Crystal Structures and Properties of Cd(II) Coordination Polymers Supported by a New Chiral Aromatic Polycarboxylate Ligand

A series of six coordination polymers, namely, [Cd_1.5(L)]_n (1), [Cd_1.5(L)­(bpp)]_n (2), {[Cd_1.5(L)­(p-bix)]­·H₂O}_n (3), [Cd_1.5(L)­(m-bix)]_n (4), {[Cd_1.5(L)­(dpa)₃­(H₂O)]­·2H₂O}_n (5), and {[Cd_1.5(L)­(bpbd)_2.5]­·2H₂O}_n (6) (Na₃L = (S)-(−)-5-(1-carboxy-ethoxymethyl)-isophthalic acid trisodium salt), have been hydrothermally synthesized through the reaction of Na₃L with divalent cadmium salts with or without the presence of ancillary nitrogen ligands (bpp = 1,3-bi­(4-pyridyl)­propane, p-bix = 1,4-bis­(imidazol-1-ylmethyl)­benzene, m-bix = 1,3-bis­(imidazol-1-ylmethyl)­benzene, dpa = 4,4′-dipyridylamine, bpbd = 2,3-bis­(4′-pyridyl)-2,3-butanediol)). Complex 1 is a three-dimensional (3D) framework and displays a (4,8)-connected framework with {4¹²·6¹²·8⁴}­{4⁶}₂ (flu) topology. 2 features a 3D architecture too, in which the one-dimensional (1D) (Cd-bpp)_n helical chains are alternately arranged in a right- and left-handed sequence. Complex 3 exhibits a homochiral 3D framework and is a new (3,8)-connected net with a Schläfli symbol of {4·5·6}₂­{4²·5⁶·6¹⁸·7·8} topology. Complex 4 bears a homochiral layered structure, which is united together to generate a 3D supramolecular structure through interlayer C–H···O and C–H···π interactions. Interlayer C–H···π and N–H···N interactions led layered complex 5 to a 3D supramolecular architecture. Complex 6 shows a new (3,5,6)-connected net with a Schläfli symbol of {4·6²}₂­{4²·6¹⁰·8²·10}­{4²·6⁶·8²}₂ topology. Complexes 3 and 4 crystallize in the chiral C2 space group, and their circular dichroism spectra exhibit obvious positive or negative Cotton effects. Moreover, 3 and 4 are second-harmonic generation (SHG) active, and the SHG efficiency is 0.5 and 0.4 times as much as that of urea, respectively.