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

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((OBu)-Bu-n)(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 Zr-6(mu(3)-O)(4)(mu(3)-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.