Preparation and vibrational spectra of N(CH3)4+IF2- and electronic structure calculations of IF2-, BrF2-, ClF2-, XeF2 and KrF2

The new IF(2)(-) salt, N(CH(3))(4)IF(2), was prepared in quantitative yield and high purity from commercially available N(CH(3))(4)I and XeF(2) at -31 degrees C in CH(3)CN solution. Its vibrational spectra were recorded and, combined with correlated ab initio calculations at the MP2/SBK + (D) and CCSD(T)/SBK + (D) levels of theory for IF(2)(-), BrF(2)(-), ClF(2)(-), XeF(2) and KrF(2), show that the infrared spectrum previously reported for IF(2)(-) is in error. The antisymmetric stretching modes in IF(2)(-) and BrF(2)(-) have lower frequencies than the symmetric ones. This highly unusual fact can be explained by mass effects and the enhancement of semi-ionic, 3 center-4 electron bonding by the antisymmetric stretching motion. (C) 1998 Elsevier Science S.A. All rights reserved.