This laboratory experiment is a quick and straightforward synthesis of a MoO₂(acac)₂ complex. The ligand set allows for two possible geometric arrangements: cis and trans. Using IR spectroscopy along with group theory analysis of the Mo-O stretching modes, students can determine which isomer they formed in their synthesis. NMR spectroscopy is also employed, and confirms the geometric arrangement due to the inequivalence of the acac methyl groups.

This is a really interesting paper in J. Am. Chem. Soc. (2025, 147, 34641-34646) involving a complex salt in which both the cation and anion are metallocenes. While a majority of the paper is focused on the characterization of two new compounds, it presents some excellent opportunities to practice counting electrons, one of which was a challenge to this author.

This literature discussion is in honor of Dr. Josh Figueroa, recipient of the 2026 F. Albert Cotton Award in Synthetic Inorganic Chemistry. Josh has done some tremendous work with isocyanide ligands and this paper is but a brief glimpse into this field. The complexes of interest contain carbonyl ligands and isocyanide ligands, so there are plenty of opportunities for students to use group theory to predict the number of IR-active vibrations for these ligands.