P, Si, Ge, B) and a monovacant Dawson derivative anion P2W1706i10-were adopted as the ligand for cerium(III). The formation of the complexes [CeL]lm-3)-and [CeL2]<2m-3>-was confirmed by means of absorption spectroscopy, where Lm~denotes an unsaturated heteropolytungstate anion of P, Si, or Ge, while clear evidence for the complexation of BW11O399-was not obtained. Electrochemical behaviors of heteropolytungstocerates(III) were studied by cyclic and differential pulse voltammetry in aqueous solution. The redox potential of the cerium(IV/III) couple was considerably lowered (below +1 V vs Ag/AgCl) upon coordination of heteropolytungstate in aqueous solution at pH 4.5. The magnitude of the potential shift for [CeL]lm"3>" increased in the order PWnOgg7-, P2W1706i10-, GeWnOag8-, and SiWuOag8-. A similar trend was observed for [CeL2]12m-3>-with larger potential shift than those of [CeL]lm-3>-. The shift of the redox potential for cerium(IV/III) is caused primarily by the large negative charge of the unsaturated heteropolytungstate.

Atomic hydrogen has been stably encapsulated in both solution and crystal at room temperature. Upon gamma-ray irradiation of [(CH(3))(3)Si](8)Si(8)O(20), which is the trimethylsilylated derivative of the silicate anion with a double four-ring (D4R) cage, electron spin resonance (ESR) spectra revealed that a single hydrogen atom is encapsulated in the center of the D4R cage and is stable for periods of many months. Attack by chemically reactive species such as oxygen was prevented by the D4R cage, but the ESR signal of the hydrogen atom was sensitive to the magnetic interaction caused by the presence of the O(2) molecule near the cage.

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