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

Abstract

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.