Compounds that resemble the halogen elements, $\ce{X2}$, in their chemistry, e.g. $\ce{(CN)2}$ cyanogen, $\ce{(SCN)2}$ thiocyanogen, $\ce{ICN}$ iodine cyanide. Certain ions that have sufficient resemblance to halide ions are sometimes referred to as pseudohalide ions, e.g. $\ce{N3^{−}}$, $\ce{SCN^{−}}$, $\ce{CN^{−}}$.