One reason why there are fewer thiocyanate-based framework materials than for other small molecular ligands such as formate, azide or cyanide, are its stringent bonding requirements. Unlike other widely investigated small ligands, the coordinative preferences of the two termini of the SCN -ligand are quite distinct: the S-terminus is soft and binds to Class B metals and the N-terminus is harder and binds to Class A metals. As forming a framework requires both ends of the ligand to coordinate to a metal, this means a simple homometallic framework will have to have intermediate hardness. There are very few metals that have been shown to form homoleptic complexes with both the S and N-termini of the SCN -ligand and of these, only Cd 2+ has been investigated for its framework forming ability [Fig. ]. Not only does this limit the range of possible compounds, as a d 10 cation, Cd 2+ is inherently unpromising for optical and magnetic applications. Double perovskites, where two different metal cations fulfil the differing bonding requirements of the two termini, offer one route for expanding the compositional space of thiocyanate.