Structure, adsorption and magnetic properties of chiral metal-organic frameworks bearing linear trinuclear secondary building blocks

The reactions of new chiral organic ligands trimesoyltri(L-alanine) (L-TMTAH(3)) or trimesoyltri(D-alanine) (D-TMTAH(3)) with transition metal salts in the presence of an ancillary ligand of 4,4'-bipyridine gave two pairs of three dimensional frameworks [Co-3(L-TMTA)(2)(4,4'-bpy)(4)]center dot 28H(2)O (1), [Co-3(D-TMTA)(2)(4,4'-bpy)(4)]center dot 28H(2)O (2) [Ni-3(L-TMTA)(2)(4,4'-bpy)(4)]center dot 2C(2)H(5)OH center dot 14H(2)O (3) and [Ni-3(D-TMTA)(2)(4,4'-bpy)(4)]center dot 2C(2)H(5)OH center dot 14H(2)O (4). These compounds were characterized by elemental analysis, IR, and X-ray powder diffraction analysis and the structures of 1-3 were determined from X-ray single crystal diffraction analysis. Complexes 1-4 feature linear trinuclear secondary building blocks [M-3(COO)(4)](2+) formed via the connection of three metal ions by four carboxylato groups from four TMTA(3-) ligands. Every adjacent two linear trinuclear secondary building blocks are linked by one and three 4,4'-bipyridine molecules along the a and c axis, respectively, to form two-dimensional sheets, which are further connected by TMTA(3-) ligands to construct a porous three dimensional framework with one-dimensional channels. Compound 3 was taken as an example to investigate the adsorption properties of compounds 1-4. It revealed a saturated hydrogen uptake of 216.6 cm(3) g(-1) (2.0wt%) at 11.1 atm measured at 77 K, a maximum CO2 uptake of 119.4 cm(3) g(-1) (23.5wt%) at 19.5 atm measured at 298 K and a saturated CH4 uptake of 77.8 cm(3) g(-1) (5.6wt%) at 27.1 atm measured at 298 K. The magnetic studies of complexes 1 and 3 indicate the presence of antiferromagnetic interactions between the metal ions in the two compounds.