Three helical chain-based 3D coordination polymers: solvent-induced syntheses, tunable structures and catalytic properties for the Strecker reaction

Three three-dimensional (3D) helical chain-based coordination polymers [Sc(aip)(OH)center dot(H2O)](n) (1), [Sc-2(aip)(3)](n) (2) and [Sc-2(nip)(3)](n) (3) (H(2)aip = 5-aminoisophthalic acid, H(2)nip = 5-nitroisophthalic acid) have been synthesized through solvent induction without any chiral auxiliary systematically. We first synthesized CP 1, a 3D network, which contains intertwined left- and right-hand helical chains {-ScO6-OH-}(n). By changing the polarity of the solvents from CH3CN/H2O to H2O, a genuine single helix of 2 was constructed, in which adjacent Sc(COO)(6) polyhedra are connected alternately by aip(2-) ligands to form a 3D framework with intertwined parallel left-hand helical chains {-Sc1(COO)-Sc2(COO)-}(n). Then by changing the substituent of the ligand, CP 3 was obtained with right-handed helical chains. As for 3, the aip(2-) ligands bridge Sc(iii) ions alternately into infinite right-handed helical chains {-Sc(COO)-}(n), which serve as secondary building units (SBU) to generate a 3D framework. Solid-state circular dichroism spectrum confirms that 3 is optically active. We also studied the catalytic properties of 1-3 in the Strecker reaction. Importantly, 1 shows excellent catalytic activity under mild conditions and can be reused at least four times without significant reduction in catalytic ability.