Single crystalline hollow metal-organic frameworks: a metal-organic polyhedron single crystal as a sacrificial template

Abstract

While the Zn-MOF [Zn24(mip)24(dabco)6(H2O)12] (where H2mip = 5-methylisophthalic acid; dabco = 1,4-diazabicyclo[2.2.2.]octane) based on the cuboctahedral MOP [Zn24(mip)24(H2O)12], as a 12-connected node could only be prepared via one-pot solvothermal reaction, similar attempts to prepare isoreticular Cu-MOFs via conventional one-pot synthetic approach in presence of 5-hydroxylisophthalic acid (H2hip) and various linkers between the potential MOP intermediate, [Cu24(hip)24(H2O)12], only produced metal-organic polyhedron (MOP), [Cu24(hip)24(DMF)8(H2O)16]. A series of isostructural and isoreticular Cu-MOFs, [Cu24(hip)24(L)6(H2O)12] (where L = dabco; pz = pyrazine; bipy = 4,4’-bipyridine), could only be obtained via stepwise reactions using the cuboctahedral MOP, [Cu24(hip)24(DMF)8(H2O)16], as a molecular precursor. Especially, single crystalline hollow metal-organic frameworks (MOFs) with cavity dimensions in the order of several micrometers and hundreds of micrometers were prepared using a MOP single crystal as a sacrificial hard template. The hollow nature of the MOF crystal was confirmed by scanning electron microscopy of the crystal sliced using a focused ion beam.