What Matters to Fabrication of Type II Porous Liquids: A Case Study on Metallocages and Bulky Ionic Liquid?

Porosity in bulky solvents can be created by the methods of dispersing and dissolving porous hosts or by their chemical adornment. And the ensuing liquids with cavities offer requisite high gas uptakes. Intriguingly, metal-organic cages (MOCs) as discrete nanoporous hosts have been utilized recently as soluble entities to obtain a series of interesting type II porous liquids (PLs). Yet, factors affecting the fabrication of type II PLs have not been disclosed. Herein, three metallocages (NUT-101, ZrT-1-NH2, and ZrT-1) with the same zirconocene nodes but different organic ligands are chosen as porous hosts and a polyethylene-glycol (PEG) linked bis-imidazolium based IL, IL(NTf2), is used as a bulky solvent. It is revealed for the first time that the generation of type II PL depends upon the flexibility of MOCs and the interaction between MOCs and solvent molecules. The maximum solubility is observed with NUT-101 (5%) in IL(NTf2) while ZrT-1-NH2 and ZrT-1 remain least soluble (0.5% and 0.2%). As a result, PL-NUT-101-5% with most intrinsic cavities shows higher CO2 uptake (0.576 mmol g-1) than PL-ZrT-1-NH2-0.5% and PL-ZrT-1-0.2% as well as those reported type II PLs.

Transformation of Type III to Type II Porous Liquids by Tuning Surface Rigidity of Rhodium(II)-Based Metal-Organic Polyhedra for CO2 Cycloaddition.

Porous liquids (PLs), a summation of porous hosts and bulky solvents bestowing permanent cavities, are the prominent emerging materials. Despite great efforts, exploration of porous hosts and bulky solvents is still needed to develop new PL systems. Metal-organic polyhedra (MOPs) with discrete molecular architectures can be considered as porous hosts; however, many of them are insoluble entities. Here we report the transformation of type III PL to type II PLs by tuning the surface rigidity of insoluble MOP, Rh24 L24 , in a bulky ionic liquid (IL). Functionalization of N-donor molecules on Rh-Rh axial sites ensue their solubilization in bulky IL which confer type II PLs. Experimental and theoretical studies reveal the bulkiness of IL as per the cage apertures, and the cause of their dissolution as well. The obtained PLs, capturing more CO2 than neat solvent, have depicted higher catalytic activity for CO2 cycloaddition compared to individual MOPs and IL.