W0165

Disproportionation of the Elements Sulfur and Iodine in Zeolite X. Karl Seff, Dept. of Chemistry, Univ. of Hawaii, Honolulu, Hawaii 96822, U.S.A., and Yang Kim, Dept. of Chemistry and Chemistry Institute for Functional Materials, Pusan National Univ., Pusan 609-735, Korea.

Sulfur and iodine each disproportionate fully upon sorption into fully dehydrated fully Cd²⁺-exchanged zeolite X to give (1) anions that are stabilized by coordination to the Cd²⁺ cations and (2) cations that associate with oxygens of the zeolite framework. The net reactions are

13 S₈ _ 24 S^2- + 4 S₄⁴⁺ + 16 n-S₄²⁺, and

7 I₂ _ 2 n-I₅^- + cyclo-I₄²⁺.

The four ions new to chemistry from these two reactions are tetrahedral S₄⁴⁺ (S-S = 2.17(2) Å, isostructural and isoelectronic with P₄ and Si₄^4-), n-S₄²⁺ (an electron deficient species whose terminal atoms each bond covalently to a framework oxygen), n-I₅^- (all bonds shorter than those in I₂(g), may be viewed as I^--I₃⁺-I^-), and rectangular planar (near square) cyclo-I₄²⁺. The unit-cell formula for the empty zeolite (Fd, a ca. 25 Å) is Cd₄₆Si₁₀₀Al₉₂O₃₈₄.

The main driving force for these reactions involves the coordination of the anion (S^2- or the terminal atoms of I^--I₃⁺-I^-) to the previously coordinatively unsaturated (three coordinate) Cd²⁺ ions. In addition, the zeolite is able to support and stabilize the product polyatomic cations in its rings and cavities.

Elemental disproportionation reactions are rare in chemistry. Only these were known before:

X₂ + H₂O _ HX + HOX, X = Cl and Br,

3I₂ + 3H₂O _ 5HI + HIO₃, and

2Na + cryptate _ Na⁺cryptate + Na^-.

Using zeolites, many more remain to be discovered.