Soumyabrata Goswami

A porous metal organic framework with a bcu-type topology involving in situ ligand formation – synthesis, structure, magnetic property and gas adsorption studies

A three-dimensional (3D) porous metal organic framework namely, {[Cu3(N3)2(4-ptz)4(DMF)2]·2DMF}n, has been synthesized using Cu(CH3COO)2·H2O and ligand 4-ptz [5-(4-pyridyl)-tetrazolate] which was formed in situ from 4-cyanopyridine and sodium azide in presence of water and CuII ions. Crystal structure analysis showed that the complex crystallizes in the monoclinic space group P21/c and has a decorated body centred cubic (bcu) topological net with 8-connected Cu3 cluster as node. Magnetic studies exhibit prominent antiferromagnetic interactions influenced by EO (end on) azide and μ2,η2-tetrazolato bridge among the metal centres. Gas adsorption studies reveal moderate carbon dioxide uptake, which is also reflected in the isosteric heat of adsorption (Qst) value of −28 kJ mol−1.

A 3D Iron(II)-Based MOF with Squashed Cuboctahedral Nanoscopic Cages Showing Spin-Canted Long-Range Antiferromagnetic Ordering

The reaction of dilithium squarate with Fe(II) perchlorate led to the formation of a new Fe(II)-based 3D MOF, [Fe3(OH)3(C4O4)(C4O4)0.5]n (1), with homoleptic squashed cuboctahedral cages. Complex 1 crystallizes in the monoclinic C2/c space group. Fe(II) centers in the complex are octahedrally coordinated by four squarate dianions in axial and equatorial positions and two hydroxyl groups in the remaining equatorial positions. The interesting structural feature of 1 is that the three-dimensional framework is an infinite extension of nanoscopic cuboctahedral cages. The framework also contains two types of voids; the larger hydrophobic ones are surrounded by aromatic squarate ligands, while the smaller ones are hydrophilic with hydroxyl groups on the surface connected by bifurcated hydrogen bonding interaction. A variable temperature magnetic study shows spin-canted long-range antiferromagnetic ordering in the low temperature regime.

Nanoscopic molecular magnets

Nanoscopic molecular magnets have attracted tremendous interest in recent years both from an experimental and a theoretical point of view because of their potential application in magnetic data storage devices, quantum computing and molecular spintronics. These molecules have crucial advantages over magnetic nanoparticles in terms of their perfectly mono-dispersed phase, chemical flexibility and high purity. This review discusses a few basic concepts that are needed to understand the magnetic properties observed in nanoscopic molecular magnets, a chemical approach for their synthesis and magneto-structural correlations. It includes a few selected examples and discusses the new trends in the field.

Correction to Serendipitous Assemblies of Two Large Phosphonate Cages: A Co15 Distorted Molecular Cube and a Co12 Butterfly Type Core Structure

This report describes the synthesis, characterization, and magnetic properties of two novel phosphonate-based Co(II) cages. Structural investigation reveals some interesting geometrical features in the molecular core that may provide new models in single molecular magnetic materials.

A 2D coordination polymer based on Co3-SBU showing spin-canting ferromagnetic behaviour

A 2D MOF with the secondary building unit [Co3(CTC)6(Py)2(OH)2] is synthesized using the sodium salt of a flexible ligand, cis,cis-cyclohexane-1,3,5-tricarboxylate (Na-CTC), and a cobalt trimer ([Co3O(CH3COO)6(Py)3]·ClO4). Structural analysis shows that the complex crystallizes in the monoclinic space group P21/n and forms a 2D framework with channel sizes of 9.0 × 4.2 A2. Magnetic characterization shows spin-canting ferromagnetic behaviour at low temperatures. Frequency dependency for in-phase (χ′M) and out-of-phase (χ′′M) signals at low temperatures is observed from the AC measurements. The gas adsorption behaviour suggests selectivity towards CO2 over N2, and demonstrates enhancement of CO2 uptake (19–33 cm3 g−1) on lowering the temperature (273–195 K).

A family of three magnetic metal organic frameworks: their synthesis, structural, magnetic and vapour adsorption study

Three flexible metal–organic frameworks (MOFs) based on aldrithiol linker and pyromellitate ligand, namely, [Co(aldrithiol)(pyromellitate)0.5(H2O)2]n (1), [Ni2(aldrithiol)2(pyromellitate)(H2O)2]n·2n(C2H5OH)·11n(H2O) (2) and [Cu(aldrithiol)2(pyromellitate)]n·2n(H2O) (3) have been synthesized through slow diffusion technique and characterized by structural, magnetic and adsorption studies. Single crystal X-ray studies show that compounds 1 and 3 have two-dimensional layered structures, whereas compound 2 adopts a three-dimensional framework structure. The observed dimensionality change might be due to the different orientation of pyridine rings in the flexible aldrithiol linker and versatile bridging modes of the pyromellitate ligand. In 1 and 2, the pyromellitate ligand coordinates to the metal centre in a monodentate fashion {(κ1)-(κ1)-(κ1)-(κ1)-μ4} and in 3, it coordinates in {(κ1)-(κ1)-μ2} fashion. The magnetic properties of 1–3 were investigated in detail and show weak antiferromagnetic coupling among the metal centres. Vapour sorption studies reveal that compounds 1 and 3 show high methanol vapour uptake, whereas compound 2 shows a decent amount of H2O adsorption. The dehydrated frameworks of 1–3 regenerate the as-synthesized framework structures upon exposure to water vapour.

