Helmut Fric

ω-Mercapto-functionalized hafnium- and zirconium-oxoclusters as nanosized building blocks for inorganic–organic hybrid materials: synthesis, characterization and photothiol-ene polymerization

Two isostructural mercapto-functionalized zirconium- and hafnium-oxoclusters [M12(μ3-O)8(μ3-OH)8(MP)24·n(MPA), MPA = HS–(CH2)2–C(O)OH; MP = HS–(CH2)2–C(O)O−; M= Zr, Hf; n = 4 for Zr, n = 5 for Hf] were prepared by reacting 3-mercaptopropionic acid with zirconium and hafnium butoxide, respectively, in an alkoxide : acid 1 : 7 molar ratio. The two oxoclusters Zr12 and Hf12, which are composed of two Zr6 and Hf6 sub-units bridged by four carboxylate ligands, were thoroughly characterized by single crystal X-ray diffraction, infrared spectroscopy (FT-IR), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, thermogravimetry (TGA), differential thermoanalysis (DTA) and extended X-ray absorption spectroscopy (EXAFS). The zirconium oxocluster was then embedded in a polymethacrylic matrix by a photothiol-ene polymerization reaction by using different cluster : monomer molar ratios. EXAFS measurements performed on the polymethacrylic-based hybrid materials showed that the structure of the oxocluster is retained even after being embedded in the polymer matrix. Solid-state 13C NMR spectroscopy as well as FT-IR spectroscopy demonstrated that the inorganic–organic hybrid materials are characterized by an almost complete polymerization of methacrylic acid, in which the oxoclusters are embedded in and covalently bound to the polymer matrix.

Amine adducts of titanium tetraalkoxides

The crystalline compounds Ti2(OiPr)8(NH2Pr)2, Ti2(OiPr)6(OEt)2[NH2(CH2)3Si(OiPr)3]2 and Ti2(OiPr)8[NH2(CH2)6NH2] were obtained by reaction of Ti(OiPr)4 with the corresponding amines. The molecular structures of the amine adducts are centrosymmetric dimers in which the titanium atoms are bridged by two OR groups. The amines are coordinated axially to the Ti2(µ-OR)2 ring and hydrogen-bonded to a neighboring propoxy ligand. In the case of the 1,6-diaminohexane derivative, this results in coordination polymers where the Ti2(OiPr)8 units are interconnected by the diamine.

Bis-Imide Derivatives of the Heterometallic Alkoxide Li4Ti4O4(OiPr)12

The imide derivatives Li4Ti4O2(NR)2(OiPr)12 (R = CH2C6H5, C6H11, C4H9) were obtained either by reaction of the amine adduct Ti2(OiPr)8(H2NR)2 with lithium diiso- propylamide or butyllithium, or when the primary amine was first reacted with the base and then with Ti(OiPr)4. The structures of the imide derivatives are the same as that of Li4Ti4O4(OiPr)12 (= Li4Ti4(μ2-O)2(μ5-O)2(μ2-OiPr)4(μ3- OiPr)4(OiPr)4) with the two μ2-oxo groups replaced by two μ2-NR groups.

Modification of Metal Alkoxide Precursors by Organofunctional Bidentate Ligands: Chemical Problems and Opportunities for Materials Syntheses

Bidentate ligands are potentially useful to modify metal alkoxides precursors for sol-gel processing. However, anionic bidentate ligands are needed to get a strong coordination, while diamines as neutral bidentate ligand form coordination polymers [Ti 2 (OR) 8 (diamine) 2 ]∞ when reacted with Ti(OR) 4 . The Lewis acidity of metal alkoxides may cause organic side reactions. The first is the formation of ester and water in the reaction with carboxylic acids, and therefore carboxylate-substituted metal oxide clusters of the general composition M n O x (OH/OR) y (OOCR) z are obtained instead of substituted monomeric precursors. The second side reaction discussed is the cleavage of β-diketones by metal alkoxides. Despite this side reaction, 3-acetyl-6-trimethoxy-silyl-hexane-2-one is a useful compound to prepare single-source precursos for silica/metal oxide composites.