Sukhen Bala

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.

Construction of Polynuclear Lanthanide (Ln = DyIII, TbIII, and NdIII) Cage Complexes Using Pyridine–Pyrazole-Based Ligands: Versatile Molecular Topologies and SMM Behavior

Employment of two different pyridyl-pyrazolyl-based ligands afforded three octanuclear lanthanide(III) (Ln = Dy, Tb) cage compounds and one hexanuclear neodymium(III) coordination cage, exhibiting versatile molecular architectures including a butterfly core. Relatively less common semirigid pyridyl-pyrazolyl-based asymmetric ligand systems show an interesting trend of forming polynuclear lanthanide cage complexes with different coordination environments around the metal centers. It is noteworthy here that construction of lanthanide complex itself is a challenging task in a ligand system as soft N-donor rich as pyridyl-pyrazol. We report herein some lanthanide complexes using ligand containing only one or two O-donors compare to five N-coordinating sites. The resultant multinuclear lanthanide complexes show interesting magnetic and spectroscopic features originating from different spatial arrangements of the metal ions. Alternating current (ac) susceptibility measurements of the two dysprosium complexes display frequency- and temperature-dependent out-of-phase signals in zero and 0.5 T direct current field, a typical characteristic feature of single-molecule magnet (SMM) behavior, indicating different energy reversal barriers due to different molecular topologies. Another aspect of this work is the occurrence of the not-so-common SMM behavior of the terbium complex, further confirmed by ac susceptibility measurement.

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.

Design of chiral Co(II)-MOFs and their application in environmental remediation and waste water treatment

The present work reports the construction of new Co-MOFs based on an amide based bispyrazole ligand and different carboxylic acids with potential applications in the sphere of CO2 adsorption and photocatalytic waste water treatment. Four multifunctional MOFs, with a wide variety of dimensionality, porosity and surface characteristics were exploited for this purpose. The unique bis-bidentate nature of the ligand with two chelating compartments along with a semi-rigid backbone leads to some interesting chiral MOFs. Detail self-assembly studies reveals that both helicity as well as local environments around the metal centres are responsible for chirality. A detailed investigation shows the importance of these materials as chiral zeolite analogues for environmental remediation. The much improved photocatalytic degradation of a representative toxic dye molecule highlights the advantages of MOFs over the usual metal oxide based semiconductors as remediation materials. Furthermore, MOFs with an ability to capture CO2 gas, offer a solution to environmental pollutions.

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.