This review highlights selected examples of supramolecular isomerism in the area of metal organic frameworks and major factors of their formation are also discussed.

Three new compounds bearing different flexible side functional groups, viz. 2-acetamidoterephthalic acid (H2L1), 2-propionamidoterephthalic acid (H2L2) and 2-benzamidoterephthalic acid (H2L3), were synthesized and their coordination reactions with zinc(II) were studied. X-ray crystallography showed the formation of novel metal organic frameworks with different dimensionalities, where the side functional groups of amidoterephthalic acid and/or auxiliary ligands were found to play significant roles. These frameworks [Zn2(L1)2(4,4'-bipyridine)2(H2O)(DMF)]n (1), [Zn4(L2)3(OH)2(DMF)2(H2O)2]n (2) and [Zn(L3)(H2O)2]n·n/2(1,4-dioxane) (3) act as heterogeneous polymeric solid catalysts not only for the diastereoselective nitroaldol (Henry) reaction of different aldehydes with nitroalkanes but also for transesterification reactions. These MOF-based heterogeneous catalysts can be recycled without losing their activity.

The single crystal structure analysis reveals that compound H 2 L1 crystallized in its salt form H 3 L1 + Cl -, obtained upon addition of dilute HCl into a methanolic solution of H 2 L1. The pyridyl N-atom of H 2 L1 was protonated and the cationic charge of the ligand was balanced by the negative charge of the chloride anion (Figure 1A). The pyridine and isophthalate units are in different planes which make an angle of 72.97 o , the C4-N1-C9-C10 torsional angle being -87.64 o . One of the carboxylic groups of H 3 L1 + is engaged in extensive strong R 2 2 (8) type O4-H4••••O3 (d D-A 2.652(3) Å,