Hai-Yang Li

Construction of a series of metal–organic frameworks based on novel flexible ligand 4-carboxy-1-(3,5-dicarboxy-benzyl)-pyridinium chloride and selective d-block metal ions: crystal structures and photoluminescence

We report here seven metal–organic complexes, {[Zn(L)(H2O)3]·H2O}n (1), {[Zn(L)]·H2O}n (2), {[Zn(L)(4,4′-bpy)0.5]·2H2O}n (3), {[Cd(L)]·H2O}n (4), {[Cd(L)(1,4-bbi)(H2O)]·H2O}n (5), {[Cu(L)(4,4′-bpy)(H2O)]·5H2O}n (6), and {[Cu(L)(bpe)]·6H2O}n (7), prepared by a hydrothermal method (H3L+Cl− = 4-carboxy-1-(3,5-dicarboxy-benzyl)-pyridinium chloride, bpy = 4,4′-bipyridine, bbi = 1,1′-(1,4-butanediyl)bis(imidazole), bpe = 1,2-di(pyridine-4-yl)-ethylene). These complexes show different structures including helical chains, novel pillared layers, 3D 3-fold interpenetrating frameworks, interesting 2D → 3D interdigitated architectures and Z-shaped double layer structures, and so on. The diversity of the structures of these complexes proves that the newly synthesized ligand H3L+Cl− is an excellent candidate for the construction of MOFs. Additionally, the thermal stabilities and photoluminescence properties are also investigated.

Photochromic and photomodulated luminescence properties of two metal–viologen complexes constructed by a tetracarboxylate-anchored bipyridinium-based ligand

In this study, two metal–viologen complexes, formulated as [Cd1.5(H2L)0.5(Cl)3(CH3OH)]n (1) and [Eu2(L)(NO3)4(HOCH2CH2OH)2]n (2), were constructed by a tetracarboxylate anchored bipyridinium-based ligand 1,1′-bis(3,5-dicarboxybenzyl)-4,4′-bipyridinium dichloride (H4L·Cl2). Single-crystal X-ray analyses revealed that complex 1 featured a 2D-layered structure, while complex 2 showed a 1D “ladder-like” chain structure. The difference in the central metal ions, anions, solvent molecules, deprotonation degree of the tetracarboxylate ligand, coordination modes and conformations of the ligand have a great influence on the final structure. As expected, incorporation of the viologen moiety to the frameworks led to the predefined photochromism: when samples 1 and 2 were exposed to UV-visible light, a reversible color change from light yellow to blue/dark blue occurred. Moreover, complex 2 exhibited the characteristic emission of Eu(III) ion in the visible region, and it also displayed an interesting reversible tunable photo-induced luminescence switching behavior: under the irradiation of UV-vis light, the luminescence emission intensity of complex 2 gradually decreased and reached 15% of the starting value after 8 min. These results may not only help to further understand the structure–photoresponse relationships of viologen-based MOFs, but also help to guide the design and synthesis of luminescent materials with photo-modulated switching ability.