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

Abstract

Chlorine resonance frequencies are reported for the following at 298°, 194°, and 77°K: CsICb, KICb, KICb·H20, CsICI" RbICI" KICl" KICI,·H20, NaICI,·2H20. 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 Me/sec, are taken as representative of ICb-and ICI,-ions, respectively, in a crystalline environment. These values are in the neighborhood of half those found for ICI, 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 KICI,· H20 and NaICI,· 2H20 are briefly discussed. *

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“…Table I summarizes important structural data for sulfuranes. Theoretical calculations (43) have suggested that d-orbitals and higher s-orbitals do not make energetically significant contributions to the wave functions describing hypervalent species. Nuclear quadrupole coupling (44) and Mossbauer spectroscopy (45) of halogen analogs of the sulfuranes and photoelectron spectroscopy of SF4 (46) provide experimental justification for an approximate bonding picture that describes the three-center four-electron bond without invoking d-orbital character.…”

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“…Os espectros Raman dos quatro complexos apresentaram, de fato, as três frequências ativas no Raman esperadas pela simetria D 4h : estiramento simétrico (A 1g ), estiramento anti-simétrico (B 2g ) e dobramento de ângulo no plano (B 1g ). 40 No caso do íon poli-halogênio (ICl 4 ) -, Stammreich 42,43 Isto motiva a análise de coordenadas normais realizada por Stammreich et al: 44 obter indícios sobre a natureza da ligação química a partir das constantes de força dos íons poli-halogênios. As frequências vibracionais dos modos de estiramento simétrico ν 1 e antissimétrico ν 3 observadas, respectivamente, nos espectros Raman e infravermelho dos íons triatômicos (ICl 2 ) -, (BrCl 2 )e (Br 3 )prontamente permitem obter as constantes de força do estiramento X-Y, f r , e a constante de interação entre as ligações adjacentes, f rr , de um campo de força de valência.…”

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“…The substance KICl4*H 2 0 has been thoroughly studied by the technique of nuclear quadrupole resonance. 15 The bonding of the iodine results in a local excess of negative charge above and below the molecular plane. That is eq=d 2 V/dz 2 <0.…”