hexaaquazincII

Hexaaquazinc(II) is the hexaaqua zinc(II) complex ion, [Zn(H2O)6]2+. It is the principal aqua complex of zinc(II) in aqueous solution, formed when zinc salts such as ZnSO4, ZnCl2, or Zn(NO3)2 dissolve in water. In solution, the zinc ion is six-coordinate, coordinated by six water molecules in an octahedral geometry. The complex is typically colorless, reflecting Zn2+’s d10 configuration, which does not produce visible d–d transitions.

Chemical behavior: The aqua ligands can undergo hydrolysis as pH increases, forming hydroxy complexes such as [Zn(H2O)5(OH)]+, and, at still higher pH, precipitating as Zn(OH)2. The hexaaqua complex acts as a Lewis acid and can exchange ligands with other donors (for example halides, amines, or carboxylates) to yield solvated zinc species such as [Zn(H2O)5(L)]+ or other mixed-ligand complexes.

Role and significance: In aqueous chemistry and biology, hexaaquazinc(II) serves as a model for zinc hydration. Zinc(II) is an essential element in many enzymes and structural proteins, and the hydration state of Zn2+ influences binding and reactivity in biological systems. The stability and speciation of the hexaaqua complex are affected by pH, ionic strength, and the presence of competing ligands or complexing agents.

See also: coordination chemistry of zinc; zinc(II) complexes; zinc salts.