The Coordination Chemistry of Solvated Metal Ions in DMPU

Lundberg, D., 2006, The Coordination Chemistry of Solvated Metal Ions in DMPU – A Study of a Space-Demanding Solvent. Doctor’s dissertation. ISSN 1652-6880, ISBN 91-576-7072-2 This thesis summarizes and discusses the results of several individual studies on the solvation of metal ions in the solvent N,N’-dimethylpropyleneurea, DMPU, including the iron(II), iron(III), zinc(II), cadmium(II), and lanthanoid(III) ions. These studies have shown that the solvation process in DMPU is sometimes very different to those in corresponding aqueous systems. This is due to the the space-demanding properties the DMPU molecule has when coordinating to metal ions, with its two methyl groups close to the coordinating oxygen atom. The methyl groups effectively hinder/hamper the metal ion from reaching the coordination numbers present in hydrate and solvate complexes with solvent molecules with much lower spatial demands. The investigations were performed with different X-ray techniques, including extended X-ray absorption fine structure (EXAFS), large angle X-ray scattering (LAXS), and single crystal X-ray diffraction (XRD) and included both studies in solution (EXAFS and LAXS) and solid state (EXAFS and XRD). A coordination number reduction, compared to the corresponding hydrates, was found in all of the studied systems, except cadmium(II). Furthermore, the coordination number in solution was in several cases not the same as in the respective solid state. In solvents where five-coordinated metal ion solvates are dominating, there is an increase in the ability to form complexes, e.g. fairly strong iron(III) bromide complexes are formed in DMPU. All DMPU solvated lanthanoid(III) ions, except lutetium(III), are seven-coordinated in solution, whereas they are six-coordinated in the solid state, as well as the DMPU solvated lutetium(III) ion in solution. The DMPU solvated zinc(II) and cadmium(II) ions are fourand six-coordinated in the solid state, but both show indications of having a relatively large fraction of transient five-coordinated complexes in solution. This indicates associative and dissociative ligand exchange processes, respectively. The first four-coordinated cadmium(II) iodide with atomic parameters, bis[1,3-dimethyl-3,4,5,6-tetrahydropyrimidin2(1H)-one-κO]diiodocadmium(II), has been structurally determined.