A variety of metal–organic and supramolecular networks constructed from a new flexible multifunctional building block bearing picolinate and terephthalate functionalities: hydrothermal self-assembly, structural features, magnetic and luminescent properties

Abstract

A novel flexible multifunctional building block (H₃L) bearing picolinate and terephthalate functionalities was designed and applied for the hydrothermal self-assembly generation of a series of coordination compounds [Co(H₂L)₂(H₂O)₂] (1), [M(HL)(H₂O)]_n {M = Cd (2) and Mn (3)}, {[Mn_1.5(L)(phen)(H₂O)₂]·H₂O}_n (4), [Zn₃(L)₂(H₂O)₆]_n (5), and {[Zn₃(L)₂(py) (H₂O)₄]·4H₂O}_n (6) {wherein H₃L = 2-(4-carboxypyridin-3-yl)-terephthalic acid, phen = 1,10-phenanthroline, py = pyridine}. All the obtained products 1–6 were fully characterized by IR spectroscopy, elemental, thermogravimetric, powder and single-crystal X-ray diffraction analyses. By adjusting the molar ratio of NaOH and H₃L ligand, the latter becomes partially deprotonated to form the H₂L⁻ blocks in 1 and HL²⁻ moieties in 2 and 3, or completely deprotonated to create the L³⁻ units in 4–6. The structures of the obtained compounds range from a discrete 0D monomer 1 and 1D coordination polymers 4 and 5 to 2D coordination polymers 2 and 3, and an intricate 3D metal–organic framework 6; their detailed topological classification was also performed. The structures of 1–5 are further extended [0D → 3D (1), 1D → 3D (4, 5), and 2D → 3D (2, 3)] into supramolecular networks by means of multiple hydrogen bonds. The results reveal that the nature of metal(II) ion, molar ratio between NaOH and H₃L ligand, and the presence (optional) of auxiliary ligand play a significant role in determining dimensionality, topology and other structural features of the obtained products. Magnetic susceptibility measurements indicate that compounds 3 and 4 have dominating antiferromagnetic couplings between metal centers. Furthermore, luminescent properties of 2, 5, and 6 were also investigated.