Nuclear Quadrupole Coupling in the Alkali Chloroiodides. I. Chlorine Resonances

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Abstract
Chlorine resonance frequencies are reported for the following at 298°, 194°, and 77°K: CsICl2, KICl2, KICl2·H2O, CsICl4, RbICl4, KICl4, KICl4·H2O, NaICl4·2H2O. Variations due to crystal effects in these substances amount in most cases to less than a megacycle. The average frequencies at room temperature, 19.2 and 22.3 Mc/sec, are taken as representative of ICl2— and ICl4— ions, respectively, in a crystalline environment. These values are in the neighborhood of half those found for ICl, and suggest a bonding scheme in which the electron distribution is shifted outward toward the chlorine atoms to such an extent that the electron population of iodine orbitals is not so large as to require the use of d orbitals. The conclusion is that d orbitals are rather less important to bonding in the polyhalides than has generally been supposed. The problem of arriving at a practical and meaningful separation of crystal and chemical effects is considered qualitatively, and marked crystal effects evident in the spectra of KICl4·H2O and NaICl4·2H2O are briefly discussed.

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