Reversible anion exchanges of porous metal-organic frameworks: Syntheses and structures of silver complexes with novel rigid tripodal nitrogen ligands

Two novel new rigid tripodal arene core based nitrogen ligands, 1,3,5-tris(pyrazol-1-yl)benzene (L-1) and 1,3,5-tris-[p-(pyrazol-1-yl)phenyl]benzene (L-2), have been synthesized. Self-assembly of L-1 with silver(I) salts generated two three-dimensional porous supramolecular networks, {[(Ag3L2X2)-X-1]X}(n) (1, X = ClO4-; 2, X = NO3-), with a common (10,3)-a topology. L-2 reacts with silver nitrate, resulting in a one-dimensional chain which constructs a three-dimensional supramolecular network, {[Ag4L22-(NO3)(4)]center dot 2CH(3)OH}(n) (3), via hydrogen bonds. Three complexes have been structurally characterized. The anion exchanges were determined by IR spectroscopy, elemental analyses, and X-ray powder diffraction for complexes 1 and 2; the counteranions located in the cationic frameworks can be exchanged reversibly without destruction of the structures. This observation demonstrates that 1 and 2 can act as zeolite-like porous materials for anion exchange. The photoluminescent properties of 1,3,5-tris[p-(pyrazol-1-yl)phenyl] benzene and its silver complex 3 have been investigated; the results indicate that the intensity of the photoluminescent emission of the ligand can be influenced by coordination with silver ion. The influence of the ligand structure on the formation of the supramolecular construction is discussed.