Albeit arsenic compounds are ubiquitous in aqueous solutions, the speciation of such a pollutant in natural water mainly depends on its binding capabilities with specific molecules. The features of most of the interactions of arsenic complexes can be established in solution, but the data related to the stability of the formed species, essentially depending on the concentration of the ligands, are elusive. For this reason, here, we report on a series of investigations where diverse approaches are combined together in order to characterize the behavior of As(III) species in aqueous solutions where simple chelating agents, such as thiolactic and thiomalic acids, are solvated. By synergistically exploiting potentiometric, calorimetric, and spectroscopic measurements along with ab initio molecular dynamics, the stability and the underlying formation mechanisms of specific species, along with the arsenic coordination modalities with the ligands, have macroscopically and microscopically been assessed. Furthermore, vibrational modes of the complexes formed by arsenic and simple thioacids have been assigned by means of Raman experiments.