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

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.