A pi-electron donor-acceptor complex of ethene and iodine monochloride: geometry, binding strength and charge redistribution determined by rotationalspectroscopy

An ethene/ICl complex was characterised by rotational spectroscopy. Rotatio nal constants, centrifugal distortion constants and halogen nuclear quadrup ole coupling constants of C2H4... (ICl)-Cl-35 and C2H4 ... (ICl)-Cl-37 were interpreted to establish several conclusions. The ICl molecule lies along the C-2 axis perpendicular to the nuclear plane of ethene, with I nearer to the pi bond than Cl and r(*... I) = 3.033(2) Angstrom (* is the centre of the pi bend). An estimated 0.054 e(-) is transferred from ethene to I on co mplexation, 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. (C) 1999 Elsevier Scienc e B.V. All rights reserved.