Tapas Kumar Maji

Supramolecular Hydrogels and High‐Aspect‐Ratio Nanofibers through Charge‐Transfer‐Induced Alternate Coassembly

Weak charge-transfer interactions between electron-rich and electron-deficient aromatic molecules have been extensively used for the design of various supramolecular assemblies in solution, such as rotaxanes, catenanes, and foldamers. The conformation of various donor–acceptor (D–A) polymers in solution has been tuned by chargetransfer interactions in synergy with either solvophobic or ion-binding interactions. In addition, extended solid-phase assemblies of alternate donor and acceptor molecules for device applications were attained by cocrystallization and liquid-crystalline mesophase coassembly. Columnar mesophases of alternate donor and acceptor molecules have enhanced columnar organization and higher charge-carrier mobilities compared to their individual components. 1D self-assembled nanowires based on organic p-conjugated systems have attracted a great deal of attention in recent years in the field of organic and supramolecular electronics. 10] Several approaches, which make use of hydrogenbonding and p-stacking interactions, have been used to design self-assembled fibers of donor–acceptor arrays, and create supramolecular p–n heterojunctions for photovoltaics. However, use of charge-transfer interactions for the design of two-component, alternate 1D supramolecular fibers of donor and acceptor molecules in solution is difficult to achieve, as the orthogonal self-assembly (phase separation) of individual components may prevent their efficient coassembly, and hence a careful design of monomers is required. 1D charge-transfer nanofibers are expected to exhibit better conductivity caused by the directional movement of their high-density charge carriers and a well-ordered, stronger p-stacked architecture as a result of better p overlapping of face-to-face-packed aromatic molecules. 13] These observations prompted us to investigate whether nanofibers of alternate donor and acceptor molecules coassembled through charge-transfer interactions can be constructed using supramolecular chemistry design principles. Herein, we show that high-aspect-ratio cylindrical micelles and hydrogels of a donor–acceptor charge-transfer complex can be constructed by self-assembly in water. Although a variety of peptide and rod–coil amphiphiles, as well as sugar derivatives, have been reported to form hydrogels, this is the first report of hydrogel formation that exploits charge-transfer interactions between chromophores. We synthesized a donor–acceptor pair, a coronene tetracarboxylate tetrapotassium salt (CS), and a dodecylfunctionalized methyl viologen derivative (DMV) for the design of coassembled nanostructures (Scheme 1). After

Chemistry of porous coordination polymers

Remarkable advances in the recent development of porous compounds based upon coordination polymers have paved the way toward functional chemistry having potential applications such as gas storage, separation, and catalysis. From the synthetic point of view, the advantage is a designable framework, which can readily be constructed from building blocks, the so-called bottom-up assembly. Compared with conventional porous materials such as zeolites and activated carbons, porous inorganic-organic hybrid frameworks have higher potential for adsorption of small molecules because of their designability with respect to the coordination geometry around the central metal ion as well as size and probable multifunctionality of bridging organic ligands. Although rigidity and robustness of porous framework with different degree of adsorption are the most studied properties of metal-organic coordination frameworks, there are few studies on dynamic porous frameworks, which could open up a new dimension in materials chemistry.

Temperature- and stoichiometry-controlled dimensionality in a magnesium 4,5-imidazoledicarboxylate system with strong hydrophilic pore surfaces.

1D, 2D, and 3D three metal-organic hybrid frameworks of Mg (II) have been synthesized using 4,5-imidazoledicarboxylic acid (H 3idc) with control of the temperature and stoichiometry in a hydrothermal technique. All of the frameworks show high thermal stability, and frameworks 1D and 3D provide highly hydrophilic pore surfaces, correlated by the selective sorption of water molecules over the organic vapor and other gases like N 2 and CO 2.

