Deuterium NMR study of amino acid coordination to chromium(III)

A series of bis(ethylenediamine)Cr(III)-amino acid complexes, synthesized with deuterium-labeled alanine, glycine, homoserine, leucine, methionine, phenylalanine, serine, and threonine, was characterized by 2H NMR spectroscopy. The spectra show that these bidentate-coordinated amino acid complexes decompose via monodentate species. In addition, the diastereomeric isomers of alanine and leucine can be distinguished in the spectra. This was confirmed by the isolation of one of the L-leucine isomers. The bis(1,3-propanediamine)Cr(III) complexes of glycine and alanine were also synthesized, and the NMR spectra of these complexes and α-cis-[Cr(ethylenediaminediacetate)(glycinate)] show changes due to variation in the ligand complement. The crystal structure of α-cis[Cr(ethylenediaminediacetate)(glycinate)] x 2H2O (CrO6N3C8H14 x 2H2O) was determined and supports the NMR observations. This complex crystallizes in the space group P21/c of the monoclinic crystal system with a = 8.9231 (19) A, b = 10.1889 (22) A, c = 15.4180 (30) A, β = 102.657 (17)0, and Z = 4. An improved method for the synthesis of bis(diamine)Cr(III)-amino acid complexes is also reported. 24 references, 3 figures, 7 tables