Multiple anion, or heteroanionic, materials are a class of compounds that have two or more anion species. This chemistry allows for complex packings of the anion sublattices as well as diversity of the chemical bond types compared to single anion materials, facilitating properties such as superconductivity , superionic transport 2 , low thermal conductivity , catalysis and quantum magnetism . Properties design via chemical tuning of single anion materials often involves either the isovalent or aliovalent substitution of the cation or metal sites, for example tuning the A and B composition in the perovskite structure ABX3. Isovalent substitution of the anion sites in multiple anion materials can also be utilised, such as band gap tuning in the BiOCl type family for photocatalytic applications or in halide perovskites with photovoltaic applications . Aliovalent anion substitution, where an anion is replaced by another anion of a different group, can also be used to tune properties. There are cases in which some O 2-replaced by some amount of H -, F -or N 3-, often charge balanced by a redox active cation becoming reduced or oxidized . Another technique is to charge balance aliovalent substitution on the anion sublattice by simultaneous aliovalent substitution on the cation sublattice or of a different anion. For example, Zn2FN can be synthesized as an analogue to ZnO to tune the band gap and photocatalytic properties , V and O can be simultaneous replaced in PbVO2(SeO3)2Cl and β-Ba2[VO2F2(IO3)2](IO3) by Ga and F to synthesize PbGaF2(SeO3)Cl and β-Ba2[GaF4(IO3)2](IO3) to engineer the nonlinear optical properties.