Flexible and Rigid Amine-Functionalized Microporous Frameworks Based on Different Secondary Building Units: Supramolecular Isomerism, Selective CO2 Capture, and Catalysis

We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH2 bdc)(bphz)0.5 ]⋅DMF⋅H2 O}n (NH2 bdc=2-aminobenzenedicarboxylic acid, bphz=1,2-bis(4-pyridylmethylene)hydrazine) composed of a mixed-ligand system. The first isomer, with a paddle-wheel-type Cd2 (COO)4 secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a μ-oxo-bridged Cd2 (μ-OCO)2 SBU. Both frameworks are two-fold interpenetrated and the pore surface is decorated with pendant -NH2 and NN functional groups. Both the frameworks are nonporous to N2 , revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double-step hysteretic CO2 adsorption profile, whereas the second isomer shows a typical type I CO2 profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO2 among other gases (N2 , O2 , H2 , and Ar), which has been correlated to the specific interaction of CO2 with the -NH2 and NN functionalized pore surface. DFT calculations for the oxo-bridged isomer unveiled that the -NH2 group is the primary binding site for CO2 . The high heat of CO2 adsorption (ΔHads =37.7 kJ mol(-1) ) in the oxo-bridged isomer is realized by NH2 ⋅⋅⋅CO2 /aromatic π⋅⋅⋅CO2 and cooperative CO2 ⋅⋅⋅CO2 interactions. Further, postsynthetic modification of the -NH2 group into -NHCOCH3 in the second isomer leads to a reduced CO2 uptake with lower binding energy, which establishes the critical role of the -NH2 group for CO2 capture. The presence of basic -NH2 sites in the oxo-bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.

A pillared-bilayer porous coordination polymer with a 1D channel and a 2D interlayer space, showing unique gas and vapor sorption

A new 2D pillared-bilayer porous coordination polymer (PCP) has been synthesized and structurally characterized that shows selective adsorption of CO(2) over other gases (N(2), O(2), Ar, H(2), CH(4)) and guest selective single/double-step adsorption of vapor correlated to the successive confinement of adsorbates in a 1D channel and a 2D interlayer space.

Amine‐Responsive Adaptable Nanospaces: Fluorescent Porous Coordination Polymer for Molecular Recognition

Flexible and dynamic porous coordination polymers (PCPs) with well-defined nanospaces composed of chromophoric organic linkers provide a scaffold for encapsulation of versatile guest molecules through noncovalent interactions. PCPs thus provide a potential platform for molecular recognition. Herein, we report a flexible 3D supramolecular framework {[Zn(ndc)(o-phen)]⋅DMF}n (o-phen = 1,10-phenanthroline, ndc = 2,6-napthalenedicarboxylate) with confined nanospaces that can accommodate different electron-donating aromatic amine guests with selective turn-on emission signaling. This system serves as a molecular recognition platform through an emission-readout process. Such unprecedented tunable emission with different amines is attributed to its emissive charge-transfer (CT) complexation with o-phen linkers. In certain cases this CT emission is further amplified by energy transfer from the chromophoric linker unit ndc, as evidenced by single-crystal X-ray structural characterization.

Synthesis, crystal structure and magnetic behavior of three polynuclear complexes: [Co(pyo)2(dca)2]n, [Co3(ac)4(bpe)3(dca)2]n and [{Co(male)(H2O)2}(H2O)]n [pyo, pyridine-N-oxide; dca, dicyanamide; ac, acetate; bpe, 1,2-bis-(4-pyridyl)ethane and male, maleate]

Three polymeric cobalt(II) complexes of formulae [Co(pyo)2(dca)2]n (1), [Co3(ac)4(bpe)3 (dca)2]n (2) and [{Co(male)(H2O)2(H2O)]n (3) [pyo, pyridine-N-oxide; dca, dicyanamide; ac, acetate; bpe, 1,2-bis-(4-pyridyl)ethane and male, maleate] have been synthesized and characterized structurally as well as magnetically. The structure determination of complex 1 shows that each octahedral Co(II) in the 1D coordination chain is attached with four μ-1,5-dicyanamide and two pendant pyridine-N-oxide ligands, which form mutual relationships with other 1D chains through non-covalent π-π interactions, giving rise to a 2D infinite sheet-like structure. The molecular structure reveals that complex 2 adopts an infinite three-leg ladder-like structure in which three parallel 1D Co(bpe) chains are connected by syn-syn and oxo bridging acetate ligands. The dicyanamide ligands are pendant to the terminal Co(II) centers. Complex 3 is an infinite 3D network in which carboxylate groups of the maleate ligand are linked to Co(II) centers in syn-anti fashion. The structure of complex 3 has already been reported. The variable temperature (300–2 K) magnetic measurements have been performed for all three complexes. In the case of 2, the full structure can be rationalized as quasi-isolated trimers; the exchange Hamiltonian that describes magnetic interactions between the effective S′ = 1/2 spins, at low temperature is . Fixing g⊥ = 6.01 and g∣∣ = 2.25, according to the EPR measurements at 4 K, 2J = −3.3 cm−1 is the best-fit parameter. For 1 and 3, complete fits are not possible for calculating the corresponding J parameters for the one- and three-dimensional structures, respectively. Only an approximate J value has been calculated for 1.

