Structure and dynamics of dinuclear zirconium(IV) complexes

Area of Science:

• Inorganic Chemistry
• Coordination Chemistry
• Crystallography

Background:

• Dinuclear zirconium(IV) complexes are of interest due to their potential applications.
• The heptadentate ligand 1,3-diamino-2-propanol-N,N,N',N'-tetraacetic acid (H(5)dhpta) can form stable complexes with metal ions.

Purpose of the Study:

• To determine the crystal structures of dinuclear zirconium(IV) complexes with H(5)dhpta and different countercations.
• To investigate the coordination environment of zirconium(IV) ions and the structural features of the complexes.
• To study the pH-dependent behavior and dynamic properties of the complexes.

Main Methods:

• X-ray crystallography was used to determine the structures of K(2)[Zr(2)(dhpta)(2)].5H(2)O, Na(2)[Zr(2)(dhpta)(2)].7H(2)O.C(2)H(5)OH, and Cs(2)[Zr(2)(dhpta)(2)].H(5)O(2).Cl.4H(2)O.
• 1D and 2D (1)H and (13)C NMR spectroscopy and potentiometric studies were employed to investigate their properties.

Main Results:

• The crystal structures revealed dinuclear zirconium(IV) units bridged by alkoxo groups, with each Zr(IV) being eight-coordinate.
• The [Zr(2)(dhpta)(2)](2-) anion structure is conserved across different countercations, with variations in alkali metal ion coordination.
• NMR and potentiometric studies indicated two deprotonations (pK(a) 9.0 and 10.0) and pH-dependent dynamic fluxional behavior involving ligand exchange.

Conclusions:

• The dinuclear zirconium(IV) complexes exhibit stable structures with distorted triangulated dodecahedral geometry around Zr(IV) ions.
• The complexes display dynamic behavior in solution, particularly at low pH, attributed to protonation and solvent-mediated configurational changes.
• The study provides insights into the structural diversity and solution behavior of zirconium(IV) complexes with polydentate ligands.