Study of Heterogeneous Catalysis by Iron-Squarate based 3D Metal Organic Framework for the Transformation of Tetrazines to Oxadiazole derivatives

We present here a simple, milder, and environmentally benign heterogeneous catalytic method for the transformation of tetrazines to oxadiazole derivatives at room temperature (25 °C) using our earlier synthesized iron-squarate based 3D metal organic framework, [Fe3(OH)3(C4O4)(C4O4)0.5]n (FeSq-MOF).

Supramolecular heterogeneity in β-turn forming synthetic tripeptides nucleated by isomers of fluorinated phenylalanine and aib as corner residues

The influences of fluorines in chemistry have emerged as a breakthrough in various arenas of bio-organic and medicinal chemistry. But its incorporation in β-turn design and its implications for supramolecular chemistry remains in a rudimentary stage. Inspired by the diversity displayed by the isomers of mono-fluorinated phenylalanine in biological sciences, here our effort is to modulate the solid state conformational analysis of three terminally protected synthetic tripeptides Boc-(Y)-F-Phe-Aib-Xaa-OMe, where (Y is (2)-F-Phe, Xaa; Leu in peptide I, (3)-F-Phe, Xaa; Leu in peptide II and (4)-F-Phe, Xaa; Ile in peptide III). Interestingly, all the three peptides display a conformational preference for β-turns, stabilized by 4→1 intramolecular hydrogen bonding. Our investigation further demonstrates that mere interchange of positions of fluorines in mono-fluorinated phenylalanine in peptides I–III introduces significant diversity in supramolecular chemistry. X-ray crystallography sheds some light at atomic resolution. Furthermore, this supramolecular heterogeneous behavior is evident from the morphologies obtained from the materials of all the three peptides grown from acetone to petroleum ether solution, studied by field emission scanning electron microscopy. Thus, these monofluorinated peptides I–III may serve as prominent candidates in understanding the structure and function of misfolded disease causing peptides like prion and Alzheimers amyloid.

Transparent, free-standing, flexible and selective CO2 adsorbent films fabricated from homopolymer/metal salt hybrid gels

This article details our efforts to prepare free-standing macroscopic films by optimized coordinative crosslinking of poly(4-vinylpyridine) (P4VP) chains using transition metal ions. We encountered homogenous gels (at <1% w/v polymer concentration) en route to the fabrication of such films. The gels and films were obtained through coordinative crosslinking of P4VP chains by Ni(II) ions while the use of other metal ions (viz. Co(II), Cu(II) or Zn(II)) for this purpose resulted in either heterogeneous gels or gelatinous precipitates. Based on the gelation kinetics and the mechanical strength of the resulting films, the most optimum coordination ratio was observed to be 1 : 1 molar ratio of 4VP : Ni(II) in the methanol–water mixed solvent system. Highly transparent, flexible, free-standing films of any dimension and shape could be fabricated through controlled evaporation of the solvent from the gels. The microscopic features of these films were quite similar to those of xerogels. Magnetic susceptibility measurements performed on the ground films showed ferromagnetic interactions between adjacent Ni(II) centres in the temperature range of 75 to 10 K. These coordinatively crosslinked pliable films exhibited selective, although moderate, adsorption of environmentally relevant CO2 at room temperature. Through variation of the metal content in the films, we further demonstrated that the metal centres present in the film are intimately involved in the adsorption of CO2. We believe such coordinatively crosslinked polymer films can be a potential alternative to metal–organic frameworks (MOFs) in gas adsorption applications, with the added benefit of flexibility and macroscopic dimensions.

Exploration of the structural features and magnetic behaviour in a novel 3-dimensional interpenetrating Co(II)-based framework

AbstractA new Co(II)-based three-dimensional (3D) framework having the molecular formula [Co(C4O4) (4-bpmh))H2O)2]n⋅ 2nH2O⋅2nMeOH ⋅(1) (4-bpmh = N, N-bis-pyridin-4-ylmethylene-hydrazine) has been synthesized using a mixed ligand system and characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis, single crystal X-ray diffraction and variable temperature magnetic study. The framework is constructed by the bridging squarate (C