This in class activity focuses on the ambidentate ligand thiocyanate. Students compare data for known compounds to data for unknowns to make the bonding assignments. Data is provided from Baer, C.; Pike, J. J. Chem. Ed. 2010, 87, 724 where the authors have the students synthesize all the compounds and then complete the data analysis. My course does not include a lab component but I want the students to use literature to support their learning.
Students are given the C-N and C-S stretching frequencies for four reference compounds and seven unknowns prior to class and told to make bonding assignments (M-NCS or M-SCN or M-SCN-M) for the next class period. The data is such that students will probably only use one of the stretching frequencies sets to make their assignments and in the process make incorrect conclusions. Once in class, we discuss their conclusions and why the analysis is not straight forward. They are then introduced to a quantitative comparison method and spreadsheets are used to quickly provide the differences between each unknown compound and each reference. Details are provided in a faculty only file.
- use literature data to determine the binding mode of thiocyanate in seven compounds
- recognize that data analysis is not always straightforward and that this problem requires a quantitative comparison method.
- recognize that a previously studied theory (HSAB) supports their final response
Because of our lack of lab for this course, it is nice to use data examples to support topics in class. I plan to use this assignment after introducing ambidentate ligands in the coordination chemistry section of my course.
Prior to class discussion:
I plan to give the students the SCN data (SCN linkage problem.docx) and ask them to make assignments for the next class period. During that prior class discuss ambidentate ligands and possible modes of binding for SCN–.
During the class:
First we will discuss their drawings of the reference structures making there are no questions about coordinations and then discuss their assignments for bonding modes of the unknowns.
See faculty only file for more details
I plan to do an informal evaluation but similar data could be given as a test question.