Isoreticular metal-organic frameworks based on a rhombic dodecahedral metal-organic polyhedron as a tertiary building unit

Abstract

It was reported that the solvothermal reaction of the tetracarboxylate ligand with a Cu(II) ion could lead to MOF based on a cuboctahedral MOP as a tertiary building unit (TBU), where the cuboctahedral MOP is made of twelve [Cu2 (COO)4 ] clusters as a 4-c secondary building unit (SBU). However, the similar solvothermal reactions using the tetracarboxylate ligands with a Zn(II) ion produced two isoreticular MOFs based on a rhombic dodecahedral MOP as a TBU, in which the rhombic dodecahedral TBU was composed of six [Zn2 (COO)4 ] clusters as a 4-c SBU and eight [Zn2 (COO)3 ] clusters as a 3-c SBU. The networks of the two isoreticular MOFs based on the rhombic dodecahedral MOP are a 3,3,4-c net with zjz topology, which is different from those of the similar MOFs, PMOF-3 and PCN-12, based on the cuboctahedral Cu-MOP as a 24-c TBU, although both the rhombic dodecahedral MOP and the cuboctahedral Cu-MOP were quadruply interlinked to six neighboring TBUs as the 24-c TBUs in all the MOFs, to form the same pcu underlying topology. This study showed that the difference in the net topology of the Zn-based MOFs and those of the reported Cu-based MOFs stems from the difference in preference for the SBUs. Although it originates in the Cu(II) ion with a ligand containing a carboxylate residue and a strong preference for the square-paddle-wheel [Cu2 (COO)4 ] SBU, a Zn(II) ion could adopt not only the square-paddle-wheel [Zn2 (COO)4 ] cluster as a 4-c SBU, but also the trigonal-paddle-wheel [Zn2 (COO)3 ] cluster as a 3-c SBU.