Synthesis, structural, spectroscopic and magnetic susceptibility studies of a soluble Cr(III)-heida (2-hydroxyethyliminodiacetic acid) complex. Relevance to aqueous chromium(III)-heida speciation

In order to delineate the interactions of Cr(III) with low molecular mass ligands, often involved in chemistries of toxic and/or biologically significant processes, the aqueous structural speciation of the binary Cr(III)-heida (2-hydroxyethyliminodiacetic acid) system was investigated. The reaction of Cr(NO₃)₃ · 9H₂O with heida at a specific pH (5.5) led to the isolation of a red crystalline (NH₄)[Cr{HOCH₂CH₂N(CH₂COO)₂}₂] · 2H₂O (1), which was characterized by elemental analysis, spectroscopic, structural, thermal, and magnetic susceptibility studies. The structure of 1 reveals a mononuclear octahedral complex of Cr(III) with two doubly ionized heida ligands bound to it. The ligand alcoholic side chains do not participate in metal binding and dangle away from the complex. The structural and spectroscopic data emphasize the physicochemical properties of 1 in the solid state and in solution, thus reflecting the profile of 1 in the overall aqueous structural speciation scheme of the Cr(III)-heida system. The employed pH-specific synthetic endeavor exemplifies (a) the potential utility of the strategy in the exploration of key structural and chemical attributes of soluble aqueous species, arising from the biologically relevant interactions of Cr(III) with the O,N-containing ligands, and (b) the potential linkage of the chemical reactivity of Cr(III) toward the O,N-containing substrates of a variable structural composition with physiological processes or toxicity events.