Steric factor in ligand displacement of zirconium alkoxides dissolved in alcohols

The present study indicates EXAFS direct structural data obtained for zirconium ethoxide, iso- and n-propoxide are alike those for zirconium n-butoxide complexes. This is evident for agreement of structural units of abovementioned alkoxides complexes. Our group developed structural model of n-butoxide earlier. Six interconnected tetramers assemble a structural unit of the alkoxides under study. The tetramers build of zirconium atoms in the highly flattened pyramid corners. Four zirconium atoms are bonded in series by double bridges through oxygen atoms of alkoxide ligands. Two of the four zirconium atoms are bias bonded by single ligand bridges. The distances between pairs of zirconium atoms inside the tetramer are 3.3 and 3.5 Å. Tetramers are linked together also by a single ligand bridges. The distance between zirconium atoms of the two neighbor tetramers is 3.9 Å. Primary particles (tetramer sextet) form aggregates in a solution. Possible shapes of the anisotropically sized aggregates is a large diameter cylinder with small height (a disk), or a small diameter cylinder with large height (a rod). Primary particles composed through ligands. The distance between the neighbor zirconium atoms of different primary particles is 4.8 or 5.1 Å depending on the coordination nature and the neighboring particles number.

Using EXAFS and Raman spectroscopy our study indicated ligand displacements on changing alcohol solvents in zirconium alkoxide complexes. Ligands of the complexes displace only with molecules that are more compact.Figure optionsDownload as PowerPoint slideHighlights
► The main structural units of Zr ethoxide, iso- and n-propoxide are alike n-butoxide.
► The main structural unit involves six zirconium tetramers bonded by alkoxide bridges.
► Zr atoms inside the tetramers are bonded by alkoxide bridges through oxygen atoms.
► Complexes’ ligands could be displaced with more compact molecules of the solvent.
► Complex of zirconium n-butoxide in n-propanol is surrounded by a thick solvation shell