Conformational diversity of flexible ligand in metal-organic frameworks controlled by size-matching mixed ligands

Hydrothermal reactions of N-auxiliary flexible exo-bidentate ligand 1,3-bis(4-pyridyl)propane (bpp) and carboxylates ligands naphthalene-2,6-dicarboxylic acid (2,6-H(2)ndc) or 4,4'-(hydroxymethylene)dibenzoic acid (H(2)hmdb), in the presence of cadmium(II) salts have given rise to two novel metal-organic frameworks based on flexible ligands (FL-MOFs), namely, [Cd-2(2,6-ndc)(2)(bpp)(DMF)] . 2DMF (1) and [Cd-3(hmdb)3(bpp)] . 2DMF . 2EtOH (2) (DMF=N,N-Dimethylformamide). Single-crystal X-ray diffraction analyses revealed that compound 1 exhibits a three-dimensional self-penetrating 6-connected framework based on dinuclear cluster second building unit. Compound 2 displays an infinite three-dimensional 'Lucky Clover' shape (2,10)-connected network based on the trinuclear cluster and V-shaped organic linkers. The flexible bpp ligand displays different conformations in 1 and 2, which are successfully controlled by size-matching mixed ligands during the self-assembly process. (C) 2015 Elsevier Inc. All rights reserved.