This study investigates the formation of amorphous tetravalent metal hydroxides, M(OH)4, based on the structural analysis by small- and wide-angle X-ray scattering (SWAXS) and on the electrical potential charge near the surface of M(OH)4 particles. The amorphous zirconium hydroxide solid phases that aged in NaCl and CaCl2 solutions at 25 °C exhibited a hierarchical structure consisting of primary particles of a few nanometers in size and their aggregates more than 100 nm in size. The SWAXS profiles suggested that the size of the primary particles depends on the ionic strength and electrolytes in the sample solutions. The smaller size of the primary particles observed in solutions with higher ionic strength can be explained by the thinner electrical double layer. Additionally, we focused on the ζ potentials of M(OH)4 suspensions in NaCl, NaNO3, and CaCl2 solutions. With the aid of reference systems of metal oxides, MO2, it was found that the ζ potentials were well interpreted by a traditional surface ionization and complexation model, and the size distributions of large aggregates were explained by the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory with the ζ potential values. The present study suggests the formation mechanism of amorphous metal hydroxides through a combination of structural analysis and investigation of electrical potentials.

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Facile methods for the introduction of alkenyl and alkynyl groups at the bridgehead position of polysilamodule HC(SiMe 2 SiMe 2 ) 3 CH are established. Deprotonation of the module with BuLi/t-BuOK in THF at -40°C followed by alkylation with bromoacetaldehyde diethyl acetal gives the corresponding acetal, which was hydrolyzed with zinc chloride, yielding a formylmethylsubstituted cage compound. Treatment of the aldehyde with triflic anhydride in the presence of 2,6-di-t-butyl-3-methylpyridine produced the corresponding enol triflate consisting of a 4:1 mixture of E and Z isomers. Palladium-catalyzed cross-coupling of the triflate with organometallic reagents afforded alkenyl group-substituted cage molecules in good yields. Meanwhile, lithiation of phenylthiosubstituted cage derivative with lithium 4,4¢-di-tert-butylbiphenylide in THF followed by transmetalation with copper iodide and subsequent coupling with iodoalkynes allowed us to prepare alkynyl-substituted polysilacage compounds. The structures were determined by X-ray diffraction of single crystals.Since s-electrons of Si-Si bonds in polysilanes can delocalize, compounds containing Si-Si bonds show unique electronic and optical properties resulting from the delocalization of s-electrons. 1 Exploration of new siliconbased organic materials has led us to design 2,3,5,6,7,8-hexasilabicyclo[2.2.2]octane 1 which bundles three parallel Si-Si bonds in a three-dimensional manner and to achieve its facile synthesis (Figure 1). 2 Bridgehead-silylated or -stannylated derivative 2 or 3 exhibited a red shift of UV absorption maxima compared to parent compound 1, 2a while s-p electronic interaction between the polysilacage moiety and a phenyl group at the bridgehead position was found operative by UV spectra of arylated derivatives C n H 2n+1 C(SiMe 2 SiMe 2 ) 3 CAr 4. 3 To gain further insights into s-p conjugation 4 between the cage moiety and a pconjugated system at the bridgehead position, it is intriguing to connect a p-conjugated moiety to the polysilacage module via a carbon-carbon unsaturated group. We report herein the facile synthesis of alkenyl-and alkynyl groupsubstituted polysilacage compounds 5 and 6, respectively, and their molecular structures determined by X-ray diffraction. Figure 1 Polysilacage compoundsAt the outset, we studied the introduction of a carbon-carbon double bond into 1. Since nucleophilic substitution at an sp 2 carbon is generally difficult to perform, we designed an indirect strategy for the purpose. Thus, 1 was first deprotonated with BuLi/t-BuOK in THF at -40°C and trapped with bromoacetaldehyde diethyl acetal, giving rise to acetal 7 in 70% yield (Scheme 1). Hydrolysis of 7 with zinc chloride gave formylmethyl-substituted cage compound 8 in 87% yield. Treatment of 8 with triflic anhydride in the presence of 2,6-di-t-butyl-4-methylpyridine produced enol triflate 9 consisting of a 4:1 mixture of E and Z isomers in 74% yield. Since recrystallization of 9 from hexane afforded E-isomer (mp 175.5-176.5°C) as single crystals, the structure w...

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