Chiral Coordination Polymers with SHG-Active and Luminescence: An Unusual Homochiral 3D MOF Constructed from Achiral Components

Six new coordination polymers, namely,
[Cd­(SO4)­(4-abpt)­(H2O)]n·3nH2O (1), [Cu3­(CN)3­(4-abpt)2]n (2), [Cd­(D-cam)­(2-Py­BIm)­(H2O)]n (3), [Co­(D-Hcam)­(cptpy)]n (4), [Cd­(D-cam)­(btmb)]n (5), and [Cd2­(D-cam)­(L-cam)­(btmbb)]n (6) (4-abpt = 4-amino-3,5-bis­(4-pyridyl)-1,2,4-triazole,
D-H2cam = d-camphoric acid, 2-Py­BIm = 2-(2-pyridyl)­benzimidazole,
Hcptpy = 4′-(4-carboxy­phenyl)-3,2′:​6′,3″-terpyridine,
btmb = 1,4-bis­(1,2,4-triazol-1-ylmethyl)­benzene, btmbb = 4,4′-bis­(1,2,4-triazol-1-ylmethyl)-1,1′-biphenyl),
have been synthesized under hydro­(solvo)­thermal conditions. Their
structures were determined by single-crystal X-ray diffraction analysis
and further characterized by elemental analysis, infrared spectra,
powder X-ray diffraction, circular dichroism, and thermogravimetric
analysis. Complex 1 features a 3D porous metal–organic
framework, which is a rare example to obtain a homochiral compound
from achiral components. Complex 2 exhibits a 2D polymeric
network constructed from μ2-cyanide, μ2-4-abpt, and monodentate 4-abpt ligands. Complex 3 is a homochiral 1D helical chain polymer. Complex 4 displays a 1D ladder-like polymeric structure in which cptpy– is tetradentate and D-Hcam– acts
as a side arm. Complex 5 displays a homochiral 2D network
with (4,4) topology. Complex 6 shows a [Cd2­(D-cam)­(L-cam)]n (4,4)-connected
network with a paddle-wheel Cd2­(COO)4 as
node, which is further pillared by a btmbb spacer into a 3D metal–organic
framework. d-Camphoric acid underwent racemization under
hydrothermal conditions. Cd­(II) complexes 1, 3, and 5 crystallize in chiral space groups, and their
circular dichroism spectra exhibit obvious positive or negative Cotton
effects. Moreover, 1, 3, and 5 are SHG-active, and the SHG efficiency, respectively, is 0.15, 0.4,
and 0.4 times as much as that of KH2­PO4. All the complexes exhibit relatively high thermal stability. 1, 3, 5, and 6 emit
violet luminescence originating from ligand-centered emission.