Metal−Organic Frameworks from Silicon- and Germanium-Centered Tetrahedral Ligands

Abstract

Metal−organic frameworks (MOFs) have been constructed from the reaction of Si(C 6 H 4 CO 2 H) 4 and of Ge(C 6 H 4 CO 2 H) 4 with Zn(II). The two structures are quite different from each other, and both are different from that of the known MOF of C(C 6 H 4 CO 2 H) 4 with Zn(II). The zinc portion of the carbon system is a dinuclear zinc-oxo cluster with square-planar geometry, that of the silicon system consists of zinc-oxo chains containing two zinc atoms with different geometries, and that of the germanium system consists of linear zinc-oxo clusters containing three zinc atoms with two different geometries. For the silicon system, the secondary building unit around zinc is a distorted tetrahedron, whereas for the germanium system, the secondary building unit around zinc is a bipyramid with eight coordination. The differences in morphology may be due to the more open geometry provided as the M−C bond increases from carbon to germanium. Both MOFs have considerable vacancy in the crystal lattice, calculated to be ca. 42% for the silicon system and ca. 46% for the germanium system. Gas sorption experiments on the germanium system indicated significant uptake of both nitrogen and carbon dioxide.