Temperature-dependent assemblies from a 2-D triple-stranded meso-helical layer to a 3-D chain-layer metal-organic framework

Two different crystal forms, namely {[Dy-2(mpda)(3)(H2O)(2)]center dot H2O}(n) (1) and [Dy-2(mpda)(3)(H2O)(4)](n) (2), were obtained from the reaction of multidentate 2,6-dimethylpyridine-3,5-dicarboxylic acid (H(2)mpda) with Dy2O3 at different temperatures. Structural analysis reveals that compound 1 is a 2-D triple-stranded meso-helical layer, and 2 a 3-D chain-layer framework. The fluorescent measure shows that compound 1 is a promising luminescent probe for various metals with a remarkable on-off switch of emission, mainly deriving from many pairs of inversely arranged 4-aza bowl-like crown ethers distributed in the 2-D helical plane. Moreover, compound 1 presents noticeable hydrogen-sorption at medium pressure.