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.

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