Transition metal complexes with thiocyanates

The initial step of the reaction with tin(II) chloride reduces the highly oxidized metal in the transition metal anions to low valency cations these are capable of forming stable colored complexes with thiocyanate. 

Polymeric complexes of 1-phenyltriazole with transition metal cyanates or thiocyanates are structurally and stereochemi ly understood (80MI41200) and an antiferromagnetic complex of triazole is of potential technical interest (80ZN(A)1387). 

Transition Metal Complexes Related to the Simon test is a family of color-producing reactions based on transition metal complexes (coordination complexes) and tightly associated ion pairs. Coordination complexes arise from a Lewis acid-base interaction between a metal cation, such as cobalt, and an atom with unshared electrons, such as water or, in the case of drugs, basic nitrogen found in alkaloids and amines. Metals that have been used in these reagents include copper, vanadium, bismuth, and cobalt Cobalt, as part of two common reagents (cobalt thiocyanate and Dilli-Koppanyi) is perhaps the most versatile. Cobalt has an electron structure of 3d 4s, while ttie cation has a 3d (2 ) or 3d (3 ") structure. 

Although thiocyanate with neutral amines (bases) has been investigated intensively with transition metals, knowledge of the respective thiocyanates with cationic amines is very limited and, in particular, with the hydrazinium cation is almost unknown. The absence of reports on the hydrazinium metal complexes of thiocyanates is not surprising as the usual method of preparation from aqueous solutions of the metal thiocyanates and hydrazinium thiocyanate always yields metal thiocyanate hydrazines. The first examples in which the hydrazinium cations are coordinated to the metal in the cis... 

Thiocyanates are rather stable to air, oxidation, and dilute nitric acid. Of considerable practical importance are the reactions of thiocyanate with metal cations. Silver, mercury, lead, and cuprous thiocyanates precipitate. Many metals form complexes. The deep red complex of ferric iron with thiocyanate, [Fe(SCN)g] , is an effective iadicator for either ion. Various metal thiocyanate complexes with transition metals can be extracted iato organic solvents. 

Uniformly, within this group of cations, perchlorate ion accompanying the transition-element cation is replaced by nitrate (7,31), thiocyanate (7,52), or halide (7,6). Nitrate is probably replaced by thiocyanate, but a secondary change takes place in many systems, which makes direct comparison difficult (see below). If one then makes the further reasonable assumption that solvent interference can be used as an inverse measure of tendency to bind to the central metal cations, thiocyanate, whose competition with alcohol is less efficient (52) than that of chloride (6), should be somewhat replaceable with chloride. Comparisons between chloride and thiocyanate in acetonitrile show also that the formation of a complex with a given anion/cation ratio takes place much more readily with chloride than with thiocyanate (55, 34). By the same criterion, from experiments in alcoholic solution (55), bromide should replace chloride, and an extrapolation of the behavior to iodide seems reasonable. 

Bautista and Hard (B8) made a comparative study of the extractability of. several of the first-transition metals from thiocyanate solutions using methyl isobutyl ketone as the organic solvent. The transition metals readily extracted were scandium (III), iron (III), and cobalt (II) while chromium (II) and manganese (II) were not. The principal extractable species were found to be the neutral scandium and iron trithiocyanate complexes, while the extractable cobalt complex was the negatively charged tetrathiocyanate radial Co(SCN)4 . The distribution ratio for scandium, iron, and cobalt decreased with increase in metal ion concentrar tion but increased with increasing ionic strength of the solutions. 

TABLE 8. Complex of nitrile oxides, organic thiocyanates, isocyanates and isothiocyanates with transition metals... 

---