Inter- and intramolecular electron transfer in the complex OC···ICl determined from iodine and chlorine nuclear quadrupole hyperfine structure in its rotational spectrum

Abstract

The ground-state rotational spectra of three isotopomers O¹²C···I³⁵Cl, O¹²C···I³⁷Cl and O¹³C···I³⁵Cl of a linear (or quasi-linear) complex formed by carbon monoxide and iodine monochloride were observed by using a pulsed-nozzle, Fourier transform microwave spectrometer. The spectroscopic constants B₀, D_J, χ_aa(I), χ_aa(Cl) and M_bb(I) were determined for each isotopomer. Simple models were used to interpret the spectroscopic constants to give details of the geometry, binding strength and electric charge redistribution in OC···ICl. It was concluded that the nuclei lie in the order OC···ICl with the distance r(C···I)=3.011(1) Å, that the quadratic intermolecular stretching force constant k_σ=8.00(3) N m^-1, and that, when CO achieves its equilibrium position in the complex, the changes in the iodine and chlorine nuclear quadrupole coupling constants of ICl are consistent with the transfer of a fraction δ₁=0.025(2) of an electronic charge from C to I and an intramolecular transfer of a fraction δ₂=0.048(2) from I to Cl. A comparison of the r(C···X), k_σ and δ₂ values for the series of complexes OC···XY, where XY=ClF, Cl₂, BrCl, Br₂ and ICl is presented. The order of k_σ is ICl>ClF>BrCl>Br₂>Cl₂, while the order of δ₂ is Cl₂∽ClF<Br₂∽BrCl<ICl. It is deduced that ICl is ‘snub-nosed’, i.e. the I atom has a smaller van der Waals radius along the ICl internuclear axis than perpendicular to it.