Guest‐Responsive Reversible Swelling and Enhanced Fluorescence in a Super‐Absorbent, Dynamic Microporous Polymer

A swell idea! The guest-responsive reversible swelling and fluorescence enhancement of a dynamic, microporous polymer network is presented. Guest-induced breathing of hydrophobic pores imparts multi-functional properties, such as super-absorbency, phase-selective swelling of oil from water and encapsulation of C(60) (see figure), to this soft micro-porous organic polymer.

Polymeric networks of copper(II) using succinate and aromatic N–N donor ligands: synthesis, crystal structure, magnetic behaviour and the effect of weak interactions on their crystal packing

Four succinato-bridged complexes of copper(II) have been synthesized. Complex 1, [Cu(2)(mu-OH(2))(2)L(bpy)(2)(NO(3))(2)](n) and 2, [Cu(2)(mu-OH(2))(2)L(phen)(2)(NO(3))(2)](n)(bpy = 2,2[prime or minute]-bipyridine; phen = 1,10-phenanthroline and LH(2)= succinic acid) exhibit 1D coordination polymer structures where both the nitrate ions are directly linked to the copper(ii) producing synthons in a 2D sheet. A novel 2D grid-like network, ([Cu(4)L(2)(bpy)(4)(H(2)O)(2)](ClO(4))(4)(H(2)O))n3, is obtained upon changing the nitrate by perchlorate anion in complex 1, where the channels are occupied by the anions. On changing the nitrate by tetrafluoroborate anion in complex 2, a novel octanuclear complex, [Cu(8)L(4)(phen)(12)](BF(4))(8).8H(2)O 4, is isolated. The coligand bpy and phen in these complexes show face-to-face (in 1,2,3,4) or edge-to-face (in 4 )pi-pi interactions forming the multidimensional supramolecular architectures. Interestingly, the appearance of edge-to-face pi-pi interactions in complex facilitates the formation of discrete octanuclear entities. Variable-temperature (300-2 K) magnetic measurements of complexes have been done. Complexes 1 and 2 show very weak antiferromagnetic (OOC-CH(2)-CH(2)-COO) and ferromagnetic coupling (mu-H(2)O). Complex 3 also shows antiferromagnetic (syn-syn mu-OCO), and ferromagnetic coupling (mu-O of the -COO group). Complex 4 with two types (syn-syn and syn-anti) of binding modes of the carboxylate group shows strong antiferromagnetic interaction.

Amide Functionalized Microporous Organic Polymer (Am-MOP) for Selective CO2 Sorption and Catalysis

We report the design and synthesis of an amide functionalized microporous organic polymer (Am-MOP) prepared from trimesic acid and p-phenylenediamine using thionyl chloride as a reagent. Polar amide (-CONH-) functional groups act as a linking unit between the node and spacer and constitute the pore wall of the continuous polymeric network. The strong covalent bonds between the building blocks (trimesic acid and p-phenylenediamine) through amide bond linkages provide high thermal and chemical stability to Am-MOP. The presence of a highly polar pore surface allows selective CO2 uptake at 195 K over other gases such as N2, Ar, and O2. The CO2 molecule interacts with amide functional groups via Lewis acid-base type interactions as demonstrated through DFT calculations. Furthermore, for the first time Am-MOP with basic functional groups has been exploited for the Knoevenagel condensation reaction between aldehydes and active methylene compounds. Availability of a large number of catalytic sites per volume and confined microporosity gives enhanced catalytic efficiency and high selectivity for small substrate molecules.