The Elusive Nitro-Functionalised Member of the IRMOF-9 Family

The solvothermal reaction of 2-nitro-[1,1′biphenyl]4,4′dicarboxylic acid (H2bpdcNO2) with Zn(NO3)2·6H2O in DMF solvent does not give a functionalised variant of IRMOF-9. Single-crystal X-ray diffraction analysis shows the major initial product of this reaction, WUF-21 (WUF = Wollongong University Framework), is a porous interpenetrated diamondoid metal-organic framework (MOF) with a secondary building unit that 'doubly straps' eight bridging bpdcNO2 ligands in a distorted tetrahedral shape around an unusual pentazinc core. A second porous MOF phase (WUF-23) containing a large and novel dodecazinc secondary building unit forms in the same reaction and eventually predominates in solutions containing formate anion, which arises from the hydrolysis of DMF. Doping the starting ligand with [1,1′biphenyl]4,4′dicarboxylic acid (H2bpdc) provides a facile way to grow nitro-functionalised IRMOF-9, hereafter denoted as WUF-22, where the dopant is carried through into the product. Activated WUF-22 is a microporous solid with an apparent Brunauer-Emmett-Teller (BET) surface area of 2497 m2 g-1, which matches well with geometric surface area calculations. The CO2 adsorption properties of WUF-22 are reported.