e) The binary sulfides Wurtzite (zinc sulfide) and Molybdenite (molybdenum disulfide) are both hexagonal crystalline materials. The former adopts a three-dimensional lattice whereas the latter adopts a layered structure. Discuss the structures these materials adopt and any reasons for the differences in these structures. f) When molybdenum disulphide is subjected to high levels of shear stress between two sliding counterfaces it can reduce the coefficient of friction between them. Discuss the structural features of the crystal structure that allows the material to act in this manner