Polyiodides (Inx-) are a class of polyhalogen anions composed of entirely iodine atoms. These ions have varied structural forms and generally explored for their conducting properties. Their structural stability depends on the cations employed for their crystallization. Triiodide (I3-) is an anion derived from the reaction of iodine (I2) and the iodide (I-) ion. In the solid state, the triiodide ion crystallizes as a linear ion of symmetrical I-I bonds, but deviations from symmetry are observed with change in the counter cation
Polyiodides (Inx-) are a class of polyhalogen anions composed of entirely iodine atoms. These ions have varied structural forms and generally explored for their conducting properties. Their structural stability depends on the cations employed for their crystallization. Triiodide (I3-) is an anion derived from the reaction of iodine (I2) and the iodide (I-) ion. In the solid state, the triiodide ion crystallizes as a linear ion of symmetrical I-I bonds, but deviations from symmetry are observed with change in the counter cation.
a) With smaller cations (NMe4+ or Cs+), an unsymmetrical triiodide ion is generally expected; while a more symmetrical one is derived using larger cations (NEt4+, AsPh4+). Rationalize this observation.
b) Potassium is a considerably smaller ion as compared to cesium. Thomas and Moore reported neutron studies (Acta Crystallogr. 1980, B36, 2869) of KI3.H2O and found that the I-I bonds are almost symmetrical. Explain this observation. If you were to dissolve some crystals of KI3.H2O in methanol to make saturated solution and allow new crystals to grow, what changes in the I-I bond lengths will you be expecting? Why?
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