There are a number of different ternary metal thiocyanates with primarily 2D connectivity (Fig. ). The most widely explored is the post-perovskite structure, first reported for Rb[Cd(SCN) 3 ], Mn. These materials, like the perovskites, are formed from two different metal coordination environments, but in this case they are MS 2 N 4 and MS 4 N 2 . These polyhedra edge-share through the length of the NCS -ligand with polyhedra of the same kind and corner-share with the others, to form anionic sheets of composition [M(NCS) 3 ] -, with the counter-cation lying between them. The post-perovskite oxides and halides are typically formed at GPa to 100 GPa pressures, e.g. and NaMF 3 (M = Mg, Zn, Ni, Co, Fe) , and so the relative accessibility of thiocyanate post-perovskites has allowed for more detailed investigation of their magnetism. Pb[Zn(NCS) 4 ] comprises Pb(SCN) 6 octahedra and Zn(NCS) 4 tetrahedra, both significantly distorted and connected into neutral layers. Unlike the other discussed ternaries thus far, there are direct Pb-S-Pb connections in this structure and the PbS 2 substructure thus resembles a 2D perovskite with {110} type layers, e.g. the MnF 2 substructure in BaMnF 4 . MnHg 2 (SCN) 6 has a large number of distinct metal environments, with four different Hg sites and two different Mn sites. All Hg atoms form part of Hg 2 (SCN) 6 dimers of tetrahedra, with one dimer consisting of edge-sharing Hg(SCN) 4 tetrahedra linked through the S atoms, and the other containing one Hg(SCN) 4 tetrahedron and one Hg(NCS)(SCN) 3 tetrahedron, edge-sharing with one M-S-M bridge and one M-SCN-M bridge. One Mn is octahedrally coordinated and the other has unusual square pyramidal coordination. The Hg 2 dimers when considered as a unit are five or six coordinate, like the Mn ions, and are connected in an alternating fashion through the length of the thiocyanate ligand. The Hg 2 and Mn coordination polyhedra edge-share along the c-axis, but are corner-sharing along the a-axis. The five coordinate square pyramidal Mn and the five-coordinated Hg 2 dimer are aligned along the a-axis and hence only have half the interchain connections due to their reduced coordination numbers. The layer structure can therefore be related to the M(NCS) 3 layer found post-perovskite structure, though with considerable additional structural complexity. K[Ag(SCN) 2 ] is formed from AgS 4 tetrahedra which edgeshare through the S atom to create dimers, and then these dimers corner-share through the S atom to form infinite anionic sheets. The N-termini of the NCS -anions point into the interlayer gallery towards the K atoms. 202,203