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Four new metal organic frameworks with bivalent cadmium, disodium succinate (Na2suc), and four different N,N′-donor ligands, i.e., {[Cd(L1)(suc)]­·(H2O)3} n (1), {[Cd(L2)(suc)]­·(H2O)2} n (2), {[Cd(L3)(suc)]­·(H2O)4} n (3), {[Cd3(L4)3(suc)2(H2O)2]­·(NO3)2 (H2O)4} n (4) [L1 = 2,5-bis-(4-pyridyl)-3,4-diaza-2,4-hexadiene, L2 = trans 4,4′-azobispyridine, L3 = 2,5-bis-(3-pyridyl)-3,4-diaza-2,4-hexadiene, L4 = 1, 2-bis(4-pyridyl) ethane and suc = succinate dianion] have been synthesized at room temperature and characterized by single-crystal X-ray diffraction and other physicochemical methods. Structure determination reveals that compounds 1 and 2 show honeycomb-like three-dimensional (3D) architecture with water-filled channels. The dehydrated frameworks of 1 and 2 exhibit hydrogen and carbon dioxide adsorption properties. In compound 3, change of linker (linear to bent) led to the blockage of such regular channels which also affected the porosity and adsorption properties of its dehydrated framework. In 4, the used spacer is linear but the resulting 3D framework contains blocked channels filled with nitrate (NO3 –) anions and lattice water.

We report the synthesis, structural characterization and adsorption properties of three new porous coordination polymers {[Cu(Meazpy)0.5(glut)](H2O)}n (2), {[Zn(azpy)0.5(terep)](H2O)}n (3), and {[Zn(Meazpy)0.5(terep)]}n (4) [glut = glutarate, terep = terephthalate, azpy = N,N'-bis-(pyridin-4-ylmethylene)hydrazine and Meazpy = N,N'-bis-(1-pyridin-4-ylethylidene)hydrazine] composed of mixed linkers systems. Structure determination reveals that all three compounds have three-dimensional (3D) coordination frameworks bridged by dicarboxylates and Schiff base linkers. In all cases 2D dicarboxylate layers are supported by paddle-wheel M2(CO2)4 SBUs extended in three dimensions by designed Schiff base linkers. Compound 1, which has been reported in a paper earlier by our group, is a robust porous three-dimensional (3D) framework whose pore surface was found to be decorated with the -CH=N- groups of a linear Schiff base (azpy) and it showed reversible single-crystal-to-single-crystal transformation and selective CO2 uptake. By using another linear Schiff base linker Meazpy, we have synthesized compound 2 which is isostructural with 1, having an additional methyl group pointing towards the pore. Like 1 it also shows a reversible single-crystal-to-single-crystal transformation upon dehydration and rehydration. The dehydrated framework of 2 exhibits 50% enhanced CO2 uptake compared to 1. This has been achieved by the pore surface modification effected upon changing the pillar backbone from a -CH=N- to -CMe=N- group. It also adsorbs water vapour at 298 K. In the case of the two isostructural 3D MOFs 3and 4, the use of a rigid carboxylate (terephthalate) linker arrested porosity by three-fold interpenetration. We showed that the use of aliphatic dicarboxylate (glutarate) results in a non-interpenetrated framework rather than the common interpenetrated framework with aromatic dicarboxylates in mixed ligand systems.

Robust metalÀorganic frameworks (MOFs), having the coordination space in terms of pores or channels, has received extensive attention in the past decade due to its potential application in several areas. 1 The study of porous metalÀorganic frameworks or precisely porous coordination polymers (PCPs) 2 is quite ubiquitous nowadays, due to their extensive applications in the field of heterogeneous catalysis, 3 gas storage, 4 separation 5 and ion exchange, 6 and sensing applications. 7 Construction methodology of functional porous coordination polymers have different ways of accomplishment; for example, the metal ion geometry, binding mode, and stability of the organic struts are keys to obtain a rigid and robust framework. There are two popular ways to functionalize channel surfaces: one is the control of coordinatively unsaturated metal centers, 8 that is, tuning the geometry of node, 1c,d and the other is the introduction of functional organic sites in the linker. 9 The last one is very important because by this way, the active site of catalysts can be functionalized in the pore wall to make it useful in heterogeneous catalysis. The fabrication of the guest accessible functional organic sites on the pore surface is a very challenging task as these functional organic groups tend to coordinate metal ions through a self-assembly process resulting in a framework

Three new dynamic metal−organic frameworks (MOFs) namely {[Cd 2 (3,4-pyrdc) 2 (4,4′-bipy)(H 2 O) 2 ]• 4H 2 O} n (1), {[Mn 2 (3,4-pyrdc) 4-pyridinedicarboxylate (3,4-pyrdc) and three different N,N′donor ligands [4,4′-bipyridine (4,4′-bipy), 1,2-bis(4-pyridyl)ethylene (bpee), and 1,3-bis(4-pyridyl)-propane (bpp)] with various divalent transition metal ions have been synthesized and characterized by single-crystal and powder X-ray diffraction and other physicochemical methods. In compounds 1 and 2, the 3,4-pyrdc ligand forms two-dimensional (2D) metal−carboxylate sheets that are connected by N,N′-donor ligands to form three-dimensional (3D) structures with water-filled channels. In compound 3, the 3,4-pyrdc ligand affords one-dimensional metal−carboxylate chains. These chains are connected by the more flexible bpp ligand to form 2D structures, which are extended to a 3D supramolecular architecture by H-bonding. Compounds 1 and 2 show a reversible crystalline-to-crystalline phase transformation upon dehydration and rehydration, whereas compound 3 exhibits an interesting reversible crystalline-toamorphous transformation. These transformations have been established and monitored by exhaustive X-ray powder diffraction, elemental analysis, IR spectroscopy, thermogravimetric analysis, and morphology studies. The dehydrated forms of 1−3 selectively adsorb CO 2 over N 2 and also exhibit stepwise water uptake.