In aqueous solution, water competes effectively with bromide ions for coordination to Cu²⁺ ions. The hexaaquacopper(II) ion is the predominant species in solution. However, in the presence of a large concentration of bromide ions, the solution becomes deep violet. This violet color is due to the presence of the tetrabromidocuprate(II) ions, which are tetrahedral. This process is reversible, and so the solution becomes light blue again upon dilution with water.

(a) Write the formulas of the two complex ions of copper(II) that form.

(b) Is the change in color from violet to blue upon dilution expected? Explain your reasoning.