Construction of open metal-organic frameworks based on predesigned carboxylate isomers: From achiral to chiral nets

The four-connected carboxylate ligand NNN',N'-tetrakis(4-carboxyphenyl)-1,4-phenylenediamine (TCPPDA) exists as three stereoisomers: a pair of enantiomers (D-delta(2)- and D-lambda(2)-TCPPDA) and a diastereomer (C-2h-TCPPDA). TCPPDA was predesigned for the construction of isomeric coordination networks. Reactions of M(NO3)(2) (M = CU, Zn, Co) or Nd(NO)(3) with TCPPDA under solvo-thermal conditions gave rise to five novel porous metal-organic frameworks: [CU2(D-2-tcppda)(H2O)(2)]center dot 2DMSO center dot 6H(2)O (1), [Cu-2(C-2h-tcppda)(H2O)(2)]center dot 2DMSO center dot 6H(2)O (2), [Co-3(D-2-Htcppda)(2)]center dot 4 DEF center dot 5H(2)O (3), [Nd-2(D-2-tcppda)(C-2h-tcppda)(0.5-)(DMSO)(3)]center dot 3DMSO-5H(2)O (4), and [Zn4O(D-2-tcppda)(1.5)]center dot DMF center dot H2O (5) (DMSO=dimethyl sulfoxide, DEF= diethylformamide, DMF = dimethylformamide). Complexes 1 and 2 are supramolecular isomers, in which all the ligands adopt pseudotetrahedral (both D-delta(2)- and D-lambda(2)-TCPPDA) and rectangular (C-2h-TCPPDA) geometries, respectively. Both compounds connect paddle-wheel secondary building units (SBUs) to form three-dimensional porous networks possessing PIS and NbO nets, respectively. In 3, all ligands possess pseudotetrahedral (both D-delta(2) and D-lambda(2)-TCPPDA) geometry and link hourglass SBUs to form a three-dimensional porous framework. Compound 4 contains all three stereoisomers (C-2-, D-delta(2)-, and D-lambda(2)-TCPPDA), thus, has both pseudotetrahedral and rectangular geometries. D-2-TCPPDA connects the binuclear neodymium units to generate a two-dimensional layer, further linked by C-2h-TCPPDA to create a three-dimensional open framework. In 5, all the ligands possess pseudotetrahedral geometry (D2-TCPPDA), as found in 1 and 3. However, all the TCPPDA ligands in 5 appear as either the D-delta(2) or the D-lambda(2) form, thus, the whole structure is homochiral. Complex 5 crystallizes in the 14,32 space group and the octahedral SBU in 5 is connected by the enantiopure TCPPDA to generate a three-dimensional porous network possessing the corundum Al2O3 net. Complexes 1, 2, and 5 possess permanent porosity, and 4 and 5 exhibit strong luminescence at lambda(max) = 423 and 424 nm, respectively, upon excitation at 268.5 nm.