This experiment explores isotopic substitution as a method to identify stretching frequencies and linking experimentally determined parameters with theoretical predictions utilizing a simple harmonic oscillator obeying Hooke’s law.
In the humanities it is common practice to read a piece of literature and discuss it. This is also practiced in science and is the purpose of this exercise. Each student is assigned a communication from the current literature (inorganic, JACS, organometallics, J. Phys.
Students are asked to choose a type of reaction from a set list (included), determine appropriate starting materials and the resulting product and present the reaction as though they accomplished it in the laboratory setting (5 min oral presentation with a 1 page paper). I asked the students to perform both a rough draft presentation (to me) and final draft presentation (to all students in laboratory).
A guided inquiry activity where students use group theory and character tables to practice determining reducible representations for all atoms and the individual bonds (like CO stretches). The students then reduce the representation, determine which are vibrational modes, and then determine which are IR active using the character table. For the second portion, they practice using this approach to differentiate between two metal isomers.
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.
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 literature discussion focuses on a paper from the Angelici lab that examines the heat of protonation of [CpʹIr(PR3)(CO)] compounds. The compounds presented in the paper provide good introductory examples for electron counting in organometallic compounds. The single carbonyl ligand in these compounds provide an excellent probe to monitor the electron richness at the metal center which is impacted by the electron donor ability of the ligands.
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.
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.
I used this as an in class activity but it may work better as a problem set for your class. I had the students read the pertinent chapters of the textbook which go through symmetry and molecular vibrations, including using both stretches and cartesian axes as bases. In class, I divided the students up into four groups. Each group did one of the problems for 30 minutes and during the last 20 minutes of class, they reported out their solution. The students had not seen the Hooke’s law in the textbook so I included it as part of the activity.