Investigating Complex Ions of Copper(II)

Transition metal ions in aqueous solutions generally exist as complex ions in which water molecules, acting as Lewis bases, "coordinate" or bond with the small cation (which acts as a Lewis acid). The water molecules in these structures are known as ligands. Historically this kind of attachment has been called either a coordinate covalent bond or a dative bond. The distinguishing characteristic of such bonds is that the shared electron pairs which constitute the bonds come from only one of the bonded species. In normal covalent bonding the assumption is that each atom donates one electron to the shared pair that is the bond.