Ti8O8(OOCR)16, a new family of titanium-oxo clusters: Potential NBUs for reticular chemistry

The reactions of titanium alkoxides with a large excess of different carboxylic acids under nonhydrolytic conditions leads to the reproducible formation of well-defined nano-building units (NBUs) with the formula [Ti 8O8(OOCR)16] [R = C6H5, C(CH3)3, CH3]. The structures of these titanium-oxo-carboxylate clusters have been determined by crossingdifferent characterization techniques and methodologies (single-crystal X-ray diffraction, 13C and 1H NMR spectroscopy, and FTIR spectroscopy). These NBUs are obtained in high yields and, since all the alkoxo ligands have been removed by using solvothermal-synthesis conditions, they present better stability upon hydrolysis than the often reported alkoxo-carboxylate-titanium- oxo clusters [TinO2n-x/2-y/2(OR) x(OOCR)y] (n ⥠2; x ⥠1; y ⥠1). In addition, the solubility and transferability of these clusters in common solvents can be tuned by selecting the nature of the organic ligand. Moreover, we also report for the first time, a robust post-modification of the carboxylate ligands by transesterification reactions on the titanium-oxo clusters. These reactions keep the integrity of the octameric titanium-oxo core intact, while completely exchanging the organic shell of the cluster. This family of [Ti8O8(OOCR)16] clusters, which present 16 points of extension, a symmetric shape, and the ability to be post-modified with conservation of the core structure, can therefore be considered as interesting NBUs to form new metal-organic frameworks.