Temperature-Controlled Synthesis of Metal-Organic Coordination Polymers: Crystal Structure, Supramolecular Isomerism, and Porous Property

Five new supramolcular metal-organic coordination polymers (MOCPs), {[Ni(bipy) (H2O4)(4)](2,6-nds)center dot 4H(2)O} (1), {[Ni(bipy)(H2O4)(4)](2,6-nds)center dot 2H(2)O} (2), {[Ni (bjpy)(H2O)(4)](2,6-nds)} (3), {[Ni (bipy)(H2O)(4)](2,6-nds)} (4). {[Cu (bipy)(H2O)(4)]-(2,6-nds)} (5) (bipy = 4,4'-bipyridyl; 2,6-nds = 2,6-naphthalenedisulphonate) have been synthesized and structurally characterized. Compounds 1 and 5 were synthesized at room temperature in H2O/EtOH medium, whereas 2-4 were isolated under hydrothermal conditions. Compounds 1-4 were synthesized maintaining the same stoichiometric ratio of metal and ligand under different reaction temperatures, and the different structures of the compounds indicate that the temperature plays a significant role in the construction of the coordination polymers. Structural characterization reveals that the one-dimensional [M(bipy)(H2O)(4)](2+) cationic chain is a basic building unit for all of the MOCPs, while 2,6-nds remains as a counteranion. In all cases, 2,6-nds counteranions interact with water and bipy molecules through strong hydrogen-bonding and pi-pi interactions to afford three-dimensional supramolecular structures. Compounds 1-4 have the same building unit with different network Superstructures and are related as supramolecular isomers. Supramolecular isomerism in 3 and 4 is very interesting since they have the same molecular formula, {[Ni(bipy)(H2O)(4)](2,6-nds)}, and are polymorphs. Compounds 4 and 5 are isomorphous. The thermogravimetric study suggests that the dehydrated compounds are stable up to 300 degrees C. Furthermore, sorption studies suggest that dehydrated compounds of 1 and 2 are permanently porous.