Nuclear Quadrupole Coupling in the Alkali Chloroiodides. II. Iodine Resonances

Abstract

Frequencies are reported for $\mathrm{m=\pm }\frac{1}{2}\mathrm{\leftrightarrow \pm }\frac{3}{2}$ transitions of I¹²⁷ nuclei in polycrystalline samples at 25°C of CsICl₂, RbICl₂, KICl₂, KICl₂·H₂O, CsICl₄, RbICl₄, KICl₄, KICl₄·H₂O, NaICl₄·2H₂O. The coaxial cavity super‐regenerative oscillator (250–610 Mc/sec) used for these measurements is described. The average quadrupole coupling constants are —3110 Mc/sec for ICl₂^— and +3090 Mc/sec for ICl₄^—. These values are shown to be entirely consistent with resonance hybrid structures which had been selected previously for the discussion of the chlorine resonance data. The coupling constants are used to estimate electron populations for valence orbitals of I and Cl, and, with certain assumptions, to find approximate MO's of LCAO form for the bonding electrons. The conclusion reached is that the attainment by iodine of higher valences in these ions is due more to transfer of charge to chlorine atoms than to promotion to higher orbitals of iodine. It appears that most of the covalent binding present arises from an MO in which an iodine p orbital is associated with a symmetry orbital made up of collinear sp hybrid orbitals of two attached chlorine atoms.