(b) Copper nitride Cu3N adopts the ReO3 structure in the cubic space group Pm3m with a=3.814A. The fractional coordinates of N and Cu are 0,0,0 and 0.5,0,0, respectively. (i) Describe the structure of Cu3N in terms of close packing. [2 marks] (ii) Sketch the structure of Cu3N. [2 marks] (iii) What are the coordination numbers of Cu and N in this structure? [2 marks] (iv) What type of centring, if any, does the structure of Cu3N show? [1 mark ] (iv) Calculate the CuN bond distance. [1 mark] (v) Given that the ionic radii of Cu+and N3 are 0.77A and 1.46A, respectively, comment on the nature of the CuN bond. [2 marks]