Ni8 Carboxylate Metal-Organic Frameworks.

Octanuclear nickel cube (Ni8) is considered as a highly attractive inorganic building block in the field of metal-organic frameworks (MOFs) due to its high symmetry (Oh), 12 connection sites, and excellent chemical stability of the constructed MOFs. In this study, we report the synthesis of Ni8-based MOFs constructed exclusively from carboxylic acid ligands, breaking from the conventional use of pyrazolate in Ni8-containing MOFs. Two carboxylate-based MOFs featuring fcu topology (NNM-2 and NNM-3) were successfully synthesized. Both materials are stable across a wide pH range. In addition, they exhibit C2H2/CO2 separation properties. For a C2H2/CO2 (v:v = 50:50) mixture, NNM-2 showed a retention time difference of 36.4 min g-1 between C2H2 and CO2 in a packed column. Furthermore, because of its hydrophobic pore environment, NNM-2 maintained its separation performance even under near-saturated humidity (∼100% relative humidity).