Synthesis, characterization and CO2 uptake of a chiral Co(ii) metal–organic framework containing a thiazolidine-based spacer

Abstract

The polytopic ligand thiazolidine-2,4-dicarboxylic acid (H₂L) has been synthesised on a large scale starting from the naturally occurring amino acid L-cysteine. The (R,R)/(S,R)diastereomeric mixture has been separated into its constituents through selective precipitation of the pure (R,R) isomer from concentrated H₂O/MeOH solutions. The enantiomerically pure ligand (H₂L-RR) has been reacted with CoCl₂·6H₂O under hydrothermal conditions, with the final product being [Co(L-RR)(H₂O)·H₂O]_∞ (1). The obtained coordination polymer is optically pure, and it maintains the chiral information that is present in its building block. Two different kinds of channels are present in the 3D structure of 1: one hydrophobic (with the sulfur atoms of the thiazolidine rings exposed) and the other hydrophilic [with the aquo ligand on Co(II) exposed, and hosting the crystallization water solvent]. 1 has been characterized through a combination of X-ray diffraction (single-crystal and powder) and spectroscopic (CD, IR, UV-Vis, XANES, EXAFS) techniques. Finally, CO₂ adsorption tests conducted at 273 K and (pCO₂)_max = 920 torr have shown a good carbon dioxide uptake, equal to 4.7 wt%.