Synthesis, structure, thermal stability and luminescence of six coordination polymers based on 3-(4-hydroxypyridinium-1-yl)phthalic acid and auxiliary dipyridyl ligands

Abstract

Hydro(solvo)thermal reactions of metal salts and 3-(4-hydroxypyridinium-1-yl)phthalic acid (H2L) with 4,4′-bipyridine (4,4′-bipy), N,N′-bis(4-pyridylmethyl)piperazine (4-bpmp), and 1,3-bis(4-pyridyl)propane (bpp) auxiliary dipyridyl ligands afforded six new coordination polymers, namely [CdL(H2O)]n (1), [CoL(4,4’-bipy)0.5(H2O)]n (2), [ZnL(4-bpmp)0.5(H2O)]n·2nH2O (3), [ZnL(bpp)]n·5nH2O (4), [Zn2L2(bpp)(H2O)2]n·nH2O (5) and [Zn2L2(bpp)(H2O)]n·4nH2O (6). They were characterized by elemental analysis, IR, PXRD, thermogravimetry and X-ray structural analysis. Complex 1 is a 1D ribbon coordination polymer. Complex 2 is a 2D coordination polymer constructed from L and 4,4′-bipy ligands, which is further extended into a 3D supramolecular framework through strong hydrogen bonds. Complex 3 features a 1D chain polymeric structure formed by [Zn2L2] dimer and 4-bpmp linker. Complex 4 exhibits a 1D nano-tubular structure with larger cavities, which are fully occupied by (H2O)5 clusters. Complex 5 displays a 1D linear chain structure. Complex 6 is a 2D layered coordination polymer. These complexes exhibit structural diversity originating from four typical coordination modes of 3-(4-hydroxypyridinium-1-yl)phthalate and various dipyridyl spacers. Thermogravimetric analyses demonstrate that the dehydrate complexes are thermally stable to ca. 260–300°C. Complexes 1 and 3 emit strong blue luminescence originating from ligand-centered emission.