A π-electron donor–acceptor complex of ethene and iodine monochloride: geometry, binding strength and charge redistribution determined by rotational spectroscopy

An ethene/ICl complex was characterised by rotational spectroscopy. Rotational constants, centrifugal distortion constants and halogen nuclear quadrupole coupling constants of C2H4⋯I 35Cl and C2H4⋯I 37Cl were interpreted to establish several conclusions. The ICl molecule lies along the C2 axis perpendicular to the nuclear plane of ethene, with I nearer to the π bond than Cl and r(*⋯I)=3.033(2) Å (* is the centre of the π bond). An estimated 0.054 e− is transferred from ethene to I on complexation, while the ICl polarisation is represented as a transfer 0.080 e− from I to Cl. Hence the net change at I is −0.026 e−. The binding of C2H4⋯ICl is stronger than for other C2H4⋯XY.