A series of Zn(II) complexes with a flexible ligand have been synthesized in the presence of different anions [Cl -(1) and (4), CH 3 COO -(2), CF 3 COO -(3), Br -(5), I -(6), HCO 2 -(7), SO 4 -(8) and ( 9), and NO 3 -(10)]. Employment of different anions have resulted in different architectures, ranging from discrete zero-dimensional to infinite one-, two-, and three-dimensional (1D, 2D, and 3D) coordination polymers. Complexes 1, 2, and 3 exhibit binuclear metallocyclic zero-dimensional structures, while 4-7 form 1D helical networks. Among the halides, Cland Brform interesting helical networks with the coexistence of both left-handed and right-handed helical chains, while the introduction of Iion results in a water mediated right-handed helical network. Complex 7, on the other hand, represents an unique example of an alternative array of a left-handed and right-handed helical network, which can also be described as a hydrogen bonded 2D (4,4) network. Complexes 8 and 9 exhibit bilayer structures containing a distinct nanoporous void and channels within the networks. Furthermore, complexes 8 and 9 can be described as resulting from the structural transformation of 1 and 2, respectively, by replacing the terminally coordinated anions with bridging sulfate ions, whereas complex 10 exhibits a 2-fold interpenetrated diamondoid network assisted by the molecular recognition of the nitrate ions. Throughout the series, hydrogen bonds, anion-π interactions, and other intermolecular interactions involving the anions play some crucial role in stabilizing the resulting networks. Different conformations adopted by the flexible ligand further facilitate to achieve a suitable coordination environment around the metal center.

The present work reports the identification of a robust and reproducible metal-carboxylate noncluster-based secondary building unit (SBU) using flexible ligands, methylenebis(3,5-dimethylpyrazole), and homologous alkanedicarboxylic acids (HOOC-(CH 2 ) n -COOH). We have successfully synthesized a series of zinc(II) coordination polymers using a tailor-made SBU, designed with the proper utilization of the hydrogen bonds of a pyrazole-based ligand. We have identified a clear correlation between the type of auxiliary linker used and the vertex geometry that is present in the resultant network. This, in effect, can pave the way for the strategic control of the vertex geometry, which should enable us to design and predict the topology and dimensionality of a metal-organic framework.

N-unsubstituted pyrazole and carboxylic acid, being self-complementary molecules, offer a broad scope of study of binary compounds based on the complementary combination of H-bonding/donating sites. We report here the construction of five extended molecular networks in cocrystals of a pyrazole-based ditopic molecule and carboxylic acids. We have been able to identify three major supramolecualr synthons that would be helpful in the prediction of structural motifs for these kinds of studies. Interestingly, these heterosynthons are strikingly similar, both from the perspective of H-bond directionality and from the size of the synthons, to those of the homosynthons of the individual functional groups.

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The present work reports two Zn­(II) based metal–organic frameworks that show excellent proton conductivity with potential application in proton exchange membrane fuel cell development. Two polymeric networks (PDA-FA and PDA-WC) were synthesized using two flexible ligands, a bispyrazole ligand and 1,4-phenyl diacetic acid. Structural studies show some intriguing crystallographic phenomena including the occurrence of different conformations in the same crystal lattice. Furthermore, the compounds exhibit excellent chemical and thermal stability. Both compounds show some important structural features that make them highly suitable candidates for proton conductivity. Compound PDA-FA shows not-so-common immobilized free COOH groups grafted onto the inner surface of the network. An extensively H-bonded water–methanol cluster, on the other hand, dominated the crystal structure of PDA-WC. The above features indicate that both MOFs are suitable for fuel cell development, while further support comes from the corroborating variable temperature proton conductivity data.