Synthesis and vibrational spectroscopic study of compounds containing the I(SCN)2–, I2(SCN)–, and I(SeCN)2– ions

Abstract

The salt [N(PPh₃)₂][I(SCN)₂] has been prepared by addition of thiocyanogen to [N(PPh₃)₂]I. Bands due to the ν(CN) and ν(IS) vibrations of the I(SCN)₂^– ion have been assigned in the i.r. and Raman spectra of this compound, and the results indicate a structure in which the S atoms of the SCN groups are bound to the iodine atom to give a linear or almost linear S–I–S arrangement. The stretching and interaction force constants for the S–I–S group are similar to those for the trihalide ions IX₂^–(X = CI, Br, or I). The salt [N(PPh₃)₂][I₂(SCN)] could not be obtained as a pure compound, but has been obtained as a mixture with the I₃^– and I(SCN)₂^– salts in several synthetic experiments. Bands due to the I₂(SCN)^– ion could be identified in the low-frequency vibrational spectra of these mixtures, and these indicate that this ion has an unsymmetrical structure with an I–I–S arrangement. The salt [N(PPh₃)₂][I(SeCN)₂] has been prepared by addition of selenocyanogen to [N(PPh₃)₂]I. The vibrational spectra of this compound do not allow definite conclusions to be drawn about the structure of the I(SeCN)₂^– ion.