Philip Power and the late F. Albert Cotton. This activity consists of two components, namely presenting the ideas on metal-metal bonding by Robinson, Cotton, and Power and writing an article critique.
There are various goals for this assignment, which reinforces concepts the student has learned in earlier courses.
1) The student will apply concepts focused on atomic orbitals.
2) The student will apply concepts about orbital interactions.
3) The student will apply concepts focused on various bonding theories (e.g. molecular orbital theory).
4) The student will re-evaluate the concept of both triple and double bonds and apply this idea to heavy main-group elements.
5) The student will write an article critique focused on Robinson, Cotton, or Power’s publications.
Chalk board and/or Powerpoint Point
All students are required to read the 1998 Chemical Engineering News article describing the “controversy” surrounding Robinson’s discovery and three additional articles published by Robinson (Organometallics 1997, 16, 4511-4513), Cotton (Organometallics 1998, 17, 128-130), and Power (JACS, 1998, 120, 2202-2203). A group of six students then were selected to present this topic to the class. Within the group, a team of two presented the arguments of Robinson (triple bond), a second team presents the arguments of Cotton (single bond) , and a third team defends the argument of Power (double bond). The students are given “loose” guidelines on presenting the topic to the class, specifically they should present a powerpoint or chalk talk, and they need to engage the audience.
The students not presenting to the class provide feedback to the focusing on what worked well and areas for improvement. The instructors of the class provided feedback focusing on various areas including, level of preparedness, level of knowledge demonstrated, balanced contributions from team members, and level of engagement with the audience.
Overall, the students that presented this topic to the class did an excellent job. First, they engaged the students by distributing a handout to work in teams and review concepts such as bond order, how bond length is related to bond order, triple bonds, double bonds, and molecular orbital theory. After a brief discussion on these ideas, the students gave an over powerpoint presentation focused on the development of bonding theories (Lewis, Heitler-London, Pauling, and MO theory). Next, each team vigorously defended the results of each researcher. At the end of the class period, most students in the class concluded that Robinsons’ compounds don’t contain a triple bond, but lies somewhere between a single and a double bond. The students also pointed out that there was a “lot of pride on the line,” because at the time, no one would back away from their original position. During the discussion, I wanted the students to explore concepts of orbital interacts. More importantly, I wanted the students to realize that they cannot use "traditional concepts" that relate bond length to bond order in order to describe the bonding interactions between the heavier elements.