Bismuth Chromothiocyanate, Bi[Cr(CNS)₆]

Bismuth Chromothiocyanate, Bi[Cr(CNS)₆], has also been described.

When a solution of potassium thiocyanate is added to a solution of bismuth thiocyanate, an orange-red coloration is obtained; various considerations have led to the view that solutions of bismuth thiocyanate in thiocyanic acid contain bismuthothiocyanic acids. It is suggested that in concentrated solutions an acid of the formula H[Bi(CNS)₄] is obtained, while in dilute solutions the tribasic acid, H₃[Bi(CNS)₆], is formed; in view of this, the formula of bismuth thiocyanate itself may be regarded as Bi[Bi(CNS)₆]. In support of this hypothesis, a number of complex thiocyanates have been prepared, which can be represented as salts of tribasic bismuthothiocyanic acid. By adding potassium thiocyanate to an aqueous solution of bismuth nitrate and mannitol, precipitating the mannitol and potassium nitrate by addition of alcohol, and crystallising from the filtrate, red, non-hygroscopic crystals of potassium bismuthothiocyanate, K₃[Bi(CNS)₆], are formed. Another potassium salt, K₃Bi(CNS)₆.3KCNS, has also been obtained. In a similar manner corresponding salts of sodium and ammonium have been prepared, although not in a pure condition. By adding thallium acetate to potassium bismuthothiocyanate in appropriate proportions two complex salts of potassium and thallium have been obtained, namely, the orange-yellow salt K₂TlBi(CNS)₆, and the pale yellow salt KTl₂Bi(CNS)₆. Attempts to make the pure thallium salt failed. Among other salts of this type that have been obtained are the zinc salt, Zn₃[Bi(CNS)₆]₂, as large, non-hygroscopic, orange-red crystals; the cobalt salt, Co₃[Bi(CNS)₆]₂.15H₂O, reddish-brown crystals, the colour of this salt supporting the view that a complex bismuth anion is formed, since Bi₂[Co(CNS)₄]₃ would presumably be dark blue; the nickel salt, Ni₃[Bi(CNS)₆]₂.10H₂O, greenish-yellow; the vanadyl salt, (VO)₃[Bi(CNS)₆]₂.7H₂O, a reddish-violet powder; and the ferric salt, Fe[Bi(CNS)₆], lustrous green crystals. The thallium salt of monobasic bismuthothiocyanic acid, Tl[Bi(CNS)₄], has also been formed as red crystals.