Control of the ratio of functional and non-functional ligands in clusters of the type Zr6O4(OH)4(carboxylate)12 for their use as building blocks for inorganic–organic hybrid polymers

Abstract

The methacrylate ligands of the cluster Zr₆O₄(OH)₄(methacrylate)₁₂ undergo degenerate exchange with methacrylic acid in solution. Addition of propionic or isobutyric acid allows partial or complete exchange of the methacrylate ligands for propionate or isobutyrate. The mixed-carboxylate cluster Zr₆O₄(OH)₄(OMc)₈(isobutyrate)₄(BuOH) was independently prepared by reaction of Zr(OⁿBu)₄ with a mixture of methacrylic acid and isobutyric acid. The structures of Zr₆O₄(OH)₄(OMc)₈(isobutyrate)₄(BuOH) and Zr₆O₄(OH)₄(isobutyrate)₁₂(H₂O) consist of an octahedral Zr₆(μ₃-O)₄(μ₃-OH)₄ core with one of the carboxylate ligands being monodentate. The H₂O or ROH molecule is coordinated to the neighbouring zirconium atom and, at the same time, hydrogen bonded to the monodentate carboxylate. A mechanism for the carboxylate exchange is suggested based on the structural observations.