A series of coordination polymers based on flexible 5-carboxy-1-(4′-carboxybenzyl)-2-oxidopyridinium and structurally related N-donor ligands: syntheses, structures and photoluminescent properties

Abstract

Seven new coordination polymers, namely, [Zn(L)(biim-4)]·3H₂O (1), [Co(L)(biim-4)_0.5] (2), [Zn(L)(btpy)]·1.75H₂O·0.25EtOH (3), [Co(L)(btpy)] (4), [Cd(L)(phen)(H₂O)]·H₂O (5), [Cd₃(L)₂(OH)₂(btb)(H₂O)₂] (6), and [Pb(L)(H₂O)_0.5] (7) (where H₂L = 5-carboxy-1-(4′-carboxybenzyl)-2-oxidopyridinium, biim-4 = 1,1′-(1,4-butanediyl)bis (imidazole), btb = 1,2-bis(1,2,4-triazole-1-yl)ethane, phen = 1,10-phenathroline, and btpy = 2-(4-(4′-tert-butylphenyl)-6-(pyrindin-2-yl)pyri-din-2-yl)pyridine) have been synthesized under hydrothermal conditions. Compound 1 shows an unusual 2D → 2D interdigitated double layer formed by π–π interactions. Compound 2 reveals a 3D 6-connected framework with the (4³·6¹¹·8) topology. Compounds 3 and 4 are isomorphous and exhibit the same 1D chain structures, which are further extended into a 2D supramolecular layer by hydrogen-bonding and π–π interactions. Compound 5 displays a 0D dimeric molecular structure, which is further linked by intermolecular hydrogen-bonding interactions to form a 2D supramolecular layer. Compound 6 shows a 2D layer structure. Intermolecular hydrogen-bonding interactions extended the 2D layers into a 3D supramolecular architecture. Compound 7 exhibits a 2D undulated (4,4) network. The complexes were structurally characterized by single-crystal X-ray diffraction analyses, thermogravimetric analyses (TGA), elemental analyses, powder X-ray diffraction (PXRD) and infrared spectra (IR). The coordination modes of the H₂L ligand, the effects of the central metals and the N-donor ligands on the structures of coordination polymers have been discussed in detail. Furthermore, the luminescent properties of compounds 1, 3, 5 and 6 have also been studied.