Porous titanium and zirconium oxo carboxylates at the interface between sol–gel and metal–organic framework structures
Reaction of Ti(OiPr)4 with several tri- and tetracarboxylic acids, followed by hydrolysis, resulted in microporous, structured materials, with microporous surface areas up to 340 m2 g−1. Depending on the kind of carboxylic acid, the Ti : COOH ratio and the Ti : H2O ratio, either pillared layered or surface fractal 3D structures were obtained according to SAXS measurements. The most pronounced layered structure was found for 1,2,4,5-benzenetetrabenzoic acid and a Ti : H2O ratio of 4, while a Ti : H2O ratio of 2 resulted in a 3D structure. The use of 1,3,5-benzenetricarboxylic acid or 1,3,5-benzenetribenzoic acid resulted in similar structures which, however, were less pronounced and less ordered. The reaction of tetrakis(4-carboxyphenyl)silicon with Ti(OiPr)4 or benzenetribenzoic acid with Zr(OiPr)4 gave 3D structures for all Ti : H2O ratios.