The differences observed between Zn-based frameworks and the other transition metals derives from the increased favourability of the tetrahedral coordination, which permits the formation of charge-neutral and coordinatively saturated frameworks from Zn(NCS) 4 tetrahedra and Bi(SCN) 6 octahedra without the need for point vacancies or coordinating water molecules. This is directly akin to the cyanide Prussian Blue family, for which Zn 3 [Fe(CN) 6 ] 2 can form both an ordered phase in which zinc is tetrahedrally coordinated, and a defective disordered cubic phase, analogous to the other Prussian Blues, in which Zn is octahedrally coordinated. In Zn 3 [Fe(CN) 6 ] 2 , the polymorphism occurs between a disordered and an ordered phase, whereas both polymorphs of Zn 3 [Bi(SCN) 6 ] 2 are ordered.