Diversity in coordination number and denticity of alkali metal-EDTA complexes

EDTA (Ethylenediaminetetraacetic acid), abbreviated as H4Y with Y4- herein, is a chelating ligand that complexes a wide range of metal ions. Alkali metal ions have rather low stability constants with EDTA; however, syntheses and crystal structures of a few alkali metal-EDTA complexes have been reported. Note that the structures have diversity, i.e., they are different from that of the EDTA complexes having typically known hexadentate Y4- with the coordination numbers (CN) 6 for cations. For example, in a lithium-EDTA complex, [Li4(EDTA-4H)], Li+ have CN 4 or 5 by tridentate μ12-Y4- . Additionally, in some sodium-, potassium- and rubidium-EDTA complexes whose crystal structures are also revealed, Na+ , K+ and Rb+ have greater CN than 6 with multidentate Y4- , HY3- and H2Y2- . Nevertheless, elucidating the structures of alkali metal-EDTA complexes in solution have still difficulties. Because in solutions the structures of the EDTA complexes do not necessarily consistent with that in crystalline states.
長崎大学大学院工学研究科研究報告, 52(99), pp.22-29; 2022