Synthesis, structures and properties of metal-organic frameworks prepared using a semi-rigid tricarboxylate linker

Abstract

The metal-organic frameworks formed from the reaction between cadmium(ii) salts and the semi-rigid 5-((carboxymethyl)amino)isophthalic acid (H(3)cmai) in water at 90 degrees C are dependent on the counter-ions, with [Cd-2(Hcmai)(2)(H2O)(2)]center dot H2O (1), [Cd(Hcmai)(H2O)(2)] (2) and [Cd-3(cmai)(2)(H2O)(4)]center dot 4H(2)O (3) forming from the nitrate, chloride and the acetate salts, respectively. Compound 3 loses both lattice and coordinated water molecules on heating to 150 degrees C and is converted into [Cd-3(cmai)(2)] (4). This reaction occurs in a single-crystal-to-single-crystal manner and was followed using variable temperature X-ray powder diffraction. The reaction of cadmium(ii) nitrate with H(3)cmai in a mixture of water and DMF afforded [Cd-6(cmai)(4)(H2O)(9.75)(DMF)(2.25)]center dot 18H(2)O center dot 1.5DMF (5) whereas the same reaction in water and DEF in the presence of 4,4'-bipyridine led to [Cd-3(cmai)(2)(H2O)(3)]center dot 6H(2)O (6). Generally, the coordination networks containing Hcmai (1-2) propagate in one or two dimensions, whereas those containing cmai (3-6) propagate in three dimensions. Use of the first row d-block salts zinc(ii), copper(ii) and cobalt(ii) nitrate resulted in compounds [M(Hcmai)(H2O)(x)] (M = Zn, x = 2 (7), M = Cu, x = 1.2 (8), M = Co, x = 2 (9)), with 8 showing photocatalytic activity for the degradation of the dye rhodamine B. Finally, the reaction of zinc(ii) acetate with H(3)cmai in water and DEF yielded [Zn-2(cmai)(OH)(H2O)(2)]center dot 3H(2)O (10). Compounds 7-10 all form two-dimensional networks.