Synthesis, Characterization, and Cell Viability Evaluation of Coordination Compounds with Rhodium(III) Ion and Nitrogen-Containing Heterocyclic Ligands

In the search for new drugs with more efficient active ingredients, various transition metals are being explored as potential metallopharmaceuticals. These compounds, which combine drugs with metals, have shown promise as chemotherapeutic agents, akin to the accidental discovery of cisplatin and its organic derivatives in the late 20th century. This discovery transformed the sciences, particularly in the fields of organic and inorganic chemistry, by offering new insights into the compositions and molecular geometries of inorganic complexes through coordination chemistry, while also intersecting with other scientific domains such as pharmacology and medicine. To contribute to the development of new chemotherapeutic compounds through simple and reproducible synthetic processes, this study utilized rhodium(III) chloride hydrate (RhCl₃.nH₂O) to synthesize a series of compounds with the following organic N-heterocyclic ligands: 4,4'-dimethyl-2,2'-bipyridine, isonicotinamide, and N-(3-pyridyl)-isonicotinamide (3-pina). Two analytical techniques were employed to characterize the resulting materials: spectroscopic analysis in the infrared region, which suggested interactions and substitutions at the metal center by the organic compounds, and thermoanalytical analyses, which led to the proposal of minimum formulas for the compounds as follows: C1 [RhCl₂(4,4'-Met-2,2'-bipy)₂]Cl？5/2H₂O and C2 [Rh(4,4'-Met-2,2'-bipy)2(Iso)₂] Cl₃？1/2H₂O. However, the complexation of the third compound could not be confirmed due to the physicochemical characteristics of the resulting complex being very similar to those of the starting material, thereby validating the effectiveness of these techniques in differentiating and characterizing the synthesized salts. Due to their solubility in water and/or alcohol and thermal stability, the complexes were tested in biological media to assess cell viability in peripheral blood mononuclear cells. The solutions of these salts demonstrated favorable cell viability under the tested conditions, according to statistical analysis, obtaining average viability in the range of 95 ≤ x ≤ 100, with standard deviations between 3.29 ≤ x ≤ 4.44 for living cells.