Solvent-mediated assembly of chiral/achiral hydrophilic Ca(II)-tetrafluoroterephthalate coordination frameworks: 3D chiral water aggregation, structural transformation and selective CO2 adsorption

The spontaneous self-assembly reactions of 2,3,5,6-tetrafluorobenzenedicarboxylic acid (H2BDC-F-4) with Ca(NO3)(2)center dot 4H(2)O in different solvents resulted in the generation of hydrophilic 3D chiral and achiral Ca(II)-organic frameworks {[Ca-4(BDC-F-4)(4)(H2O)(4)]center dot 4H(2)O}(n) (1) and [Ca(BDC-F-4)(MeOH)(2)](n) (2), respectively. Complex 1 exhibits higher water solubility compared to 2, and further dissolution of 1 in water results in a new achiral crystal, [Ca(BDC-F-4)(H2O)(4)](n) (3). All complexes have been characterized by elemental analysis, IR spectroscopy, and single-crystal and powder X-ray diffraction techniques. Complex 1 crystallizes in the tetragonal P4(1)2(1)2 chiral space group and features a rare binodal 5-connected network, directed by a unique 3D chiral (10,3)-a water aggregation consisting of two distinct helical arrays. Complex 2 crystallizes in the space group C2/c and has a binodal 4-connected pts net. Complex 3 crystallizes in the space group P2(1)/m and presents a 2D layer framework containing the unprecedented polymeric [Ca-II-H2O](n) chain based on triple mu(2)-O aqua bridges. The structural discrepancies illustrate the solvent-induced effect on the construction and structural transformation of chiral and achiral coordination frameworks. Moreover, gas (N-2 and CO2) adsorption studies show that the dehydrated framework 1a exhibits excellent selective CO2 gas uptake at 195 K.