The second most common structure type is the 3D Ba(NCS) 2 structure which forms for the alkaline earths Ca, Sr, Ba, and other large divalent cations such as Pb and Eu (Fig. ). They all crystallize with the C2/c space group and contain one crystallographically independent M 2+ cation and NCS -anion. Each M cation is coordinated by four N atoms and four S atoms in a distorted square antiprism. These polyhedra edge-share along the c-axis through N atoms, and corner-share in the ab-plane. Each NCS -anion is coordinated by four M 2+ cations in a distorted tetrahedron, and simplification of the structure by considering only the centre-of-mass of the NCS -anion reveals a distorted fluorite structure. These compounds can be synthesized by reaction between NaNCS and MCl 2 in sealed glass ampoules. Ba(NCS) 2 , Ca(NCS) 2 and Pb(NCS) 2 can be formed through dehydration of the readily synthesisable hydrates. Ba(NCS) 2 • 3 H 2 O is a convenient starting point from any thiocyanate that is synthesized in water due to the insolubility of BaSO 4 . Eu(NCS) 2 is the only known binary thiocyanate containing a paramagnetic ion that does not adopt the Hg(NCS) 2 structure, though its magnetic properties have not been reported. As an isotypic family, Eu(II) can be doped into the other non-fluorescent members hosts to produce materials with green fluorescence at low temperatures. 59,60