Sumi Ganguly

Identification of a robust and reproducible noncluster-type SBU: effect of coexistent groups on network topologies, helicity, and properties

The present work is part of our ongoing quest for a robust and reproducible noncluster-type secondary building unit (SBU) using pyrazole based ditopic ligands and benzene polycarboxylic acids. We report here the construction of a series of Zn(II) coordination polymers using a tailor-made SBU, designed with the proper utilization of the hydrogen bonds of a pyrazole-based ligand 4,4′-methylene-bispyrazole (H2MBP) and isophthalic acid (H2IPA), and its derivatives (R-H2IPA; R = OH, OCH3, CH3, tBu, Br, I, NH2, N3). The results demonstrate that the substituent effect of R-isophthalates does play a decisive role in directing the structural assemblies of this system. One of the promising features of the 2D networks of this series is the presence of SBU-based helical motifs, which by and large remain elusive despite the plethora of reports on various SBU based networks. Throughout the series, hydrogen bonds, π–π interactions and other intermolecular interactions play a crucial role in stabilizing the resulting networks. Furthermore, some of these complexes exhibit some interesting photoluminescent properties in the solid state.

Metallogels from Coordination Complexes, Organometallic, and Coordination Polymers

A supramolecular gel results from the immobilization of solvent molecules on a 3D network of gelator molecules stabilized by various supramolecular interactions that include hydrogen bonding, π-π stacking, van der Waals interactions, and halogen bonding. In a metallogel, a metal is a part of the gel network as a coordinated metal ion (in a discrete coordination complex), as a cross-linking metal node with a multitopic ligand (in coordination polymer), and as metal nanoparticles adhered to the gel network. Although the field is relatively new, research into metallogels has experienced a considerable upsurge owing to its fundamental importance in supramolecular chemistry and various potential applications. This focus review aims to provide an insight into the development of designing metallogelators. Because of the limited scope, discussions are confined to examples pertaining to metallogelators derived from discrete coordination complexes, organometallic gelators, and coordination polymers. This review is expected to enlighten readers on the current development of designing metallogelators of the abovementioned class of molecules.

Azide-Functionalized Lanthanide-Based Metal–Organic Frameworks Showing Selective CO2 Gas Adsorption and Postsynthetic Cavity Expansion

We report herein selective CO2 gas adsorption by two azide-functionalized lanthanide-based metal-organic frameworks (MOFs). This work also demonstrates that azide-functionalized MOFs can be used for postsynthetic cavity expansion, further corroborated by enhanced gas-sorption data.

Construction of Co(II) coordination polymers comprising of helical units using a flexible pyrazole based ligand

1H-Pyrazole based molecules are potentially important in crystal engineering because of their ability to play a dual role in metal coordination as well as hydrogen bond formation using an in-built hydrogen bonding site. We report here the construction of a series of coordination polymers using a flexible pyrazole based ditopic ligand and different benzene polycarboxylic acids as auxiliary ligands. For all the structures, hydrogen bonding and π–π stacking were found to be instrumental in bringing additional stability to the self-assembly of these polymeric networks. Furthermore, we have successfully demonstrated the strategy of introducing helicity in the resultant polymeric network using a V-shaped ligand, H2MBP for the present work.

Influence of chloro⋯chloro interaction and π–π stacking in 3D supramolecular framework construction

A series of 1D and 2D coordination polymers have been synthesized under solvothermal conditions using a terminal ligand, 3,5,6-trichlorosalicylic acid (H2TCSA) and different bipyridine based ligands, 2,2′-bipyridyl (2,2′-BIPY), 4,4′-bipyridyl (4,4′-BIPY), 4,4′-trimethylene bipyridine (TMBP) and trans-1,2-bis(4-pyridyl)-ethylene (TBPE). The major aim of this work was to study the influence of weak interactions in constructing 3D supramolecular frameworks. A two-step crystal engineering strategy has been adopted for generating 3D supramolecular frameworks. Firstly, various lower dimensional coordination networks have been achieved and then 3D supramolecular frameworks were constructed from the self-assembly of these networks via weak intermolecular interactions among the organic parts. The latter was achieved with the usage of ligand systems that are devoid of any conventional hydrogen bonding functional group. On the other hand, employment of a terminal ligand serves the purpose of generating different lower dimensional architectures, ranging from discrete zero dimensional coordination complexes to 1D, 2D coordination polymeric networks. We report herein, two 0D complexes, [Zn(HTCSA)2(TBPE)2] (1), [{Zn(TCSA)(2,2′-BIPY)}4] (2), five 1D coordination polymers, [Zn(TCSA)(4,4′-BIPY)0.5(DMF)]n(3), [Zn(HTCSA)2(4,4′-BIPY)]n(4), [Zn(HTCSA)2(TMBP)]n(5), [Zn(HTCSA)2(TMBP)]n (6), [Zn(HTCSA)2(TBPE)(H2O)]n (7), and two 2D polymeric networks, [Zn(TCSA)(4,4′-BIPY)]n (8) and [{Zn(TCSA)(TBPE)}·(TBPE)]n (9), and two related cobalt and nickel complexes, [{Co(TCSA)(TBPE)}·(TBPE)]n (10) and [Ni(HTCSA)(TBPE)1.5·(NO3)]n (11). For all the structures, π–π stacking and halogen bonding were found to be instrumental in bringing the additional dimensions to the self-assembly of the lower dimensional networks and lead to diverse 3D supramolecular frameworks.

Chapter 2:Designing Soft Supramolecular Materials Using Intermolecular Interactions

Gelation of solvent(s) by low molecular weight gelators (LMWGs – small molecules having MW <3000) is a supramolecular phenomenon. Aggregation of 1D fibres resulting from supramolecular self-assembly of gelator molecules, giving rise to a 3D gel network known as self-assembled fibrillar networks (SAFiNs), is believed to be the key factor in gelation. Molecules containing metal atoms that take part in forming SAFiNs resulting in gels (known as metallogels) are also known. Solvent molecules are immobilized due to surface tension or capillary force actions within such 3D network resulting in gel. The wide range of applications that these soft materials offer attracted worldwide attention and there has been an upsurge in research activities involving LMWGs in recent years. Due to the lack of molecular level insights of the gelation mechanism, designing LMWGs is a daunting task and as a consequence, serendipity plays a prominent role in discovering most of the gelators and subsequent design of the next generation gelators are based on modifying the serendipitously-obtained parent gelator molecules. This chapter focuses on the designing aspects and applications of LMWGs, including metal-containing gelator molecules. It particularly covers the development of supramolecular synthon approach in the context of crystal engineering along with the other strategies to design such rewarding soft-materials.

Stimuli-Responsive Metallogels for Synthesizing Ag Nanoparticles and Sensing Hazardous Gases

A newly synthesized bis-pyridyl ligand having a diphenyl ether backbone (LP6) displayed the ability to form crystalline coordination polymers (CP1-CP6) which were fully characterized by single crystal X-ray diffraction. Most of the resulting polymers were lattice-occluded crystalline solids-a structural characteristic reminiscent to gels. The reactants of the coordination polymers produced metallogels in DMSO/water confirming the validity of the design principles with which the coordination polymers were synthesized. Some of the metallogels displayed material properties like in situ synthesis of Ag nanoparticles and stimuli-responsive gel-sol transition including sensing hazardous gases like ammonia and hydrogen sulfide.