Solid complexes with tetravalent metal ions and ethylenediamime tetra-acetic acid (EDTA)

Abstract

Stable, crystalline acidic 1:1 EDTA chelates could be obtained with tetravalent germanium, tin, titanium, zirconium, hafnium and thorium. In acidic solution, the preparation of these slightly soluble compounds is straightforward—in contrast to other, previously reported methods—and yields very pure materials. All chelates are hydrated. In the case of octa-co-ordinated metals, the water is loosely bound, for hexa-co-ordinated metals, it is part of the molecule and has a strong influence on the infra-red spectra. This difference in water co-ordination has been shown by analytical data, infra-red spectra, and heat treatments. Addition of base leads to hydrolysis which is complicated for all Group IVB metal chelates, but which results in characteristic salt formation for both germanium and tin EDTA. Changes in the infra-red absorptions after hydrolysis and after heat treatment have been helpful for the interpretation of bonding in the original chelates.