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, DJ, χaa(I), χaa(Cl) and Mbb(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) A, that the quadratic intermolecular stretching force constant kσ=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), kσ and δ2 values for the series of complexes OC···XY, where XY=ClF, Cl2, BrCl, Br2 and ICl is presented. The order of kσ 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.