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

Abstract

A series of six coordination polymers, namely, [Cd1.5(L)]n (1), [Cd1.5(L)(bpp)]n (2), {[Cd1.5(L)(p-bix)]·H2O}n (3), [Cd1.5(L)(m-bix)]n (4), {[Cd1.5(L)(dpa)3(H2O)]·2H2O}n (5), and {[Cd1.5(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.