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

Abstract

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.