Suresh Sanda

Third-Generation Breathing Metal–Organic Framework with Selective, Stepwise, Reversible, and Hysteretic Adsorption Properties

A new 2D interdigitated and highly flexible, breathing metal-organic framework has been synthesized through a diffusion technique by using the aldrithiol linker and pyromellitate ligand. The compound shows selective, stepwise, reversible, and hysteretic adsorption properties for CO2 gas and H2O, MeOH, and CH3CN vapors.

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.

Study of Proton Conductivity of a 2D Flexible MOF and a 1D Coordination Polymer at Higher Temperature

We report the proton conduction properties of a 2D flexible MOF and a 1D coordination polymer having the molecular formulas {[Zn(C10H2O8)0.5(C10S2N2H8)]·5H2O]}n (1) and {[Zn(C10H2O8)0.5(C10S2N2H8)]·2H2O]}n (2), respectively. Compounds 1 and 2 show high conductivity values of 2.55 × 10(-7) and 4.39 × 10(-4) S cm(-1) at 80 °C and 95% RH. The conductivity value of compound 1 is in the range of those for previously reported flexible MOFs, and compound 2 shows the highest proton conductivity among the carboxylate-based 1D CPs. The dimensionality and the internal hydrogen bonding connectivity play a vital role in the resultant conductivity. Variable-temperature experiments of both compounds at high humidity reveal that the conductivity values increase with increasing temperature, whereas the variable humidity studies signify the influence of relative humidity on high-temperature proton conductivity. The time-dependent measurements for both compounds demonstrate their ability to retain conductivity up to 10 h.

Tuning CO2 Uptake and Reversible Iodine Adsorption in Two Isoreticular MOFs through Ligand Functionalization

The synthesis and characterization of two isoreticular metal-organic frameworks (MOFs), {[Cd(bdc)(4-bpmh)]}n⋅2 n(H2O) (1) and {[Cd(2-NH2bdc)(4-bpmh)]}n⋅2 n(H2O) (2) [bdc = benzene dicarboxylic acid; 2-NH2bdc = 2-amino benzene dicarboxylic acid; 4-bpmh = N,N-bis-pyridin-4-ylmethylene-hydrazine], are reported. Both compounds possess similar two-fold interpenetrated 3D frameworks bridged by dicarboxylates and a 4-bpmh linker. The 2D Cd-dicarboxylate layers are extended along the a-axis to form distorted square grids which are further pillared by 4-bpmh linkers to result in a 3D pillared-bilayer interpenetrated framework. Gas adsorption studies demonstrate that the amino-functionalized MOF 2 shows high selectivity for CO2 (8.4 wt % 273 K and 7.0 wt % 298 K) over CH4 , and the uptake amounts are almost double that of non-functional MOF 1. Iodine (I2 ) adsorption studies reveal that amino-functionalized MOF 2 exhibits a faster I2 adsorption rate and controlled delivery of I2 over the non-functionalized homolog 1.

Proton‐Conducting Magnetic Coordination Polymers

Three isostructural lanthanide-based two- dimensional coordination polymers (CPs) {[Ln2(L)3(H2O)2]n⋅2n CH3OH)⋅2n H2O} (Ln=Gd(3+) (1), Tb(3+) (2), Dy(3+) (3); H2L=cyclobutane-1,1-dicarboxylic acid) were synthesized by using a low molecular weight dicarboxylate ligand and characterized. Single-crystal structure analysis showed that in complexes 1-3 lanthanide centers are connected by μ3-bridging cyclobutanedicarboxylate ligands along the c axis to form a rod-shaped infinite 1D coordination chain, which is further linked with nearby chains by μ4-connected cyclobutanedicarboxylate ligands to form 2D CPs in the bc plane. Viewing the packing of the complexes down the b axis reveals that the lattice methanol molecules are located in the interlayer space between the adjacent 2D layers and form H-bonds with lattice and coordinated water molecules to form 1D chains. Magnetic properties of complexes 1-3 were thoroughly investigated. Complex 1 exhibits dominant ferromagnetic interaction between two nearby gadolinium centers and also acts as a cryogenic magnetic refrigerant having a significant magnetic entropy change of -ΔSm=32.8 J kg(-1) K(-1) for ΔH=7 T at 4 K (calculated from isothermal magnetization data). Complex 3 shows slow relaxation of magnetization below 10 K. Impedance analysis revealed that the complexes show humidity-dependent proton conductivity (σ=1.5×10(-5) S cm(-1) for 1, σ=2.07×10(-4) S cm(-1) for 2, and σ=1.1×10(-3) S cm(-1) for 3) at elevated temperature (>75 °C). They retain the conductivity for up to 10 h at high temperature and high humidity. Furthermore, the proton conductivity results were correlated with the number of water molecules from the water-vapor adsorption measurements. Water-vapor adsorption studies showed hysteretic and two-step water vapor adsorption (182,000 μL g(-1) for 1, 184,000 μL g(-1) for 2, and 1,874,000 μL g(-1) for 3) in the experimental pressure range. Simulation of water-vapor adsorption by the Monte Carlo method (for 1) confirmed the high density of adsorbed water molecules, preferentially in the interlayer space between the 2D layers.

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.

Synthesis, characterisation, water adsorption and proton conductivity of three Cd( ii ) based luminescent metal–organic frameworks

Three hydrogen bonded three-dimensional (3D) metal–organic frameworks (MOFs) namely [Cd(L-tart)(bpy)(H2O)]n·9n(H2O) (1), [Cd(D-tart)(bpy)(H2O)]n·9n(H2O) (2) and [Cd(DL-tart)(bpy)(H2O)]n·6n(H2O) (3) (tart = tartaric acid, bpy = 4,4-bipyridine) have been synthesized by the solvent diffusion technique at room temperature. Compounds 1 and 2 have been characterized by single crystal X-ray analysis, whereas the powder X-ray diffraction patterns show that the structural integrity of compound 3 is similar to 1 and 2. Structural analysis of 1 and 2 shows H-bonded homochiral 3D MOFs, fabricated by the hydrogen bonding interactions between the nearby 2D pillared-layer frameworks through the metal-bound water, metal-bound carboxylate, free carboxylic acid and the hydroxy group of L-/D- tart. The absolute configuration of all the compounds was investigated by solid state circular dichroism (CD) spectroscopy, which signifies that 1 and 2 are enantiomers whereas 3 is racemic. The adsorption studies reveal that compounds 1–3 show a significant amount of uptake for water vapor (∼239 mL g−1 for 1, ∼240 mL g−1 in 2, whereas 184 mL g−1 for 3 at P/P0 ≈ 1 bar) over other solvents (MeOH, EtOH) and an impedance measurement indicates that these compounds show proton conduction (1.3 × 10−6 S cm−1 in 1, 1.3 × 10−6 S cm−1 in 2 and 4.5 × 10−7 S cm−1 in 3) at a higher temperature (358 K) and at 95% relative humidity. The observed conductivity is explained by the so-called vehicle mechanism (activation energy (Ea) = 0.63–0.77 eV). Since all the compounds contain H3O+ cations in the interlayer space, the hydronium ions might act as vehicles to transport the protons in the interlayer space. The photoluminescence properties of all the compounds are also reported.