Organic and transition metal derivatives of the thiocyanate ion can exist as "linkage isomers". In thiocyanates, the organic group (or metal ion) is attached to sulfur: R−S−C≡N has a S–C single bond and a C≡N triple bond.[2] In isothiocyanates, the substituent is attached to nitrogen: R−N=C=S has a S=C double bond and a C=N double bond: