Arpan Hazra

A flexible supramolecular host with a crowned chair octameric water cluster and highly selective adsorption properties

A novel supramolecular host {[Fe(CN)6]·(H-bipy)3·8H2O} (1) was obtained by the reaction of K3[Fe(CN)6] and 4,4′-bipyridyl (bipy) under an acidic medium (pH ≈ 3). The supramolecular structure of 1 is made up of non-covalent forces viz. hydrogen bonding and π–π interactions. The host houses a discrete octameric water cluster with the conformation of a 1,4-substituted cyclohexane molecule where six water molecules are positioned on the vertices of the cyclohexane ring and the seventh and eighth occupy the 1,4-equatorial positions of the ring. DFT calculations suggest that this conformation is more stable (−73.08 kcal mol−1) when compared to the a,a conformation. Upon removal of the water molecules, the host network of 1 undergoes a structural transformation and the dehydrated phase exhibits a stepwise uptake of H2O vapour and completely excludes CO2 and other organic solvent molecules (CH3OH, CH3CN and EtOH).

A nanoporous borocarbonitride (BC4N) with novel properties derived from a boron-imidazolate-based metal-organic framework.

Soak it up: A boron‐imidazolate metal–organic framework composed of a mixed ligand system acts as a precursor for the synthesis of a high‐surface‐area borocarbonitride (BC4N) with remarkable H2 and CO2 storage properties (see figure; ndc=naphthalenedicarboxylate). Furthermore, BC4N has been exploited for the stabilisation of metal (Au and Pd) nanoparticles.

Host-Guest [2+2] Cycloaddition Reaction: Postsynthetic Modulation of CO2 Selectivity and Magnetic Properties in a Bimodal Metal-Organic Framework.

Simultaneous tuning of permanent porosity and modulation of magnetic properties by postsynthetic modification (PSM) with light in a metal-organic framework is unprecedented. With the aim of achieving such a photoresponsive porous magnetic material, a 3D photoresponsive biporous framework, MOF1, which has 2D channels occupied by the guest 1,2-bis(4-pyridyl)ethylene (bpee), H2 O, and EtOH molecules, has been synthesized. The guest bpee in 1 is aligned parallel to pillared bpee with a distance of 3.9 Å between the ethylenic groups; this allows photoinduced PSM of the pore surface through a [2+2] cycloaddition reaction to yield MOF2. Such photoinduced PSM of the framework structure introduces enhanced CO2 selectivity over that of N2 . The higher selectivity in MOF2 than that of MOF1 is studied through theoretical calculations. Moreover, MOF2 unveils reversible changes in Tc with response to dehydration-rehydration. This result demonstrates that photoinduced PSM is a powerful tool for fabricating novel functional materials.

First examples of two ferromagnetic end-to-end cyanate bridged 1D linear coordination polymers of nickel(II) containing an unsymmetrical diamine

Two new end-to-end (EE) cyanate bridged 1D coordination polymers of Ni(II) are isolated which contain linear (180°) Ni-N-C and Ni-O-C angles in Ni-NCO-Ni bridges and show ferromagnetic (F) coupling in agreement with the reported theoretical model for linear EE bridges.

Crystal Dynamics in Multi‐stimuli‐Responsive Entangled Metal–Organic Frameworks

An understanding of solid-state crystal dynamics or flexibility in metal-organic frameworks (MOFs) showing multiple structural changes is highly demanding for the design of materials with potential applications in sensing and recognition. However, entangled MOFs showing such flexible behavior pose a great challenge in terms of extracting information on their dynamics because of their poor single-crystallinity. In this article, detailed experimental studies on a twofold entangled MOF (f-MOF-1) are reported, which unveil its structural response toward external stimuli such as temperature, pressure, and guest molecules. The crystallographic study shows multiple structural changes in f-MOF-1, by which the 3 D net deforms and slides upon guest removal. Two distinct desolvated phases, that is, f-MOF-1 a and f-MOF-1 b, could be isolated; the former is a metastable one and transformable to the latter phase upon heating. The two phases show different gated CO2 adsorption profiles. DFT-based calculations provide an insight into the selective and gated adsorption behavior with CO2 of f-MOF-1 b. The gate-opening threshold pressure of CO2 adsorption can be tuned strategically by changing the chemical functionality of the linker from ethanylene (-CH2 -CH2 -) in f-MOF-1 to an azo (-N=N-) functionality in an analogous MOF, f-MOF-2. The modulation of functionality has an indirect influence on the gate-opening pressure owing to the difference in inter-net interaction. The framework of f-MOF-1 is highly responsive toward CO2 gas molecules, and these results are supported by DFT calculations.

Binder driven self-assembly of metal-organic cubes towards functional hydrogels

The process of assembling astutely designed, well-defined metal-organic cube (MOC) into hydrogel by using a suitable molecular binder is a promising method for preparing processable functional soft materials. Here, we demonstrate charge-assisted H-bonding driven hydrogel formation from Ga3+-based anionic MOC ((Ga8(ImDC)12)12−) and molecular binders, like, ammonium ion (NH4+), N-(2-aminoethyl)-1,3-propanediamine, guanidine hydrochloride and β-alanine. The morphology of the resulting hydrogel depends upon the size, shape and geometry of the molecular binder. Hydrogel with NH4+ shows nanotubular morphology with negative surface charge and is used for gel-chromatographic separation of cationic species from anionic counterparts. Furthermore, a photo-responsive luminescent hydrogel is prepared using a cationic tetraphenylethene-based molecular binder (DATPE), which is employed as a light harvesting antenna for tuning emission colour including pure white light. This photo-responsive hydrogel is utilized for writing and preparing flexible light-emitting display.A possible route to producing processable soft materials is by assembling metal organic cubes into hydrogels. Here the authors show charge-assisted H-bond driven self-assembly of Ga3+-based anionic metal organic cubes and suitable molecular binders towards multi-functional hydrogels.

Solvent-Modulated Emission Properties in a Superhydrophobic Oligo(p-phenyleneethynylene)-Based 3D Porous Supramolecular Framework

A chromophoric oligo( p-phenyleneethynylene) (OPE) bola-amphiphile with dioxyoctyl side chains (H2OPE-C8) has been self-assembled with CdII to form a 1D coordination polymer, {Cd(OPE-C8)(DMF)2(H2O)} (1), which is further interdigitated to form a 2D network. Such 2D networks are further interwoven to form a 3D supramolecular framework with surface-projected alkyl chains. The desolvated framework showed permanent porosity, as realized from the CO2 adsorption profile. 1 showed high water contact angles, portraying its superhydrophobic nature. 1 also showed a linker-based cyan luminescence. Solvent removal led to a bathochromic shift in emission into the green region. Resolvation with N, N-dimethylformamide brought back the original cyan emission, whereas for tetrahydrofuran, ethanol, and methanol, it persisted at an intermediate state. Density functional theory calculations unraveled that, twisting of the OPE phenyl rings generated the red shift in emission.

Tetracarboxylate Linker-Based Flexible CuII Frameworks: Efficient Separation of CO2 from CO2/N2 and C2H2 from C2H2/C2H4 Mixtures

We report the synthesis, structure, and adsorption properties of two new metal–organic frameworks (MOFs) {[Cu2(bpp)3(L1)]·(bpp)·(4H2O)} (1) and {[Cu2(bipy)2(L2)(H2O)2]·(bipy)·(5H2O)} (2) obtained from two different flexible tetracarboxylate linkers (L1 and L2) of variable lengths and flexibility. While 1 comprising CuII, L1, and 1,3-bis(4-pyridyl) propane (bpp) is a 2D MOF with a cage-type structure, 2 consisting of CuII, L2, and 4,4′-bipyridine (bipy) has a 3D twofold interpenetrated structure. Both frameworks manifest permanent porosity, as realized from CO2 adsorption at 195 K. 2 shows excellent CO2/N2 and C2H2/C2H4 adsorption selectivity at 298 K. This has been established by using 2 as a separating medium in a breakthrough column for separating mixtures of CO2/N2 (15:85, v/v) and C2H2/C2H4 (1:99, v/v). The selectivity of 2 toward CO2 over N2 and C2H2 over C2H4 is governed by favorable thermodynamic interactions owing to its structural flexibility, unsaturated metal sites, and polar carboxylate groups. Thus, 2 proves to be an extremely efficient material for specific gas separation.