Deep-blue crystals formed upon refluxing anhydrous cobalt(II) chloride and quinoline in DMSO (dimethyl sulfoxide) solvent. Following the synthesis of the unknown compound, X-ray crystallography characterized the complex salt as [Co(II)(DMSO)6][Co(II)Cl3quinoline]2. In order to characterize the compound further, Infrared (IR) Spectroscopy and Ultraviolet-visible (UV-Vis) Spectroscopy were used to analyze its properties.
Preparatory to analyzing the obtained compound itself, infrared spectra were recorded of all reagents used in the experiment. IR Spectroscopy can be used to identify the presence of functional groups in a molecule. This instrument shines a range of infrared frequencies (light) through a sample of a molecule, causing some of the frequencies to be absorbed by the compound. Light provides energy for the compound to absorb, and if absorbed it causes a bond to stretch or bend. These stretching vibrations are then recorded as an IR spectrum, which then enables one to observe which frequencies were absorbed. Typically, the x-axis of an IR spectrum represents the frequency of light, while the y-axis represents percent (%) transmittance. If 100% transmittance is shown, it could lead one to conclude that all of the infrared light passed right through the sample, meaning that no light was absorbed. The set of specific frequencies that were absorbed by the molecule are represented by peaks in the IR spectra. The positions of the peaks tell us something about the way that the molecule is vibrating. Since the frequency of light is directly proportional to the wavenumber, the units (1/cm) are used to represent the x-axis (in the 4000 – 500 cm-1 range).
A collection of IR reference spectra for each reagent (anhydrous cobalt(II) chloride, quinoline, and DMSO) used in the experiment were obtained. Several scans of each sample were recorded, to ensure that we were not observing artifacts that may be introduced by contamination. Each reagent sample was collected four times, and the peaks present for all were carefully analyzed. During analysis of IR spectra, these following rules are applied. (1) Pay attention to the strongest absorptions and (2) recognize whether all peaks are present across all spectra for certain sample (Fieser, 1992).
While IR radiation results in bonds within a molecule to stretch and rotate, the radiation of Ultraviolet (UV) light records the absorption of light carried by electrons moving energy levels and even breaking certain chemical bonds (Fieser, 1992). A new UV-Vis instrument (Jasco V-760 Spectrophotometer) has been recently added to our research laboratory. I had the opportunity to write a protocol on how to use this instrument for not only myself, but also for future students and professors to utilize towards their research. The UV-Visible light region has a range between 300 – 800 nm, meaning that range of wavelengths of light is shined through the sample of the reagents and then an absorption spectrum is obtained. The x-axis for the UV-Vis spectrum represents the wavelength (nm), while the y-axis represents the absorbance. A similar procedure was performed to obtain the absorption spectra for all reagents.
The various spectra of the standard solutions will then be used to compare to the IR & UV-Vis spectra of the synthesized complex salt. I am currently in the midst of obtaining IR spectra along with UV-Vis spectra of my complex salt, [Co(II)(DMSO)6][Co(II)Cl3quinoline]2. During further analysis we hope to be able to assign all the peaks in the IR and UV-Vis spectra. Also, we’re currently curious to see if certain environmental factors (e.g. atmospheric humidity, ambient temperature) will have an effect on the complex salt over a matter of time.
Fieser L, Williamson K. Organic Experiments. 7th Edition. D.C. Heath and Company. 203-215, 235-241.