Arijit Goswami

Co-MOF as a sacrificial template: manifesting a new Co3O4/TiO2 system with a p–n heterojunction for photocatalytic hydrogen evolution

The present work reports a novel method for preparing an elusive Co3O4/TiO2 p–n heterojunction using Co-based metal organic frameworks (Co-MOFs) as a TiO2-absorbent cum sacrificial template for nanocomposite formation. Four new Co-MOFs based on a bispyrazole ligand and different carboxylic acids, with a wide variety of dimensionality, porosity and surface characteristics, were exploited for this purpose. We detail here the synthesis of cobalt MOFs using the hydro(solvo)thermal method and structural characterization by single crystal X-ray diffraction (XRD). We have also successfully demonstrated our strategy of using MOFs for fabricating superior p–n diode-type Co3O4/TiO2 hetero-nanocomposites for photocatalytic hydrogen production. The characterization results suggested that the nanocomposites consisted of highly crystalline desired anatase TiO2 nanoparticles and spinel Co3O4-like species. The nanocomposite with 2 wt% Co loading exhibited the maximum photoactivity with a hydrogen evolution rate of ∼7 mmol g−1 h−1 under UV-vis light irradiation. The above results indicate that the present preparative strategy is an amenable route for the synthesis of desirable synergistic photocatalysts combining a remarkable reactivity relevant to solar energy conversion.

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.

Construction of helical networks by using multiple V-shaped mixed ligand systems

Helical coordination polymers constructed from multiple ligand systems are not common despite the plethora of recent reports on helical networks. We report here the construction of a series of mixed ligand based helical coordination polymers showing metal dependent architecture. The strategy of using a combination of ligand molecules, each capable of forming helical networks, is novel and should enable us to design helical MOFs of interesting topology.

Silver-promoted gelation studies of an unorthodox chelating tripodal pyridine–pyrazole-based ligand: templated growth of catalytic silver nanoparticles, gas and dye adsorption

A novel tripodal pyridine–pyrazole based tris amide ligand, namely, N1,N3,N5-tris(3-(pyridin-2-yl)-1H-pyrazol-5-yl)benzene-1,3,5-tricarboxamide was synthesized. The ligand acts as a promising low molecular weight gelator that gels silver salts in presence of water. The gels formed were found to be highly stable to heat and stress. Moreover, silver ions not only act as a gelling agent but also participate in nanoparticulate formation. The three-dimensional ligand–silver gel matrix serves as an excellent platform for the growth of these silver nanoparticles. The gels were characterized thoroughly using IR spectroscopy, UV-visible spectroscopy, SEM, TEM and rheological studies. TEM pictures revealed the nanoparticles to be attached exclusively onto the gel fibres confirming template formation. The silver nanoparticles not only provide high strength and stability to the gel network but also show excellent catalytic properties in reducing 4-nitrophenol and Methylene Blue dye in presence of sodium borohydride. In addition to the catalytic properties, xerogels displayed gas and dye adsorption properties.

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.