The first class of missing binaries are those formed from the hard, oxophilic metals, where although M-NCS bonds are facile to form, M-SCN is not competitive with most solvents. There are two missing group 2 thiocyanates, Be(NCS) 2 and Mg(NCS) 2 . Beryllium thiocyanate complexes are known, 105 but the solid state preparation has rarely been attempted, and appears to be challenging. 106 Mg(NCS) 2 • xH 2 O has been extensively studied and investigation of its dehydration suggests that preparation of the anhydrate from the hydrate is not feasible and previous reports of Mg(NCS) 2 were erroneous. Likewise the oxophilicity of group 3 and lanthanide elements means hydrates are readily formed. Attempts to synthesize Sc(NCS) 3 from solution readily produce solvates of stoichiometry Sc(NCS) 3 L 3 , though a poorly characterized 'yellow scandium trithiocyanate' has been hinted at. Other group 3 and lanthanide binary thiocyanates are unknown, though many octahedral molecular solvates Ln(NCS) 3 L 3 and homoleptic anionic complexes with N-bound thiocyanate have been reported. Moving right along the periodic table, the synthesis of Ti(NCS) 4 has been reported by the desolvation of THF solvates at 150ºC under vacuum, producing a red-black crystalline powder. Analysis of the IR spectrum of Ti(NCS) 4 suggests octahedrally coordinated Ti cations with at least some bridging NCS -anions. These data thus imply the structure is more similar to TiF 4 , a 1D structure comprising corner-sharing TiF 6 octahedra, 113 rather than the later halides, TiX 4 , X = Cl, Br, I, which are all tetrahedral molecular materials, with no Ti-X-Ti bridges. There are no reports of Zr(NCS) 4 or Hf(NCS) 4 , though the DMF solvates of both are reported. It is worth noting that one of the few ways to readily separate Zr and Hf is by preparing the thiocyanato oxohydroxy metal complexes, and so it is possible that Zr(NCS) 4 and Hf(NCS) 4 will have different structures and chemistries. All binary group 5 thiocyanates are attested, with the most thoroughly investigated being V(NCS) 3 , which can be made through salt metathesis in diethyl ether between NaNCS and VCl 3 , producing a red-brown powder 119 . V(II) and V(IV) thiocyanate complexes are also stable, though only solvates have been reported. 120,121 Nb(NCS) 5 and Ta(NCS) 5 are reported to be dimers on the basis of IR spectroscopy, and were prepared by desolvation of the acetonitrile solvates. Group 6 binary thiocyanates are less well understood. Cr(NCS) 2 L 2 is well known for a range of solvents, but the ansolvate has not proved possible to prepare, likely in part due to the high sensitivity of Cr(II) to oxidation. Cr(NCS) 3 is reported to be a deliquescent dark green powder, though characterization is scant. A variety of solvated Mo(V) and W(VI) thiocyanates can be made through the reaction of K(NCS) or Na(NCS) with MoCl 5 and WCl 6 in organic solvents forming dark red (Mo) or dark brown (W) crystals, but desolvation was not possible by applying a vacuum. Oxothiocyanato metal complexes are common in these high oxidation states, 125-127 but lower oxidation-state molecular molybdenum and tungsten thiocyanate complexes with coligands and/or additional counter cations are common and can include metal-metal bonding. DFT investigations of the binary Mo(NCS) 2 and W(NCS) 2 suggest they are stable and adopt layered structures, analogous to the Hg(NCS) 2 structure, though with trigonal prismatic metal coordination and metal-metal bonding. The computational stability of these hypothetical layered structures relative to cluster structures, e.g. a M 6 (NCS) 12 hexametallic cluster, is not reported, despite these being the stable structures of the analogous halides. The 3d late transition metals all form divalent binary thiocyanates with the Ni(NCS) 2 structure, as described above, though other oxidation states are unknown except for hints of Fe(NCS 3 ) . The late 4d-and 5d-block binary metal thiocyanates are much less well understood in contrast. Technetium and rhenium thiocyanate complexes are known in a variety of oxidation states, 134,135 but there are no reports of the binary compounds aside brief discussion of an orange-red solid complex formed on reaction of ReO 4 with KNCS and SnCl 2 , of probably composition Re(NCS) 4 or ReO(NCS) 4 . Rh(NCS) 2 is reported to be a brown powder formed by the reaction of Rh 2 (CCl 3 COO 2 ) 4 dimers with potassium thiocyanate which is insoluble in water, though the presence of an infra-red absorption band at 1614 cm -1 suggests perhaps more extensive reaction than simple salt metathesis has occurred. The synthesis of Rh(NCS) 3 and Ru(NCS) 3 as orange-red (Rh) and dark brown (Ru) powders from the salt metathesis in acetonitrile between K(NCS) and the metal trihalide has been reported. There are no reports of the synthesis of binary Os(NCS)x or Ir(NCS)x though both are likely to be stable in the +3 oxidation state as implied by the existence of molecular [M(NCS) 6 ] 3 -anions 141,142 I note that Os(NCS) 3 is likely to be the best candidate for a magnetic ReO 3 -structured metal thiocyanate as it has the most extensive linkage isomerism with thiocyanate of any paramagnetic metal. 143 Pd(NCS) 2 , Pt(NCS) 2 and Au(NCS) have all been reported and chemical elemental analysis suggests they are pure phase compounds. Pd(NCS) 2 and Pt(NCS) 2 are reported from the thermal decomposition of M(NCS) 2 (NH 3 ) 2 . Aurous thiocyanate has also been reported to form as a white powder of by thermal decomposition of the organometallic complex [Et 2 Au(NCS)] 2 through addition to hot xylene (125ºC). Warning: the decomposition of the solid [Et 2 Au(NCS)] 2 at temperatures above 80ºC is reported to be explosive. 146 Au(NCS) 3 has been reported to form from the reaction of excess AuCl 3 with soluble alkali metal thiocyanate salts, though further detail of the synthesis and characterization is unreported. The only crystal structure of a group 13 binary thiocyanate is Tl(NCS), however many more should exist. A number of routes for the synthesis of In(NCS) 3 have been reported: salt metathesis in ethanol between Na(NCS) and InCl 3 ; metathesis in water between Ba(NCS) 2 and In 2 (SO 4 ) 3 ; reaction between In metal and Hg(NCS) 2 and sulfuration of In(CN 3 ). 147,148 Analysis of Xray powder diffraction measurements suggests cubic cell of 12 Å, which implies a ReO 3 -type model consisting of alternating InN 6 and InS 6 octahedra, though there is no atomistic structural model or quantitative refinement of the diffraction data. This structure would be related to the observed CsCd(NCS) 3 structure (Section 3.1). An analogous route to create Ga(NCS) 3 , that is the aqueous metathesis reaction between Ba(NCS) 2 and Ga 2 (SO 4 ) 3 , produced a hydrate with N-bound thiocyanate which could not be further dehydrated. The formation of a stable N-bound thiocyanate hydrate is also reported for aluminium, though again desolvation was not possible. The potential for Tl(III) or In(I) thiocyanates has not been extensively explored, though the aqueous reaction of TlCl 3 with KNCS has been reported to oxidize NCS -to HCN and H 2 SO 4 . In addition to the well-known Pb(NCS) 2 and Sn(NCS) 2 , group 14 metal thiocyanates with +4 oxidation state should be feasible. Sn(NCS) 4 is reported to form from the reaction of thiocyanogen (NCS) 2 and Sn(OH) 4 in ethereal solution, 152 though without any further characterization.