Raman and infrared spectra and structure of some caesium monohalocyanoiodate (I) salts, Cs[XICN] (XCl, Br or I)

The [I2CN]− ion, previously only known in aqueous solution, has been isolated as its caesium salt; and the previously unknown [BrICN]− ions [ClICN]− have been isolated as their caesium salts. The Raman and IR vibrational spectra of these three caesium salts have been investigated in detail and indicate that the halide ions coordinate to the I atom of ICN to form linear (C∞ν) [X—I—CN]− ions (X=I, Br or Cl), contained in a centrosymmetric unit cell. This C∞ν structure is supported by a normal coordinate analysis for the [IICN]− ion.