Infrared Spectroscopic Analysis of the Novel Complex Salt

My research, thus far, has involved the synthesis and X-ray crystallographic characterization of a complex salt, that was identified as [Co(II)(DMSO)6][Co(II)Cl3quinoline]2. In order to characterize the product further, we have used infra-red (IR) spectroscopy, which can tell us more about the frequency of specific vibrations within the molecule, and thus give us more structural information. Several Infrared (IR) spectra were acquired of each reagent used (i.e., anhydrous cobalt(II) chloride, quinoline, and dimethyl sulfoxide), and they were compared to that of the product, [Co(II)(DMSO)6][Co(II)Cl3quinoline]2. When analyzing IR spectra, one aims to identify the frequencies at which infrared radiation is absorbed by the molecule. The frequencies (reported as wavenumbers, 1/cm) that are absorbed are due to bonds within the molecule stretching or bending. The middle region, which includes the 4000-400 1/cm range is most useful for the analysis of organic compounds using IR spectroscopy.

Some common misconceptions about IR spectroscopy are that this technique is used to identify entire structures of an unknown molecule along with the necessity to identify each individual peak. IR is useful towards identifying certain functional groups, such as carbon-hydrogen vibrations in alkanes or alkenes and oxygen-hydrogen vibrations in alcohols. Oftentimes, the data acquired through this tool is complementary to other techniques such as UV-Visible (UV-Vis) spectroscopy, which will also be used in this study.

The preparation of a manuscript describing the results of this experiment took several months to prepare during the end of the fall semester. This process has provided me an introduction to research methodology (i.e., critical reading of scientific journals, preparation of an abstract, presentation of findings by poster). The finished paper was submitted to Acta Crystallographica and we are very excited that the manuscript was accepted in January of 2018. Along with analyzing the spectroscopic data acquired, I am also in the process of preparing my poster presentation for the convened poster session at the Society of Fellows Conference in March.

Spectroscopic Characterization of [Co(II)(DMSO)6][Co(II)Cl3quinoline]2

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.

 

References

Fieser L, Williamson K. Organic Experiments. 7th Edition. D.C. Heath and Company. 203-215, 235-241.

 

Synthesis and Characterization of Metal Complexes Containing Nitrogen Ligands

The purpose of this research is to synthesize metal compounds complexed to various nitrogen-containing ligands. In particular, we have an immediate goal of synthesizing a variety of metal compounds (e.g. copper, cobalt, palladium) that are complexed to nitrogen-containing ligands, such as quinoline. One may recognize quinolone, as it is predominantly used when manufacturing nicotinic acid, which is preventative towards pellagra outbreaks in humans, along with other chemicals. Other applications of quinoline include quinoline-containing drugs, such as Chloroquine (CQ), which is used for the prevention and treatment of malaria. Recent studies have also discovered that this quinoline-based drug may consist of antitumor properties, whereby this medication allows an accumulation of CQ in lysosomes to inhibit the reformation of cancer cells.

In my research, we have been interested in the reaction of cobalt chloride with quinoline, with the goal of preparing crystals that can be characterized by X-ray crystallography (Columbia University).  We are using this approach with the idea of preparing compounds that have not been previously observed, or reported in the literature.

Thus far, I have reacted cobalt(II) chloride hexahydrate with quinoline in water, allowing a hot plate stirrer to mix the solution for three hours. The solution was filtered twice with ethyl alcohol, boiled for an hour and then left to evaporate for two weeks. The product acquired a lilac pigment in powdered form and did not lead to the identification of a new compound.

The same reaction was performed again, but by using anhydrous cobalt(II) chloride in ethanol, where a reflux condenser was also incorporated. The refluxing technique increases reaction rates in order for equilibrium to be reached more rapidly. It also boils the solution indefinitely without losing volume, which involves recollecting condensed solvent vapor in the same boiling flask from which it originated. Blue crystals formed and X-ray diffraction showed that we had prepared Co(Cl)2(quinoline)2, which is a known compound, and has previously been reported in the literature. The cobalt atom in this compound is surrounded, in tetrahedral fashion, by two chloro and two quinoline ligands.

We performed the same reaction again, but this time in dimethyl sulfoxide (DMSO) solvent instead of ethanol. Excitingly, we have prepared crystals that, upon analysis, revealed that we had formed a previously unknown compound. This compound has been characterized as a complex salt [Co(II)(DMSO)6][Co(II)Cl3quinoline]2.

Figure 1. X-ray diffraction showing complex salt [Co(II)(DMSO)6][Co(II)Cl3quinoline]2.