Germanium(II)‐, Zinn(II)‐ und Blei(II)‐Derivate des polycyclischen Alumosiloxans [Ph2SiO]8[Al(O)OH]4

Germanium(II)‐, Tin(II)‐ and Lead(II)‐Derivatives of the polycyclic Alumosiloxane [Ph₂SiO]₈[Al(O)OH]₄ Five new derivatives of the polycyclic alumosiloxane [Ph₂SiO]₈[Al(O)OH]₄ have been synthesized by replacement of the protic hydrogen atoms on the hydroxy‐groups attached to the aluminium atoms by the divalent group 14 elements germanium, tin and lead. The compounds can be divided in those with one metal atom per alumosiloxane moiety, [Ph₂SiO]₈[Al(O)OH]₂[AlO₂]M (M=Ge, Sn), and those with complete substitution of the protic hydrogen atoms by metal atoms like [Ph₂SiO]₈[AlO₂]₄M₂ (M= Sn, Pb). Always one element of the series Ge, Sn, Pb is missing in the two types of compounds. Crystal structure analyses of [Ph₂SiO]₈[Al(O)OH]₂[AlO₂]₂M · 2 C₄H₈O₂ (M= Ge ( 1 ), Sn ( 2a )), [Ph₂SiO]₈[Al(O)OH]₂[AlO₂]₂Sn · 2 THF ( 2b ) and [Ph₂SiO]₈[AlO₂]₄M₂ (M= Sn ( 3 ), Pb ( 4 )) have been performed elucidating either polycyclic basket‐type ( 1 , 2a , 2b ) or closed polyhedral structures ( 3 , 4 ).     

Hybrid sol–gel coatings doped with transition metal ions for the protection of AA 2024-T3

The protective capabilities of sol–gel coatings are determined by their physical barrier properties. For an effective protection, a homogenous crack-free material is required, which prevents from attacks of corrosive species. When the coating is damaged, active corrosion protection is usually achieved by the use of inhibitors. Among the different inhibitors rare earth ions and especially cerium have shown effective inhibiting properties. Due to the complexity of the corrosion processes, a combination of inhibitors is expected to be superior to a monocomponent inhibiting. The aim of this study was to prove which other ions, used in combination with cerium, can improve the corrosion protection abilities of hybrid silica based inorganic–organic sol–gel coatings applied on aluminium alloy 2024 substrates. Mixtures of cerium nitrate with two other potential inhibitor substances were incorporated into a sol–gel matrix and their behaviour in neutral salt spray test and during EIS measurements was investigated. The Ce–P–Pr inhibitor combination (Ce³⁺, PO₄ ³⁻, Pr³⁺) has shown the best long-term corrosion protection properties at low doping levels.     

Two new metal derivates of the alumosiloxane [Ph2SiO]8[AlO(OH)]4: [Ph2SiO]8[AlO2(Na)]4 · 5(THF) and [Ph2SiO]8[AlO(OH)]2[AlO2]2[Zn(OH)]2 · 2(OEt2)

When the polycyclic alumosiloxane [Ph₂SiO]₈[AlO(OH)]₄ is allowed to react with either cyclopentadienyl sodium in tetrahydrofuran or with dimethyl zinc in diethyl ether the organic ligands on the metal elements are eliminated as cyclopentadiene or methane and the metals are bonded to oxygen atoms in the alumosiloxane forming [Ph₂SiO]₈[AlO₂(Na)]₄ · 5(THF) or [Ph₂SiO]₈[AlO(OH)]₂[AlO₂]₂[Zn(OH)]₂ · 2(OEt₂), respectively. X-ray structure determinations reveal that in the sodium derivative the original polycycle rests almost unchanged while in the zinc derivative the inner skeleton is rearranged.     

POLYCYCLES AND CAGES IN MOLECULAR ALUMO-POLYSILOXANES—(Ph2SiO)8[Al(O)OH]4 Used as a Supramolecular Target and “Auto-Condensation” Within the Molecule

In this preliminary review the reaction of [Ph₂SiO]₈[AlO(OH)]₄ toward 1,3-diaminopropane and hexamethyldisilazane is discussed in view of supramolecular chemistry and access to structural transformations of the original polycycle. Two distinct adducts may be isolated in the first case: [Ph₂SiO]₈[AlO(OH)]₄· 3H₂N-CH₂CH₂CH₂-NH₂ and [Ph₂SiO]₈[AlO(OH)]₄· 2H₂N-CH₂CH₂CH₂-NH₂. Whereas in the 1:3 adduct the four protic hydrogen atoms of the inner Al₄(OH)₄ ring are involved in O…H…N hydrogen bridges to two terminal diaminopropanes and a bridging diaminopropane thus forming an O…H…N(H)₂-CH₂CH₂CH₂N(H)₂ …H…O loop, in the 1:2 adduct two such O…H…N(H)₂-CH₂CH₂CH₂N(H)₂…H…O loops are present. When [Ph₂SiO]₈[AlO(OH)]₄ is allowed to react with hexamethyldisilazane, again two different products may be obtained depending on the solvent: [Ph₂SiO]₈[AlO₂]₂[AlOO-SiMe₃]₂[NH₄· THF]₂ or [Ph₂SiO]₈[AlOO_0.5]₄· 2 py. This last reaction may be viewed as an inner condensation within [Ph₂SiO]₈[AlO(OH)]₄ loosing two equivalents of water. Both products of the reaction with hexamethyldisilazane have an inner Al₂O₂ four-membered cycle in common, to which Al₂O₄Si₂ eight-membered cycles are partly fused.