Cross-linking silica aerogels with organic groups has been shown to improve the strength over un-cross-linked aerogels by as much as 2 orders of magnitude. Previous cross-linking chemistry has been developed using solvents specifically chosen to dissolve the monomers and accommodate the reaction temperature. Because the process of making the aerogels requires so much solvent, it is of interest to consider less toxic solvents such as ethanol to increase safety and enhance scale up. To this end, two different epoxy precursors with suitable solubility in ethanol were evaluated as cross-linkers for silica gels prepared from (3-aminopropyl)triethoxysilane and tetraethylorthosilicate. In addition, 1,6-bis(trimethoxysilyl)hexane (BTMSH) was used as an additive in the underlying silica structure to add flexibility to the aerogels. It was found that the ethanol-derived aerogels exhibited more shrinkage than those prepared from other solvents but that including BTMSH in the aerogels significantly reduced this shrinkage. Inclusion of BTMSH also imparted the ability of the aerogel monoliths to recover elastically when compressed up to 50% strain. In addition, optimized cross-linked aerogels prepared in this study have mechanical properties comparable to those using other more undesirable solvents and cross-linkers.

Treatment of bis(phosphine)platinum(II) carbonate complexes (LL)Pt(COs) (e.g., LL = 1,3-bis(diphenylphosphino)propane) with vicinal diols (Le., HOCR1R2CR3R40H) gives equilibrium conversion to the corresponding diolate complexes (LL)Pt(OCR'RZCR3RQ), which are readily isolated in good yield. From competition experiments, relative diol complexation constants were determined as a function of both the diol and the phosphine substituents and found to span a range of over 104. Corresponding triolate and alditolate complexes were similarly prepared, for which very distinct equilibrium isomeric regioselectivities are observed, favoring complexation of y,b-threo diols. An X-ray structure of (dppp)Pt(D-mannitolate) shows that the mannitol is bonded to the platinum as its dianion via the oxygens on C3 and C4 to form a 2,5-dioxaplatinacyclopentane chelate ring and that three different strong intramolecular hydrogen-bonding interactions are present between the hydroxyl hydrogens and the metallacycle oxygens (O*-O (av) = 2.65(2) A), forming five-, six-, and seven-membered rings. Crystal data for P~P z O & H~& H~C~Z : P212121,Z = -4, T = 20 OC, a = 11.225(2) A, b = 15.875(3) A, c =

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