Syntheses and Characterization of Ruthenium(II) Tetrakis(Pyridine) Complexes. An Advanced Coordination Chemistry Experiment or Mini-Project

Abstract

This experiment involves the syntheses of several coordination complexes of ruthenium(II) and their characterization by using various spectroscopic and spectrometric techniques. Because ruthenium is a precious metal all of the reactions are carried out on a small scale, giving students experience in careful laboratory manipulation. This experiment includes the option of extension to allow students to carry out simple experiments of their own devising, acting as an introduction to research work. The known complex trans-RuIICl2(py)4 (2, py = pyridine) is prepared from cis-RuIICl2(DMSO)4 (1, DMSO = dimethylsulfoxide) and then used as a precursor to the chloride-substituted derivative trans-RuII(NCS)2(py)4, 4. Further reactions of 2 with chosen salts can also be carried out, if desired. The new complex trans-RuIICl2(acpy)4 (3, acpy = 4-acetylpyridine) is also prepared from 1. Complexes 2–4 and any further product(s) are characterized by using 1H NMR, infrared, and UV-visible spectroscopies and positive ion electrospray or FAB mass spectrometry. The results of these measurements are related to the molecular structures. In particular, the 1H NMR spectra confirm the trans coordination geometries, while the UV–visible spectra show intense dπ(RuII) → π*(py or acpy) metal-to-ligand charge-transfer (MLCT) absorptions. The relative energies of these MLCT bands can be qualitatively correlated with the electronic properties of the ligands.