Four novel multifunctional polyoxometalate (POM)-based inorganic-organic hybrid compounds, [α(2)-P(2)W(17)O(61){(RGe)}](7-) (Ge-1, R(1) = HOOC(CH(2))(2(-)) and Ge-2, R(2) = H(2)C═CHCH(2(-))) and [α(2)-P(2)W(17)O(61){(RSi)(2)O}](6-) (Si-1, R(1) and Si-2, R(2)), were prepared by incorporating organic chains having terminal functional groups (carboxylic acid and allyl groups) into monolacunary site of Dawson polyoxoanion [α(2)-P(2)W(17)O(61)](10-). In these POMs, new modification of the terminal functional groups was attained by introducing organogermyl and organosilyl groups. Dimethylammonium salts of the organogermyl complexes, (Me(2)NH(2))(7)[α(2)-P(2)W(17)O(61)(R(1)Ge)]·H(2)O MeN-Ge-1 and (Me(2)NH(2))(7)[α(2)-P(2)W(17)O(61)(R(2)Ge)]·4H(2)O MeN-Ge-2, were obtained as analytically pure crystals, in 22.8% and 55.3% yields, respectively, by stoichiometric reactions of [α(2)-P(2)W(17)O(61)](10-) with separately prepared Cl(3)GeC(2)H(4)COOH in water, and H(2)C═CHCH(2)GeCl(3) in a solvent mixture of water/acetonitrile. Synthesis and X-ray structure analysis of the Dawson POM-based organogermyl complexes were first successful. Dimethylammonium salts of the corresponding organosilyl complexes, (Me(2)NH(2))(6)[α(2)-P(2)W(17)O(61){(R(1)Si)(2)O}]·4H(2)O MeN-Si-1 and (Me(2)NH(2))(6)[α(2)-P(2)W(17)O(61){(R(2)Si)(2)O}]·6H(2)O MeN-Si-2, were also obtained as analytically pure crystalline crystals, in 17.1% and 63.5% yields, respectively, by stoichiometric reactions of [α(2)-P(2)W(17)O(61)](10-) with NaOOC(CH(2))(2)Si(OH)(2)(ONa) and H(2)C═CHCH(2)Si(OEt)(3). These complexes were characterized by elemental analysis, thermogravimetric and differential thermal analyses (TG/DTA), FTIR, solid-state ((31)P) and solution ((31)P, (1)H, and (13)C) NMR, and X-ray crystallography.

Curium-doped titanate ceramic containing sodium-rich high-level nuclear waste showed a gradual decrease in density up to a dose of 8.5 X 1017 a decays ng-'. After that, the rate of density change increased apparently because of crack formation. Optical microscopy showed cracks >0.1 mm long and > I pm wide after a dose of 7.9 X lo" a decays-g-'.Leach tests suggested that the dissolution-control phases for sodium and cesium changed from freudenbergite and hollandite, respectively, to intergranular phases after significant cracking. Aging also enhanced strontium losses, relative to calcium, indicating that strontium may also be partitioned to the intergranular phases. After the fresh surfaces produced by cracking were exposed to leachant, and the dissolution of soluble intergranular surfaces was complete, the leaching of nonradioactive elements from the samples having a dose of 12.3 X lOI7 a decays. g-' was limited by the following dissolution-control phases: freudenbergite (Na), hollandite (Cs and Ba), perovskite and/or zirconolite (Sr and Ca), and alloys (Mo). The leaching behavior of the nonradioactive indicator elements revealed that chemical durability was reduced by two main factors: (1) increasing the effective surface area by crack formation and (2) decreasing the stability of the actinide-host phases by n-recoil damage. In combination these factors increased longer-term (>7 days) leach rates of sodium and cesium, and strontium and calcium by 1 and 2 orders of magnitude, respectively. In spite of deterioration of the actinide-host phases, the curium leach rate after a dose of 12.3 X 10" a decaysg -' decreased by 2 orders of magnitude, possibly as a result of precipitation of curium hydrolysis products. [

A polyphase titanate ceramic incorporating sodium-free simulated high-level nuclear waste was doped with 0.91 wt% of 244Cm to accelerate the effects of long-term selfirradiation arising from (Y decays. The ceramic included three main constituent minerals: hollandite, perovskite, and zirconolite, with some minor phases. Although hollandite showed the broadening of its X-ray diffraction lines and small lattice parameter changes during damage ingrowth, the unit cell was substantially unaltered. Perovskite and zirconolite, which are the primary hosts of curium, showed 2.7% and 2.6% expansions, respectively, of their unit cell volumes after a dose of 12 X l O I 7 (Y decayvg-'. Volume swelling due to damage ingrowth caused an exponential (almost linear) decrease in density, which reached 1.7% after a dose of 12.4 X l O I 7 a decaysg-'. Leach tests on samples that had incurred doses of 2.0 X 1017 and 4.5 X l O I 7 a decays.g-' showed that the rates of dissolution of cesium and barium were similar to analogous leach rates from the equivalent cold ceramic, while strontium and calcium leach rates were 2-15 times higher. Although the curium, molybdenum, strontium, and calcium leach rates in the present material were similar to those in the curium-doped sodiumbearing titanate ceramic reported previously, the cesium leach rate was 3-8 times lower.