These complexes have few applications but played significant role in the development of coordination chemistry.
[1] Hard metal cations, as classified by HSAB theory, tend to form N-bonded complexes (isothiocyanates), whereas class B or soft metal cations tend to form S-bonded thiocyanate complexes.
[10] Thiocyanate shares its negative charge approximately equally between sulfur and nitrogen.
For example, [Co(NH3)5(NCS)]2+ is the thermodynamic isomer, but [Co(NH3)5(SCN)]2+ forms as the kinetic product of the reaction of thiocyanate salts with [Co(NH3)5(H2O)]3+.
Examples are found for heavy metals in the middle of the d-period: Ir(III),[13] and Re(IV).
Copper(I) thiocyanate is a reagent for the conversion of aryl diazonium salts to arylthiocyanates, a version of the Sandmeyer reaction.
A cobalt-containing hydrolase catalyzes its conversion to carbonyl sulfide:[17] A copper-containing thiocyanate hydrolase catalyzes its conversion to cyanate:[18] In both cases, metal-SCN complexes are invoked as intermediates.
An unusual route to thiocyanate complexes involves oxidative addition of thiocyanogen to low valent metal complexes:[21] Even though the reaction involves cleavage of the S-S bond in thiocyanogen, the product is the Ru-NCS linkage isomer.
In another unusual method, thiocyanate functions as both a ligand and as a reductant in its reaction with dichromate to give [Cr(NCS)4(NH3)2]−.