Three series of MOFs featuring various metal(ii)-carboxylate chains cross-linked by dipyridyl-typed coligands: synthesis, structure, and solvent-dependent luminescence

Abstract

This work presents seven M(II) metal–organic frameworks (MOFs) with three types of topology, which are hydrothermally synthesized by using a mixed ligand system including a functional group substituted phthalate (CF₃-H₂bdc or F₄-H₂bdc) and a dipyridyl-typed molecule (bpy, bpp, bpa, and bpe) (CF₃-H₂bdc = 4-(trifluoromethyl)phthalic acid, F₄-H₂bdc = tetrafluorophthalic acid, bpy = 4,4′-dipyridyl, bpp = 1,3-di(4-pyridyl)propane, bpa = 1,2-bis(4-pyridyl)ethane, and bpe = 1,2-di(4-pyridyl)ethylene). All these complexes display 3D MOFs featuring various metal(II)-carboxylate chains cross-linked further by dipyridyl-typed coligands. 1/1a serial possesses Cd(II)-carboxylate 2₁ helices forming the uninodal 5-connected nets with sev-5-Cccm topology, 2/2a serial contains Co(II)-carboxylate spiral-like chains assembling into the uninodal 5-connected nets with 5/4/t47 topology, and 3/3a/3b serial consists of Cu(II)-carboxylate 2₁ helices affording the uninodal 4-connected nets with a new framework topology (designated as lyu-3 here). Note that 1 undergoes a slight framework contraction in a single crystal to a single crystal form upon dehydration, whereas the framework expansion occurs in a single crystal to powder form upon rehydration. Interestingly, such reversible dehydrated–rehydrated behaviour is accompanied evidently by a rarely observed fluorescent transformation between 500 nm and 425 nm.