Zn(II)-Siloxane Clusters as Versatile Building Blocks for Carboxylate-Based Metal-Organic Frameworks

Siloxanes have long been known for their highly desirablepropertiessuited for a wide range of practical applications; however, theirutilization as modular building blocks for crystalline open frameworkshas been limited. In this study, a simple solvothermal pathway hasbeen found to synthesize unprecedented Zn(II)-siloxane clusterssupported by acetate ligands, [(RSiO2)(8)Zn-8(CH3CO2)(8)] (R = Me or Ph).The same reaction using a dicarboxylate ligand such as 1,4-benzenedicarboxylateor 2,6-naphthalenedicarboxylate produces a new type of metal-organicframework, named SiMOF here, based on the [Si8Zn8] units. With the maximum connectivity of 8, the building block isshown to form topologically interesting structures such as octahedralsupercages or uninodal 8-connected frameworks. All SiMOFs synthesizedpossess permanent porosity and high thermal stability and are naturallyhydrophobic, as demonstrated by adsorptions of toluene, ethanol, methanol,and water vapor as well as water contact angle measurements. Thesepromising characteristics for well-defined porous solids are attributedto metal-bound siloxane groups in the structural building units.