Study of ligand field strength through the experimental analysis of chromium complexes with ligands of different ligand-field splitting parameters
Tabulate all of the spectral data. Using the Tanabe-Sugano diagram (Figure IV-1) and your UV spectra calculate the octahedral crystal field splitting parameter D0 for the ligands water, oxalate, chloride and ethylenediamine. Determine the Racah parameters for each ligand using the supplied Tanabe-Sugano diagram. From a qualitative examination of the spectra for the mixed chloro/aqua complexes, deduce which gives the greater d-orbital splitting. Construct a short spectrochemical series for the ligands used. Your discussion should address at least the following points: 1. Which selection rules govern the spectra you have recorded?[unique_solution] Discuss with reference to your data. Chemistry 3840 Laboratory Manual Page 4-4 Part II – Ligand Field Theory Experiment 4 2. Explain briefly why chromium(III) complexes give more than one d–d band in the electronic spectrum. 3. What effect do the ligands have on the electronic spectra? Discuss the field-strength effects observed in your data. 4. What factors affect the breadth of the observed spectral bands? 5. What effect does chelation have on the symmetry of the ligand fields for chromium(III) complexes? 6. Is the NCS– ligand in [Cr(NCS)6]3– bound via the sulfur or nitrogen atom? Base your argument on the spectra you have recorded and by comparison with the other complexes studied in this laboratory. 7. Discuss all IR spectra.