the elements determined, in spite of substantial variations between bulk Allende and that meteorite's spheroidal Ca-Al-rich inclusions (Chou et al., 1976). ACKNOWLEDGMENTS.-We are indebted to R. Bild, R. Glimp, J. Kimberlin, K. Robinson, and L. Sundberg for assistance. Neutron irradiations at the UCLA and Ames Laboratories reactors were handled by J. Brower and A.F. Voight and their associates. This work was supported by NSF Grant GA 32084. 1450±40 c , 1400 e , 1300 f , l700 g 3370±100 c , 3300±100 d , 3300', 3000 f 200 e , 250 f , 1800±1200 g 130±22 c , 70 e , l70 f 3680±100 c , 3900±100 d , 3600 e , 4200 f , 4200 g 640±20 c , 650±40 d , 600 e , 700 f , 600 g 11.0±0.5 c , 12.2±0.2 d , ll e , 10 g 0.027±0.001 c 0.19±0.01 c 3.0±0.1 c , 2 e 0.44±0.02 c , 0.7 e 1.25±0.06 c , l e 0.20±0.01 c , 0.2 e 0.91±0.05 c , 0.9 e 0.29±0.01 c , 0.5 e 0.107±0.005 c ,0.1 e 0.43±0.02 c , 0.6 e 0.074±0.005 c , 0.09 e 0.42±0.02 c , 0.6 e 0.12±0.1 c ,0.1 e 0.31±0.02 c , 0.3 e 0.049±0.001 c 0.32±0.02 c , 0.4 e 0.058±0.002 c * The In value determined for 10-2 is 0.02±0.01; the large error limit is imposed due to an analyzer malfunction during counting. b The Cd value for 12-2 could not be determined because of a laboratory accident during the chemical processing.

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The electronic structures of mixed-valence heteropoly 12-molybdo phosphate anions (heteropoly blues) were investigated by electronic absorption spectroscopy and by 17 O and 31 P NMR spectroscopy in aqueous and acetonitrile solutions. The one-, two-, and four-electron reduced forms of a-PMo12O403-(aI, aII, and aIV), are shown to retain, on the NMR time scale, the tetrahedral symmetry of the ox idized Keggin structure. These anions are class II mixed-valence spe cies, with the additional electrons weakly trapped on molybdenum centers. The particularly stable four-electron reduced species β-Η χΡΜo12O40(7-x)-(βIV) is derived from the C3v isomer of the Keggin structure. This anion is shown, on the basis of its intense narrow optical absorption band, 17 O NMR, and anomalous 31 P chemical shift, to contain delocalized valences (class III). Upon deprotonation, βIV reverts to a class II species with "normal" spectroscopic properties.

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